Effects of Predator Removal and Gull Control at a Breeding Site
for Piping Plovers and Common Terns on
Lake of the Woods, Minnesota
STEPHEN J. MAXSON AND KATHERINE V. HAWS
Minnesota Department of Natural Resources, 102 23rd Street,
Bemidji, MN 56601
The piping plover is classified as endangered in Minnesota while the common tern is classified as a species of special concern. Both species nest on Pine and Curry Island Scientific and Natural Area (SNA) in Lake of the Woods. A variety of factors influence reproductive success of piping plovers and common terns at this site. These include human disturbance, lake water levels, weather, encroachment on breeding areas by nesting ring-billed gulls, and predation on eggs and chicks. Human disturbance has been minimized by posting the nesting areas against trespass. We have no control over lake water levels which fluctuate 2-3 feet, or the vagaries of weather. In some years high water levels in combination with severe storms destroy many plover and tern nests. In 1987, ring-billed gulls, whose numbers are rapidly increasing in the Lake of the Woods area, began to establish a breeding colony on Pine and Curry Island. The now colony site is located in prime piping plover habitat and is adjacent to the common tern colony. A colony of ring-billed gulls would have detrimental effects on both plovers and terns by competing for breeding space and by preying on eggs and chicks. Some mammalian predators including mink, red fox, and striped skunk are also typically present on the SNA. During 1987-90, we implemented two predator management strategies. First, all eggs of ring-billed gulls were removed and nests were destroyed in an attempt to discourage these birds from nesting on the SNA. Second, a trapper was employed to remove mammalian predators from the SNA each year beginning shortly after ice-out in the spring.
We will describe the extent of gull nest and predator removal over the past four years and the effect this has had on plover and tern reproductive success. Overall, we believe the predator management strategies have given both plovers and terns a better chance at successful nesting than they would otherwise have and we think these strategies should be continued. Breeding success of piping plovers and common terns has fluctuated since we implemented predator management, but a substantial portion of breeding failures are attributable to weather in combination with high water levels. Removal of gull nests has prevented ring-billed gulls from establishing a major breeding colony on the SNA though these birds are very persistent in their attempts to nest and continue to return to the site each spring. Trapping of mammalian predators has reduced the predation problem from this source, but in some years a few individuals (especially mink) are not captured and continue to cause problems.
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