Preferential Begging Responses of Shiny Cowbirds to the Conspecific Chatter Call

Avian brood parasites lay their eggs into the nests of other species, which incubate them and raise the chicks until their independence. Despite living their early weeks of life surrounded by heterospecifics, young brood parasites have the ability to recognize and associate to conspecifics after independence. It has been proposed that the initial conspecific recognition develops when a young parasite encounters a unique species-specific signal that triggers the learning of other aspects of the producer of the signal. For cowbirds (Molothrus spp.), this species-specific signal is hypothesized to be the chatter call. Young birds also could express auditory biases, which in some cases lead to discrimination in favor of conspecific songs. Therefore, the perceptual selectivity for chatters might be also present in nestlings. Our aim was to assess if nestlings of the shiny cowbird (M. bonariensis) present a preferential begging response to conspecific chatter calls. We evaluated if they respond more to the parasitic vocalization than host chicks and if they respond more to the chatter than to heterospecific nonhost calls. We tested shiny cowbird chicks reared by chalk-browed mockingbirds (Mimus saturninus) or house wrens (Troglodytes aedon) and host chicks, as control species. We randomly presented to 6-day-old chicks the following playback treatments: (1) conspecific chatter calls, (2) host calls, used as positive controls, and (3) nonhost calls, used as negative control. We measured if chicks begged during the playback treatments and the begging intensity. When responding to the playback of chatter calls, shiny cowbird chicks begged at a higher frequency and more intensively than host chicks. Shiny cowbird chicks reared by mockingbirds begged more intensively to playbacks of conspecific chatter calls than to host calls, while those reared by wrens begged with a similar intensity to playbacks of conspecific chatter and host calls. On the contrary, wren nestlings begged more intensively to playbacks of the wren call than to chatter calls. Mockingbird nestlings did not beg during any treatment. None of the three species begged during the playback of nonhost calls. Our results show that the chatter call produced a preferential begging response in cowbird nestlings, which may be the beginning of a process of conspecific recognition.

Alarm calls of house wrens (Troglodytes aedon bonariae) elicit responses of conspecific and heterospecific species

Nesting house wrens (Troglodytes aedon bonariae) use two basic alarm calls (Type I and Type II) when detect a threat near the nest. We experimentally analysed if calls distract predators or serve to recruit other birds to create a mobbing flock to deter predators. The results show that individuals preferentially position themselves in front of the threat, disclosing the location of the nest. Also, using playbacks of house wren alarm calls we found that these calls recruited both conspecific and heterospecific individuals to create a mobbing response. The alarm calls of house wrens seem to fulfil multiple functions, not only conveying information about the threat to their mates and nestling as revealed in previous studies, but also as a signal that attracts the attention of other conspecific and heterospecific individuals and can trigger a mobbing response to deter the predator.

Incubation Behavior Differences in Urban and Rural House Wrens, Troglodytes aedon

As global land surfaces are being converted to urban areas at an alarming rate, understanding how individuals respond to urbanization is a key focus for behavioral ecology. As a critical component of avian parental care, incubating adults face a tradeoff between maintaining an optimal thermal environment for the developing embryos while meeting their own energetic demands. Urban habitats are biotically and abiotically different from their rural counterparts, i.e., in food availability, predator compositions, and the thermal environment. Therefore, urban birds may face different incubation challenges than their natural counterparts. We measured incubation behavior of rural and urban house wrens, Troglodytes aedon, with temperature loggers throughout the 12-day period. We found that urban females had more incubation bouts of shorter duration and spent less total time incubating per day than rural females. Results could provide evidence of behavioral shifts of wrens in cities, which have implications for the evolution of parental care. Our findings contribute to our understanding of the behavioral traits needed for city life and possible environmental pressures driving urban adaptations.