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1.
Ecol Evol ; 12(1): e8489, 2022 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-35127023

RESUMO

Animals with dependent and vulnerable young need to decide where to raise their offspring to minimize ill effects of weather, competition, parasitism, and predation. These decisions have critical fitness consequences through impacting the survival of both adults and progeny. Birds routinely place their nest in specific sites, allowing species to be broadly classified based on nest location (e.g., ground- or tree-nesting). However, from 2018 to 2020, we observed 24 American robin (Turdus migratorius) nests placed not on their species-typical arboreal substrates or human-made structures but on the ground at a predator-rich commercial tree-farm in Illinois, USA. This behavior does not appear to be in response to competition and did not affect nest daily survival rate but was restricted to the early half of the breeding season. We hypothesize that ground nesting may be an adaptive response to avoid exposure and colder temperatures at sites above the ground early in the breeding season or a nonadaptive consequence of latent robin nest-placement flexibility.

2.
Biol Lett ; 17(9): 20210377, 2021 09.
Artigo em Inglês | MEDLINE | ID: mdl-34520683

RESUMO

Yellow warblers (Setophaga petechia) use referential 'seet' calls to warn mates of brood parasitic brown-headed cowbirds (Molothrus ater). In response to seet calls during the day, female warblers swiftly move to sit tightly on their nests, which may prevent parasitism by physically blocking female cowbirds from inspecting and laying in the nest. However, cowbirds lay their eggs just prior to sunrise, not during daytime. We experimentally tested whether female warblers, warned by seet calls on one day, extend their anti-parasitic responses into the future by engaging in vigilance at sunrise on the next day, when parasitism may occur. As predicted, daytime seet call playbacks caused female warblers to leave their nests less often on the following morning, relative to playbacks of both their generic anti-predator calls and silent controls. Thus, referential calls do not only convey the identity or the type of threat at present but also elicit vigilance in the future to provide protection from threats during periods of heightened vulnerability.


Assuntos
Parasitos , Passeriformes , Aves Canoras , Animais , Feminino , Comportamento de Nidação
3.
R Soc Open Sci ; 8(1): 201615, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33614093

RESUMO

Some hosts of avian brood parasites reduce or eliminate the costs of parasitism by removing foreign eggs from the nest (rejecter hosts). In turn, even acceptor hosts typically remove most non-egg-shaped objects from the nest, including broken shells, fallen leaves and other detritus. In search for the evolutionary origins and sensory mechanisms of egg rejection, we assessed where the potential threshold between egg recognition and nest hygiene may lie when it comes to stimulus shape. Most previous studies applied comparisons of egg-sized objects with non-continuous variation in shape. Here, instead, we used two series of three-dimensional-printed objects, designed a priori to increasingly diverge from natural eggs along two axes (width or angularity) of shape variation. As predicted, we detected transitions from mostly acceptance to mostly rejection in the nests of American robins Turdus migratorius along each of the two axes. Our methods parallel previous innovations in egg-rejection studies through the use of continuous variation in egg coloration and maculation contrast, to better understand the sensory limits and thresholds of variation in egg recognition and rejection in diverse hosts of avian brood parasites.

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