Are prey remains accurate indicators of chick diet? A comparison of diet quantification techniques for Black Oystercatchers
April 15, 2018
The quantification of prey remains is a common method for estimating the diet of a variety of birds. However, these estimates may be subject to biases based on prey body type, nesting habitat, and collection date. To better understand biases and limitations associated with this method, we compared it with two others commonly used to characterize diet: direct observation of parents feeding young and diet reconstruction by stable isotope analysis. In 2013-14, we monitored the diet of 20 Black Oystercatcher broods in south-central Alaska using all three methods, having collected 2126 prey remains, observed 1979 prey items fed to chicks, and obtained stable isotopes values of 39 blood samples from 22 chicks. Direct observations and stable isotope techniques similarly characterized diet composition but these approaches yielded different results from those obtained using prey remains. Soft-bodied prey, such as worms, were not detected in prey remains, and filter-feeders were under-represented. For example, mussels and barnacles, which have flesh that can be removed without having to detach the shell from the substrate, were underestimated using prey remains (mussels: 33% for prey remains vs. 44%, 43% for observations and stable isotopes, respectively; barnacles: 2% vs. 9%, 8%, respectively). On rocky islands, where chicks are confined to a small area around the nest, there were significantly greater quantities of prey remains constituting different diets than on gravel beaches, where chicks leave the nest site within days of hatching. For researchers using prey remains to monitor diet, we suggest that they combine this method with direct observations or stable isotope analysis to understand what prey items may be missed or under-represented.
Citation Information
Publication Year | 2018 |
---|---|
Title | Are prey remains accurate indicators of chick diet? A comparison of diet quantification techniques for Black Oystercatchers |
DOI | 10.18194/ws.00105 |
Authors | B.H. Robinson, H.A. Coletti, L.M. Phillips, Abby Powell |
Publication Type | Article |
Publication Subtype | Journal Article |
Series Title | Wader Study |
Index ID | 70208022 |
Record Source | USGS Publications Warehouse |
USGS Organization | Coop Res Unit Atlanta |
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1 Gifford Pinchot Drive
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United States
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These data are part of the Gulf Watch Alaska (GWA) long-term monitoring program, nearshore monitoring component. The dataset is comprised of six comma separated values (.csv) file exported from a relational database. The data consist of: 1) transect summary, 2) nest details, 3) egg float and stage data, 4) chicks diets, 5) chick diet taxonomy, and 6) Gulf Watch Alaska contributors.
Upper Midwest Water Science Center - Madison, WI, Office
1 Gifford Pinchot Drive
Madison, WI 53726
United States
Brian H Robinson (Former Employee)
Wildlife Biologist
Wildlife Biologist
Abby Powell, PhD
Research Wildlife Biologist
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Email
Phone