Factors affecting Snowy Plover chick survival in a managed population

Understanding survival of precocial chicks in the period immediately following hatching has important conservation implications because population growth is often sensitive to post-hatching survival. We studied federally threatened Western Snowy Plover (Charadrius nivosus nivosus) broods at the northern limit of their range in coastal Oregon (n = 1,157) and Washington (n = 84) from 1991 to 2011 in an attempt to understand seasonal, annual, and spatial patterns of chick survival. In Oregon, plover chick survival increased with age, varied between sites, and was greater at sites with predator management. The mean probability of surviving from hatch to fledging at 28 days of age in Oregon was 0.57 (95% CI: 0.50, 0.63). In Washington, where predator management was not employed, we conducted separate analyses using individually banded and unbanded chicks and results indicated that survival generally increased with chick age. The mean estimated probability of surviving from hatch to fledging at 28 days of age in Washington was 0.27 (95% CI: 0.20, 0.35) for individually banded chicks when perfect detection was assumed. This probability increased to 0.67 (95% CI: 0.41, 0.83) when we analyzed unbanded chicks and included detection probability. Our findings confirm the importance of considering age effects in the survival of Snowy Plover chicks and raise questions about the validity of assuming perfect detection of plover chicks during brood checks. This work also highlights the benefit of predator management on chick survival.