Seabird 2000
Black-headed Gull Larus
ridibundus
The Black-headed Gull is the most widely distributed seabird
breeding in Britain and Ireland, with similar numbers breeding
inland as on the coast. The majority of the breeding population are
resident throughout the year, with numbers being greatly bolstered
during the winter months by birds from northern and eastern Europe,
especially in the east and southeast of England. Black-headed Gulls
breed throughout the middle latitudes of the Palaearctic and have
recently formed a breeding outpost in north eastern North America.
Britain and Ireland hold approximately 6% of the world breeding
population. Black-headed Gulls tend to nest on open ground and
occasionally in low trees and bushes, in colonies of anywhere from
a few to over 10,000 apparently occupied nests (AON). Habitats such
as wetlands, bogs, marshes and artificial ponds are favoured
breeding sites, but dry areas adjacent to water are also
used.
Prior to Seabird 2000, the population of Black-headed Gulls in
Britain and Ireland had only ever been surveyed incompletely.
During Operation Seafarer (1969-70) complete coverage of coastal
colonies was achieved, but no inland colonies were counted, and
these hold just under half of the Black-headed Gulls breeding in
Britain and Ireland. Both coastal and inland colonies were surveyed during the
SCR Census (1985-88), but coverage inland was incomplete and so
only provided a minimum estimate of the number of Black-headed
gulls nesting away from the coast. During Seabird 2000, survey
coverage was based on a list of colonies extracted from the SCR
Database that were known to have existed at some time between 1969
and 1998. However, this list was neither comprehensive nor up to
date and was amended by BTO County Bird Recorders with records of
new colonies and of those that had ceased to exist. Coverage of
Black-headed Gull colonies in Britain during Seabird 2000 was
comprehensive, with the exception of inland colonies in Durham and
in western parts of North Yorkshire, where some colonies may have
been missed, however the numbers involved are not thought to be
large. In Ireland, the only colonies not surveyed were those on the
islands of Lough Derg (Clare, Tipperary and Galway), which held a
total of 1,400 AON during the SCR Census (1985-88), however, it is
thought that numbers here have declined markedly since then.
During Seabird 2000, the recommended census unit for
Black-headed Gulls was the apparently occupied nest (AON). Counts
of AONs were conducted from either within the colony or from a
suitable vantage point. Large colonies were surveyed using sample
quadrat counts of AONs. The colonies at Insh Marshes (Badenoch and
Strathspey) and Loch of Kinnordy (Perth and Kinross), were surveyed
from the air, as they are located on low-lying marshy areas that
are unsuitable to walk on and contain few suitable vantage points.
At colonies that could not be accessed (e.g. on marshy ground or on
islands) and where there was no suitable vantage point, flush
counts of individuals attending the colony were made. Counts of
individuals were divided by two to provide a rough approximation of
the number of AONs present. This is the least accurate method for
censusing breeding gulls, as such counts will include an unknown
percentage of non-breeders and attendance at the colony by both
breeders in a pair is highly variable throughout the day and
throughout the breeding season. During Seabird 2000 only 13% of the
total population estimate of AONs for Britain and Ireland was
determined from flush counts of individuals, which compares
favourably to 18% during the SCR Census (1985-88).
Counts of breeding gulls within each admin area during Seabird
2000 and during previous censuses from gull surveys are presented
differently from other species to take into account the variation
in coverage of inland and coastal colonies during Seabird 2000 and
the previous two censuses. Since no inland colonies were surveyed
during Operation Seafarer (1969-70), Table 1a presents counts from
all three censuses from coastal colonies only; and Table 1b
compares Seabird 2000 totals for both inland and coastal colonies
with data from the SCR Census only.
[1] Coastal colonies were regarded as those being within 5km
of the high water mark; inland colonies were further from the sea
than this. All colonies in Orkney, Shetland and the Western Isles
were regarded as coastal.
Image appears courtesy of
Ian Rendall ©, is subject to
international copyright law and may not be reproduced in any form
whatsoever.