Brood size manipulations in herring gulls

Abstract

Herring gull broods were artificially increased to four and five chicks while others were reduced to one chick. The growth rates of chicks and chick weights at fledging were similar among all control and experimental broods. The experimentally increased brood sizes had a slightly higher fledging success than control broods, and the fledging success of one-chick experimental broods was higher than that of one-chick control broods. Thus, chick survival was not reduced in larger brood sizes and the number of young fledged per pair of adults increased with brood size. Further. chicks in large broods were at no weight (or viability) disadvantage despite the presence of a larger number of brood mates. We conclude that food was not limiting either the growth rate or fledging success of chicks from broods larger than the modal clutch size, and suggest that parents used local, abundant, artificial food sources in addition to their natural food supply.

FACTORS DETERMINING A CLUTCH SIZE REDUCTION IN CALIFORNIA GULLS (LARUS CALIFORNICUS) : A MULTI-HYPOTHESIS APPROACH

“…5 days (Harris and Plumb, 1965;Haymes and Morris, 1977). Gulls readily adopt chicks before chick ages of ca.…”

Parental Investments by Seabirds at the Breeding Area with Emphasis on Northern Gannets, Morus bassanus

“…Jarvis (1974) finds no reproductive advantage due to artificial twinning in Cape Gannets, although Nelson (1978b) points out ecological differences that might account for the Northern Gannets' ability to rear twins and the Cape Gannets' lack of it. Some gulls are also exceptions to Lack's clutch size hypothesis, because they can rear larger than normal broods (e.g., Verrneer, 1963;Harris and Plurnb, 1965;Pearson, 1968;Haymes and Morris, 1977). By comparison with gulls, Procellariiformes, gannets, and Alcidae-birds that usually forage farther from shore and for more patchily distributed food-cannot rear larger than normal broods (Harris, 1966(Harris, , 1978Lack, 1968;Lloyd, 1978).…”

Current Ornithology

“…Lack's hypothesis may thus be restated to read that birds lay that number of eggs that results in the parents operating at the optimal working capacity. This modification of Lack's hypothesis may make it applicable not only to those species incapable of rearing a larger than normal brood (e. g., Crossner, 1977;Schifferli, 1978), but also to those species able to do so (e. g., von Haartman, 1971;Perrins and Moss, 1975;Haymes and Morris, 1977;Drent and Daan, 1980;Moss et a1., 1981).…”

“…The evidence that precocial species with larger clutches are limited in this way is less convincing. For example, gulls of various species are able to raise larger numbers of young than their normal brood size, and young in these artificially-enlarged broods fledge in as good a condition and at as great a weight as chicks from broods of normal or smaller sizes (e.g., Coulson and White, 1958;Harris and Plumb, 1965;Pearson, 1968;Ward, 1973;Haymes and Morris, 1977). Lack (1968) and others have attributed this ability to raise extra young to artificially favorable feeding conditions due to use of refuse dumps and fish cleaning stations.…”