The Roseate Tern population in Britain and Ireland experienced
the most dramatic decline of any seabird species between Operation
Seafarer (1969-70) and the SCR Census (1985-88). It also has one of
the most restricted ranges of any seabird in Britain and Ireland,
with most of the population breeding in just three colonies.
Consequently, Roseate Terns are of high conservation concern in
both Britain and Ireland and are the only red-listed seabird
species in both the United Kingdom and Ireland. Roseate Terns have
probably always been a rare and localised species of seabird in
Britain and Ireland owing to their specialised foraging and nesting
habitat requirements. Roseate Terns were driven to the brink of
extinction by exploitation for the millinery trade during the
19
th century, but recovered through the early
20
th century as a result of protective legislation and
management. Numbers peaked at 3,812 pairs in 1968, but declined
rapidly to just 521 pairs in 1985. The decline during the 1970s and
early 1980s was likely to have been due to poor immature survival
rates, and this may have been partially attributable to deliberate
trapping in the Ghanaian wintering grounds. Factors such as
predation and nesting habitat loss (due to erosion, competition
with gulls and/or disturbance) may have also played a role. The
population stabilised at around 500 pairs until 1992 when it staged
a slow recovery. The population of at least 816 pairs in 2003 was
the highest since 1980. Conservation efforts such as education
programmes in the wintering areas in NW Africa and site management
at breeding colonies have probably contributed to the population
recovery over the last decade. The recovery has been manifested
only at the three largest colonies, with smaller peripheral
colonies declining to perilously low levels or being abandoned
despite intensive efforts to maintain them. Movements of birds
among colonies within the metapopulation has been an important
determinant of regional population trends during the past three
decades, and so maintaining or enhancing the range of Roseate Terns
is likely to depend on conservation efforts to promote growth of
relict colonies, restore breeding at abandoned sites and create new
breeding sites.
Census Methods
Roseate Terns were all counted in units of apparently occupied
nests (AON) during Seabird 2000. Most AONs (i.e.98%) were surveyed
by systematically counting all nests situated along transect lines
set up through the colony, since nests are usually hidden in long
vegetation, among boulders, in rabbit burrows or in nest boxes and
so counts of AONs from a vantage point will miss a large proportion
of nests. Roseate Terns may move among colonies between years in
response to predation or habitat change and so a census of a
population should ideally survey all colonies within a single year
to avoid double-counting or missing some pairs. Therefore, for
Seabird 2000, counts of Roseate Terns breeding in Britain, Northern
Ireland & the Irish Sea coast of the Republic of Ireland were
made in 2000 except for the colony at Lady's Island Lake (Wexford)
where a count of 116 AON in 1999 was been used rather than the
count of 78 AON in 2000. Numbers of Roseate Terns at Lady's Island
Lake have fluctuated between 50 and 120 AON between the mid 1990s
and 2003, probably owing to variations in the proportion of mature
birds that attempt to nest. Inspection of counts made at other
large colonies in both 1999 and 2000 suggest that no large
inter-colony movements of birds occurred between these two years
and so the counts used for Seabird 2000 should provide a
representative snapshot of the status of Roseate Terns in Britain
and Ireland.
To estimate the size of the British and Irish population
during the SCR Census (1985-88), Lloyd et al. (1991) used
counts conducted in different years at some colonies, but did not
specify in which year each colony was surveyed. In order to be
comparable with Seabird 2000, we used counts for the SCR Census
that were conducted only in 1986 when the most comprehensive
coverage of colonies was achieved during the period 1985-88. The
total number of breeding Roseate Terns in 1986 was 550 pairs
whereas Lloyd et al. (1991) give an estimate of 470 pairs
for the period 1985-87. The discrepancy is due to the fact that
Lloyd et al. (1991) used a count of 69 pairs for the
colonies on Anglesey (Gwynedd) which, was conducted in 1987 after
numbers there had fallen dramatically from 209 in 1986.
Survey Coverage
Roseate Terns are restricted to a small number of well-known
colonies and all of those in Britain and along the east coast of
Ireland have been counted annually since 1969, such that their
populations are monitored in more detail than any other seabird
species breeding here. The small colonies found along the west
coast of Ireland during the All Ireland Tern Survey in 1984 (Whilde
1985) were not counted in 2000, but a repeat Census in 1995 (Hannon
et al. 1997) found all these had been abandoned. The
coverage of Roseate Tern colonies during Seabird 2000 is therefore
likely to have been comprehensive, although any birds recolonising
the sites along the west coast of Ireland will have been
overlooked.