Showing 1 - 3 of 3 Items
The development of begging calls in Yellow Warblers
Date: 2015-05-01
Creator: Jackson F Bloch
Access: Open access
- Nestling birds use begging calls to solicit resources from adults. Efficient transmission of calls is necessary for motivating parental feeding and outcompeting siblings. However, ambient acoustic masking and costs such as predation may influence the structure of the calls. While many interspecific comparisons of begging behavior have been made, the ontogeny of calls is understudied. In this study, Yellow Warbler (Setophaga petechia) begging calls were recorded and analyzed at different stages of nestling development to document changes in acoustic structure and gain insight into the selective forces that influence call development. Begging calls increased in peak frequency, frequency range, and amplitude during the 5-day recording period. Call duration did not change with age. Call structure did not differ between nestlings living in distinct acoustic environments. As begging calls increase in amplitude with age, perhaps due to increased food needs and competition from nestmates, nestlings may compensate for increased predation risk by increasing the peak frequency of the calls. Higher frequency calls attenuate more quickly than do low frequency calls and fall outside the frequency range of maximum hearing sensitivity for some potential predators. Previous studies on warbler begging have shown that nestlings of ground-nesting warblers, which are subject to higher rates of predation, beg at higher frequencies than do nestlings of tree-nesting warblers. This study supports the hypothesis that changes to begging call structure during development mirror the differences in call structure of species under different predation risks.
Egg Size, Breeding Phenology, and Parental Investment in Leach’s Storm Petrels Access to this record is restricted to members of the Bowdoin community. Log in here to view.
Date: 2020-01-01
Creator: James L. O'Shea
Access: Access restricted to the Bowdoin Community
Demography of a Collapsing Aerial Insectivore Population
Date: 2017-05-01
Creator: Liam Taylor
Access: Open access
- Aerial insectivores have been declining across northeastern North America since the end of the 20th century. The mechanisms and demographic patterns of this decline are unclear. On Kent Island, New Brunswick, Canada, an isolated population of Tree Swallows (Tachycineta bicolor) collapsed between 1987 and 2010. To explore how demographic rates (i.e., survival, reproduction, and immigration) drove the population dynamics of these northeastern aerial insectivores, we combined productivity, population survey, and capture-recapture data in an integrated population model analysis. Neither consistently low juvenile survival rates, adult survival rates, nor clutch size were correlated with population growth rate across years. Alternatively, male and female immigration, hatching success, and fledging success rates were correlated with population growth rate. Because local hatching and fledging success rates cannot influence a population without local recruitment, we argue that the demography of these Tree Swallows is mainly structured by immigration. Parameter-substitution simulations revealed that overall decline was likely even if the population had avoided the worst years of demographic collapse. Breeding Bird Survey comparisons demonstrated how the Kent Island population represents both a demographic and geographical extreme at the edge of a declining region. These demographic patterns highlight the sensitivity, even to the point of local extinction, of some isolated populations to region-scale patterns in the production of potential immigrants.