The Influence of
Connectivity on Migration Stopover Strategies
My research seeks to increase our understanding of migration ecology by connecting migration with other periods of the annual cycle through the use of intrinsic markers such as stable isotopes, genetic markers, and plumage coloration. Our understanding of the physiology, behavior, and ecology of migratory birds during stopover has been limited by the lack of knowledge of a bird’s point of departure as well as their ultimate destination. Recent advances in the use of intrinsic markers such as stable isotopes have enhanced our ability to discern at broad scales how breeding populations are spatially distributed throughout the annual cycle. Specifically, stable hydrogen isotopes (δD) are a powerful research tool in assigning origin for a migratory species because predictable continental patterns of
δD in precipitation are highly correlated with δD of body tissues of birds due to trophic level interactions.
This relationship is primarily associated with latitude, as southern latitudes are more enriched in
δD than northern latitudes. Since many species of migrant warblers molt their feathers on or near their breeding grounds before migration, the isotopic signature of their feather should reflect the isotopic signature of that breeding site. The integration of stable isotopes with other intrinsic markers such as genetic markers and plumage coloration enhances our ability to identify the breeding area destination of migratory birds during migration and enables the examination of in-depth questions about stopover ecology which were previously not possible. We can now integrate information about a bird’s breeding location with factors known to be important to the success of migration for innovative approaches that provide a more comprehensive understanding of stopover ecology of small passerines.
I propose to utilize information from stable isotopes, genetic markers, and plumage coloration to identify breeding area destination of Wilson’s Warblers (Wilsonia pusilla) utilizing riparian habitat in the
southwestern U.S. during spring migration. Once I know the breeding destination of migrating warblers, I can assess (1) how far migrants must travel from the stopover site to their breeding area and (2) whether migrants are early or late relative to other birds traveling to the same breeding region. The addition of quantitative measure of relative timing of migration and distance to destination area allows for a more comprehensive, integrated understanding of the strategies used by migratory birds during stopover. Migration stopover strategies of interest include fuel deposition rates, stopover duration, orientation, and immune function. To further our understanding of stopover ecology, results from the proposed research will be integrated with other factors known to influence migration strategies such as competition, predation, weather, and age of the bird
Spatial and Temporal Migration Patterns of
Wilson’s Warbler (Wilsonia pusilla) in the Southwest
as Revealed by Stable Isotopes
I used stable hydrogen isotopes (δD) to identify the breeding locations of Wilson’s Warbler (Wilsonia pusilla) migrating through five sites spanning a cross-section of the species’ southwestern migration route during the springs of 2003 and 2004. At all five migration sites, I found a significant negative relationship between the date Wilson’s Warblers passed through the sampling station and
δD values of their feathers. These data were consistent with a pattern of “leap-frog” migration, in which individuals that bred the previous season at southern latitudes migrated through migration stations earlier than individuals that had previously bred at more northern latitudes. I documented that this pattern was consistent across sites and in multiple years. This finding corroborates previous research conducted on Wilson’s Warbler during the fall migration. In addition, mean
δD values became more negative across sampling stations from west to east, with the mean
δD values at each station corresponding to different geographic regions of the Wilson’s Warblers’ western breeding range. These data indicate that Wilson’s Warblers passing through each station represented a specific regional subset of the entire Wilson’s Warbler western breeding range. As a result, habitat alterations at specific areas across the east-west expanse of the bird’s migratory route in the southwestern United States could differentially affect Wilson’s Warblers at different breeding areas. This migration information is critical for management of Neotropical migrants, especially in light of the rapid changes presently occurring over the southwestern landscape.
Paxton KL, van Ripper C III, and O’Brien C. 2008. Movement patterns and stopover ecology of Wilson’s Warblers during spring migration on lower Colorado River in southwestern Arizona.
Condor [in press].
van Ripper C III, Paxton KL, O’Brien C, Shafroth P, and McGrath LJ 2008. Rethinking avian response to Tamarix on the Lower Colorado River: a threshold hypothesis. Restoration Ecology 16:155-167.
Paxton KL, van Riper C III, Theimer TC and Paxton EH. 2007. Spatial and temporal migration patterns of Wilson’s Warblers (Wilsonia pusilla) in the southwest as revealed by stable isotopes. Auk 124:162-175
Gitlin AR, Stultx CM, Bowker MA, Stumpf S, Paxton KL, Kennedy K, Munoz A, Bailey JK and Whitham TG. 2006. Dominant plants as “barometers of change” during record droughts: local and regional patterns of mortality. Conservation Biology 20: 1477-1486.
Department of Biological Sciences The University of Southern
Mississippi 118 College Drive # 5018 Hattiesburg, MS