Experimental evidence for limited vocal recognition in a wild primate: implications for the social complexity hypothesis

Although monitoring social information is a key aspect of the social complexity hypothesis, surprisingly little work has compared social knowledge across different species of wild animals. In the present study, I use playback experiments to test for individual recognition in wild male geladas (Theropithecus gelada) to compare with published accounts of social knowledge in chacma baboons (Papio ursinus). Geladas and baboons are closely related primates living in socially complex groups that differ dramatically in group size—geladas routinely associate with more than 10 times the number of conspecifics than do baboons. Using grunts from non-rival males to simulate approaches, I examined the strength of a subject male''s response when the ‘approach’ was from the direction of (i) non-rival males (control), or (ii) rival males (a more salient stimulus if playback grunts are not recognized by the subject). I compared responses separately based on the degree of social overlap between the caller and the subject. Responses indicate that male geladas, unlike baboons, do not use vocalizations to recognize all of the individuals they regularly encounter. This represents, to my knowledge, the first documented evidence of ‘missing’ social knowledge in a natural primate population. The sharp distinction between baboons and geladas suggests that geladas are either unable or unmotivated to keep track of the individual identity of other males in their multi-level society—even males with whom they have a large degree of social overlap. Thus, these results are consistent with the central assumption of the social complexity hypothesis that social cognition is costly.     

Impact of season and social challenge on testosterone and corticosterone levels in a year-round territorial bird

Plasma testosterone increases during breeding in many male vertebrates and has long been implicated in the promotion of aggressive behaviors relating to territory and mate defense. Males of some species also defend territories outside of the breeding period. For example, the European nuthatch (Sitta europaea) defends an all-purpose territory throughout the year. To contribute to the growing literature regarding the hormonal correlates of non-breeding territoriality, we investigated the seasonal testosterone and corticosterone profile of male (and female) nuthatches and determined how observed hormone patterns relate to expression of territorial aggression. Given that non-breeding territoriality in the nuthatch relates to the reproductive context (i.e., defense of a future breeding site), we predicted that males would exhibit surges in plasma testosterone throughout the year. However, we found that males showed elevated testosterone levels only during breeding. Thus, testosterone of gonadal origin does not appear to be involved in the expression of non-breeding territoriality. Interestingly, territorial behaviors of male nuthatches were stronger in spring than in autumn, suggesting that in year-round territorial species, breeding-related testosterone elevations may upregulate male-male aggression above non-breeding levels. In females, plasma testosterone was largely undetectable. We also examined effects of simulated territorial intrusions (STIs) on testosterone and corticosterone levels of breeding males. We found that STIs did not elicit a testosterone response, but caused a dramatic increase in plasma corticosterone. These data support the hypothesis that corticosterone rather than testosterone may play a role in the support of behavior and/or physiology during acute territorial encounters in single-brooded species.     

Developmental experience alters information coding in auditory midbrain and forebrain neurons

In songbirds, species identity and developmental experience shape vocal behavior and behavioral responses to vocalizations. The interaction of species identity and developmental experience may also shape the coding properties of sensory neurons. We tested whether responses of auditory midbrain and forebrain neurons to songs differed between species and between groups of conspecific birds with different developmental exposure to song. We also compared responses of individual neurons to conspecific and heterospecific songs. Zebra and Bengalese finches that were raised and tutored by conspecific birds, and zebra finches that were cross‐tutored by Bengalese finches were studied. Single‐unit responses to zebra and Bengalese finch songs were recorded and analyzed by calculating mutual information (MI), response reliability, mean spike rate, fluctuations in time‐varying spike rate, distributions of time‐varying spike rates, and neural discrimination of individual songs. MI quantifies a response's capacity to encode information about a stimulus. In midbrain and forebrain neurons, MI was significantly higher in normal zebra finch neurons than in Bengalese finch and cross‐tutored zebra finch neurons, but not between Bengalese finch and cross‐tutored zebra finch neurons. Information rate differences were largely due to spike rate differences. MI did not differ between responses to conspecific and heterospecific songs. Therefore, neurons from normal zebra finches encoded more information about songs than did neurons from other birds, but conspecific and heterospecific songs were encoded equally. Neural discrimination of songs and MI were highly correlated. Results demonstrate that developmental exposure to vocalizations shapes the information coding properties of songbird auditory neurons. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 70: 235–252, 2010.     

Encounter-induced hostility to neighbors in the ant Pristomyrmex pungens

Field observations have demonstrated that internest hostilityis negatively correlated with the distance between nests inthe Japanese queenless ant, Pristomyrmex pungens. This runscounter to the "dear enemy" phenomenon. This result led us tohypothesize the existence of encounter-induced hostility inP. pungens. We created "neighbor(s)" and "stranger(s)" by anexperimental method and tested the ant's ability to discriminatethe neighbors from strangers. The results indicated that theant could distinguish the neighbors from the strangers and displayedsignificantly stronger hostility toward the neighbors. The recognitionof neighbors was quickly established after a few encountersand was maintained for at least 10 days after the most recentencounter. Nest mates without direct encounter experience withneighbors did not show hostile behavior toward neighbors. Thesefindings suggest that information about neighbors (probablycolony odor) is not transmitted to nest mates within the colonies.Aggressiveness toward the neighbors appears to be caused andmaintained on the basis of individual memories from direct contact.It may be adaptive for a species that changes nest sites frequentlyto discriminate strangers from neighbors and selectively attackthe latter.     

Motor control of birdsong

One of the challenges when considering the motor control of birdsong is to understand how such a wide variety of temporally and spectrally diverse vocalizations are learned and produced. A better understanding of central neural processing, together with direct endoscopic observations and physiological studies of peripheral motor function during singing, has resulted in the formation of new theoretical models of song production. Recent work suggests that it may be more profitable to focus on the temporal relationship between control parameters than to attempt to directly correlate neural processing with details of the acoustic output.     

Sound production and reproductive behaviour of the armoured catfish Corydoras paleatus (Callichthyidae)

Sound production during reproductive behaviour, dyadic encounters and distress situations was investigated in the callichthyid catfish Corydoras paleatus. Sounds were broad-band, pulsed, acoustic signals produced during abduction of the pectoral spines. Only males emitted trains of sounds during courting and trains of sounds of shorter duration during dyadic encounters. Several males, which are usually smaller than females, courted one gravid female without obvious cooperation or competition between them. During mating, one previously vocalizing male clasped the female's barbels with one pectoral spine and inseminated the eggs. The number of successful spawnings, days until spawning, and number of eggs laid was not related to the number of males (one, two or three) combined with one female. Males did not behave aggressively towards each other during courting or in dyadic encounters. In distress situations, when fish were hand held, both sexes and juveniles produced single sounds. The dominant frequency was negatively correlated with body size and the sound duration was positively correlated with relative length of pectoral spines (standardized to body length). This acoustical behaviour in C. paleatus differs considerably from Hoplosternum thoracatum, a representative of the callichthyine subfamily, in which vocalization was observed during territorial behaviour in males and aggressive behaviour in both sexes. This is the first report of a major difference in vocalizing behaviour within one teleost family.     

褐鹛属鸟类的鸣声特征及种间比较

在雀形目鸟类系统分类和进化研究中,鸣声有重要作用。褐鹛属（Fulvetta）是近年从雀鹛类（Alcippe）独立的属,其鸣声特征及种间差异尚缺乏定量研究。我们于2016至2022年在野外录制了该属7种463只个体的鸣声,包括棕头雀鹛（F. ruficapilla,n=64）、褐头雀鹛（F. manipurensis,n=71）、白眉雀鹛（F. vinipectus,n=124）、中华雀鹛（F. striaticollis,n=64）、路氏雀鹛（F. ludlowi,n=33）、灰头雀鹛（F. cinereiceps,n=84）和玉山雀鹛（F. formosana,n=23）。基于野外行为观察,将鸣声区分为鸣叫和鸣唱,并将鸣叫分为联络鸣叫、呼唤鸣叫、报警鸣叫及觅食鸣叫4种类型。对鸣唱的声谱图进行人工检视,划分为1～8种鸣唱型。采用多变量方差分析（MANOVA）比较鸣声参数种间差异,显示最高频率、最低频率、峰频率、句子持续时间、频率宽度、平均熵6个参数在该属7种间均有显著性差异。将7种褐鹛鸣声特征的马氏距离与种间遗传距离进行Mantel检验,表明鸣唱特征与种间遗传距离呈正相关（r=0.51...     

Motor stereotypy and diversity in songs of mimic thrushes

The relationship between the motor and acoustic similarity of song was examined in brown thrashers (Toxostoma rufum) and grey catbirds (Dumetella carolinensis) (family Mimidae), which have very large song repertoires and sometimes mimic other species. Motor similarity was assessed by cross correlation of syringeal airflows and air sac pressures that accompany sound production. Although most syllables were sung only once in the song analyzed, some were repeated, either immediately forming a couplet, or after a period of intervening song, as a distant repetition. Both couplets and distant repetitions are produced by distinctive, stereotyped motor patterns. Their motor similarity does not decrease as the time interval between repetitions increases, suggesting that repeated syllables are stored in memory as fixed motor programs. The acoustic similarity between nonrepeated syllables, as indicated by correlation of their spectrograms, has a significant positive correlation with their motor similarity. This correlation is weak, however, suggesting that there is no simple linear relationship between motor action and acoustic output and that similar sounds may sometimes be produced by different motor mechanisms. When compared without regard to the sequence in which they are sung, syllables paired for maximum spectral similarity form a continuum with repeated syllables in terms of their acoustic and motor similarity. The prominence of couplets in the “syntax” of normal song is enhanced by the dissimilarity of successive nonrepeated syllables that make up the remainder of the song. © 1996 John Wiley & Sons, Inc.