Nesting ecology of grassland songbirds: effects of predation, parasitism, and weather

Abstract

Understanding the breeding ecology of grassland birds is vital for understanding the mechanisms underlying their widespread population declines. We describe the breeding biology of Sprague's Pipit (Anthus spragueii), Vesper Sparrow (Pooecetes gramineus), Savannah Sparrow (Passerculus sandwichensis), Baird's Sparrow (Ammodramus bairdii), and Western Meadowlark (Sturnella neglecta) and quantify the effects of nest predation, brood parasitism, and weather on the nest survival of these species in southeastern Alberta. Nest predation was the primary cause of nest failure, accounting for 75% of all nest losses. Daily survival rates were higher during incubation than the nestling stage for the three sparrow species, and nest survival of Baird's Sparrows was highest at intermediate temperatures. For all five species, clutch size, hatching success, and fledging success were within the range of values previously reported for these species in other parts of their range. Brown-headed Cowbirds parasitized nests of all species except Sprague's Pipit, with 4–11% of nests containing cowbird eggs. Savannah Sparrow experienced the highest frequency of brood parasitism and was the only species to successfully fledge cowbird young. Parasitized nests of Savannah Sparrows had reduced clutch size and hatching success, and fledged fewer young compared to non-parasitized nests. The overall cost of parasitism to Savannah Sparrows was at least 1.7 young per successful nest.