Diets of Norway rats, Rattus norvegicus, on Langara Island, Queen Charlotte Islands, British Columbia: Implications for conservation of breeding seabirds

Abstract

Diets of introduced Norway Rats (Rattus norvegicus) on Langara Island, Queen Charlotte Islands (Haida Gwaii), British Columbia, were investigated in May-June 1995 to evaluate the role of rats as predators of breeding Ancient Murrelets (Synthliboramphus antiquus). We examined the contents of 80 stomachs collected from rats trapped in three areas of the island. Items occurring in high percent volumes (> 50%) and with highest frequency included plant shoots, Salal berries (Gaultheria shallon), amphipods (Arthropoda: Amphipoda), and tissues of Ancient Murrelets. Occurrence and volume of each food type varied positively with their apparent availability on the island. Rats near the coast fed primarily on marine invertebrates, fruits and seeds, whereas rats in interior habitats fed primarily on terrestrial invertebrates and plant shoots. Tissues of Ancient Murrelets occurred with highest frequency (53% of stomachs examined, n = 19) and volume (mean percent volume of stomach: mean = 41 ± 11% (SE)) in diets of rats trapped in the Ancient Murrelet colony. Along with previous findings of dead adult Ancient Murrelets exhibiting wounds typical of rat predation on seabirds, and murrelet bones found in almost 30% of breeding murrelet burrows, this study implicates introduced Norway Rats as important predators of Ancient Murrelets.