Northern Prairie Wildlife Research Center
IRWIN W. AILES AND ROBERT R. CROSS
U.S. Fish and Wildlife Service, Chincoteague National Wildlife Refuge,
P.0. Box 62, Chincoteague, VA 23336; Virginia Department of Game and
Inland Fisheries, P.0. Box 92, Locustville, VA 23404
Nest exclosures were constructed of 2x4 inch mesh, 14 gauge welded wire fence, 48 inches high. The fence was buried 6-8 inches in the ground and anchored by four, 5-foot long steel reinforcement bars (rebar). The bars were woven through the mesh and driven into the ground to a depth of approximately 1 foot. Fencing lengths were precut, then formed into a 10-foot diameter circular design around the nest. Sixty-pound test monofilament fishing line was used to create a series of parallel lines six inches apart covering the top of the exclosure to deter avian predators.
Exclosures were constructed around nests by two to four individuals only after a full clutch of four eggs was completed or when it became evident that a fourth egg would not be laid. A ventilated plastic bowl was used to cover the eggs during construction of the exclosure in order to prevent overheating or accidental damage to the eggs. Once construction of the exclosure was completed, all tracks were swept from the area, and the exclosure was examined to assure that adult birds had maximum access to mesh openings at ground level. The exclosure was then observed from a distance until an adult entered and resumed incubation. Most birds entered the exclosure and resumed incubation within 15 minutes. Further observations were made until an exchange of incubation duties occurred, assuring acceptance of the structure by both parental adults. If a bird did not return within 60 minutes, the exclosure was removed, and no further attempt was made to exclose the nest. This only occurred once during the 2 years.
Predator-proof exclosures were found to be very effective in protecting nests. Of 44 nests protected during the study, 85% successfully hatched in 1988 and 92% in 1989. Only 7 of 21 (33%) unexclosed nests were successful in producing young during the 2 years.