Use of tips by nesting Kelp Gulls at a growing colony in Patagonia

We evaluated the magnitude of use of waste tips by Kelp Gulls (Larus domini canus) nesting at Isla de los Pajaros, a large and growing colony in Patago nia, Argentina, and we assessed the difference in use between tips with urb an and fishery waste. We marked with color dye 1347 adult breeding Kelp Gul ls to determine if they fed in urban and fishery tips and to estimate the n umber of birds which used those tips during incubation. Kelp Gulls were pre sent during 100% and 64% of counts at the fisher, waste tip and the urban w aste tip. respectively. The number of adult gulls was always larger at the fishery waste tip (mean +/- SD = 1694 +/- 664) than in the urban waste tip (mean +/- SD = 59 +/- 68). Considering the total number of gulls flying fro m the colony to the tips and the proportion of marked gulls in the tips, we estimated that at least 54-69% of the birds of the colony were present at the tips. The use of fishery waste may have contributed to the increase in the number of Kelp Gulls breeding at Isla de los Pajaros, and the quality, abundance, and predictability of food disposed at the fishery waste tip cou ld foster the use of this site relative to natural food sources located clo ser to their breeding colon,: Removal of artificial food sources may be ass essed at the Puerto Madryn and other Paragonian waste tips to reduce confli cts between human and gull populations.