Recent advances in the analysis of intrinsic markers, particularly stable isotopes, have allowed great insight into interactions between different stages of the annual cycle of migratory birds. Hydrogen isotope ratios, because of strong latitudinal trends in their distribution, have been widely used to address long-distance movements of migratory birds. Likewise, carbon isotope ratios have been useful in examinations of habitat quality because of their responsiveness to changes in plant community composition. However, basic assumptions underlying the use of certain isotopes have yet to be adequately examined. Additionally, much of the research regarding seasonal interactions in migratory songbirds comes from study of a single species, and it is unclear whether these findings are applicable to a wider range of migrant songbirds. In this study, I collected tissue samples from black-throated blue warblers (Dendroica caerulescens) at a breeding site in New Hampshire to address two important questions regarding stable isotopes and the investigation of seasonal interactions. First, using feather samples from both adult and juvenile birds, I investigated the influence of age, molt timing, and reproductive effort in determining the stable hydrogen isotope ratios that are incorporated into tissue samples. Secondly, I took claw samples from adult birds to examine the importance of winter habitat quality, as inferred through carbon isotope ratios, in determining subsequent reproductive success. I found that hydrogen isotope ratios in feather samples were significantly influenced by both age and molt timing, though not by reproductive effort. The mechanism underlying age-related isotopic variation is unclear, but may be widespread among passerines. In addition, this study is the first to note a significant seasonal trend in feathers grown throughout a breeding season, although the mechanism for this pattern is also unclear. Taken together, these findings have important implications for the use of hydrogen isotope ratios for purposes of geographic assignment. Further research is needed to determine the prevalence and magnitude of age-related and seasonal trends in hydrogen isotope ratios. I recommend that future studies note the age class of birds when sampling for hydrogen isotopes, and researchers should attempt to collect feathers grown early in the molt cycle. Analysis of carbon isotope ratios from claw samples indicated that winter habitat quality did not directly influence subsequent reproductive success. However, winter habitat quality may have an indirect influence on reproductive output. Females from higher quality wintering sites were in significantly better body condition on the breeding grounds, and settled on more insect-rich breeding territories. Both body condition on the breeding grounds and breeding territory quality have previously been shown to influence subsequent reproductive success, in this and other songbird species. These results indicate that winter habitat quality may be important in determining future reproductive success for black-throated blue warblers, and interactions between events during the wintering and breeding periods may need to be incorporated into future population models for this species.

Thesis (Ph.D.)--Tufts University, 2001. / Adviser: J. Michael Reed. Submitted to the Dept. of Biology. Includes bibliographical references (leaves 115-144). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph. D.)--Washington State University, May 2009. / Title from PDF title page (viewed on Apr. 20, 2010). "School of Biological Sciences." Includes bibliographical references.

Nest and perch locations of Black-throated Blue Warblers in West Virginia, Virginia, and New Hampshire were examined to determine the structural similarities of the vegetation surrounding these sites and to determine the contribution of each location to the description of the territory. Principle component analysis (PCA) was used to determine habitual variables correlated with the location of the nest and perches. Factors derived from the analyses were combinations of either macro or microhabitat subsets of vegetational variables. In the nest site analysis, four macrohabitat factors described the presence of major tree species, along with structural characteristics of the overstory and understory. The interaction of overstory and understory was expressed by the density of vegetation in various layers in the nests. The 4 microhabitat factors were concerned with structures within 1 meter of the nest. Pattern analysis of vegetation structure suggests nest site placement depends on the layering of a discrete overstory and on a particular subset of structural variables which are present in the understory across habitats. Principal component analysis of perch data produced a set of 4 factors describing the contribution of macro and microhabitat variables. Microhabitat factors were highly correlated with the variables DISTANCE FROM TRUNK, LENGTH OF BRANCH, SIZE OF BRANCH, and PERCH HEIGHT. The most strongly correlated macrohabitat variables were BIRCH IMPORTANCE VALUE and % CANOPl COVER. These data indicate males are located at the lower edge of the canopy in mature forests in areas relatively free of understory. Comparison of these data with similar variables measured at nest sites showed male perches are not correlated with nesting locations. In addition, the variation in habitat models based on perches was twice as large as models based on nest sites. When male Black-throated Blue Warblers obtain a territory, habitat is incorporated which is used by the female for nesting, but not by the male for singing or foraging. These nesting sites have less variation in the vegetation surrounding them than perches utilized by the males. / Ph. D.