Distribution, biology and prey selection of the introduced Norway Rat Rattus norvegicus at Kiska Island, Aleutian Islands, Alaska

Abstract

At Kiska Island, Alaska, USA we quantified age, sex, size, distribution and predation of Least Auklets Aethia pusilla by non-indigenous Norway Rats Rattus norvegicus, to evaluate their impact on auklet reproductive success. Rat distribution was assessed by surveying accessible parts of Kiska Island for rat sign and prey hoards. To quantify prey selection and infer diet, the contents of all hoards found were identified. Age, sex and size structure of the rat population was assessed using limited snap trapping on and off the Sirius Point auklet colony. Norway Rat sign was abundant in all areas near breeding seabirds and marine sources of food but rat sign abundance varied among years at Sirius Point. Although we found a larger proportion of juvenile to adult rats (0.54 : 0.46, p < 0.01) at Sirius Point, no significant differences were found in the proportion of reproductive to non-reproductive females (0.50 : 0.27, p > 0.05) or in overall adult body size (257 g and 37 cm : 236 g and 35 cm, p > 0.05) between Sirius Point and Christine Lake where breeding auklets are absent. Surplus killing and food hoarding by rats was noted in all years during the auklet laying period, with adult Least Auklets being the principal prey taken (4-148 individuals per hoard, n = 16 hoards). Our observations were consistent with the notion that rats have a negative impact on auklet populations, but for management purposes further information on whether rats are the sole cause of auklet reproductive failure is required.