Visual nest controls can provide reliable information on hatching and nest loss rates in meadow-breeding Dunlins

Camera observations have revealed that traditional visual nest control visits can yield misleading results about nest predation. It is important to know how biases from traditional nest control visits may compromise the conclusions of a study. In this paper I assess these biases for known-fate nests of Baltic Dunlins Calidris alpina schinzii and, for comparison, a smaller sample of Northern Lapwing Vanellus vanellus nests. In Dunlin, all successful nests had shell fragments inside the nest lining, but this was never observed in failed nests. In contrast, Lapwing nests with one or two egg shell fragments inside the nest lining could have either hatched or failed. Therefore, the fate of nests could reliably be determined on the basis of egg shell remnants for Dunlins, but not always for Lapwings. This difference is likely related to nest structure, where egg shell fragments are more likely to be trampled into the lining during a predation event in Lapwings than in Dunlins. I conclude that visual nest controls can provide reliable information on hatching and nest loss rates in Baltic Dunlins.