Reproductive Parameters and Egg Contaminant Levels of Great Lakes Herring Gulls

Abstract

Poor reproductive success and declines in colony size of herring gulls (Larus argentatus) have occurred in Lake Ontario at a time that dramatic increases of this species have been reported on the Atlantic seaboard. In 1975 herring gull productivity on Scotch Bonnet Island, Lake Ontario, was 0.15 chicks per pair of adults, one-tenth the productivity of colonies studied on Lakes Erie, Huron and Superior. Reduced nest site defense and decreases in eggs found, egg hatchability and chick survival were observed in the Lake Ontario colony. The major causes of egg failure were disappearance and embryonic death. Hatching success of Lake Ontario eggs by artificial incubation was 23-26 percent compared to 5379 percent for eggs from other areas. Analyses of eggs from 9 gull colonies for organochlorine contaminants indicated that the pattern of relative contamination was: Lakes Ontario > Michigan > Superior > Huron > Erie. Mirex levels were nearly 10 times higher in Lake Ontario than in the other lakes. Movements of herring gulls within the Great Lakes basin are offered as an explanation of variation in individual egg residues in each colony and the moderately high levels of chemical residues in some Lake Superior eggs. J. WILDL. MANAGE. 41(3):458-468 Recent declines have been noted in several herring gull colonies in Lake Ontario (Quilliam 1973, Canadian Wildlife Service unpublished data) and Lake Michigan (Ludwig and Ludwig 1969, J. J. Hickey personal communication). In contrast, herring gull populations have increased since the early 1900's along the eastern seaboard of both the United States (Kadlec and Drury 1968) and Canada (Haycock and Threlfall 1975). Reproductive success (the number of chicks fledged per pair of breeding adults) in 6 Lake Ontario herring gull colonies between 1972 and 1974 was reported as 0.1 to 0.44 (Gilbertson 1974, Teeple 1977, R. D. Morris personal communication). This is in contrast to the range in herring gull productivity (0.5-1.5) reported from other areas (reviewed by Kadlec and Drury 1968). The poor reproductive success of Lake Ontario herring gulls is the result of excessive embryonic mortality and egg disappearance, and poor survival of hatched chicks. Attention has been focused on organochlorine contaminants as causative a ents (Keith 1966, Ludwig and Tomoff 1966, Gilbertson 1974, Teeple 1977). The herring gull consumes a large variety of foods including fish and other aquatic organisms, insects, garbage, small rodents, and the young of other birds. Its capacity for accumulating organochlorine compounds has been well documented (Hickey et al. 1966, Anderson and Hickey 1976). Reproductive success and eggshell quality of herring gulls nesting in Lakes Superior, Huron, Erie and Ontario are reported in this paper. Seasonal movements and levels of several environmental contaminants in eggs are presented for herring gulls nesting in all 5 Great Lakes. In addition, the 458 J. Wildl. Manage. 41(3):1977 This content downloaded from 207.46.13.106 on Wed, 15 Mar 2017 18:01:31 UTC All use subject to http://about.jstor.org/terms REPRODUCTION AND CONTAMINANTS OF HERRING GULLS Gilman et al. 459