Population dynamics of tundra swans on the lower Alaska Peninsula

Abstract

This study was initiated in response to concerns regarding apparent declines in abundance and breeding pair density of tundra swans on and adjacent to Izembek National Wildlife Refuge (NWR) on the lower Alaska Peninsula. I conducted an analysis of long-term data (1978-1996) to estimate demographic parameters and assess the relationship between survival probabilities and a number of environmental and ecological factors. Rates of productivity (egg, nest, cygnet survival) and annual rates of apparent adult survival were lower and more variable than previously observed for other swan populations and species. A negative relationship between nesting success and brown bear density indicates that depredation by bears is a primary determinant of tundra swan reproductive success. Changes in apparent survival probability were primarily influenced by high and variable rates of permanent emigration. Because of low rates of production and apparent survival, immigration by swans from other breeding areas may be important for sustaining a breeding population of tundra swans on and adjacent to Izembek NWR.