Describing vocal repertoires represents an essential step towards gaining an overview about the complexity of acoustic communication in a given species. The analysis of infant vocalisations is essential for understanding the development and usage of species-specific vocalisations, but is often underrepresented, especially in species with long inter-birth intervals such as the white rhinoceros. Thus, this study aimed for the first time to characterise the infant and juvenile vocal repertoire of the Southern white rhinoceros and to relate these findings to the adult vocal repertoire. The behaviour of seven mother-reared white rhinoceros calves (two males, five females) and one hand-reared calf (male), ranging from one month to four years, was simultaneously audio and video-taped at three zoos. Normally reared infants and juveniles uttered four discriminable call types (Whine, Snort, Threat, and Pant) that were produced in different behavioural contexts. All call types were also uttered by the hand-reared calf. Call rates of Whines, but not of the other call types, decreased with age. These findings provide the first evidence that infant and juvenile rhinoceros utter specific call types in distinct contexts, even if they grow up with limited social interaction with conspecifics. By comparing our findings with the current literature on vocalisations of adult white rhinoceros and other solitary rhinoceros species, we discuss to which extent differences in the social lifestyle across species affect acoustic communication in mammals.
Citation: Linn SN, Boeer M, Scheumann M (2018) First insights into the vocal repertoire of infant and juvenile Southern white rhinoceros. PLoS ONE 13(3): e0192166. https://doi.org/10.1371/journal.pone.0192166
Editor: Jon T. Sakata, McGill University, CANADA
Received: August 28, 2017; Accepted: January 17, 2018; Published: March 7, 2018
Copyright: © 2018 Linn et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data for the statistical analyses are within the paper and its Supporting Information files. Due to the data size, video and audio data are available from the Institute of Zoology at the University of Veterinary Medicine Hanover. Contact information for an institutional body to which data requests may be sent is as follows: Dr. Marina Scheumann, University of Veterinary Medicine, Institute of Zoology, Bünteweg 17, 30559 Hannover. Marina.Scheumann@tiho-hannover.de.
Funding: This study was financially supported by the Serengeti-Park-Stiftung (MS; http://www.serengeti-park-stiftung.de/) and the Studienstiftung des Deutschen Volkes (SL; https://www.studienstiftung.de/). Furthermore, this publication was supported by Deutsche Forschungsgemeinschaft and University of Veterinary Medicine Hannover, Foundation within the funding programme Open Access Publishing. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors received funding from the Serengeti-Park-Stiftung (MS; http://www.serengeti-park-stiftung.de/), non-profit foundation, for this study. There are no patents, products in development or marketed products to declare. This does not alter our adherence to all the PLOS ONE policies on sharing data and materials.
In many mammalian species vocal communication is essential to coordinate social interactions such as mating rituals (e.g., [1,2]), alarm calling (e.g., [3,4]), mother-infant care (e.g., [5,6]), group cohesion (e.g., [7,8]), or territorial displays (e.g., [9,10]). One of the first steps towards understanding the complexity of acoustic communication in a given species is to establish a vocal repertoire . This provides definitions of different types of vocalisation by describing the acoustic parameters of these vocalisations and displaying exemplary sonograms as well as a description of the context in which they were uttered. Thereby, vocal repertoires play not only an important role in the bioacoustic discipline but also help to understand complex social behavioural patterns.
Even though a number of previous studies established vocal repertoires in many different mammalian species of different mammalian taxa (e.g., rodentia: ; scandentia: ; chiroptera: ; carnivores: [15,16]; perissodactyla: ; artiodactyla: ; cetacea: ; primates: , ), infant vocalisations have been understudied especially in species with a long inter-birth interval and a low number of offspring. By investigating infant vocal behaviour and comparing infant and adult vocal repertoires the role of innate mechanism, vocal learning or ontogenetic changes during development such as maturational effects can be clarified (e.g. [21–27]). Therefore, research on vocal communication of infants has recently been of great interest (e.g., [28–34]).
While data on the vocal communication systems of many mammalian taxa have grown in recent decades, so far relatively little effort has been dedicated to the study of vocal communication in rhinoceros. Pioneering bioacoustic studies (; White rhinoceros: [17,36–38]; Black rhinoceros: ; Sumatra rhinoceros: ; Greater one-horned rhinoceros: ) have provided first insights into the field of rhinoceros vocal communication. Focussing on the White Rhinoceros, two studies exist documenting the vocal repertoire of this species [17,38]. Both showed a distinct acoustic communication system with ten to eleven different call types emitted in a variety of different contexts ranging from aggressive to cohesive interactions (e.g. [17,36–38]). Furthermore, there is first evidence, that the Pant call of white rhinoceros carries information about the sender such as individuality, sex or subspecies [36,37]. However, only one of these former studies provided a comprehensive vocal repertoire with displays of sonograms and a multi-parametric sound analysis (, the other study was based on onomatopoetic descriptions). Furthermore, infants and juveniles were not included in their investigations (the youngest individual within this study was six years old). Thus, until now systematic data on the vocal repertoire of infant and juvenile white rhinoceros are still missing.
To fill this gap, we investigated the vocal behaviour of infant and juvenile white rhinoceros at three different zoological institutions. White rhinoceros are described as “semi-social”. Long-lasting associations of adult females and subadults have been observed [41,42] whereas the adult bulls live solitarily ([41,42]; this semi-social lifestyle is in contrast to all other rhinoceros species). Females give birth to their first calf at approximately six to seven years of age, whereas males are socially matured between ten to twelve years of age . After a 16-month gestation period, a female gives birth to one calf . The calf can stand up after birth . However, it remains in close proximity to the mother and as soon as there is any disturbance the calf returns to her . Calves start to graze at two months of age, but continue suckling for over 12 months . Calves maintain a close bond to their mothers usually until the birth of the next calf [38,43]. After that the mothers chase them away and the infants have to search for other rhinoceros to form stable social associations . The more complex social organisation of this rhinoceros species may lead to a more pronounced acoustic communication system as compared to all the other solitary living rhinoceros species.
The aim of this study was to provide the first vocal repertoire of infant and juvenile white rhinoceros by defining structural and functional characteristics of call types and determining age-dependent variations by comparing our findings with the adult vocal repertoires of Owen-Smith  and Policht et al. . Recordings were made from eight Southern white rhinoceros ranging from one month to four years of age at different zoos. One calf had been rejected by his mother and was therefore hand-raised, which provided us with an opportunity to investigate whether social interactions are required to establish species-specific vocal behaviour.
Materials and methods
The article contains only observational data of zoo animals during their daily routine. No animal was manipulated by the authors. The authors received the permission to record the data of the animals on the private land of the respective zoo.
Subjects and study site
Recordings were made on eight Southern white rhinoceros (Ceratotherium simum simum) ranging from one month to four years of age at the following zoological institutions: Serengeti-Park Hodenhagen (February—March 2012, May-June 2014, April-May 2015), Dortmund Zoo (September–October 2014) and Augsburg Zoo (April 2016; Table 1). At Serengeti-Park Hodenhagen the whole rhinoceros group consisted of nine individuals in 2012 (six adult females, one adult male, two infants) and of eleven individuals in 2014 and 2015 (five adult females, one adult male, two juveniles, three infants). The adult male was occasionally separated from the herd. Two calves were recorded in all three years and three calves in two consecutive years. The rhinoceros were mainly observed in their 9 ha drive-through outdoor enclosure where they live together with watusis (Bos primigenius f. taurus), zebras (Equus quagga chapmani), ostriches (Struthio camelus), lechwes (Kobus leche), addax antelopes (Addax nasomaculatus), and dromedaries (Camelus dromedaries). Rhinoceros were used to being followed by car (also off the visitor route; ). Thus, we could approach them up to a distance of approximately five metres. Occasionally when the rhinoceros had to stay indoors due to inclement weather conditions, recordings were made in the indoor enclosure, where the animals were observed from the keeper area. At Dortmund Zoo we recorded a five-month-old female calf that was kept together with her mother and an adult female in their outdoor enclosure. At Augsburg Zoo we recorded a two-month-old male and a one-month-old female calf. Due to the young age of the female calf her mother did not leave the indoor area. Thus, recordings were made in the indoor enclosure where both were observed from the keeper area. The male calf had been rejected by his mother at birth. Therefore, he was hand-reared and bottle-fed (approximately every two hours) in the indoor enclosure by zookeepers. He was kept in a separate stable within the rhinoceros facility. Recordings were made in the indoor as well as in the outdoor enclosure.
We assigned our subjects to two main age classes: Infant and juvenile. Moreover, the acoustic analyses also included some calls (N = 41) of subadult individuals (N = 2; Table 1), which had already been recorded as infant and juvenile and which still lived together with their mothers and the current calves. Due to the fact that for white rhinoceros intercalving intervals of less than two years can be observed (, personal observations), subjects were classified as infants from birth to 18 months of age. All infant subjects were reared by their mothers with one exception. Subjects were classified as juvenile from 18 months to 3.5 years of age, which can be considered as nutritionally independent (Table 1). As white rhinoceros females can be regarded as adults from the age of six years and males from the age of ten years , subjects were classified as subadults up to this age.
For all subjects of the rhinoceros groups audio and video data were collected using the focal animal sampling method . Each subject of the group was observed for a ten-minute interval. The order in which the subjects were observed was block randomised. After all subjects had been observed once in a randomised order, a new block of focal observation started. It was not possible to record data blind because our study involved focal animals. In general, recordings took place between 6.00 a.m. and 5.00 p.m.. Overall, a total of 164 hours of data were recorded and analysed. We recorded 91 hours at Serengeti-Park Hodenhagen, 52 hours at Dortmund Zoo and 21 hours at Augsburg Zoo.
Audio recordings were made with a Sennheiser omni-directional microphone (MKH 8020; Sennheiser, Wedemark, Germany; frequency response: 10–60000 Hz, flat frequency response from 10–20000 Hz ± 5db) equipped with a wind shield and a boom pole. The microphone was connected to a Sound Devices 722 State Recorder (Sound Devices, LLC, Reedsburg, USA; frequency response of the recorder: 10–40000 Hz; settings: 44.1 Hz sampling rate, 16 Bit, uncompressed.wav format). Due to logistic reasons in 2015 we had to change the audio recording system for the infants of the Serengeti-Park Hodenhagen. Thus, we used a Sennheiser microphone (ME 67, Sennheiser, Wedemark, Germany; frequency response: 40–20000 Hz ± 2.5db) linked to a Marantz recorder (PMD 660, Marantz, D&M Holdings Inc., Mahwah, NJ, USA; settings: 44.1 kHz sampling rate, 16 Bit, uncompressed.wav format). The behaviour was videotaped using a digital camcorder (Sony DCR-SR36E, Tokyo, Japan). The identity of the caller was identified by hearing and was noted for each call.
We inspected the spectrograms of all audio recordings visually using Batsound Pro 4.1 (Pettersson Elektronik AB, Uppsala, Sweden; settings: FFT 512, Hanning window) and visually classified four different call types according to the literature : Whine, Snort, Threat and Pant (Fig 1). No other call types were found. A call was defined as a continued sound element having no sound gap . A series of consecutive sound elements of the same call type was defined as a bout. Call types were defined as sound elements of the same pattern of spectral content.
Fig 1. Examples of sonograms for the different call types.
Whines (A-D) showing temporal and spectral variations of the contour of the fundamental frequency; Snort without and with pulsed structure; Threat and Pant.
For the acoustic characterisation of infant calls, we selected all calls of high sound quality (no overlap with other sound, not over-amplified, good signal to noise ratio). Since Pants were the call type with the lowest number of high quality calls (N = 120, Table 1), we randomly selected 120 calls for each of the other call types for acoustic analysis to have a balanced data set. Thus, 120 calls per call type were included in the acoustic analysis using PRAAT (self-written script; http://www.praat.org; Phonetic Sciences, University of Amsterdam, the Netherlands; ) and AVISOFT (Avisoft Bioacoustics, Glienicke, Germany).
First, we measured the following six acoustic parameters to describe the spectral composition of the call types (for definition of acoustic parameters see Table 2): call duration (DUR), percentage of voiced frames (VOI), centre of gravity (COG), standard deviation of the frequency in the spectrum (SD), Skewness (SKE) and Kurtosis (KUR) of the spectrum. To measure the number of voiced frames (VOI), we used a semiautomatic procedure for pitch tracking. Thus, if necessary, we corrected the pitch tracking manually by matching the extracted contour with the sonogram (settings: Submenu: “To pitch”: min pitch: 100 Hz; max pitch: 3000 Hz; time steps: 0.005). If no fundamental frequency contour could be determined in the sonogram (noisy calls) we set all frames at unvoiced. For the tonal calls, we additionally measured four parameters characterising the contour of the fundamental frequency (F0): Minimum F0 (MINF0), maximum F0 (MAXF0), mean F0 (MEANF0), and standard deviation of the F0 (SDF0).
Second, using the automatic measurement routine of AVISOFT, we additionally measured the following five parameters at the point of maximum energy of the call (FFT 1024, Hanning window) to compare measurements with Policht et al. : Quartiles of the spectrum (25%QUART, 50%QUART, 75%QUART), entropy (ENTR), and harmonic-to-noise ratio (HNR).
For analysing call rate, behavioural context, mouth and tail position, we focussed our analyses only on focal observations of infants and juveniles and on dyadic observations of mothers when infants were younger than 18 months. Due to the fact that infants maintain a close bond to their mothers until the birth of the next calf , infants younger than 18 months were almost always visible in the focal observations of the mother. Therefore, we decided to include these focal observations to increase observation time. As observation time varied between infants (dependent on the size of the group and number of infants in the group), we focussed our analysis on approximately ten hours of focal observation per infant and analysed the video recordings using VLC Player. Based on the video recordings we noted for each call: (1) the identity of the caller (the identity of the caller was noted for each call during the recording), (2) the behavioural context, (3) the interaction partner and the distance to the interaction partner with regard to social behaviours, (4) the nearest-neighbour and the distance to the nearest neighbour with regard to non-social behaviours, (5) the reaction of the interaction partner or nearest neighbour, (6) the aperture angle of the mouth during vocalisation, as well as (7) the position of the tail. For the behavioural contexts we established the following categories based on an ethogram (Table 3): General activity, comfort & manipulation behaviour, olfactory behaviour, social interactions, suckling behaviour, and isolation. For the interaction partner and the nearest neighbour we classified three categories: The mother, other group members, or foreign species (keeper/other species in mixed-species enclosures). For the distance of the sender to the interaction partner/nearest neighbour, we defined three categories: Distance less than one adult body length (approximate body length is 3.5 to 4 m; , personal observations), distance of approximately one adult body length, and distance greater than one adult body length. For the aperture angle of the mouth, we distinguished between open mouth, closed mouth, and feeding. For the position of the tail we classified hanging or curled (tail was lifted at least 90°) as a sign of excitement . As reactions to vocalisations by other rhinoceros were only rare, we only counted whether there was a behavioural reaction in response to the vocalisation or not. In cases where the behavioural context, the position of other rhinoceros, the position of mouth and tail, or a reaction of other rhinoceros could not clearly be determined (e.g. not visible in the video recording), the respective category was coded as unknown.
The raw data for the statistical analyses can be found in the supporting information S1 Table. To validate our visual classification of call types, a statistical analysis of the acoustic measurements was performed. In the first step, we performed univariate ANOVAs using the subject as random factor to investigate which acoustic parameters differ significantly between call types. To control for multiple testing, we performed the Fisher-Omnibus test . In the second step, we performed a stepwise discriminant function analysis (DFA) using the one-leave-out method for cross-validation. We tested whether classification results were above chance level using Binomial tests and calculated the level of agreement using the Kappa test. For each call type we calculated the call rate [calls/hour] by dividing the number of calls by the analysed observation time. We used the Wilcoxon signed-rank test to assess whether the call rates for infant and juvenile white rhinoceros differ. For the description of the acoustic parameters, we calculated the mean and the standard deviation for each acoustic parameter for all subjects. To test for Snort subtypes, we performed a step-wise discriminant function analysis according to the description above. To investigate the occurrence across context and interaction partner/nearest neighbour for each call type, we calculated the percentage of calls by dividing the number of calls of the respective context and the interaction partner/nearest neighbour respectively by the total number of calls of the respective call type. The same was performed for the distance of the interactions partner/nearest neighbour, mouth and tail positions as well as reaction of other group members with the exception that we excluded calls for which these parameters could not clearly be determined. For the calves of the Serengeti-Park Hodenhagen, we tested whether calls were more emitted in proximity to or during social interactions with the mother as compared to other group members than expected by chance for each call type using the Binomial test (chance level was adapted to group size: 9% or 11%). All tests were performed using the statistical software SPSS 24 except the Fisher Omnibus test. The Fisher Omnibus test was calculated manually using Excel. The level of significance was set to p≤0.05.
We recorded 3660 calls which were classified by visual inspection of the spectrograms into four call types (Fig 1): Whine, Snort, Threat, and Pant. To validate the visual classifications, a stepwise DFA was performed to prove whether the calls can statistically be classified based on their acoustic measurements. Four out of 11 acoustic parameters differed significantly between call types (ANOVA: F≥4.65, df = 3, p≤0.015 for DUR, VOI, ENTR, HNR; Fisher Omnibustest: χ2 = 116.77, df = 22, p<0.001; Table 4; see Table A in S1 Table). The stepwise DFA selected eight out of these 11 acoustic parameters (in decreasing order: VOI, HNR, DUR, 75%QUART, ENTR, 25%QUART, SD, COG) to calculate three discriminant functions which significantly correctly classified 79.0% of the calls to the respective call type (p<0.001; cross-validation: 78.5%; p<0.001; Fig 2). Thus, 92.5% of the Whines, 79.2% of the Snorts, 73.3% of the Threats and 70.8% of the Pants were classified correctly above chance level (p<0.001; for all call types). The Kappa test confirmed the good agreement between the results of the DFA and the visual classification (Kappa = 0.719). The first DFA function explained 91.4% of the variance and correlated strongly with the tonality-related acoustic parameter VOI (r = 0.890) separating the Whines from the three noisy call types (Fig 2A). The second and third DFA function showed strongest correlations with measurements of hoarseness (DFA2: r = 0.777 for HNR) and spectral parameters (DFA3: r>0.369 for SD and 75%QUART) separating the three noisy call types (Fig 2B).
Fig 2. Scatterplot of the discriminant function analysis.
(a) DFA function 1 separates the Whines from the noisy call types. (b) DFA functions 2 and 3 separate the three noisy call types Snort, Threat and Pant.
Description of call types
Whines (Fig 1) occur singly or in bouts and can be easily distinguished from the other call types by their high-frequency tonal structure. We recorded Whines in all eight individuals ranging from one to 20 months of age. Whines showed, compared to the other call types, a higher HNR (±SD = 31.87±6.23 db), higher COG (±SD = 837.02±644.87 Hz) and lower entropy values (±SD = 0.16±0.06). Furthermore, Whines were characterised by a highly variable fundamental frequency contour ranging from almost constant to modulated F0 contours (Fig 1) and a highly variable call duration ranging from 0.111 to 3.511 seconds. Whines were mainly uttered when the mouth was closed (72.79%) or emitted during feeding/suckling (27.04%).
Whines were mainly recorded in the suckling context (58.22%, N = 517, Fig 3A, see Table C and Table D in S1 Table) in proximity to or during interactions with the mother (92.79%, N = 824, Fig 3B, see Table E in S1 Table). Testing this statistically for the subjects of the Serengeti-Park Hodenhagen revealed that all subjects emitted Whines more often in proximity to or during interactions with the mother than expected by chance (p<0.001 for all subjects). Only in 2.08% of the cases did the mother/group members show a behavioural reaction in response to the call such as following, social pushing, or position changes.
Fig 3. Cumulative barplots for the occurrence of calls.
(a) in different behavioural contexts and (b) directed to different interaction partners (in case of non-social behaviours the nearest neighbour).
Snorts are noisy calls which occur mainly singly and seem like air blows through the nostrils or the mouth. We recorded Snorts in all eight infants ranging from one to 50 months of age. Snorts differed in their acoustic structure from Threats and Pants by their higher SD (±SD = 943.95±449.21 Hz), higher entropy (±SD = 0.23±0.10) and lower HNR (±SD = 19.49±7.92 db) values. Based on visual inspection of the spectrogram two potential subtypes of Snorts could be identified; constant air blows (N = 58) and Snorts with a pulsed structure (N = 62, Fig 1). However, performing a stepwise DFA failed to classify these two potential subtypes statistically and also the Kappa test showed only a fair agreement (original: 64.2%; cross-validated: 64.2%; Chance level: 50%; Kappa = 0.276). Thereby, Snorts without pulses were classified by chance (p = 0.535). Snorts with and without pulses were mainly recorded in the context of general activity (with pulses: 72.58%, N = 45; without pulses: 67.24%, N = 39; Fig 3A, see Table C and Table D in S1 Table). Thereby, Snorts with pulses occurred more often during feeding context (46.67%, N = 21), whereas Snorts without pulses occurred during resting (48.72%, N = 19). Infants mainly emitted Snorts when the mouth was closed (56.28%) or during feeding (37.69%), in proximity to or during interactions with the mother (47.37%, N = 117, Fig 3B, see Table E in S1 Table).
Threats are low frequency noisy calls which can occur singly or in bouts. We recorded Threats in all eight individuals ranging from one to 50 months of age. Threats differed in their acoustic structure from Snorts by their lower entropy (±SD = 0.19±0.08), lower SD (±SD = 538.03±368.58 Hz), and higher HNR values (±SD = 29.54±7.46 db), and from Pants by their lower Cog (±SD = 405.95±424.86 Hz). Threats were normally uttered with a closed mouth (78.18%) or during feeding (20.00%).
Threats were mainly used in social interactions (65.52%, N = 57, Fig 3A, see Table C and Table D in S1 Table) during active and passive approach, following (51.73%, N = 45) and during socio-negative interactions (11.49%, N = 10). While calling, the infant often walked several steps towards other group members. In comparison to Pant and Snorts, Threat calls were mainly emitted in proximity to or during interactions with group members (32.18%, N = 28, Fig 3B, see Table E in S1 Table) and only rarely in proximity to or during interactions with the mother (5.75%, N = 5). One infant regularly emitted Threats in proximity to the keepers and to the observer. In one case, an infant was observed emitting a Threat during an interaction with an ostrich. In almost all these cases, infants were in close proximity to the interaction partner (less than one adult body length away: 92.96%, N = 66, see Table E in S1 Table). In 22.06% (N = 15) of the cases recipients responded to the Threats by avoiding, fleeing or by also producing Threat vocalisations.
Pants consist of bouts of repetitive noisy calls produced during inhalation or exhalation (in rare cases a single call can occur). Thereby, a bout consists on average of four calls (min: 1 to max: 17). Pants were recorded in six infants ranging from two to 50 months of age. Pants were acoustically characterised by higher COG (±SD = 474.87±489.91) and a higher 25QUART (±SD = 348.75±481.50) compared to the other two noisy call types. The mouth of the infants was normally closed (95.65%).
Pants were mainly emitted during social cohesive interactions when approaching or following an individual or a group of rhinoceros (66.67%, N = 26, Fig 3A, see Table C and Table D in S1 Table) and mainly during interactions with the mother (48.72%, N = 19, Fig 3B, see Table E in S1 Table). While calling, infants were normally further away from the mother/other group members (distance greater than one body length; 68.97%, N = 20, see Table E in S1 Table). Only in 40.00% (N = 8) of the cases could behavioural reactions (following/approaching or vocalisations) be observed. Interestingly, in comparison to the other call types, where the tail of the infants was in more than 87.65% of the cases in a hanging position, when producing Pants infants lifted their tail in 42.31% (N = 11) of the cases.
Vocal communication of a hand-reared infant rhinoceros
Comparable to the mother-reared calves, we recorded all four call types Whines, Snorts, Threats, and Pants also for Kibo, the two-month-old hand-reared calf. However, we found differences in the call rate for the Whine. The call rate for Whines (169.29 calls/hour) exceeded the call rate in mother-reared calves ( ±SD = 12.31±7.35 calls/hour) tremendously. Since Kibo was isolated from the other rhinoceros, behavioural contexts were not comparable with mother-reared calves. Whines and Pants were exclusively emitted in proximity to or during interactions with the keepers. The call rate of Whines was particularly high in the morning (after a long period of isolation, when keepers entered the enclosure) and before and during bottle-milk feeding, whereas Pants were uttered when Kibo approached the keepers. Snort production was predominantly associated with general activity such as resting and locomotion. Threats were only observed when the adult females were in the indoor enclosure next to him and approached the edge of his enclosure.
This study provides first systematic data on the vocal repertoire of infant and juvenile white rhinoceros and on the behavioural contexts in which they are emitted. Four different call types could be acoustically distinguished which were used in different behavioural contexts. Whines were mainly uttered in proximity to the mother to signal suckle intention or as a reaction when being disturbed during suckling. Snorts were also emitted in close proximity to the mother but mainly uttered during general activity. Threats were directed at other rhinoceros, animals or keepers and were uttered during social interactions as a response to the approach or proximity of another individual as well as socio-negative social interactions. Pants were uttered in proximity to the mother or other group members while approaching/ following them or during socio-positive interactions. Moreover, even the hand-reared infant produced the same call types in a similar context, suggesting that these call types are already present at birth and maybe based on innate mechanisms of vocal production and usage.
Comparing our results to the literature [17,38], the important role of Whines in mother-infant interactions especially during suckling could be supported. However, Owen-Smith  reported a second tonal call type, the Squeak, specific for mother-infant communication. The Squeak was also observed by Policht et al.  for a subadult female communicating with its mother. In comparison to the Whine, the Squeak seems to be a shorter, high-pitched call produced when the calf is separated from the mother. There are two possible explanations why we did not find Squeaks in our dataset. First, during our observations infants were rarely separated from the mother, thus, they might have had no need to use this call type. Second, we observed a high variability in duration and frequency contour including very short, high-pitched calls reaching the maximum amplitude very fast as described by Owen-Smith  and Policht et al. . These calls may correspond to the Squeak call type described by Owen-Smith  and Policht et al. . However, all kind of Whines were emitted during suckling or suckling attempts and could not clearly be associated with a specific context. It cannot be ruled out that differences in temporal or spectral parameters just code a different degree of sender urgency as found in a variety of other mammalian species (e.g., [52–55]). Thus, we suggest that in infant white rhinoceros tonal calls (termed here Whines) signal general discomfort or distress of the infant in various behavioural contexts such as isolation or hunger. They might serve to maintain contact or to draw the mother`s attention. The fact that the occurrence of Whines decreases with age supports this theory as the infants become more independent of their mothers.
In contrast to Whines, the other three call types (Snort, Threat, Pant) have also been described for adult rhinoceros (Table 5). We recorded Snorts in non-social situations such as feeding, resting, or locomotion. Thus, our data correspond to those of Policht et al. . We assumed that they were mainly addressed to the mother since mothers were almost always within a close distance to the calves. In contrast, Owen-Smith  described the Snort as a mild “keep-away warning”. However, based on the call description we think that the call type Snort of Owen-Smith  is related to the term Threat of Policht et al.  as well as in our study. In addition to the Snort, Policht et al.  describe a further puffing sound also recorded mainly during foraging; the Puff, which is longer compared to the Snort. We found a high variability in call duration of Snorts. However, since there is no distinct context and receiver for both acoustic variations, we assume that both belong to the same call type, termed here Snort. Pulsed Snorts were mainly recorded during feeding, whereas Snorts without pulses were mainly recorded during resting. Thus, we presume that the pulsed structure may be the result of forced air out of the nostrils (thereby nostrils vibrate) to clear them from grass, straw, or insects but did not appear to have any communicational function.
Threat vocalisations of the infant and juvenile white rhinoceros occurred during approach (active and passive) of group members/keepers and socio-negative interactions comparable to adult white rhinoceros. Policht et al.  observed Threats in adults as a “first warning”, for example, as a reaction to the approaching or presence of another individual. When the recipient did not react, Threats were followed by agonistics displays (e.g., growling, horn clashing).
Similar to adults (Table 5), infant white rhinoceros produced Pants during cohesive interactions such as approaching or following, serving as a kind of contact or greeting call [17,38]. During infancy, Pants were mainly addressed to the mother, but when infants became older, Pants were also directed towards other group members. Thereby, call series in infants (average: 4 calls per bout) seem to be much shorter compared to those of adults (average: 13 calls per bout; ). In adults, the Pant carries various information about the sender (species, age class and context; [36,37]). Nevertheless, further research is necessary to clarify the information encoded in infant white rhinoceros Pants.
To sum up, we found that infant white rhinoceros are vocally active from birth on. The Whine seems to be an infant-specific call type, whereas the three noisy call types Snort, Threat, and Pant are also part of the adult vocal repertoire and correspond in acoustic pattern and context to those of adults. Moreover, all call types were also uttered by the hand-reared calf and even used in the appropriate behavioural context, suggesting that there is a strong innate component to the development of vocal usage and production in white rhinoceros. These findings support the assumption that in most mammalian species both vocal production and usage are largely fixed at birth (e.g. [56,57]). We observed no sex-dependent variations, neither in call rate, nor in call structure or usage. However, separating males and females was limited by sample size and a skewed ratio of sexes. Owen-Smith  and Policht et al.  described further adult call types (Table 5), which we did not find in infants : Snarl, Hic, Shriek, Squeal, Grasp-puff, Gruff-Squeal; : Snarl, Grunt, Grouch, Groan, Hoarse). Even though, sometimes the terminology and the definition of call types are not clear, most of these call types are uttered during aggressive interactions, mating attempts or territory defence, contexts which might not be relevant for infants. Further studies targeting different ontogenetic stages by collection longitudinal data will be necessary to determine the onset of adult vocalisations and potential vocal sexual dimorphism. Moreover, payback studies could help to validate the hypothesised function of the different call types.
Comparing infant vocalisations of white rhinoceros with those of other rhinoceros species reveals that tonal vocalisations similar to Whine seem to be common in other rhinoceros species, too (Sumatran rhinoceros: [58,59]; Black rhinoceros: [50,60]; Greater one-horned rhinoceros: ; Java rhinoceros: ). However, the usage of tonal calls during adulthood differs between the species. For the Asiatic rhinoceros species, these tonal calls seem to function as mating calls or songs (Sumatra rhinoceros: [62,63]; Greater one-horned rhinoceros: ) or at least as long distance contact calls between dispersed individuals (Java rhinoceros: [50,65]). Adult black rhinoceros emit tonal Whines, for example, when begging for food [39,50]. In contrast, we found that for white rhinoceros the call rate of Whines decreased with age. It seems that the tonal call type Whine is not used in adulthood. Nonetheless, there is some evidence that adult white rhinoceros bulls emit tonal calls comparable to the infant Whine, the Shriek and the Squeal, in dominant, mating, and territory behaviour (personal observations, ). It is argued that this infant-like call might inhibit aggression by the female . Unfortunately, our knowledge about rhinoceros vocalisation is very limited. Thus, it is difficult to compare the vocal behaviour among different species. Despite everything, rhinoceros vocal communication is a highly interesting area of research, not only due to the fact that rhinoceros are one of the largest terrestrial mammals, but also in terms of the different socio-ecological niches they inhabit, ranging from semi-social to solitary and from forest- to savanna living species. Thus, rhinoceroses would be a promising group to investigate how different socio-ecological adaptations effect vocal communication in mammals.
S1 Table. Data sets.
(Table A) Acoustic Measurements of selected high-quality calls. (Table B) Call rates for different call types. (Table C) Context analysis. (Table D) Absolute number (N) and percentage of calls (%) recorded in the different behavioural contexts. (Table E) Absolute number (N) and percentage of calls (%) for interaction partner (in case of non-social behaviours the nearest neighbour), distance to interaction partner/nearest neighbour and reaction of other group members.
We wish to thank Serengeti-Park Hodenhagen, Dortmund Zoo and Augsburg Zoo for the given opportunity to investigate their rhinoceros and their hospitality. We would particularly like to thank Mirjam Becker, Daniela Lahn, Thomas Lipp, Stephanie Zech, and all the rhinoceros keepers for their patience and support during data collection and Garry White for the interesting and stimulating discussions. Furthermore, we would like to acknowledge Sönke von den Berg for his support in preparing the figures and F. Sherwood-Brock for proofreading the English as well as Elke Zimmermann for critical comments.
- 1. Hanson JL, Hurley LM (2012) Female presence and estrous state influence mouse ultrasonic courtship vocalizations. Plos One 7: e40782. pmid:22815817
- 2. Pfefferle D, Heistermann M, Pirow R, Hodges JK, Fischer J (2011) Estrogen and progestogen correlates of the structure of female copulation calls in semi-free-ranging Barbary macaques (Macaca sylvanus). International Journal of Primatology 32: 992–1006. pmid:21892238
- 3. Schneiderova I, Policht R (2012) Acoustic analysis of the alarm call of the Anatolian ground squirrel Spermophilus xanthoprymnus: a description and comparison with alarm calls of the Taurus S. taurensis and European S. citellus ground squirrels. Naturwissenschaften 99: 55–64. pmid:22159565
- 4. Schibler F, Manser MB (2007) The irrelevance of individual discrimination in meerkat alarm calls. Animal Behaviour 74: 1259–1268.
- 5. Herler A, Stoeger AS (2012) Vocalizations and associated behaviour of Asian elephant (Elephas maximus) calves. Behaviour 149: 575–599.
- 6. Scheumann M, Zimmermann E, Deichsel G (2007) Context-specific calls signal infants' needs in a strepsirrhine primate, the gray mouse lemur (Microcebus murinus). Dev Psychobiol 49: 708–718. pmid:17943980
- 7. Braune P, Schmidt S, Zimmermann E (2005) Spacing and group coordination in a nocturnal primate, the golden brown mouse lemur (Microcebus ravelobensis): the role of olfactory and acoustic signals. Behavioral Ecology and Sociobiology 58: 587–596.
- 8. Soltis J, Leong K, Savage A (2005) African elephant vocal communication I: antiphonal calling behaviour among affiliated females. Animal Behaviour 70: 579–587.
Since it first emerged in 2013 that the U.S. National Security Agency (NSA), together with the British Government Communication Headquarters, had carried out a massive program of surveillance of German citizens, there has been much talk of a crisis in relations between Germany and the United States. The revelations, which were made by a former NSA contractor, Edward Snowden, caused a huge wave of anger in Germany. Chancellor Angela Merkel, whose own cellphone, it later emerged, had also been monitored, said: “Friends don’t spy on friends.” (It subsequently emerged, however, that German intelligence agencies had also spied on European Union partners.) Many Germans said the revelations had shattered their “trust” in the United States. The Bundestag established a committee to investigate the revelations of spying, which is still ongoing.
However, the NSA scandal should be seen as a catalyst rather than a cause of the crisis in relations between Germany and the United States. The current rift has much deeper roots that go back to the end of the Cold War. Until reunification in 1990, the Federal Republic was a “semi-sovereign state, dependent on its allies for protection against the Soviet threat and inhibited by the history of the Second World War from defining or explicitly pursuing its own national interests.” In this context, the United States was crucial for the Federal Republic — particularly for security. But now that Germany is reunified and “encircled by friends,” as former Defense Minister Volker Rühe put it, it has much greater strategic space to define its interests as it wants to. The case for a close relationship with the United States is now more complicated, and much harder to make, than it was during the Cold War.
Many Germans are no longer convinced that the United States is...a “friend.”
Against the background of this changed strategic environment, Germany’s relationship with the United States has undergone a gradual transformation in the last 25 years. In particular, the relationship has become much more complicated as threat perceptions in the two countries have diverged during the 15 years since 9/11. This divergence is, in turn, based on the different ways Americans and Germans understand international politics in the post-Cold War world. In this context, many in Germany have begun to question whether they still share interests and values with the United States. Put simply, many Germans are no longer convinced that the United States is — to use the language Merkel herself used in the context of the NSA scandal — a “friend.”
An Incremental Estrangement
After the end of the Cold War, the United States wanted the reunified Germany to play a more active role in international security and to become, as President George H. W. Bush put it, a “partner in leadership.” In Germany, meanwhile, there was much discussion about becoming a more “normal” country. During this period, as I have argued elsewhere, the concept of “normality” was used largely as a synonym for Bündnisfähigkeit, or “the ability to be a member of the Atlantic alliance.” In response to the series of ethnic and regional conflicts that flared up over the next decade, particularly in the Balkans, the Federal Republic took a series of small steps toward a more activist foreign policy, culminating in the deployment of four Tornado jets on combat missions as part of the NATO military intervention against Serbia in 1999.
However, during the subsequent decade, German-U.S. relations worsened. Even before the September 11 attacks on the United States, President George W. Bush had already alienated many Germans by refusing to ratify the Kyoto Protocol and to sign up to the International Criminal Court. But the attacks created a “powerful wave of support for the United States” in Europe in general and in Germany in particular. Chancellor Gerhard Schröder promised the United States Germany’s “unlimited solidarity” and even put his own job on the line when he called a vote of confidence in conjunction with a Bundestag vote on the deployment of the Bundeswehr as part of the NATO deployment in Afghanistan. Yet even as Germany deployed troops as part of the International Security Assistance Force (ISAF) mission, U.S. and German threat perceptions and strategic culture were diverging.
This came to a head in the run-up to the Iraq war. In August 2002, Schröder launched his re-election campaign with a speech in which he opposed the war and spoke of a “Deutscher Weg,” or “German Way” — an implicit contrast with the “American Way.” A few days before the election in September 2002, in which Schröder was successfully reelected, U.S. National Security Adviser Condoleezza Rice said relations between Germany and the United States had been “poisoned.” (It was around this time that the NSA seems to have begun monitoring the chancellor’s cellphone.) According to Stephen Szabo, with the rift over the Iraq war, “the post-Cold War period in the German-U.S. relationship ended.” Henry Kissinger wrote that he had never thought that the relationship could deteriorate so quickly and worried that “a kind of anti-Americanism may become a permanent temptation of German politics.”
What made the rift so significant was not so much the fact that Germany had opposed the war, but the way it had done so.
What made the rift so significant was not so much the fact that Germany had opposed the war, but the way it had done so. It was not just that a German chancellor had never before so publicly opposed the United States on such an important issue, but also that, beyond the decision to invade Iraq, Schröder also distanced himself from the United States in a much more general way. “The era in which America and others should be a model for us in terms of the economy is really over,” he declared. Moreover, Schröder not only used anti-American rhetoric, but also sought to form a counter-coalition against the United States as part of what one international relations theorist called a strategy of “soft balancing.” The rift between Germany and the United States over Iraq even led some analysts to worry that it “could signal the end of ‘the West’ as a meaningful concept.”
The second critical juncture in Germany’s incremental estrangement from the United States was the financial crisis that began with the collapse of Lehman Brothers in the autumn of 2008. Despite the extensive investment of large German banks in “sub-prime” mortgage-backed securities, Germans saw it above all as a crisis of Anglo-Saxon capitalism. To many Germans, particularly on the left, the crisis demonstrated how wrong the United Kingdom and the United States had been to focus on the “new economy” and on financial services. They saw in the crisis a vindication of the German social market economy — in other words, exactly what Schröder had talked about in his “German Way” speech in 2002. Thus, if the Iraq War had given Germans the confidence to go their own way on matters of war and peace, the financial crisis gave them the confidence to do so on economic issues as well.
In particular, the financial crisis also strengthened German skepticism of Keynesianism, which Germans associated with Anglo-Saxon economists. This anti-Keynesian turn led to disagreements between Germany (a surplus country) and the United States (a deficit country) about how to “rebalance” the global economy. Many Anglo-Saxon economists thought that the crisis was a Keynesian moment that was, as Paul Krugman put it, “essentially the same kind of situation that John Maynard Keynes described back in the 1930s.” In particular, they thought that the problem in the global economy was a lack of aggregate demand and that the solution was economic stimulus. But the Germans disagreed. As finance minister in December 2008, the Social Democrat Peer Steinbrück attacked the “crass Keynesianism” of the British government under Gordon Brown, who had urged stimulus measures. That in turn prompted an angry response from Krugman, who called the German government “bone-headed.”
Others have suggested that U.S. critics are motivated by a kind of anti-German racism.
These arguments between Americans and Germans foreshadowed the debates that would take place after the euro crisis began in 2010. Since the beginning of that crisis, many Americans have vociferously criticized the German-led response. The U.S. Treasury has also repeatedly called on Germany to do more to reduce its current account surplus and stimulate growth in the eurozone. But Germans have tended to dismiss such criticisms and rejected such demands. They often suggest that U.S. critics of German and eurozone policy — embodied in the German imagination by the figure of Krugman, a target of much German anger — simply do not understand Europe or the euro. For example, in an interview with Der Spiegel, German Finance Minister Wolfgang Schäuble said that although Krugman might have won a Nobel Prize in economics, he has “no idea about the architecture and foundation of the European currency union.” Others have suggested that U.S. critics are motivated by a kind of anti-German racism.
A Generational Shift?
Against the background of these arguments about foreign and economic policy, attitudes to the United States in Germany have fluctuated wildly over the last 15 years. Public support for the United States in Germany dramatically collapsed during the Bush administration. According to the Pew Research Center, for example, the United States’ favorability rating went from 78 percent in 2000 to 31 percent in 2008. But this collapse was reversed by the election of Barack Obama, who was seen in Germany as a kind of “savior.” According to the 2009 edition of the German Marshall Fund’s Transatlantic Trends, 92 percent of Germans approved of Obama after he had been in office for half a year, compared to only 12 percent who approved of Bush the year before — in other words, a whopping 80-point “Obama bounce,” as the authors of the report called it.
However, since then, support for the United States has once again plummeted, reflecting disappointment among many Germans that Obama’s foreign policy did not break with that of his predecessor as much as they had hoped. According to one of Germany’s leading polling organizations, trust in the United States fell from 80 percent in 2009 to 35 percent in 2014. A Pew survey in June 2015 found that German views of the United States were now more negative than those of any other NATO country. Whereas large majorities in Canada, France, Italy, Poland, Spain and the U.K. had favorable views of the United States, only 50 percent of German respondents gave the United States a positive rating, and 45 percent expressed a negative view. In some ways, the situation is now worse than during the Bush era: at that time, anger was more selectively directed toward Bush and the neoconservatives; now, it is generally directed toward the United States as a whole.
Many have sought to explain the increasingly negative perception of the United States in Germany in generational terms. As German Foreign Minister Frank-Walter Steinmeier put it, “to the generation of tomorrow, the value of the transatlantic partnership is in no way as self-evident as it is to my generation.” However, there is a danger of committing what Robert Kagan, in a different context, has called the “nostalgic fallacy” — that is, romanticizing the past. There is a long history of anti-Americanism in Germany on both the left and the right, which was closely linked to anti-Western, anti-liberal, anti-capitalist, and even anti-Semitic currents in German thought.  The tropes that link present-day anti-Americanism with anti-Semitism even led Dan Diner to argue in the aftermath of the Gulf War in 1991 that anti-Americanism can be seen as a kind of “disguised anti-Semitism.”
After World War II, the United States was both liberator and occupier — gratitude therefore co-existed with resentment among the West German population. This came to the surface during the 1960s, when the post-war generation, which had grown up idealizing the United States, turned against it during the Vietnam War. For many young West Germans, the B-52 dropping bombs over North Vietnam replaced the C-47 delivering food to West Berlin as the symbol of U.S. power. During the 1970s, students threw Molotov cocktails at U.S. institutions such as the Amerika Haus in Berlin and equated the United States with Nazism (“USA—SA—SS” was a popular slogan of the time). In the 1970s, left-wing terrorists even murdered U.S. soldiers. Though there is little available polling data to make a rigorous comparison, the “1968 generation” to which Schröder belonged — in Steinmeier’s terms, the “generation of yesterday” — was probably the most anti-American of all.
There are striking parallels between the current moment and the moment after the end of the Vietnam War.
Indeed, there are striking parallels between the current moment and the moment after the end of the Vietnam War. What seems to have happened is that, for a generation of young Germans, the Iraq War had a similar effect that the Vietnam War had for the post-war generation: it shattered their illusions about the United States. The current situation is also, in a wider sense, somewhat analogous to the situation in the late 1970s after the Vietnam War came to an end. Then, as now, there was both a perception of U.S. decline and anger in Germany about U.S. foreign policy, particularly among a generation of young people. Then, as now, economic success had produced a sense of pride in Germany captured by the idea of Modell Deutschland. Then, as now, the Federal Republic sought to pursue a more assertive foreign policy based on economic strength.
The real difference between then and now is not so much the existence or level of anti-Americanism but the strategic situation in which Germany finds itself. While German Atlanticists and many foreign policy experts stress that the relationship with the United States is as important as ever, as the liberal international order is threatened and in order to work together on shared challenges such as climate change and terrorism, the case for cooperation is now a more complicated and much harder one to make to ordinary Germans. “During the decades when Soviet power cast a dark shadow across the entire continent, the importance of the German-American alliance was self-evident,” as the GMF task force report published last year puts it. “That has not been the case since German unification 25 years ago.”
Germany is much less likely than in the past to accede to U.S. demands or succumb to U.S. pressure.
The upshot of all this is that Germany is much less likely than in the past to accede to U.S. demands or succumb to U.S. pressure. Germans are now much more skeptical of U.S. (or Anglo-Saxon) ideas — whether on foreign policy or on economic policy — and are more comfortable with the idea of going their own way and disagreeing with, and being criticized by, Americans. A shift in the meaning of the concept of “normality” reflects this change: it is now associated with the pursuit of national interests rather than Bündnisfähigkeit. This is significant, because whereas the earlier idea of “normality” was used to justify foreign-policy choices that coincided with those of Germany’s NATO allies, such as participation in the Kosovo war and the deployment of troops to Afghanistan, this new idea of “normality” is one that can be used to justify a divergence by Germany from allies and especially from the United States.
A New Strategic Situation?
In this post-Cold War context, Germany has increasingly come to see itself as a Friedensmacht, or “force for peace,” defined in opposition to the United States. The term was originally used as a self-description by the German Democratic Republic and was applied to the Federal Republic in 1993 by Alfred Merchtesheimer, a former German air force colonel who joined the Green Party in the 1980s and later moved to the far right. In particular, Merchtesheimer saw the United States as a “negative model” against which Germany should define itself. Similar arguments were later made by Egon Bahr, Willy Brandt’s adviser and the architect of Ostpolitik. In a book called Der Deutsche Weg, published shortly after the Iraq war, he argued that Germany should distinguish itself from the United States through its opposition to the use of military force. Since then, the SPD has also increasingly used the term Friedensmacht.
However, Germany’s strategic situation has changed to some extent since the Ukraine crisis. In particular, the renewed threat from Russia to European security — some analysts even speak of a “new Cold War” — has allowed German Atlanticists and foreign policy experts to put incidents like the NSA scandal in a bigger strategic context and to make the case for a stronger relationship with the United States. In this sense, the Russian annexation of Crimea in 2014 can be seen as analogous to the Soviet invasion of Afghanistan in 1979, which brought the period of détente that had begun under U.S. President Richard Nixon to an end. It was in this new context (the “Second Cold War”) that Chancellor Helmut Schmidt — who believed West Germany was now vulnerable to an attack by the Soviet Union using conventional forces — called for NATO to install medium-range nuclear missiles in Europe.
The new strategic situation in Europe has the potential to divide Americans and Germans even further.
Nevertheless, as reassuring as this might be for Atlanticists, the new strategic situation in Europe also has the potential to divide Americans and Germans even further. Perhaps the most significant difference between the situation since 2014 and the situation after 1979 is Germany’s position in the center of an enlarged Europe. Even now, Germans do not see Russia as a direct threat to them in the way they saw the Soviet Union as a direct threat to them during the Cold War. Rather, the threat from Russia now is to NATO allies such as the Baltic states and Poland — and, according to one poll in 2015, only 38 percent of Germans would be willing to use military force to defend these countries if they were attacked. Many Germans also see the U.S. approach to Russia as part of the problem rather than the solution. Ironically, what some see as an aggressive U.S. approach to Russia is the policy that led to Germany being “encircled by friends” — the enlargement of NATO.
While Germany has supported economic sanctions against Russia, it has opposed other steps to reassure NATO allies and deter Russia. Even after the strategic shock of the annexation of Crimea, Germany did not significantly increase defense spending as a proportion of GDP. Ahead of the NATO summit in Wales in September 2014, Germany opposed plans to strengthen NATO’s presence in Central and Eastern Europe because it worried this would violate the NATO-Russia Founding Act, which was signed in 1997. In February 2015, when a debate started in the United States about providing direct lethal military assistance to Ukraine and reports suggested that the Obama administration was taking a “fresh look” at the issue, Merkel immediately, and publicly, opposed it. If the Minsk Agreement has not yet been fully implemented by the time Obama’s successor is in office in 2017, and he or she decides to arm Ukraine, it could lead to a rift with Germany — particularly if the Ukrainian government subsequently gave up on a political solution.
The refugee crisis could yet be a game changer in terms of German defense policy in a way that the Ukraine crisis was not. In January, German Defense Minister Ursula von der Leyen announced that she wants to spend €130 billion on defense equipment over the next 15 years. However, even if approved by the government and lawmakers, this is unlikely to significantly increase spending as a proportion of GDP, let alone reach the 2 percent target — about which von der Leyen has long expressed skepticism. The increase in defense spending is also unlikely to lead to a significant improvement in terms of capabilities because much of it will go toward repairing or replacing old equipment. During the last couple of years, a series of reports have revealed that only a fraction of Germany’s jets, tanks, and helicopters are operational because of cuts in spending on maintenance since 2010.
Meanwhile the refugee crisis in Europe has also added another potential source of tension between Germany and the United States. Some German policymakers were frustrated that the United States did not do more to help Germany deal with the crisis — which many in Germany believe the United States caused through its military intervention in Iraq. This illustrates how the relationship has changed since German reunification. For a long time after the end of the Cold War, the United States made demands of Germany and put it under pressure to fulfill them, particularly in relation to security policy. Now, however, Germany has a much clearer sense of its own national interest than it used to. In the future, tensions could arise from a perception in Germany that the United States is failing to help it pursue its objectives, particularly within the EU, as much as the other way around.
 Christopher Hill, The actors in Europe’s foreign policy (London: Routledge, 1996), Amazon Kindle edition, Location 430.
 Hans Kundnani, “The Concept of ‘Normality’ in German Foreign Policy since Unification,” German Politics and Society, Volume 30, Issue 2, Summer 2012, pp. 38-58.
 Stephen F. Szabo, Parting Ways. The Crisis in German-American Relations (Washington, DC: Brookings Institution, 2004), p. 1.
 Quoted in Szabo, Parting Ways, pp. 129, 79.
 Robert A. Pape, “Soft Balancing against the United States,” International Security, Vol. 30, No. 1 (Summer 2005), pp. 7-45. Pape defines “soft balancing” against the United States as “the use of nonmilitary tools to delay, frustrate, and undermine aggressive unilateral U.S. military policies.”
 Szabo, Parting Ways, p. 6.
 Paul Krugman, End this Depression Now! (New York: Norton, 2012), p. xxii.
 See Dan Diner, America in the Eyes of the Germans: An Essay on Anti-Americanism (Princeton: Markus Wiener, 1996).
 Dan Diner, Der Krieg der Erinnerungen und die Ordnung der Welt [The memory war and world order], Berlin: Rotbuch, 1991), p. 62.
 On the re-emergence of the idea of Modell Deutschland, see Andreas Rödder, “‘Modell Deutschland’ 1950-2011. Konjunkturen einer bundesdeutschen Ordnungsvorstellung” [‘Model Germany’ 1950-2011: The rise and fall of a German idea of order], in Tilman Mayer, Karl-Heinz Paqué and Andreas H. Apelt, Modell Deutschland (Berlin: Duncker & Humblot, 2013), pp. 39-51.
 “Longstanding Partners in Changing Times,” p. 3.
 Alfred Merchtesheimer, Friedensmacht Deutschland. Plädoyer für einen neuen Patriotismus [Germany, a Force for Peace: A Plea for a New Patriotism] (Frankfurt: Ullstein, 1993).
 Egon Bahr, Der deutsche Weg: Selbstverständlich und normal [The German Way: Natural and Normal] (Munich: Blessing, 2003).
 See Werner Link, Christian Weber and Frank Sauer (eds.), Die Semantik der neuen deutschen Außenpolitik: Eine Analyse des außenpolitischen Vokabulars seit Mitte der 1980er Jahre [The Semantics of the New German Foreign Policy: An Analysis of the Vocabulary of German Foreign Policy Since the Mid-1980s] (Wiesbaden: VS Verlag für Sozialwissenschaften 2008), p. 110.
 On the debate in the United States, see Michael R. Gordon and Eric Schmitt, “U.S. Considers Supplying Arms to Ukraine Forces, Officials Say,” The New York Times, February 1, 2015, http://www.nytimes.com/2015/02/02/world/us-taking-a-fresh-look-at-arming... on Merkel’s rejection of military assistance to Ukraine, see Michael R. Gordon, Alison Smale, and Steven Erlanger, “Western Nations Split on Arming Kiev Forces,” The New York Times, February 7, 2015, http://www.nytimes.com/2015/02/08/world/europe/divisions-on-display-over....