POPULATION TRENDS OF TUNDRA-NESTING BIRDS IN CHURCHILL, MANITOBA: POTENTIAL EFFECTS OF INCREASING LESSER SNOW GOOSE (CHEN CAERULESCENS CAERULESCENS) POPULATIONS

Abstract

Recent increases in lesser snow goose (Chen caerulescens caerulescens) abundance have raised the question of how populations of other tundra-nesting birds are impacted by increased goose herbivory and habitat degradation. Line transect surveys were conducted on 30 transects at the Nestor 1 study site outside of Churchill, Manitoba in June 1984, 1999, and 2000 to obtain estimates of population densities of tundranesting birds and determine if density changes have occurred in relation to increased goose habitat damage. We also compared bird abundance at a smaller scale between degraded and non-degraded freshwater sedge meadows. Herring gulls (Larus argentatus) and semipalmated sandpipers (Calidris pusilla) exhibited significant (P < 0.05) increases in population densities from 1984 to 1999 and 2000. Dunlins (Calidris alpina) had significantly lower densities from 1984 to 1999 (P < 0.10) and nonsignificant declines from 1984 to 2000. Horned larks (Eremophila alpestris), lapland longspurs (Calcarius lapponicus), savannah sparrows (Passerculus sandwichensis), and the sedge meadow shorebird guild exhibited nonsignificant increases in density. The tundra-nesting passerine guild exhibited a significant (P < 0.05) increase in density from 1984 to 1999. Arctic terns (Sterna paradiseaea), pectoral sandpipers (Calidris melantos), and willow ptarmigan (Lagopus lagopus) indicated significant (P < 0.05) declines in densities of birds seen on transects and in the numbers of transects birds were detected on. Significantly lower abundances of passerines and shorebird guild birds were detected in degraded freshwater sedge meadows versus non-degraded meadows. Results indicate that most species did not exhibit population density declines over time on the study area, despite increased snow goose damage and density. However, at the scale of the habitat patch, the same groups of species had lower abundances in degraded habitats versus non-degraded habitats. Results suggest that habitat degradation led to lower bird abundance, however habitat damage may have to be widespread and severe to elicit population density declines over a large area, like Nestor 1. The species that exhibited density declines over the study area were larger, ground-nesting species.