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

Diets of introduced Norway Rats (Rattus norvegicus) on Langara Island, Quee n Charlotte Islands (Haida Gwaii), British Columbia, were investigated in M ay-June 1995 to evaluate the role of rats as predators of breeding Ancient Murrelets (Synthliboramphus antiquus). We examined the contents of 80 stoma chs collected from rats trapped in three areas of the island. Items occurri ng in high percent volumes (> 50%) and with highest frequency included plan t shoots, Salal berries (Gaultheria shallon), amphipods (Arthropoda: Amphip oda), 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, wh ereas rats in interior habitats fed primarily on terrestrial invertebrates and plant shoots. Tissues of Ancient Murrelets occurred with highest freque ncy (53% of stomachs examined, n = 19) and volume (mean percent volume of s tomach: mean = 41 +/- 11% (SE) in diets of rats trapped in the Ancient Murr elet colony. Along with previous findings of dead adult Ancient Murrelets e xhibiting wounds typical of rat predation on seabirds, and murrelet bones f ound in almost 30% of breeding murrelet burrows, this study implicates intr oduced Norway Rats as important predators of Ancient Murrelets.