Content area
Full Text
ABSTRACT.
-Common Loons (Gavia immer) normally lay a single clutch of two eggs each breeding season. They occasionally lay one- or three-egg clutches, and rarely, four-egg clutches. Participants of the Canadian Lakes Loon Survey provided seven independent observations of loon pairs rearing four-chick broods. Photographic evidence confirmed two separate instances of adult loon pairs at Anglin Lake, Saskatchewan, and Kasshabog Lake, Ontario, exhibiting parental behavior toward a four-chick brood. Occurrence of four-chick broods may be the result of supernumerary clutches, nest parasitism, post-hatch brood amalgamation, or a combination of these factors. Received 8 July 2003, accepted 24 March 2004.
Supernumerary broods, either as a result of nest parasitism by unrelated conspecifics, supernumerary clutches, or post-hatch brood amalgamation, are relatively common among grebes (Storer and Nuechterlein 1992, Cullen et al. 1999, Muller and Storer 1999, Stout and Nuechterlein 1999, Stedman 2000) and waterfowl (Afton and Paulus 1992:90, table 3-21; Sayler 1992). However, there are few documented instances of supernumerary broods in loons (Barr et al. 2000), including the most widely studied species, the Common Loon (Gavia immer; McIntyre 1988:30, McNicholl 1993).
Common Loons are large, long-lived waterbirds that normally lay a single clutch of two eggs each breeding season, although occasionally they will lay one or, even less frequently, three-egg clutches (Peck and James 1983, Croskery 1991, McIntyre and Ban1997). The frequency of three-egg clutches reported for Common Loons is low and ranges from 0.5% (Campbell et al. 1990) to 0.8% (Peck and James 1983, McIntyre 1988:table 2-5). Clutches containing four eggs are rare, but have been noted several times (Nelson 1983, Peck and James 1983, Zicus et al. 1983, McNicholl 1993). To our knowledge, there is no confirmed record of Common Loons rearing four-chick broods. In this paper we report seven instances of Common Loon adults accompanying and rearing four-chick broods, two of these confirmed by photographic records.
METHODS
Data were gathered by volunteer participants of the Canadian Lakes Loon Survey (CLLS), who monitored Common Loon breeding pairs on lakes, rivers, and bays throughout Canada. Participants selected their own water body or portion of a water body to survey breeding loons and recorded observations of breeding pairs at least once during each of three time periods: nesting (early June to mid-July), hatching and early...