Breeding Status of Ancient Murrelets Attending Gathering Grounds Near Langara Island, British Columbia, 1970–1971

Abstract

A conspicuous but incompletely studied activity of breeding Ancient Murrelets (Synthliboramphus antiquus) is the gradual increase in the number of individuals on the sea near the colonies from midto late afternoon until darkness each day during the breeding season. Ancient Murrelets fly from the foraging area to the ‘‘staging area’’ (Sealy 1976; Vermeer and others 1984) or ‘‘gathering ground’’ (Gaston 1992, 1996) adjacent to the breeding colony, and spend up to several hours each day for more than 2 months each year engaging in social activities (Fig. 1), possibly strengthening pair bonds and prospecting for mates. An undetermined proportion of individuals then fly to the colony during the 3 to 4 h of darkness, where socialization continues (Jones and others 1990; SGS, pers. obs.). As the breeding season progresses, incubation duties are exchanged between females and males, and the off-duty individuals return to the sea before sunrise (Gaston 1992). By late May the precocial chicks begin to leave the colonies about 2 d after hatching and, accompanied by 1 or both parents, swim rapidly offshore where the chicks are reared (Sealy 1976; Sealy and Campbell 1979; Gaston 1992; Sealy and others 2013). Several authors have noted Ancient Murrelets on the gathering grounds near colonies on Haida Gwaii, British Columbia (Guiguet 1953; Sealy 1976; Vermeer and others 1985; Gaston 1992), but whether breeding adults and nonbreeders, which may include subadults, visit them over the course of the breeding season has not been ascertained. The function of the activities that occur on the gathering ground, therefore, remains for the most part conjecture. Gaston (1992) acknowledged that it would be difficult to distinguish between breeding adults and non-breeders on the gathering ground without collecting birds over the course of the breeding season, as the age and sex of individuals are indistinguishable at sea. He stated, however (p 146), that ‘‘we must presume that the majority of birds on the gathering grounds were non-breeders,’’ during the latter part of the chick-departure period, but went on to say ‘‘We do not know whether the majority of birds attending the gathering grounds in late April [when clutches are initiated] were breeders or non-breeders. However, I think that they were mainly breeders, because few non-breeders came ashore at that date.’’ Results of a study of breeding and feeding ecology of the Ancient Murrelet, involving individuals collected on gathering grounds from 6 May to 10 July 1970 and 17 March to 9 August 1971, in the vicinity of Langara Island, Haida Gwaii, British Columbia (Sealy 1972, 1975a, 1976), shed light on the seasonal pattern of visitation by breeders and non-breeders on the gathering grounds. In 1970–1971, I collected 75 Ancient Murrelets (56 breeding adults, 19 non-breeders [criteria for separating groups in Sealy 1972, 1976; also see Table 1]) between 15:30 and 22:45 PST on gathering grounds approximately adjacent to 3 colonies on Langara Island (Fig. 2: colony A, Iphigenia Point [see also Fig. 3A]; colony B, southern headland of Egeria Bay; colony C, McPherson Point [Fig. 3B]). (The build-up of murrelets at each gathering ground occurs anew each day, and area and shape of the ground may be variable.) The collections of specimens spanned the period individuals first began to attend gathering grounds in the last 2 wk of March through the end of July (Table 1). I had previously lumped data obtained from each GENERAL NOTES