Stability of a Seabird Population in the Presence of an Introduced Predator

We hypothesized that although large populations may appear able to withstand predation and disturbance, added stochasticity in population growth rate ([lambda]) increases the risk of dramatic population declines. Approximately half of the Aleutian Islands' population of Least Auklets (Aethia pusilla) breed at one large colony at Kiska Island in the presence of introduced Norway rats (Rattus norvegicus) whose population erupts periodically. We evaluated two management plans, do nothing or eradicate rats, for this colony, and performed stochastic elasticity analysis to focus future research and management. Our results indicated that Least Auklets breeding at Kiska Island had the lowest absolute value of growth rate and more variable [lambda]'s (neither statistically significant) during 2001-2010, when compared with rat-free colonies at Buldir and Kasatochi islands. We found variability in the annual proportional change in population size among islands with Kiska Island having the fastest rate of decline, 78% over 20 years. Under the assumption that the eradication of rats would result in vital rates similar to those observed at rat-free Buldir and Kasatochi islands, we found the projected population decline decreased from 78% to 24% over 20 years. Overall, eradicating rats at Kiska Island is not likely to increase Least Auklet vital rates, but will decrease the amount of variation in [lambda], resulting in a significantly slower rate of population decline. We recommend the eradication of rats from Kiska Island to decrease the probability of dramatic population declines and ensure the future persistence of this important colony.Original Abstract: Nous avons emis l'hypothese voulant que, meme si des populations elevees semblent capables de resister a la predation et aux perturbations, la stochasticite augmente le risque d'un declin demographique important lorsqu'elle est prise en compte dans le taux de croissance des populations ([lambda]). Pres de la moitie de la population de Stariques minuscules (Aethia pusilla) qui niche sur les iles Aleoutiennes se concentre dans une grande colonie sur l'ile Kiska, en presence de rats surmulots (Rattus norvegiens) introduits, dont la population explose periodiquement. Nous avons evalue deux plans de gestion pour cette colonie de stariques emdash soit ne pas intervenir, soit eradiquer les rats emdash et effectue des analyses d'elasticite stochastique dans le but d'orienter la recherche et la gestion futures. Nos resultats