Neotropical migrants face multiple challenges throughout their annual cycle. During migration, birds must avoid predation, face adverse weather, and find stopover sites with food adequate to support their needs. Upon return to the breeding grounds following migration, males must find and defend territory from other males. Females incubate eggs and both males and females may participate in feeding young leaving less time to feed themselves. After the breeding season birds undergo the energy intensive process of molt. Declines in populations of Neotropical migrants have been reported over the past several decades. In order to prevent further population declines of Neotropical migrants it is important to understand what stress and physiological changes take place between and within breeding, molt, and migration seasons in order to prioritize management of critical habitats and resources. In order to better understand these seasonal changes in stress and physiology, mass index, plasma triglyceride and uric acid concentrations were measured to determine physiological condition and the heterophil to lymphocyte ratio (H/L ratio) was determined as a measure of chronic stress in Gray Catbirds, Song Sparrows, and Yellow Warblers captured near the south shore of Lake Ontario in the spring, summer, and fall. Seasonal differences were found in plasma metabolite concentrations and H/L ratios in Gray Catbirds and Song Sparrows. These differences indicated that birds deposit more fat in spring and fall, and are more dependent on protein-rich food sources in spring and summer compared to fall. These results demonstrate that birds utilize different nutrients in different seasons and may require different habitats and food resources depending on the season. Plasma triglyceride concentrations were highest in Gray Catbirds and Song Sparrows in the fall while uric acid concentration was highest in spring and summer for all species. Gray Catbirds experienced the highest amount of chronic stress and parasite loads in the early spring when compared with late spring, summer, and fall. Birds may be particularly vulnerable at this time of year to infection and require high quality stopover sites at which to refuel.

Library of Congress Subject Headings

Migratory birds--Effect of stress on; Migratory birds--Effect of habitat modification on

Publication Date


Document Type


Student Type


Degree Name

Environmental Science (MS)

Department, Program, or Center

Thomas H. Gosnell School of Life Sciences (COS)


Susan Smith Pagano

Advisor/Committee Member

Elizabeth Hane

Advisor/Committee Member

Richard Shearman


Physical copy available from RIT's Wallace Library at QL698.9 .O34 2015


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