The American Oystercatcher is listed as a “species of special concern” in North Carolina. The objectives of our research are to evaluate the status and viability of North Carolina’s oystercatcher population, as well as factors that may be affecting the population. We would also like to understand the relationship of North Carolina’s population to other populations along the east coast of the United States.
A study of breeding American Oystercatchers in North Carolina was initiated in 1995 on South Core Banks, Cape Lookout National Seashore to document nesting success. Subsequent research expanded the study area to include all nesting oystercatcher pairs on Cape Lookout and Cape Hatteras National Seashores and expanded the scope of the work to investigate survival, fidelity, movement, disturbance and depredation.
We are currently monitoring oystercatcher breeding success at several locations in North Carolina. Cape Hatteras and Cape Lookout National Seashores comprise over 160 km of barrier island habitats and are monitored by the National Park Service. Audubon North Carolina monitors estuary islands in Ocracoke Inlet, off the west end of Ocracoke Island, and in the Cape Fear River region. The North Carolina Wildlife Resources Commission manages dredge islands in Oregon Inlet, located between Hatteras and Bodie Islands. Habitat in these locations consists of a combination of natural and man-made islands: some provide public access and human habitation, while others are closed to public use.
The North Carolina Wildlife Resources Commission coordinates American Oystercatcher breeding surveys of the entire coast of North Carolina every three years, with previous surveys occurring in 2004, 2007, and 2010. For these surveys, all nesting pairs and single American Oystercatchers are counted.
In 2013, NCWRC worked with North Carolina State University (NCSU) and the Virginia Department of Game and Inland Fisheries to develop a sampling protocol that would build upon previous survey efforts, striving to survey more sites and to obtain estimates of the probability of detecting oystercatchers. For this more intensive sampling, the North Carolina coast was divided into plots, which were defined by habitat, management jurisdiction and ownership, and location size. Collaborators selected plots to survey for oystercatchers either once or multiple times (≥3) during the breeding season (mid-April through June), identifying nesting territories and single American Oystercatchers. These surveys were collaborative efforts that included the NCWRC, NCSU, Audubon North Carolina, Cape Lookout National Seashore, Rachel Carson National Estuarine Research Reserve, Cape Hatteras National Seashore, U.S. Marine Corps, Fort Fisher State Park, and Bald Head Island Conservancy. Data from this multi-agency study are currently being compiled.
The North Carolina Wildlife Resources Commission performs non-breeding surveys in Back and Bogue Sounds, Carteret County.
Since fall 2009, Audubon North Carolina has conducted regular non-breeding surveys in southeastern North Carolina to document use of habitat by non-breeding oystercatchers and resight bands. Survey sites are the Lower Cape Fear River, Masonboro Sound, Masonboro Inlet, Mason Inlet, Rich Inlet, and Topsail Inlet.
In the spring and summer of 2013, six adult oystercatchers were outfitted with 9.5-gram solar-powered satellite transmitters in order to study habitat use and migration strategies, as well as provide a portal for public interaction with and education about the species. A website, oystercatchertracking.org was created for internet users to follow the birds, two of which were successfully tracked on their migrations to Capers Island, South Carolina and Cedar Key, Florida. In subsequent years, we hope to deploy additional transmitters, including more advanced models that will provide GPS points for finer scale evaluation of habitat use during breeding, migration, and wintering.
To determine how cameras fared as a resight tool compared to spotting scopes, we had pairs of observers resight oystercatchers where one observer used an inexpensive Canon SX50 camera (~$300), and the other observer used a spotting scope. Below is a graph of the results.
We also tested the resighting range of the camera by photographing a banded oystercatcher decoy at four different distances: 25, 50, 75, and 100 meters. See the photos below.
Cape Lookout National Seashore is a site of traditional American Oystercatcher breeding habitat. Although relatively undeveloped, the Seashore and surrounding area still host an array of human activities. We are conducting research through North Carolina State University to assess the effects of human noise and activity on American Oystercatchers nesting at Cape Lookout National Seashore in North Carolina. Our study is focused on the effects of various forms of anthropogenic activity, including military jet overflights, vehicles, and park visitors, on the behavior, physiology, reproductive success, and survival of American Oystercatchers at Cape Lookout. We employed a variety of technologies including; audio recorders to monitor sound levels, video cameras to monitor oystercatcher incubating behavior and beach activity, and microphones to monitor heart rates of incubating birds, to assess effects. Initial results show a minimal behavioral response to aircraft, and a potential behavioral response to vehicles.
For more information, contact Tracy Borneman.
Between increased human use and rising seas, America’s coastline is changing at unprecedented rates – barrier beaches are disappearing for those species who call it home. As an obligate coastal species exhibiting high visibility and site fidelity, the oystercatcher is an ideal species through which to consider those changes. Evidence suggests that the proportion of oystercatchers nesting on dredge spoil islands has increased but that success is reduced in these locations. The primary tradeoff for birds nesting on these islands is that there are no mammalian predators, but food acquisition requires leaving the nesting territory. Oystercatcher chicks are dependent upon their parents for food until after fledging. Therefore, one adult is forced to fly to a distant food source, leaving the second adult alone to defend the brood. This is energetically taxing on all members of the family group and may explain reduced nesting success of pairs on the dredge-spoil islands, as compared to barrier islands. We evaluate reproductive success by two metrics: the condition of chicks prior to fledging and the daily survival rate of nests. Chicks in 2011 were handled multiple times prior to fledging, in order to determine condition growth rates. This is being combined with a story of several years of productivity data to compare the overall success in the two types of site (barrier and dredge).
For more information, contact Jessica Stocking.
Predator management to benefit breeding American Oystercatchers has been identified as a priority management strategy by the American Oystercatcher Working Group. Raccoon populations on the barrier islands of North Carolina are artificially high because raccoons benefit from the food, water, and shelter provided by humans. Closed systems such as isolated barrier islands provide an ideal opportunity to manipulate predator populations with minimal confounding factors. We are continuing research to evaluate the effects of a 50% reduction of the raccoon population on South Core Banks, Cape Lookout National Seashore in 2009-2010. We use a combination of telemetry and camera trapping to estimate the raccoon population before and after the removal and examine correlation between these estimates and productivity of prey species on the island. Results will be used to inform park management and other American Oystercatcher conservation programs about the costs and benefits of managing predator populations to benefit nesting oystercatchers.
For more information, contact Jessica Stocking.
In 2010 and 2011 Audubon North Carolina collected data on the effect of boat disturbance on breeding oystercatchers on the Lower Cape Fear River and Ocracoke Inlet in order to quantify the impact of boat activity on oystercatchers using the intertidal zone and shoreline of islands.
Our research focused on obtaining reliable estimates of survival, recruitment, and other key demographic parameters through a large scale mark-recapture study. We also implemented a radio telemetry study to investigate factors affecting pre-fledging chick survival.
Previous research began with a study of South Core Banks in 1995, documenting low American Oystercatcher nest success and attributing loss to human disturbance. The low success sparked interest in the species and increased monitoring in the National Seashores and interior sites. Studies have since shown that mammalian predators are the major predator on both nests and chicks on the barrier island sites. Also, there appears to be an interaction between nest disturbance and predation rates. A radio telemetry study on pre-fledging oystercatcher chicks illuminated causes of chick loss. A large-scale mark-recapture study was begun in 2008 to obtain reliable estimates of survival, recruitment, and other key demographic parameters and currently continues throughout much of the oystercatcher’s range.
We have been trapping and banding breeding American Oystercatchers on the Outer Banks of North Carolina since 1999. Our goal is to establish a color-banded population to study patterns of dispersal and survival of birds nesting along the Atlantic coast of the southeastern United States. We continually observe oystercatchers for re-sighting of these color bands. We are currently developing demographic models to investigate population trends.
Fecundity and annual adult survival are the only demographic parameters for which we have reasonably reliable estimates for our oystercatcher populations. Other important demographic parameters, including juvenile and sub-adult survival, are not known for American Oystercatchers. Long-term banding studies are important to generate better estimates of demographic rates.
We are currently initiating a pilot study of the use of bands with flag extensions. In the past, we have banded American Oystercatchers with round leg bands engraved with two-digit alphanumeric codes. However, we have used all possible combinations of two digit codes, so to continue to create uniquely-identifying codes, we must add another digit. Flag extensions on the bands are a method for allowing space for three digits on a band. In 2011, we began placing these flags on chick and adult oystercatchers.
(there may be occasional variation in timing and leg placement of banding schemes)
2013 – present: Duplicate green bands with white triangle-code configuration (three white engraved horizontally-oriented letters/numbers with one character above two characters) on upper legs; single metal band on either lower leg
2011 – 2012: Green flag with white horizontal code (three white engraved horizontally-oriented letters/numbers) on one upper leg; green round band with white vertical code (three white engraved vertically-oriented letters/numbers) on other upper leg; single metal band on either lower leg
2004 – 2011: Duplicate green bands with white horizontal code (two white engraved horizontally-oriented letters/numbers) on upper legs; single metal band on either lower leg
2003: Colors used: Red, Yellow, Dark Blue, Green, Orange, White
Upper Left: No band or one color band
Lower Left: Green Flag over USFWS metal band
Upper Right: No band or one color band
Lower Right: No band or one color band or two color bands