David C. Lahti

Chapter 5 Vocal Performance and Sensorimotor Learning in Songbirds

Abstract This chapter addresses the interplay of vocal performance, sensorimotor learning, and vocal evolution in songbirds. Vocal performance is increasingly recognized as an influential factor in song evolution, particularly with respect to vocal output, song consistency, and trill structure. We argue here that a comprehensive understanding of vocal performance requires attention to sensorimotor learning, a developmental phase during which birds attempt to reproduce song models memorized earlier in life. New research indicates that birds calibrate song structure during sensorimotor ontogeny in order to best match their own vocal performance capacities. Because of this relationship, performance-related features may provide reliable indicators of male quality as manifest during sensorimotor learning. We review evidence in support of the “developmental stress” hypothesis and propose that this hypothesis be expanded to also consider vocal features crystallized during sensorimotor learning. We suggest avenues for future research that document relationships between vocal performance, morphology, and song learning programs.

The Correlated History of Social Organization, Morality, and Religion

Morality and religion have evolutionary and cultural roots in the social behavior of our ancestors . Fundamental precursors and major features of morality and religion appear to have changed gradually in concert with social transitions in our history. These correlated changes involve trends toward increased breadth and complexity of social interaction, leading to a stepwise extension of the scope of human sympathies to more inclusive social categories, and eventually the universalization of moral and religious concepts, practices, and explanations. These changes can be integrated provisionally into an eight-stage model of human social history, beginning with nepotism and dominance that are characteristic of many social mammals, and culminating in the intellectual ability and (sometimes) social freedom of modern human individuals to examine moral and religious conventions, to modify or reject them, and even to propose new ones.

Light Dulls and Darkens Bird Eggs

Although egg color is generally consistent within individual birds and robust to environmental variation, recent evidence suggests a degree of susceptibility to environmental perturbation or modulation of egg color. Most of this variation manifests via the physiology of the laying female, but some direct impacts of the environment on laid eggs have also been discovered. Here we test whether light changes bird egg color and we quantify its effect, by subjecting variable blue-green eggs of Rüppells weaver (Ploceus galbula) to a broad-spectrum light source under laboratory conditions, and measuring egg reflectance every few hours. Eggshells gradually decreased in reflectance across the entire measured wavelength spectrum of 250–800 nm. Reflectance peaks were disproportionately affected, such that the height decreased of both the blue-green peak and the smaller UV peak typical of blue-green eggs. The reflectance of lighter eggs was affected slightly more than that of darker eggs. These changes are similar to previous results for changes over long periods of time in darkness, suggesting that light might hasten the same process of pigment degradation that proceeds even without light. Comparison between the experimental light source and both sunlight and typical artificial lighting situations raises the possibility that significant color change might occur during incubation in some birds, but indicates that eggshell illumination in museums for short periods of study is unlikely to affect their color to a detectable extent. Additional research should be performed on eggs of other species and in other light environments, with an eye to an eventual generalized model of the effect of light on eggshell color.

Combating the Assumption of Evolutionary Progress: Lessons from the Decay and Loss of Traits

Contrary to popular belief, evolution is not necessarily progressive. Indeed, traits are often lost or substantially reduced in the process of evolution. In this article, we present several case studies that can be used in the classroom to illustrate both the ubiquity and diversity of cases of trait loss. Our recently acquired knowledge of genetic and developmental processes can provide insight into how traits are gained and lost through evolution. Several practical applications also emerge from studies of trait loss and degeneration, and we focus on those with medical relevance. Examining trait loss also provides perspective on the crucial differences between Darwinian evolution and social Darwinism. We encourage educators to devote greater attention to trait loss in secondary biology and undergraduate evolution courses, and discuss how such information may be best incorporated into evolution curricula.

Male risk-taking is related to number of mates in a polygynous bird

Lay Summary The male with the most mates is the bravest. If a male village weaverbird leaves his breeding colony when it is threatened, he saves himself but abandons his territory to predators and fierce rivals. This study shows that polygynous male weavers stand their ground during a disturbance according to how much they have to lose, especially how many females occupy their nests. Even the same male will get braver as he gains more females.

Heterospecific intrusions, synchronous fleeing, and nest attendance in a weaverbird colony

AbstractSynchronous fleeing (i.e. “dreads” or “panic flights”) is a frequently observed but rarely quantified behaviour in colonial birds. Here we analyse video recordings to assess synchronous fleeing behaviour in a Village Weaver (Ploceus cucullatus) colony. Our results indicate that intrusions by heterospecific avian species are frequent and create significant daily differences in female nest attendance. Overall, different sizes, masses and species of intruding heterospecifics appear to affect weaver nesting similarly. Our findings suggest that in colonial birds, with the advantage of “many eyes”, a rapid response to a potential threat nevertheless comes at the apparent cost of many “false alarms”.ZusammenfassungFremdartige Eindringlinge, synchrone Flucht und Nestbewachung in einer Kolonie Webervögel Die synchrone Flucht (auch „Panikflug“) ist eine häufig beobachtete aber selten quantifizierte Verhaltensweise von Koloniebrütern. In dieser Studie analysierten wir Videoaufnahmen, um das synchrone Fluchtverhalten in einer Kolonie Dorfweber (Ploceus cucullatus) zu untersuchen. Es zeigte sich, dass Störungen durch fremdartige Vögel häufig waren und diese signifikante Unterschiede in der täglichen Nestbewachung durch Weibchen zur Folge hatten. Insgesamt schienen alle fremdartigen Eindringlinge einen ähnlichen Effekt auf die Dorfweber zu haben, unabhängig von deren Größe, Masse oder Artzugehörigkeit. Diese Ergebnisse verdeutlichen, dass eine schnelle Reaktion auf mögliche Gefahren in Koloniebrütern durch den Vorteil der „vielen Augen“dennoch den Nachteil vieler Fehlalarme mit sich bringt.

The sociality of nesting in Rüppell's Weaver Ploceus galbula and the Lesser Masked Weaver Ploceus intermedius in an Ethiopian acacia woodland

Rüppells Weaver Ploceus galbula and the Lesser Masked Weaver Ploceus intermedius nest prominently in the Awash National Park, Ethiopia. In both species the sociality or degree of aggregation of their nesting is varied. Rüppells Weaver can nest singly or in small clusters, or in association with the Lesser Masked Weaver, which itself can nest in loose aggregations or bustling colonies. This variation suggests a continuum of nesting sociality in weavers, from solitary nesting through associative and gregarious nesting to full coloniality.