Prey of Ring-Billed Gulls in Lake County, Montana: Identification and Quantification of Prey and Management Implications

Abstract

The diet of Ring-billed gulls (Larus delawarensis) was determined from pellet analysis on Ninepipe National Wildlife Refuge, Charlo, Montana, during 1990 to 1992, and 1994. Results showed that small mammals were the most numerous prey found within pellets; however, species composition varied significantly. Voles were numerically the most abundant prey from the pellet analysis. Skulls were used to identify species, but paired bones yielded significantly higher values for numbers of prey eaten. For example, using pelves, humeri, femora, tibia-fibulae, or jaws yielded from 1.5 to 8.5 times more prey individuals than using the skull only. Soft-bodied earthworms and insects were likely under-represented in this analysis. Evidence from this dietary methodology suggests that ring-billed gulls were not a major predator on egg or nestling waterfowl and upland gamebirds. Thus, reducing gull numbers may not be warranted at this time.