Recent Literature

1. Within-season variation in nest numbers of Double-crested Cormorants (Phalacrocorax auritus) on the Great Lakes: implications for censusing. P.J. Ewins, D. V. Weseloh, and H. Blokpoel. 1995. Colon. Waterbirds 18:179-192.--Double-crested Cormorants have experienced a rapid population increase in the past few decades (recently nearly 30%/year) and are increasingly in conflict with commercial and sport fishermen. Thus it is important to gain a fuller understanding of the breeding chronology and reproductive success of this species. The authors examined available data on breeding chronology and compared census counts of nesting cormorants at different stages of the breeding cycle at )40 colonies in Lakes Superior, Huron, and Ontario. The census unit was the "Apparently Occupied Nest" (AON) which included any aggregation of sticks or other nesting material constructed uring that breeding season whether or not it held eggs or young. Two counts were made at each colony, an early count during mid-incubation phase and a late count 3-5 weeks later during the mid-nestling period. The later counts averaged 22% higher for Lake Superior and Huron colonies, and 74% higher for Lake Ontario. The time of nesting was about two weeks later in the upper Great Lakes, and later in newly established colonies. The authors suggest hat both differences in timing of nest initiation and stage of nesting must be taken into consideration when censusing and that consistent and repeatable census techniques should be employed. They also suggest hat until the breeding biology of the Great Lakes cormorants is more fully understood counts of AONs will remain but an index of trends in cormorant breeding numbers and may underestimate the actual breeding population. This study raises some important issues about census procedures, and should be of interest to anyone concerned with census techniques or colonially nesting birds. [Canadian Wildlife Service-Ontario region, Environment Canada, 4905 Dufferin St., Downsview, Ontario M3H 5T4, Canada.]-William E. Davis, Jr.