Fróðskaparrit - 01.01.2004, Side 263

HVUSSU MÚSABRÓÐIR (TROGLODYTES TROGLODYTES) YVIRLIVIR,
SPJAÐIR SEG OG HVUSSU STAÐBUNDIN HANN ER í FØROYUM
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to the next, may be particularly important
to the males. In addition, aquaintance with
the breeding site is beneficial with respect
to the utilization of various other resources
and is therefore likely to contribute to en-
hanced survival and fitness. Moreover, as
experience increases with age it seems like
a good strategy to be relatively long-lived
and highly philopatric, particularly when
the environmental conditions are harsh and
unpredictable as in the Faroes. These ar-
guments obviously do not help to explain
the markedly lower site fidelity observed
for the females. A recent phylogenetic
study shows that philopatry is associated
with low adult mortality, deferred matura-
tion and low reproductive rate (Arnold and
Owens, 1998). The Faroese wren is, in con-
trast to mainland wrens, single-brooded (no
second brood has yet been confirmed) and
the observed minimum survival rate (across
years and study areas) of breeding males
corresponds to a mean life expectancy of
2.1 years, which is about twice that of Brit-
*sh, less philopatric and multiple-brooded,
male wrens (assuming 63% annual mor-
tality; Hawthorn and Mead, 1975). Wrens
breed at the age of one year which means
that mean longevity of Faroese male wrens
is more than three years, and as the re-sight-
ings show at least two males were still alive
at the age of five. However, a male of the
same age was also recorded in a Dutch and
English study, respectively (Kluijver et al.,
1940; Armstrong and Whitehouse, 1977).
Longlivedness and low recruitment is typi-
cal of tropical passerine species compared
to their counterparts (equivalent in size) liv-
>ng in the temperate zone (e.g. Lack, 1968;
Fogden, 1972; Ricklefs, 1973, 1983; Snow
and Lill, 1974), though also for species liv-
ing in an environment with highly variable
food supplies like the tropical Darwin's
Finches (Gibbs and Grant, 1987; Grant
and Grant, 1989). The male-biased natal
philopatry in yearlings suggested by the re-
sightings may be a strategy associated with
the prospects of a relatively long life. Many
of the one-year old males appear to return
to their natal sites and although they seem
to be less successful than the older males
in obtaining mates. Presumably they gain
more in terms of lifetime fitness by being
philopatric and competing with relatives
for territories, and abiding their time (see
e.g. Komdeur and Edelaar, 2001), than by
dispersing and competing with conspecific
non-relatives. No behavioural observations
were made of parent-offspring interactions
that could be interpreted as nepotism or pa-
rental tolerance, or some kind of parental
facilitation (Brown and Brown, 1984). As
to female-biased dispersal it is commonly
argued that by dispersing females get ac-
cess to a wider choice of mates (Green-
wood, 1980), or that intra-sexual competi-
tion and inbreeding avoidance are involved
(see e.g. Pusey, 1987). For the Faroese fe-
male wrens the very few re-sightings give
little indications as to their post-breeding
whereabouts, except that just a few females
were seen in autumn at the breeding sites
(Tab. 1). It is difficult to see why a female
should divorce a good male and/or abandon
a good area unless it is ousted, but for the
time being there are no observations sug-
gesting such behavioural interactions. One
may speculate that, while some females