Fróðskaparrit - 01.01.2004, Side 258

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PHILOPATRY, DISPERSAL, AND SURVIVAL OF WREN
(TROGLODYTES TROGLODYTES) IN THE FAROE ISLANDS
1), mostly in 1984 (n=51)). They were
mist-netted on the breeding grounds, often
entire family-groups, and only once (on
Mykines) was a brood of nestling ringed;
nests with young were used for studies
of parental food provisioning and there-
fore too precious to put at risk. The sex of
adults was determined from behaviour but
that of fledglings could only be established
for those that were re-sighted in subsequent
year.
The study areas were visited in autumn
(mid-August-October) following ringing,
and in the subsequent breeding season
(June-July) by myself or co-workers. Usu-
ally only the study areas and their immedi-
ate surroundings (< 300 m) were surveyed,
though with highly variable degrees of ef-
ficiency. A few birds (none of which was
re-sighted) were ringed in sites that were
not at all re-visited in the following year
(e.g. on Kalsoy) and therefore not included
in the analysis. In the Faroes the scarcity of
dense, shrubby vegetation and the wren's
habit of approaching and often entering
buildings (/núsabródir, ”the brother of the
mouse”) greatly increases its detectability.
The wren is familiar to most islanders and
therefore public media (newspapers, radio,
and TV) were alerted resulting in a number
of sightings (from all seasons) of colour-
ringed wrens, where in most cases the re-
ported colour-combinations made positive
individual identifications possible.
Despite recent methodological advances
in statistical techniques and software in
analysing ringing recovery and re-sighting
data (see e.g. Nichols and Kaiser, 1999),
the small sample size of the present study
renders comparisons between areas and
years meaningless and pooled data are pre-
sented descriptivly. From mortality rates
(m) the mean life expectancy (MLE) can
be calculated using the formula: MLE =
(2 - m)/2m, and by using minimum annual
survival rate (i.e. return rates of marked
individuals) instead a conservative (i.e. un-
derestimate) estimate is obtained.
Results
Tab. 1 gives the numbers and frequencies
of marked individuals re-sighted during
autumn (i.e. within c. 3 months of ringing)
and in subsequent summer. One fledgling
was found dead after a few days where it
had been ringed on Fugloy.
Autumn dispersal
Newly fledged young usually remain in the
vicinity of the nest (< 200 m) for the first 8-
10 days, but longer movements may occur;
e.g. on Mykines one newly fledged young
moved 850 m in just short of 3 hours fol-
lowing ringing. About one-forth of the year-
lings were observed again before the end of
October (mostly in September), nearly all
in, or close to their respective natal areas.
Four yearlings, two each on Fugloy and
at Haldarsvík, that were observed in Sep-
tember had dispersed between 2 and 4 km
from the ringing sites. The only case of in-
ter-island dispersal was a fledging ringed
on Mykines on 18 July 1984 and reported
25 November on Nólsoy, i.e. 50 km ESE
of Mykines. Among breeders a higher,
though statistically non-significant propor-
tion of the males than of the females were
re-sighted during autumn in the study areas;