Browsing by Autor "Michael S. Husak"

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Ecological determinants of<i>Tyrannus</i>flycatcher nestling growth at north- and south-temperate latitudes
(Oxford University Press, 2018) Diego T. Tuero; Alex E. Jahn; Michael S. Husak; Diane V. Roeder; Diego Masson; Florencia M. Pucheta; Tyler J. Michels; Aaron Quickle; Julián Quillén Vidoz; Marisol Domínguez
An organism's life history strategy is made up of a suite of physiological, behavioral, and ecological traits, which vary at both the interspecific and intraspecific levels in accordance with selective pressures operating on individuals. For birds, 2 primary ecological factors have been proposed to explain intraspecific and interspecific variation in nestling growth: nest predation and food availability. Individual nestling growth rates have important consequences for overall fitness because growth speed could influence subsequent reproductive performance and survival. We studied the relationship between ecological factors (i.e. precipitation level and predation rate) and nestling growth patterns of 2 New World flycatcher species (Tyrannidae) of the genus Tyrannus (Fork-tailed Flycatcher [T. savana] and Scissor-tailed Flycatcher [T. forficatus]) breeding at south-and north-temperate latitudes. We tested the hypothesis that nestling growth rates are driven by nest predation rates and predicted that nestling growth rates would be higher in species experiencing higher nest predation rates. We also tested the hypothesis that nestling growth rates are related to precipitation levels (a proxy for food abundance) and predicted that nestling growth rates would be higher at sites with higher precipitation levels. Growth rate was not associated with predation rate, but it varied with precipitation level, with faster nestling growth rates during wet years for the Scissor-tailed Flycatcher living at north-temperate latitudes. Among species, similar growth rates were found during wet years. These results indicate that, at least as proximate causes, precipitation explains intraspecific and interspecific growth rate variation in Tyrannus species to a larger degree than predation. Additionally, the variation in growth rate we observed between wet and dry years indicates a high level of plasticity in growth rate in this group of insectivorous birds.
Migration timing and wintering areas of three species of flycatchers (<i>Tyrannus</i>) breeding in the Great Plains of North America
(Oxford University Press, 2013) Alex E. Jahn; Víctor R. Cueto; James W. Fox; Michael S. Husak; Daniel H. Kim; Diane V. Landoll; Jesús N. Pinto‐Ledezma; Heather K. Lepage; Douglas J. Levey; Michael T. Murphy
Descriptions of intra-and interspecific variation in migratory patterns of closely related species are rare yet valuable because they can help assess how differences in ecology and life-history strategies drive the evolution of migration. We report data on timing and location of migration routes and wintering areas, and on migratory speed and phenology, of Eastern Kingbirds (Tyrannus tyrannus) from Nebraska and Oklahoma and of Western Kingbirds (T. verticalis) and Scissor-tailed Flycatchers (T. forficatus) from Oklahoma. Eastern Kingbirds primarily departed the breeding site in September, migrating to the Amazon Basin (Bolivia and Brazil), >6,400 km from their breeding site, then used a second wintering site in northwestern South America (Colombia, Ecuador, and Peru) before returning to the breeding site in April. Western Kingbirds left Oklahoma in late July, migrating >1,400 km to northwestern Mexico, then to central Mexico and finally to Central America before returning to Oklahoma in April. Scissor-tailed Flycatchers departed Oklahoma mainly in mid-October, migrating to Central America (El Salvador, Guatemala, Honduras, and Nicaragua), ~2,600 km from the breeding site, remaining there until early April before returning to Oklahoma. Timing of migration appears to be tightly linked to molt. Early departure of Western Kingbirds from the breeding site appears to be timed so that they molt in the Sonoran Desert region during the monsoon, whereas Scissor-tailed Flycatchers remain at their breeding site to complete molt in late summer, when insect prey are abundant. Eastern Kingbirds delay molt until reaching South America where, possibly, abundant fruit supports molt.