Assessing habitat selection by foraging egrets in salt marshes at multiple spatial scales

We assessed salt marsh use by foraging egrets in coastal Rhode Island, USA. Two species [great egret (Ardea alba) and snowy egret (Egretta thula)] nest in mixed-species colonies on islands in Narragansett Bay and regularly forage in adjacent salt marshes. We surveyed 13 salt marshes approximately twice weekly during the breeding and post-breeding seasons in 2001 and 2002. Based on resource selection functions, foraging great and snowy egrets strongly preferred pools within salt marshes, while mosquito control ditches were rarely used. Foraging egrets were never detected in stands of common reed (Phragmites australis). The number of egrets using individual marshes varied considerably, although density estimates were far less variable. Salt marsh area was better at predicting the mean number of foraging egrets using a marsh than landscape-level parameters, such as distance to the nearest nesting colony or the total area of salt marsh within 5 km. Carefully designed salt marsh restoration projects could benefit local egret populations because it appears that foraging habitat availability may be a limiting factor. To ensure use by foraging egrets, salt marsh restoration designs should increase the availability of pool and open water habitat, reduce common reed, and modify deep ditches and channels to make them more accessible for foraging egrets.