The aim of this project is to assess both the direct impacts of the Deepwater Horizon oil spill on migrating shorebirds as well as the carry-over effects of the spill on distant ecosystems where these birds breed during summer months. Carry-over effects on breeding success resulting from the degradation of winter habitat have been documented in several avian species and are important not only to shorebird populations but also to the entire ecosystems in which the shorebirds breed. The investigators will compare oil-exposed versus unaffected control sites with respect to the toxicological status of individual birds, contamination levels in the environment, food availability, survival, correlates of subsequent breeding success, and other indicators of fitness for four small wintering shorebirds. The outcome will be to determine how individual toxicological status and environmental status contribute to variation in measures of fitness and correlates of breeding success. This work will provide a foundation for the development of population models and further studies aimed at documenting the effects of the oil spill on the distant, Arctic ecosystems where these birds breed.
This work will highlight the importance of Gulf of Mexico habitats as wintering grounds for migrating shorebirds, providing baseline information for the conservation of threatened coastal habitats and bird species and demonstrating the multiple ways in which a major environment disaster can affect ecosystems on a global scale. Part of this project will be to develop a novel assay for measuring oil ingestion using fecal samples of birds. This project will provide training for one PhD student, four undergraduates and one postdoctoral researcher. Citizen scientists will be engaged to help re-sight banded birds.
NSF Final Outcomes Report December 17, 2012 Introduction: The wetlands impacted by the Deepwater Horizon oil spill are important habitats for 34 species of shorebirds, including 28 migratory species that spend all or part of their non-breeding seasons on the Gulf coast. Migration success in birds is highly dependent on a birds’ ability to refuel (put on fat) at migratory stopover sites. Changes to shorebird foraging habitat due to habitat degradation, such as from an oil spill could therefore severely impact their populations. Predicting these impacts requires a detailed understanding of the interactions between shorebirds and their habitats. However, the refueling performance and migration ecology of shorebirds on the northern Gulf have not been well studied. Some coastal wintering shorebird species are believed to use a "jump" migration strategy; migrating long distances in the spring from coastal habitats on the northern Gulf of Mexico (NGOM) to the northern Prairie pothole region of North America without stopping. Other species use a "hop" migration strategy stopping at shorter intervals in agricultural fields and natural wetlands along their migratory journey. (Figure 1) We investigated the importance of NGOM habitats to the migration ecology of shorebirds. We trapped a shorebirds across 8 species from October 2010-May 2012 at 6 study sites of varying habitat types and level of oiling from the Deepwater Horizon spill. We measured each bird and assessed body condition. Blood samples from birds from three species (Western sandpipers (Calidris mauri), Semipalmated sandpipers (C. semipalmatus) and Dunlin (C. alpina) were analyzed for plasma metabolite levels, which have been shown to be indicators of fattening rates in shorebirds. For migrating shorebirds, one of the primary factors determining migration success is the efficiency of refueling rates at stopover sites. Therefore fattening rates of birds on migration can be used as a proxy for habitat quality when comparing stopover sites. Differences in fattening rates were investigated within species across 4 types of habitats as well as across varying levels of oiling from the Deepwater Horizon spill. In order to investigate variation in food resource abundance and quality at our study sites we also collected invertebrate and sediment core samples and the abundance and diversity of invertebrates was measured. Findings: We have trapped and sampled a total of 688 shorebirds across 8 species. Blood samples from 372 birds from three species (Western sandpipers, Semipalmated sandpipers and Dunlin) were analyzed for plasma metabolite levels. Of birds trapped, 8.6% of the shorebirds showed visible signs of oiling. Preliminary results suggest support for our hypotheses regarding differences in departure fuel loads for species migrating across different distances. Dunlin, which are considered longer distance migrants, appear to reach much higher fuel loads (ie., Fat scores) before departing stopover sites in comparison with the Semipalmated and Western sandpiper, species that are believed to ‘hop’ or ‘skip’ their way up to near-arctic breeding grounds. However, while longer distance migrants appear to be reaching higher fuel departure loads before departing on migration, these differences do not seem to be supported by differences in refueling rates as measured through plasma metabolites. We have identified the invertebrates in 40 samples to date, with 125 additional samples to analyze. Preliminary trends observed in oiled sites that suggest oiled sites have proportionally fewer sensitive species (amphipods), and the diversity in oiled sites is lower than in the most pristine site. Although these effects are not contributable directly to the Deepwater Horizon oil spill, this study may serve as background for future studies and provide information on coastal benthic invertebrate communities in habitats that have not been well studied in the Gulf of Mexico previously. In addition to the traditional field and laboratory work described above, we have conducted in depth research into the primary literature concerning shorebirds on the northern Gulf of Mexico and the potential impacts of an oil spill on migratory shorebirds. We have calculated that more than one million migratory shorebirds representing 28 species were potentially exposed to Deepwater Horizon oil during their 2010-2011 nonbreeding season. Although only 8.6% of the shorebirds we trapped from fall 2010 to spring 2011 showed visible signs of oiling, nonlethal effects and degradation of habitat can affect populations in ways that carry over into subsequent seasons. Nonlethal effects on birds could include diminished health, diminished plumage quality, prey and habitat switching, delayed migration and more. All of these setbacks can lead to reduced productivity in breeding shorebirds, which in turn could impact food chains in places far and wide in ecosystems where migratory shorebirds breed, such as the Canada Prairies, the Great Plains, the Great Lakes, and even the Arctic. We, therefore, suggest that migratory shorebirds provide a system for evaluating the direct and indirect effects of an oil spill on affected habitats and the potential for carryover effects to other ecosystems.
