Calling at a cost: elevated nestling calling attracts predators to active nests

Begging by nestling birds has been used to test evolutionary models of signalling but theory has outstripped evidence. Eavesdropping predators potentially impose a cost on begging that ensures signal honesty, yet little experimental evidence exists for such a cost at active nests because the use of artificial nests, long playback bouts and absence of parents may have exaggerated costs. We broadcast short periods (1 h) of either nestling vocalizations or background noise at active white-browed scrubwren, Sericornis frontalis, nests. Nestlings called naturally during both treatments, allowing us to test whether elevated calling increases risk, a key but rarely tested assumption of evolutionary models. Predators visited nests exclusively during periods of elevated calling. Furthermore, playbacks affected neither adult visits nor nestling activity, suggesting that calling alone attracted predators. Adults gave alarm calls and nestlings usually called less when predators approached nests. Predation risk to broods is, therefore, likely to fluctuate substantially over short periods of time, depending on nestling hunger and whether adults or young have detected predators. This study confirms a present-day cost of nestling begging, demonstrates that this cost can be incurred over short periods and supports the importance of parent-offspring antipredator strategies in reducing predation risk.     

Song learning in domesticated canaries in a restricted acoustic environment

Many songbirds learn their songs early in life from a song model. In the absence of such a model, they develop an improvised song that often lacks the species-typical song structure. Open-ended learners, such as the domesticated canary, are able to modify their songs in adulthood, although the mechanisms that guide and time the song-learning process are still not fully understood. In a previous study, we showed that male domesticated canaries lacking an adult song model in their first year substantially change their song repertoire and composition when exposed to normally reared conspecifics in their second year. Here, we investigate song development in descendants of canaries that were raised and kept as a peer group without a song model. Such males represent tutors with abnormal song characteristics. Interestingly, the F₁ generation developed quite normal song structure, and when brought into an environment with normally raised canaries in their second year, they did not modify their songs substantially. These results suggest that contact with an adult song model early in life is crucial for song crystallization, but also that song development is at least partly guided by innate rules. They also question the existing classification of canaries as open-ended learners.     

Are northern mockingbirds classic open-ended song learners?

The northern mockingbird (Mimus polyglottos, Linnaeus) is considered a classic example of a species in which individuals learn songs throughout adulthood, but this assumption has not been tested rigorously. To assess whether mockingbirds should be categorized as open-ended learners, I conducted a longitudinal study and a field-based song-tutoring experiment. I recorded songs from 15 free-living, banded, adult males in an earlier year and a later year, and I classified 400 mimetic songs per year per individual, based on the species and vocalization type mimicked. For two of these “mimetic types,” I further classified all the song types of all individuals in their early and later samples. The number of song types increased significantly across years for both mimetic types, and the average number of observed mimetic types per individual was 46.4 and 47.7 in the early and late samples (p = .055). I found no evidence adults learned any tutor stimuli after six months of tutoring, but examples from the scientific literature suggest the tutoring regime might not have been adequate to pass the motivational threshold required for learning. I conclude that mockingbirds probably are open-ended learners, but that future research is needed to verify experimentally that adults can indeed imitate novel song types.     

Sex-specific responses to vocal convergence and divergence of contact calls in orange-fronted conures (Aratinga canicularis)

We investigated the signal function of vocal imitation of contact calls in orange-fronted conures (OFCs; Aratinga canicularis) in Costa Rica. OFCs live in dynamic social systems with frequent flock fusions and fissions. Exchanges of contact calls precede these flock changes. During call exchanges, the similarity between the contact calls of different individuals may either increase (converge) or decrease (diverge). We conducted a playback experiment on wild-caught captive birds in which we simulated convergent, divergent and no-change interaction series with male and female contact calls. OFCs responded differently to convergent and divergent series of contact calls, but only when we considered the sex of the test birds. Males called most in response to convergent series, whereas females demonstrated high calling rates in response to both convergent and divergent interactions. Both sexes responded most to contact calls from the opposite sex, but overall females produced more calls and had shorter latencies to calling than males. These results demonstrate that OFCs can discriminate between male and female contact calls and that subtle changes in contact call structure during interactions have signal function. The stronger overall response to convergent series suggests that convergence of contact calls is an affiliative signal.     

Wild Birds Learn Songs from Experimental Vocal Tutors

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Daytime noise predicts nocturnal singing in urban robins

Ambient noise interferes with the propagation of acoustic signals through the environment from sender to receiver. Over the past few centuries, urbanization and the development of busy transport networks have led to dramatic increases in the levels of ambient noise with which animal acoustic communications must compete. Here we show that urban European robins Erithacus rubecula, highly territorial birds reliant on vocal communication, reduce acoustic interference by singing during the night in areas that are noisy during the day. The effect of ambient light pollution, to which nocturnal singing in urban birds is frequently attributed, is much weaker than that of daytime noise.     

不同生长发育期的虎皮鹦鹉发声行为与发声控制神经核团的研究

鸟类的鸣叫依赖于发育完善的鸣管并接受各级发声中枢组成的机能控制系统的调控,善鸣唱的鸟类前脑控制发声的神经核团发达.用石蜡切片法和生物信号采集处理系统对不同生长发育期的虎皮鹦鹉的发声控制神经核团的体积和声音进行了比较性研究.结果发现:(1)随着虎皮鹦鹉的成长,核团体积逐渐增大,核团轮廓逐渐清晰,而且雄鸟的核团明显大于雌鸟;(2)在鸟类成长的过程中,鸟的叫声越来越复杂,幅度越来越高,雄鸟的叫声比雌鸟更复杂,雌鸟的叫声比雄鸟的叫声幅度更高;(3)鸟类鸣叫的复杂程度和发声控制神经核团的体积呈相关性.