Pied-Billed Grebe Nesting Ecology on Squaw Creek National Wildlife Refuge,1996–2007

Abstract

Pied-billed Grebes (Podilymbus podiceps) are secretive water-birds that build floating nests in smaller wetlands. Our study focused on the nesting ecology, including phenology, of Pied-billed Grebes at Squaw Creek National Wildlife Refuge in northwest Missouri during an 11 year period. We located 956 Pied-billed Grebe nests in wetlands from April to July 1996–2007 and documented the number of eggs in the nest, water depth at the nest, and surrounding vegetation. Using this information, the mean clutch size, mean nest initiation date, mean hatching date, mean water depth at nesting sites, and most common vegetation types surrounding nests were determined and analyzed for differences among years. The mean clutch size for all nests was 7.18 eggs/nest (SE = 0. 09, n = 249) although clutch size significantly varied among years (F=3.51, df=7, P=0.0013). Mean nest initiation date from 414 nests was 18 May while the mean hatching date was 11 June. Both dates were significantly different among years (F=31.86, df=11, P<0.0001 and F=31.93, df=11, P<0.0001). Mean water depth at nest sites was 62.03 cm (SE=0.45, n=561) and varied significantly across years (F=46.50, df= 7, P<0.0001). River bulrush (Schoenoplectus fluviatilis) was the most common vegetation type found at 72.2% of 573 nesting sites followed by arrowhead (Sagitarria latifolia) (23.2%), smartweed (Polygonum sp.) (20.8%), and American lotus (Nelumbo lutea) (19.5%). All Pied-billed Grebe nesting data from Squaw Creek NWR falls within the ranges reported in other nesting studies. It appears current management on the refuge is adequate to support quality Pied-billed Grebe nesting habitat.