Fróðskaparrit - 01.01.2009, Blaðsíða 106

104
YEAR-ROUND VIDEO SURVEILLANCE OF INDIVIDUAL NEST-SITE
ATTENDANCE OF NORTHERN FULMARS IN THE FAROE ISLANDS
copulations were recorded at effectively all
hours (between 02 and 23 hrs), hence not
only during daylight. Besides there was no
peak in frequency but a considerable varia-
tion between the pairs with regard to fre-
quency and days between first and last cop-
ulation as well as total number of
inseminations (Table 6). In all cases at least
one of the birds in the pair departed for a
pre-laying exodus shortly after the last cop-
ulation and all but two of the pairs laid eggs
upon the return to the nest-site 3-4 weeks
later. The Northern Fulmar, like Leach's
Storm-petrel (Oceanodroma leucorhoa),
Horned Puffin (Fratercula corniculata) and
probably some other pelagic seabirds, have
sperm-storage glands which allows the part-
ners to be separated for weeks (Hatch, 1983).
It is believed that fertilization occurs within
a few days prior to laying and it is suggested
that the probability of paternity is deter-
mined by the frequency and timing of in-
seminations due to physiological constraints
(Hunter, 1998). Female fulmars engage in
extra-pair copulations (EPCs) but the extra-
pair paternity appears to be < 5% (Hatch,
1987a; Hunter et al„ 1992; Hunter, 1998). We
did not record any EPCs, possibly because of
the small sample size and too few individu-
ally marked birds.
A pre-laying exodus is a common feature
to most procellariids, including the North-
ern Fulmar (see Introduction); though with
some intra- and interspecific variation with
regard to length in time and sex-biased par-
ticipation (Warham, 1990, Brooke, 1990;
Mallory and Forbes, 2007). In our study
colony the exodus was more noticeable in
2006, when fewer birds occupied the moni-
tored nest-sites in May than at correspon-
ding time in 2007 (Fig. 1). However, this dif-
ference is attributable to nest-site no. 2 in
May 2007 when one of the birds was present
all the time, but when these data are ex-
cluded in the analysis the exodus is equally
pronounced as in 2006. This also exemplifies
the great between-nest variation in atten-
dance in May. While the length of the pre-
laying exodus ranged from 21 to 32 days the
number of days when a given site was visiting
during that period ranged from 1 to 25 days
(Table 7). In two of three cases when ringed
birds were involved it was the male that
stayed behind and more or less regularly at-
tended the nest-site, which is consistent with
previous studies of the species and some
other procellariids (Dunnet et al„ 1963;
Hatch, 1983; Brooke, 1990). This sex-biased
exodus is often discussed in terms of the fe-
males' need to build up substantial food re-
serves to be able to form the relatively large
egg (Lack, 1966) and to participate in the in-
cubation duties, whereas the males need to
prepare for the first stints of incubation and
to endure the long spells of fasting (Warham,
1990; Mallory and Forbes, 2007). In a study
of Cory's Shearwaters (Calonectris diomedea)
it was argued that the cost of forming the
egg is less than 0.5% of total costs of repro-
duction and therefore not adequate in ex-
plaining the long pre-laying absence of the
females; instead it was suggested that, since
they are more at home at sea than on land
and already mated, they prefer to stay out at
sea until egg-laying (Jouanin etal., 2001). As
regards the fulmars, the fact that non-breed-
ers also leave the colony for a period of time
prior to the commencement of egg-laying
seems to support the notion that the pre-
laying exodus may not entirely be a matter