An Investigation of Herring Gull Population Decline in Pukaskwa National Park, Lake Superior

Abstract

In Pukaskwa National Park(PNP) on Lake Superior, Herring Gull(Larus argentatus) population is used as an indicator of ecological integrity. Since the 1970s, their populations have declined by 70%. Lake-wide declines in prey fish may be limiting natural food sources for Pukaskwa gulls. In the southern section of the park there's little access to human sources of food. In the northern section of the park, impacts of food declines may be buffered as birds can obtain anthropogenic food from nearby dumps. To assess regional differences, Herring Gull eggs were collected from northern and southern PNP. Markers of diet composition, stable isotopes of nitrogen and carbon, fatty acids, were measured in the eggs. Analysis supports the hypothesis that gulls from the southern PNP rely to a greater extent on natural foods. Understanding the degree to which anthropogenic food supports Gull populations is critical when utilizing gulls as indicators of ecological integrity in PNP.