The St. Lawrence River Estuary and Gulf: A stronghold for Barrow’s Goldeneyes Wintering in Eastern North America

Abstract

From 1997 to 2005, the distribution, seasonal abundance, and age and sex ratios of wintering Barrow’s Goldeneyes (Bucephala islandica) was documented in the St. Lawrence River Estuary and Gulf, Canada, with a combination of ground and helicopter surveys. Ground surveys showed that Baie-Comeau and Baie-des-Rochers were the most important localities, with monthly averages of 250 (max. = 1020) and 273 (604) individuals, respectively, from November through April. Helicopter surveys showed that four areas (Baie-Comeau, Baie-des-Rochers, Baie-Sainte-Catherine and La Malbaie/Cap-à-l’Aigle) harboured on average 74% of all Barrow’s Goldeneyes in the estuary, that numbers of individuals were more stable at these sites, and that the distribution of Common Goldeneyes (Bucephala clangula) within the estuary differed from that of Barrow’s Goldeneyes. Because of ice conditions, goldeneyes were not found on the south shore of the estuary during the coldest winter months, although they were quite numerous in spring and fall. In contrast, large numbers of goldeneyes used the north shore of the estuary all winter long and through the end of April. In January-February of 1999, 2002 and 2005, helicopter surveys (N = 8) yielded on average 2428 Barrow’s Goldeneyes (CV = 8%), 2503 Common Goldeneyes (6%) and 1320 Red-breasted Mergansers (Mergus serrator; 70%) per year in the estuary. These species averaged 2087 (CV = 81%), 2214 (41%) and 2898 (34%) individuals/year, respectively, in the gulf in January-February of 2002 and 2005 (N = 3). Helicopter survey results indicated possible identification errors between these three species, stressing the need to survey them concurrently. The January-February ratio of adult males and ‘brownheads’ was greater in 1998 (57.0%) than in 1999 (51.8%), partly because there were more immatures in the population in 1999 (18.1%) than in 1998 (10.2%). Adult sex ratios were significantly different from 1/1 in January-February of 1998 (P < 0.0001) and 1999 (P = 0.0072), whereas immature sex ratios were not (P ≥ 0.27). The monthly proportion of immatures increased between January and May of 1998 (P < 0.0001) and 1999 (P < 0.0001), because of adults departing for breeding areas. The eastern North American wintering population of Barrow’s Goldeneyes may include a maximum of 6187 individuals, of which >90% would winter along the St. Lawrence Estuary and Gulf. Thus, the St. Lawrence corridor should undoubtedly be considered as the winter stronghold for Barrow’s Goldeneyes in eastern North America