Since 1974 a population study of Black Guillemots has been
conducted on Flatey Island, NW Iceland. The main aspects
are summarized below.
Population numbers and distribution. The population has
been censused several years, also those of 20 islets near Flatey.
Information was collected on past status. Great changes have
occurred since turn of the century. Last major change began in
1967; the population started increasing of such a scale that
it can only have resulted from massive immigration. These
changes are thought to be due to rats and Mink.
Attendance and population structure. Data was gathered
on timing of spring return to nesting areas, status of attending
birds, sex ratio, area and nest-site fidelity, pair-bond
maintenance, and post-breeding departure. Special attention
has been given to the problem of censusing birds attending
nesting areas.
Breeding biology. Breeding biology variables were quantified
and studied on a seasonal basisj;timing of laying, clutch
size, interval between eggs, egg size, reproductive output,
lengths of incubation and nestling periods. Supernormal clutch
and brood experiments were conducted. I looked at length of
replacement time of lost clutches, factors influencing timing of
laying, its effect and that of clutch and egg size on breeding
performance. Egg and chick losses were analyzed. Many interesting
population phenomena seem to have been associated with the unusually
rapid population increase.
Feeding ecology. Analyses were made of prey taken,
feeding rhythm and areas, and factors influencing feeding
rate and prey selection. Some information was collected on
share of the sexes in feeding chicks, and kleptoparasitism.
Study was made of chick growth, fledging condition and postfledging
survival.
Population dynamics. About 3300 birds were ringed,
providing basis for determining age at maturity, adult survival,
and mortality. Pre-breeding survival was calculated
using data from ringing schemes. A population model was
constructed for the population, showing magnitude of immigration.
Ringing provided data on dispersal.</p