Isolation calls and retrieving behavior in laboratory and wild-derived golden hamsters—No sign for inbreeding depression

Isolated juvenile golden hamsters produce ultrasonic and audible vocalizations, so-called isolation calls, as a reaction to being separated from their mother and nest and their cooling down. Their aim is to stimulate mothers to search and retrieve the pups. In this work, the vocalization of juvenile laboratory (Zoh:GOHA; Institute of Zoology, Martin-Luther-University Halle-Wittenberg) and juvenile wild-derived golden hamsters (captured in northern Syria and southern Turkey) from birth up to the age of 18 days were digitally recorded, analyzed and compared using an ultrasonic microphone and the software Avisoft. Furthermore, the retrieving behavior of the mothers was observed and compared. The results showed that the number of isolation calls was age-specific and the structure of the calls was influenced by body temperature, body mass and sex of the pups. The age of the pups determined retrieval by the maternal golden hamsters; however these did not discriminate between their own pups or foreign pups. In spite of enormous genetic differences between wild-derived and laboratory golden hamsters, only minor differences between the strains were found.     

Confirmation of right whales near a nineteenth-century whaling ground east of southern Greenland

North Atlantic right whales (Eubalaena glacialis) were found in an important nineteenth century whaling area east of southern Greenland, from which they were once thought to have been extirpated. In 2007-2008, a 1-year passive acoustic survey was conducted at five sites in and near the 'Cape Farewell Ground', the former whaling ground. Over 2000 right whale calls were recorded at these sites, primarily during July-November. Most calls were northwest of the historic ground, suggesting a broader range in this region than previously known. Geographical and temporal separation of calls confirms use of this area by multiple animals.     

Birds adjust acoustic directionality to beam their antipredator calls to predators and conspecifics

Animals in many vertebrate species vocalize in response to predators, but it is often unclear whether these antipredator calls function to communicate with predators, conspecifics or both. We evaluated the function of antipredator calls in 10 species of passerines by measuring the acoustic directionality of these calls in response to experimental presentations of a model predator. Acoustic directionality quantifies the radiation pattern of vocalizations and may provide evidence about the receiver of these calls. We predicted that antipredator calls would have a lower directionality if they function to communicate with surrounding conspecifics, and a higher directionality and aimed at the receiver if they function to communicate with the predator. Our results support both of these functions. Overall, the birds produce antipredator calls that have a relatively low directionality, suggesting that the calls radiate in many directions to alert conspecifics. However, birds in some species increase the directionality of their calls when facing the predator. They can even direct their calls towards the predator when facing lateral to it—effectively vocalizing sideways towards the predator. These results suggest that antipredator calls in some species are used to communicate both to conspecifics and to predators, and that birds adjust the directionality of their calls with remarkable sophistication according to the context in which they are used.     

Molecular patterns of differentiation in canyon treefrogs (Hyla arenicolor): evidence for introgressive hybridization with the Arizona treefrog (H. wrightorum) and correlations with advertisement call differences

Detection of genetic and behavioural diversity within morphologically similar species has led to the discovery of cryptic species complexes. We tested the hypothesis that US populations of the canyon treefrog (Hyla arenicolor) may consist of cryptic species by examining mate‐attraction signals among three divergent clades defined by mtDNA. Using a multi‐locus approach, we re‐analysed phylogenetic relationships among the three clades and a closely related, but morphologically and behaviourally dissimilar species, the Arizona treefrog (H. wrightorum). We found evidence for introgression of H. wrightorum’s mitochondrial genome into H. arenicolor. Additionally, the two‐clade topology based on nuclear data is more congruent with patterns of call variation than the three‐clade topology from the mitochondrial dataset. The magnitude of the call divergence is probably insufficient to promote isolation of the nuclear DNA‐defined clades should they become sympatric, but further divergence in call properties significant in species identification could promote speciation in the future.     

Vocal communication in adult greater horseshoe bats, Rhinolophus ferrumequinum

Whereas echolocation in horseshoe bats is well studied, virtually nothing is known about characteristics and function of their communication calls. Therefore, the communication calls produced by a group of captive adult greater horseshoe bats were recorded during various social interactions in a free-flight facility. Analysis revealed that this species exhibited an amazingly rich repertoire of vocalizations varying in numerous spectro-temporal aspects. Calls were classified into 17 syllable types (ten simple syllables and seven composites). Syllables were combined into six types of simple phrases and four combination phrases. The majority of syllables had durations of more than 100 ms with multiple harmonics and fundamental frequencies usually above 20 kHz, although some of them were also audible to humans. Preliminary behavioral observations indicated that many calls were emitted during direct interaction with and in response to social calls from conspecifics without requiring physical contact. Some echolocation-like vocalizations also appeared to clearly serve a communication role. These results not only shed light upon a so far widely neglected aspect of horseshoe bat vocalizations, but also provide the basis for future studies on the neural control of the production of communicative vocalizations in contrast to the production of echolocation pulse sequences.     

The behavioral context of common dolphin (Delphinus sp.) vocalizations

Correlations between surface behavior and concurrent underwater vocalizations were modeled for common dolphins (Delphinus spp.) in the Southern California Bight (SCB) over multiple field seasons. Clicks, pulsed calls, and whistles were examined, with a total of 50 call features identified. Call features were used to classify behavior using random forest decision trees, with rates of correct classification reaching 80.6% for fast travel, 84.6% for moderate travel, 59.8% for slow travel, and 58% for foraging behavior. Common dolphins spent most of their time traveling. The highest number of clicks, pulsed calls, and complex whistles were produced during fast travel. In contrast, during foraging there were few pulsed calls and whistles produced, and the whistles were simple with narrow bandwidths and few harmonics. Behavior and vocalization patterns suggest nocturnal foraging in offshore waters as the primary feeding strategy. Group size and spacing were strongly correlated with behavior and rates of calling, with higher call rates in dispersed traveling groups and lower call rates in loosely aggregated foraging groups. These results demonstrate that surface behavior can be classified using vocalization data, which builds the framework for behavioral studies of common dolphins using passive acoustic monitoring techniques.     

Individual variation in pup vocalizations and absence of behavioral signs of maternal vocal recognition in Weddell seals (Leptonychotes weddellii)

Individually stereotyped vocalizations often play an important role in relocation of offspring in gregarious breeders. In phocids, mothers often alternate between foraging at sea and attending their pup. Pup calls are individually distinctive in various phocid species. However, experimental evidence for maternal recognition is rare. In this study, we recorded Weddell seal (Leptonychotes weddellii) pup vocalizations at two whelping patches in Atka Bay, Antarctica, and explored individual vocal variation based on eight vocal parameters. Overall, 58% of calls were correctly classified according to individual. For males (n= 12) and females (n= 9), respectively, nine and seven individuals were correctly identified based on vocal parameters. To investigate whether mothers respond differently to calls of familiar vs. unfamiliar pups, we conducted playback experiments with 21 mothers. Maternal responses did not differ between playbacks of own, familiar, and unfamiliar pup calls. We suggest that Weddell seal pup calls may need to contain only a critical amount of individually distinct information because mothers and pups use a combination of sensory modalities for identification. However, it cannot be excluded that pup developmental factors and differing environmental factors between colonies affect pup acoustic behavior and the role of acoustic cues in the relocation process.     

Genome size rather than content might affect call properties in toads of three ploidy levels (Anura: Bufonidae: Bufo viridis subgroup)

In vertebrates, genome size has been shown to correlate with nuclear and cell sizes, and influences phenotypic features, such as brain complexity. In three different anuran families, advertisement calls of polyploids exhibit longer notes and intervals than diploids, and difference in cellular dimensions have been hypothesized to cause these modifications. We investigated this phenomenon in green toads (Bufo viridis subgroup) of three ploidy levels, in a different call type (release calls) that may evolve independently from advertisement calls, examining 1205 calls, from ten species, subspecies, and hybrid forms. Significant differences between pulse rates of six diploid and four polyploid (3n, 4n) green toad forms across a range of temperatures from 7 to 27 °C were found. Laboratory data supported differences in pulse rates of triploids vs. tetraploids, but failed to reach significance when including field recordings. This study supports the idea that genome size, irrespective of call type, phylogenetic context, and geographical background, might affect call properties in anurans and suggests a common principle governing this relationship. The nuclear‐cell size ratio, affected by genome size, seems the most plausible explanation. However, we cannot rule out hypotheses under which call‐influencing genes from an unexamined diploid ancestral species might also affect call properties in the hybrid‐origin polyploids. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 584–590.     

Alarm calls modulate the spatial structure of a breeding owl community

Animals should continuously assess the threat of predation. Alarm calls inform on predation risk and are often used as cues to shape behavioural responses in birds and mammals. Hitherto, however, the ecological consequences of alarm calls in terms of organization of animal communities have been neglected. Here, we show experimentally that calls of a resident nocturnal raptor, the little owl Athene noctua, triggered a response in terms of breeding habitat selection and investment in current reproduction in conspecifics and heterospecifics. Little owls preferred to settle in territories where calls of conspecifics, irrespective of their type (i.e. alarm versus contact calls), were broadcasted, indicating that either conspecific attraction exists or calls are interpreted as foreign calls, eliciting settlement as a mode of defence against competitors. Also, we found that little owls seemed to invest more in current reproduction in safe territories as revealed by conspecific calls. Innovatively, we reported that a second owl species, the migratory scops owl Otus scops, preferred to breed in safe territories as indicated by little owls' calls. These results evidence that the emission of alarm calls may have, apart from well-known behavioural effects, ecological consequences in natural communities by inducing species-specific biases in breeding habitat selection. This study demonstrates a previously unsuspected informative role of avian alarm calls which may modulate the spatial structure of species within communities.     

Echolocation calls of Rhinolophus ferrumequinum in relation to habitat type and environmental factors

The present experiment was carried out in Luotong Mountain Natural Reserve in Jilin Province of China in 2007. We recorded and analyzed the echolocation calls of Rhinolophus ferrumequinum in different habitats by using Avisoft Bioacoustics USG 116 and Avisoft-SASLAB PRO (Avisoft Bioacoustics, Berlin, Germany). Our results showed that R. ferrumequinum foraged in diverse habitats in the study area, and their echolocation calls were significantly variable in different habitats (One-Way ANOVA, P < 0.05). Vegetative, climatic and topographical factors were selected by using the principal component analysis and the correlations between the parameters of echolocation calls and these environmental factors were analyzed. The results indicated that although R. ferrumequinum always emitted FM/CF/FM echolocation calls in different habitats, the parameters of echolocation calls varied with variable environmental factors. Significant negative correlation existed between FM1 bandwidth and arbor height (r = ?0.948, P < 0.05), FM₂ bandwidth and arbor height (r = ?0.825; P < 0.05), FM1 starting frequency and canopy area (r = ?0.967, P < 0.05), FM₂ ending frequency and canopy area (r = ?0.958, P < 0.05), FM1 starting frequency and air relative humidity (r = ?0.776, P < 0.05), FM₂ ending frequency and air relative humidity (r = ?0.875, P < 0.05), peak frequency and air relative humidity (r = ?0.794, P < 0.05), pulse duration and average shrub height (r = ?0.911, P < 0.05), and inter-pulse interval and average shrub height (r = ?0.990, P < 0.05). Significant positive correlation existed between peak frequency and number of plants (r = 0.756, P < 0.05), and pulse duration and height below the canopy (r = 0.870, P < 0.05). Our results suggested that many kinds of ecological factors (such as vegetation factor, climatic factor and topographical factor) affected the structure of echolocation calls and made them diverse in different habitats, i.e., echolocation calls of bats had phenotypic flexibility and eco-adaptability. These characteristics determined the degree of available habitats and natural resources for R. ferrumequinum.