Diet of double-crested cormorants wintering in Texas

Abstract

-The diets of 420 Double-crested Cormorants (Phalacrocorax auritus) were studied during November 1986-March 1987 on eight public reservoirs in Texas. Prey included 29 fish species and the mean live weight of fish per bird was 122 g. Fishes -415 mm long were ingested, but those 125 mm accounted for 90% of cormorant food contents by number. Shad (Dorosoma spp.) and sunfishes (Lepomis spp.) accounted for 90% of the total food items by number. Consumption of fishes (percent by weight) was different for male vs. female and adult vs. juvenile cormorants. Total consumption of fish by weight was consistent throughout the period; however, fewer but much larger fish were consumed after 15 February. Cormorants ate fishes that were most abundant in reservoirs. Sport fishes made up a substantial portion of cormorant food by weight, but not by number on some reservoirs. Cormorants ate very few large sport fish, however. DIETA DE INDIVIDUOS DE PHALACROCORAX AURITUS QUE PASAN EL INVIERNO EN TEXAS Sinopsis.-De noviembre de 1986 a 1987, se estudi6 la dieta de 420 cormoranes (Phalacrocorax auritus) en ocho reservorios p6blicos de Texas. La dieta incluy6 29 especies de peces y el promedio de peso de pez vivo por ave fue de 122 g. Peces con longitud <415 mm fueron ingeridos. Aquellos con tamaiio <125 mm formaron el 90% del contenido alimentario por numero. Peces de los generos Dorosoma y Lepomis formaron el 90% de la dieta de las aves por n6mero. El consumo de peces (porciento por peso) por parte de los cormoranes result6 diferente para machos vs. hembras y adultos vs. juveniles. El consumo de peces por peso, fue uniforme a traves del periodo de estudio. Sin embargo, despues del 15 de febrero, menos peces pero de mayor peso fueron consumidos. Las aves consumieron los peces que resultaron ser mas abundantes en los reservorios. Lepomis spp. form6 una porci6n sustancial por peso de la dieta de las aves, pero no asi por n6mero en algunos reservorios; los cormoranes ingirieron muy pocas presas de alto peso. I Current address: Geo-Marine, Inc. 201 Napoleon Street, Baton Rouge, Louisiana 70802 USA. 2 Current address: Cooperative Fish and Wildlife Research Unit, U.S. Fish and Wildlife Service, New Mexico State University, Box 30003, Dept. 4901, Las Cruces, New Mexico 88003 USA.