Great Egret Preference for Catfish Size Classes

Abstract

-Several species of fish-eating birds are commonly observed near aquaculture facilities in the southern United States. An understanding of the relationships between these birds and specific commodities is needed to interpret and manage bird impacts to aquacultural production. We conducted two foraging experiments to evaluate the preference of Great Egrets (Ardea alba) for three specific size classes of Channel Catfish (Ictalurus punctatus). During six no-choice feeding trials, egrets consumed significantly more small (7.5-10 cm) fingerlings than medium (1518 cm) or large (23-25 cm) catfish. Egrets captured 19 large catfish, and ingested only two, even when no other fish were available. During two-choice trials, Great Egrets significantly preferred small fingerlings to medium-sized fish, and medium-sized catfish to large fish. Handling time was directly related to the size of catfish ingested. Handling time was inversely related to the number of catfish ingested from each size class, particularly when Great Egrets were given a choice between two catfish size classes. Thus, we infer that the ease of capture and physical defenses (e.g., catfish spines) associated with particular foods affect Great Egret foraging preferences. Management of Great Egret impacts to aquacultural production should focus on dispersing egrets from ponds containing small (<18 cm) Channel Catfish, rather than generalized dispersal at all ponds on all farms. Received 1 October 2000, accepted 18 April 2001.