Nest-Predation Rates in Relation to Colony Size of Black Brant

I compared data on nesting success of black brant (Branta bernicla nigricans) from 4 different sized colonies on the Yukon-Kuskokwim Delta, Alaska, to investigate how predation may affect reproductive success, numbers, and distribution of these geese. Black brant lost 55 and 85% of their nests, primarily to predators, in 2 small colonies (10-37 pairs/yr) compared to losses of 31-32% in each of 2 colonies containing thousands of individuals. Predators, especially arctic fox (Alopex lagopus), can limit numbers and distribution of nesting brant and prevent or slow increases in size of brant colonies diminished by other mortality factors such as exploitation by humans. Therefore, removal or management of arctic fox at and near small colonies of brant may assist re-establishment or expansion of depleted brant colonies. J. WILDL. MANAGE. 53(1):87-90 Colonial nesting by some avian species may have evolved because high densities minimize losses to predators through swamping (Wittenberger and Hunt 1985). Proportions of nests or birds taken by predators should be inversely related to colony size or, at least, lower in colonies than for solitary nesting individuals provided that the increase in prey availability is large and ephemeral, and overwhelms the ability of predators to consume it or increase their own numbers in response to such increased food availability. Conversely, predators may prevent or slow establishment of new colonies until some c itical colony size is attained (Gochfeld 1980). Several arctic goose species nest colonially and exhibit faithful return to previously used colony sites (Owen 1980), but comparative data on predation rates in different sized colonies are lackThis content downloaded from 207.46.13.76 on Wed, 24 Aug 2016 06:03:10 UTC All use subject to http://about.jstor.org/terms 88 PREDATION AND SIZE OF BRANT COLONIES * Raveling J. Wildl. Manage. 53(1):1989