Seabird 2000
Lesser Black-backed Gull
Larus fuscus
The following was adapted from original text by John
Calladine in
Seabird Populations of Britain and Ireland (with
permission from A&C Black, London).
The Lesser Black-backed Gull breeds in north and west Europe and
has increased in numbers throughout its range during much of the
20th century. During this time, they have become less
migratory and can now be found within much of their breeding range
throughout the year. Lesser Black-backed Gulls nest colonially,
often with other gull species, especially the Herring Gull.
Colonies are found on islands offshore and within inland freshwater
bodies, coastal cliffs, sand dunes, salt marshes, moorland and on
the rooftops of buildings. Seemingly, many sites that are either
inaccessible to ground predators (e.g. islands and urban rooftops)
or where the latter are particularly scarce (e.g. narrow peninsulas
or on moorland managed as sporting estate) can prove attractive for
nesting Lesser Black-backed Gulls. Though often sharing breeding
areas with Herring Gulls, their nest sites and feeding strategies
generally differ; Lesser Black-backed Gulls can forage over larger
distances and they tend to nest within more vegetated areas.
Census Methods
During Seabird 2000, the recommended census unit for Lesser
Black-backed 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. 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. The
accuracy of counts of individuals is difficult to assess. However,
during Seabird 2000, 91% of counts were of nests, the rest were
derived from counts of birds, apparently occupied sites or
territories. In mixed colonies the determination of the proportion
of a count to assign to a particular species provides a further
potential source of error, as the eggs of the two species can not
be readily distinguished during counts. In all but the smallest
colonies, where individual nests may be attributed to any given
species, it was recommended that the proportion of Lesser
Black-backed Gulls be determined from sample head counts
representative of the colony as a whole.
Survey Coverage
Prior to Seabird 2000, the population of Lesser Black-backed
Gulls in the whole of Britain and Ireland has only ever been
surveyed incompletely. During Operation Seafarer (1969-70),
complete coverage of coastal colonies was achieved, but no inland
colonies were counted, and during Seabird 2000, these held 22% of
the Lesser Black-backs breeding in Britain and Ireland. Both
coastal and inland [1] 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 Lesser Black-backed Gulls
nesting away from the coast. Seabird 2000 represents the first
attempt to census all inland breeding colonies and 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. While coverage was good in
most areas, inland Durham was not surveyed, but only 2 AON were
recorded there in 1987. Furthermore, the several hundred pairs that
are believed to be nesting on the rooftops of Edinburgh proved
practically impossible to survey. Elsewhere, coverage of
roof-nesting gulls was good, with the aid of aerial surveys in
places like south Wales, Gloucester, Glasgow and Inverness.
Data presentation
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 1 compares counts from
all three censuses from coastal colonies only, but also gives the
total number present in both inland and coastal colonies during
Seabird 2000. Table 3 gives counts of breeding Lesser Black-backed
Gulls within each admin area during Seabird 2000 and during two
previous surveys of roof-nesting gulls in Britain and Ireland,
conducted in 1976 (Monaghan & Coulson 1977) and in 1993-95
(Raven & Coulson 1997).
Census Methods Data Processing and
Analysis References Seabird 2000
[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.
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