Surveys indicate that Lesser Scaup (Aythya affinis) populations declined during the early 1980s and have since remained below conservation goals. Reasons suggested for the decline include chemical contamination, climate change, and reduced food resources. According to the latter theory, reproductive success of Lesser Scaup has declined because females now arrive on the breeding grounds with fewer nutrient reserves than in the past and this diminished body condition is the result of reduced food resources available at wintering and/or migration areas. To determine whether reproductive success has declined over time, I examined selected Lesser Scaup reproductive rates from 2008 to 2014 in southwestern Manitoba and compared them with those recorded before the continental population decline. Estimated productivity (age class IIa broods/pair), hatching date, Ia and IIa brood size, duckling survival rate (first sighting to age class IIa), and proportion of age class IIa broods with females in attendance were unchanged from values recorded in 1970–1972. Thus, if females are arriving on southern breeding areas with reduced body reserves, they may be recovering these losses before nesting, enabling them to attain reproductive rates similar to those in the past. In addition, these results are consistent with the hypothesis that reduced food resources at non-breeding areas could affect recruitment of southern prairie-parkland breeders to a lesser extent than northern breeders because of the longer time between arrival and egg-laying in the south.
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.
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