The Chincoteague Oystercatcher Project
American Oystercatchers
Photo: Ken King ©
American Oystercatchers are fellow beachgoers -- shorebirds that breed on beaches along the Atlantic Coast, and are a species of conservation concern. Poor food supply, climate change, rising sea levels, predators, and human disturbance threaten oystercatchers. Virginia has the highest proportion of breeding oystercatchers throughout their range, but the number of chicks fledged on two barrier islands in Chincoteague, VA has declined to an unsustainable level. In 3 out of the last 5 years, 0 chicks fledged on one of the islands. Predator and human disturbance management occurs on Chincoteague, but the population continues to decline. Therefore, other factors like foraging habitat quality could be involved.
![IMG_0482[12963].jpg](https://static.wixstatic.com/media/fbceb6_3fe4e672d6d849e2a828e4fa3c0c4897~mv2.jpg/v1/fill/w_147,h_53,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/fbceb6_3fe4e672d6d849e2a828e4fa3c0c4897~mv2.jpg)
Write a title here. Click to edit and add your own.
Foraging
Photo: Ken King ©
Oystercatchers eat bivalves including oysters, mussels, clams and marine invertebrates.
Previous studies indicate that oystercatchers who nest closer to their foraging sites fledge more chicks [1], and areas with more prey have higher chick survival [2]. Oystercatchers provision their chicks until they reach foraging independence at 60 days old [3]. This lengthy provisioning is uncommon among bird species, and stems from the time required to develop the musculature necessary to pry open bivalves and the skill to do so [4].
Connecting food and breeding success
What makes a habitat good for hungry oystercatchers?
Feeding areas closer to nests are higher quality [1]. This is because adults are limited to transporting single prey items to chicks, so feeding closer to the nesting area reduces energy costs of travel for provisioning [5]. Additionally, areas with high food profitability (prey weight/handling time of the prey item) support efficient feeding [6].
Our Research
At Chincoteague it is unknown if foraging habitat quality limits breeding success. We do not know how foraging habitat is distributed, if there is sufficient prey, or what the quality of that habitat is. We hope to develop greater understanding on how the birds use the foraging habitat, and how this relates to individual reproductive success.
To study this we are combining GPS tracking data on foraging habitat use with focal behavioral watches of chick provisioning and foraging, and environmental sampling of factors that drive prey distribution.
Photo: U.S. Fish and Wildlife Service
Photo: U.S. Fish and Wildlife Service
The GPS data loggers allow us to identify distant foraging areas, foraging site fidelity, and when the birds feed relative to the tidal cycle and day-night cycle. Our behavioral observations consist of recording the habitat where the birds feed, the prey species eaten, the size of the prey, how much is eaten, and how much of that adults give to their chicks. We are taking water quality measurements that drive prey distribution including water temperature, salinity, dissolved oxygen, and chlorophyll. Chlorophyll is an indicator of phytoplankton abundance, which is the primary food source for the bivalves that oystercatchers eat.
References
1. Nol, E. (1989). Food supply and reproductive performance of the American Oystercatcher in Virginia. The Condor, 91, 429-435. https://doi.org/10.2307/1368321
Ens, B. J., Kersten, M., Brenninkmeijer, A., & Hulscher, J. B. (1992). Territory quality, parental effort and reproductive success of oystercatchers (Haematopus ostralegus). Journal of Animal Ecology, 61(3), 703–715. https://doi.org/10.2307/5625
2. Vitale, N., Brush, J., & Powell, A. (2022). Factors limiting reproductive success of American Oystercatchers (Haematopus palliatus) in Florida's Southern Big Bend Region. Waterbirds, 44(4), 449-462. https://doi.org/10.1675/063.044.0406
3. Virzi, T. (2022). American Oystercatcher: Birds of the World Account. American Oystercatcher Working Group. http://amoywg.org/american-oystercatcher/breeding/
4. Hand, C. E. (2008). Foraging ecology of American oystercatchers in the Cape Romain region, South Carolina (Doctoral dissertation, Clemson University). https://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1468&context=all_theses
5. Kersten, M. (1996). Time and energy budgets of oystercatchers Haematopus ostralegus occupying territories of different quality. Ardea, 84, 291-310. https://research.rug.nl/en/publications/time-and-energy-budgets-of-oystercatchers-ihaematopus-ostralegusi
6. Zwarts, L., Cayford, J. T., Hulscher, J. B., Kersten, M., Meire, P. M., & Triplet, P. (1996). Prey size selection and intake rate. In J. D. Goss-Custard (Ed.), The oystercatchers from individuals to populations (pp. 30-55). Oxford University Press, Oxford.