Copulation and mate guarding in the Northern Fulmar

-I studied the timing and frequency of copulation in mated pairs and the occurrence of extra-pair copulation (EPC) among Northern Fulmars (Fulmarus glacialis) for 2 yr. Copulation peaked 24 days before laying, a few days before females departed on a prelaying exodus of about 3 weeks. I estimated that females were inseminated at least 34 times each season. A total of 44 EPC attempts was seen, 9 (20%) of which apparently resulted in insemination. Five successful EPCs were solicitated by females visiting neighboring males. Multiple copulations during a single mounting were rare within pairs but occurred in nearly half of the successful EPCs. Both sexes visited neighbors during the prelaying period, and males employed a special behavioral display to gain acceptance by unattended females. Males invested time in nest-site attendance during the prelaying period to guard their mates and pursue EPC. However, the occurrence of EPC in fulmars was largely a matter of female choice. Received 29 September 1986, accepted 16 February 1987. THE occurrence and significance of extra-pair copulation (EPC) in monogamous birds has generated much interest and discussion (Gladstone 1979; Oring 1982; Ford 1983; McKinney et al. 1983, 1984). Because the males of monogamous species typically make a large investment in the care of eggs and young, the cost of being cuckolded is high, as are the benefits to the successful cuckolder. Males are expected to pursue opportunities for copulation outside the pair bond (Trivers 1972) and to reduce as far as possible the uncertainty of paternity for the young they help raise. The incidence of EPC may in general be higher in colonial species than in solitary nesters, and the threat of cuckoldry is postulated to be one of the principal disadvantages of colonial breeding (Alexander 1974, Hoogland and Sherman 1976). Mate guarding may be defined as any behavior by a mated male whose principal function is to reduce the likelihood of encounters between his mate and other males during the time when fertilization of her eggs is possible. The importance of mate guarding in the monogamous male's reproductive strategy has been recognized in a variety of species (e.g. Beecher and Beecher 1979; Birkhead 1979, 1982; Power and Doner 1980; Power et al. 1981; Werschkul 1982a; 1 Present address. Bjorkland and Westman 1983; Buitron 1983; Birkhead et al. 1985). I attempted to document the occurrence and behavioral context of extra-pair copulation and mate guarding in a colonial seabird, the Northern Fulmar (Fulmarus glacialis). Fulmars are among the longest-lived birds known, and fidelity to the same mate and nest site between years is high (Macdonald 1977, Ollason and Dunnet 1978, Hatch 1985). Only one egg is laid per clutch, and re-laying in the same season after the loss of a clutch is unknown. The sexes share about equally in incubation and chickrearing duties (Hatch 1985). Thus, fulmars exhibit a highly conservative social system. Some features of the breeding biology make this species (and perhaps other Procellariiformes) particularly interesting from the standpoint of copulation behavior and potential sperm competition. At Pacific colonies, fulmars arrive synchronously some 6-8 weeks before the first eggs are laid. There is thus a considerable prelaying period for social interaction. Foraging occurs over large ocean areas in bouts of several days, and it is difficult for males and females to coordinate perfectly their attendance patterns at the nest site. Females are receptive to copulation over the whole prelaying period, and sperm are stored in special glands in the utero-vaginal (UV) region of the oviduct (Hatch 1983). Sperm remain viable in the UV glands for several 450 The Auk 104: 450-461. July 1987 This content downloaded from 157.55. 39.148 on Fri, 16 Dec 2016 07:41:35 UTC All use subject to http://about.jstor. org/terms July 1987] Copulation and Mate Guarding in Fulmars 451 weeks, as frequently there is no contact between the male and female during the "prelaying exodus" (Warham 1964), a time of continuous foraging immediately before egg laying (lasting up to 38 days in fulmars; Hatch 1985). The combination of intermittent attendance patterns, sperm storage, and a prolonged receptive period in the female renders the male fulmar particularly susceptible to being cuckolded. I studied the timing and frequency of copulation in mated pairs, both in relation to calendar date and relative to the laying dates of individual females. Social relations outside the pair bond, including EPC, were documented in a series of extended watches on a group of known individuals during 2 yr. Finally, I examined patterns of nest-site attendance during the prelaying period during 6 yr for evidence of mate guarding.