We evaluated the magnitude of use of waste tips by Kelp Gulls (Larus dominicanus) nesting at Isla de los Pájaros, a large and growing colony in Patagonia, Argentina, and we assessed the difference in use between tips with urban and fishery waste. We marked with color dye 1347 adult breeding Kelp Gulls to determine if they fed in urban and fishery tips and to estimate the number of birds which used those tips during incubation. Kelp Gulls were present during 100% and 64% of counts at the fishery waste tip and the urban waste 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 from 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 Pájaros, and the quality, abundance, and predictability of food disposed at the fishery waste tip could foster the use of this site relative to natural food sources located closer to their breeding colony. Removal of artificial food sources may be assessed at the Puerto Madryn and other Patagonian waste tips to reduce conflicts between human and gull populations.