Painted Bunting Migration
The Painted Bunting (Passerina ciris) is one of the most colorful and unusual songbirds in North America. This species of songbird has a very peculiar migration strategy showing delayed plumage maturation, which is very rare in songbird. Males wait until their second year to molt into their characteristic “painted” bright plumage. While field observations suggest the buntings molt in the thorn scrub of western Mexico, chemical signatures in the buntings feathers (stable isotope ratios) suggest that there may be more than one migration destination; or at least two different migration strategies within the same Oklahoma breeding population.
Stable isotope ratios in feathers reflect the nature of dietary hydrogen and carbon sources used during feather growth. Examination of feathers grown during the post-breeding period (during or after fall migration) revealed a bimodal distribution of stable carbon isotope ratios (δ13C), indicating that some birds molted in areas dominated by C3 photosynthesis whereas others grew feathers in a C4 environment.
These dietary differences were also associated with shifts in stable hydrogen isotope ratios (δD) during molt, which indicate regional scale geographic movement.
The above map is of Painted Bunting breeding distribution (shown in blue), wintering grounds (brown), and potential molt stopover area (yellow). The purple arrows indicate a possible migratory route for xeric squatters, which includes a molt stopover in the Sonoran Desert. The green arrows indicate possible routes taken by mesic movers. Question marks denote aspects of migration that cannot be inferred from feather isotopes. Red asterisks show collection sites of molting specimens, and green circles indicate proposed feather collection sites.
Female Painted Bunting
Migration is energetically taxing and dangerous. A few studies indicate that mortality risk faced by a migrating songbird is ten times greater during migration than during either the summer or winter. One reason that most birds in North America grow new feathers at the end of the breeding season and before fall migration is to increase the speed and efficiency of migration. Painted buntings in the southwest, however, take a different approach. They head south soon after they finish raising their young, but they don’t fly all the way to their winter home. Instead they stop-over in western Mexico where the monsoons have started and the food is super abundant and the number of predators (and parasites) is relatively few. It may be possible that this environment allows the buntings to grow better feathers faster than they would be able to in the summer range.
We use geolocation tags to investigate the large-scale movements of the birds. If such a device is attached to a bird and later retrieved, the large-scale movements of the animal can be inferred based on the length of each day (which indicates latitude) and the time of solar noon (which indicates longitude). Geologgers are being fitted to individual birds using a simple leg harness made of elastic beading cord.
To help us understand the unusual breeding distribution of Painted Buntings and the evidence of multiple migration strategies, we are working to establish genetic markers that can distinguish different breeding populations and provide insight into their evolutionary history. More on Genetic Markers ...
GOALS OF THE PROJECT
Recent studies linking changes in migration phenology to warming trends make it clear that understanding migratory plasticity is critical for predicting avian responses to changing climate and land use. Our preliminary work has identified the Painted Bunting as an intriguing candidate for studies of migratory plasticity, and our proposed work will take place in an area that will undergo relatively intensive climatic changes in the coming decades, according to conservative projections.
Our goal is to quantify the connections between Oklahoma breeding locations, molting locations, and winter locations. These data will help us understand if there is a single or multiple migration strategies in our population of painted buntings. This information will improve our understanding of how migration behaviors evolve and how we might manage habitats to increase the survival and reproductive success of migrants.