An Investigation of Reproductive Failures for American Oystercatchers on Fisherman Island National Wildlife Refuge
Abstract
Fisherman Island National Wildlife Refuge provides breeding habitat that is significant for the conservation of American Oystercatchers (Haematopus palliates). The island supports approximately 5-10% of the Virginia breeding population. Although reproductive rates documented in recent years are comparable to other populations and to historic data from the island itself, they are considerably lower than those measured from some of the other Virginia barrier islands. Several factors may contribute to reproductive failures including tidal flooding associated with storm events, exposure to heat resulting from chronic disturbance, and predation of eggs or young from a diversity of potential predators. Our objective for this investigation was to document factors causing American Oystercatcher nest failures on Fisherman Island during the incubation period. We used a video-monitoring approach to quantify disturbance events and causes of reproductive failure for oystercatchers breeding on Fisherman Island. We recorded 7,570 hrs of digital video footage of American Oystercatcher nests between 6 April and 15 July, 2005. We quantified the type and duration of oystercatcher reactions to 289 human and 318 nonhuman intrusions into breeding territories. Oystercatcher reaction to humans varied according to the type of activity and time off the nest was positively related to the duration of the activity. Non-human interactions involved 21 species. The most common species entering territories included Boat-tailed Grackle, White-tailed Deer, Brown Pelican, Willet, Ghost Crab, Marsh Rat, and American Black Duck. Oystercatcher response varied according to species and was considerably longer during the night hours. Reproductive performance for monitored nests was relatively poor. Of 58 eggs monitored only 20 (34.5%) hatched. Of the 20 chicks that hatched only 18 (31%) survived to disperse from the nest site. Of 25 nesting attempts only 11 (44%) were successful to the dispersal phase. Pairs hatched all eggs laid and successfully moved chicks from the nest site in only 4 (16%) of 25 attempts. High tide events associated with coastal storms represented the largest source of nest loss. A total of 6 nests containing 18 eggs were lost during 3 storm events. Storms occurred on 14 April, 6 May, and 21 June. The second highest cause of loss was to predation by Fish Crows. Crows were documented to take 12 eggs during the course of 7 nesting attempts. Ghost crabs were documented to take 1 egg and 2 chicks. A Boattailed Grackle was observed taking a single egg on 18 May. A raccoon predated a single-egg clutch on 19 June.
