Changes to the Population Status of Horned Grebes (Podiceps auritus) and Red-necked Grebes (Podiceps grisegena) in Southwestern Manitoba, Canada

摘要

Continental trend data for North America suggest that Horned Grebe (Podiceps auritus) breeding populations are declining and Red-necked Grebe (P. grisegena) populations are increasing. However, data reliability is low due to lack of survey routes in the northern boreal and taiga ecozones, areas encompassing much of the breeding range of both species. Locally in the southern Manitoba prairie ecozone, reliability of long-term trend data is also considered low and these data suggest that Horned Grebe populations are declining faster than the continental trend and that Red-necked Grebe populations are increasing rapidly. The lack of current quantitative information on population densities of these two species in southern Manitoba prompted me to compare 1970s historical data from two sites to recent data collected at the same locations in 2008-2016. I surveyed 42 (1970-1972) and 38 (2008-2016), and 144 (2009-2015) Class III-V wetlands at Erickson and Minnedosa, Manitoba, respectively. Historical Minnedosa data were available from previous field studies. At both locations, Horned Grebe breeding populations have fallen significantly, and Red-necked Grebe populations have risen significantly since the 1970s. The results of this study corroborate the Breeding Bird Survey's trend data for Horned and Red-necked Grebes in southwestern Manitoba pothole habitat.