Regional Variation in the Food of Nestling Cattle Egrets

Abstract

IN their spread into and across North America, Cattle Egrets (Bubulcus ibis) appear to be occupying a previously vacant niche.Most breeding colonies established in North America have been in preexisting heronties, but the Cattle Egrets do not compete with the indigenous species for food.At a heronry in north central Florida, the diet of Cattle Egret nestlings differed from the diets of the nestlings of three other heron species (Jenni 1969).At another locality in north central Florida, adults ate a diet that was noncompetitive with the diets of other species (Fogarty and Hetrick 1973).This paper compares the food of nestling Cattle Egrets at four different Florida localities.I systematically collected boluses of undigested food regurgitated by Cattle Egret nestlings in response to my intrusion into their colonies during the late morning and early afternoon.The samples were preserved immediately in 10% formalin.Later they were washed and transferred to 30% isopropanol.The food items were identified, counted, dried on paper toweling, and their volumes measured.Collections from four Florida colonies (Figure 1) were made in 1960: Lake Alice, Alachua County, collected between 27 May and 26 July; Lake Griffin, Lake County, 27 June; Lake Okeechobee spoilbanks, Glades County, 7 July; and Tampa Bay, Alafia River spoilbanks,