Surveying populations of breeding grebes in prairie parkland Canada: Estimation problems and conservation applications

Annual ground surveys of mid-continent waterfowl may provide a monitoring framework for other wetland-associated species. We used a repeated-counts method to estimate detection probabilities (ρ̂) of adult horned (Podiceps auritus) and pied-billed (Podylimbus podiceps) grebes on the Waterfowl Breeding Population and Habitat Survey (WBPHS) ground component conducted annually each May in the prairie and parkland ecoregions of Canada. Detection probabilities (ρ̂±SE) were higher, more precise, and more consistent through time for horned grebes (0.52±0.06 and 0.44±0.05 in 2010 and 2011, respectively) than for pied-billed grebes (0.25±0.08 and 0.11±0.05 in 2010 and 2011, respectively). Our results suggest that the ground component of the WBPHS could be used to monitor horned grebes in these ecoregions. Although an active call-broadcast component would be valuable for obtaining unbiased abundance estimates for horned grebes, such a component would be critical for monitoring pied-billed grebes.