Roseate Tern Sterna dougallii
Status; International importance;
Population
estimates; Distribution; Annual abundance/
productivity; Phenology/diet/survival
Description
The following was adapted from
original text by Stephen F. Newton in
Seabird Populations of Britain and Ireland (with
permission from A&C Black, London).
The roseate tern population in the UK 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 around the British Isles, with
most of the population breeding in just a few colonies.
Consequently, the species is of high conservation concern and
is one of three red-listed seabirds in the United Kingdom.
Roseate terns have probably always been rare and localised in
the UK owing to their specialised foraging and nesting habitat
requirements. Driven to the brink of extinction by exploitation for
the millinery trade during the 19th century, the
population recovered through the early 20th century as a
result of protective legislation and management. Numbers peaked in
the late 1960s, but declined thereafter possibly 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.
Conservation efforts are directed toward education programmes in
the wintering areas in NW Africa and management of breeding
sites. However, recovery is evident only at the largest
colony, with smaller peripheral colonies declining to 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 species
range is likely to depend on conservation efforts to promote
growth of relict colonies, restore breeding at abandoned
sites, and create new colonies.
Conservation status
Roseate Tern is currently identified as a conservation priority
in the following:
Red listed in Birds
of Conservation Concern 3 (2009 update)
Wildlife and Countryside Act
1981 - protected under Schedule 1
EC Birds Directive -
listed in Annex 1
UK BAP - priority
species
(further information on Conservation Designations for UK Taxa)
Amber listed in
Birds of Conservation Concern in Ireland 2 (2007
update)
International importance
*AON = Apparently Occupied Nests
The UK population figure (rounded to the nearest hundred) was
derived from data in Mitchell, P.I., Newton, S.F., Ratcliffe, N. and Dunn, T.E.
(eds.) 2004. Seabird Populations of Britain and Ireland. Poyser, London. This was also the
source of figures for the Biogeographic and World populations.
UK population estimates and change 1969-2002 (census data)
Roseate terns are restricted to a small number of well-known
colonies in the UK all of which have been counted near
annually since 1969, such that their populations are monitored in
more detail than any other seabird breeding here. Roseate
terns were surveyed during Seabird 2000 by systematically counting
all nests situated along transect lines set up through colonies.
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. The
species may move among colonies between years in response to
predation or habitat change and so, to avoid double-counting or
missing some pairs, all colonies were counted in 2000. During the
SCR Census (1985-88) counts were conducted in different years at
some colonies. In order to be comparable with Seabird
2000, only counts from the SCR Census conducted in
1986 were used; this was when the most comprehensive coverage
of colonies was achieved during the period 1985-88.
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1986)
|
Seabird 2000
(2000)
|
| UK Population estimate (AON*) |
955 |
323 |
56 |
| % change since previous census |
N/a |
-66 |
-83 |
*AON = Apparently Occupied Nests
For census results for individual countries and Ireland, the
Channel Islands and the Isle of Man see under relevant
sections below.
Distribution/abundance
The Seabird
2000 census provides the most comprehensive recent
assessment of the distribution and abundance of breeding seabirds.
Numbers of roseate tern found in different regions, and a
map showing where colonies are found and how large they are is
provided in the Seabird 2000 roseate tern
results page (PDF, 1.0 mb).
An
interactive map is available on the NBN Gateway, where you can
filter to display only the Seabird 2000 data. For more
recent, but less comprehensive, coverage view the distribution on
the NBN with all available contributing datasets.
The locations sampled during the annual
Seabird Monitoring Programme provide some information on
distribution and are accessible via the Seabird Monitoring Programme
online database.
Annual abundance and productivity by geographical
area
Breeding abundance
Figure 1: Trend in UK abundance index (solid
line) of roseate tern 1986-2010 with 95% confidence limits (dotted
lines). Based on SMP data; view the methods
of analysis (PDF 158 kb).
The UK roseate tern population decreased from 950 pairs in
1969-70 to 320 in 1985-88 and fell further between 1986-1991,
mostly due to mortality of immature birds in their winter quarters
on the Ghana coast, which reduced subsequent recruitment into the
breeding population. There, boys trapped and killed mainly immature
birds for food, sport or profit, and while education programmes in
the late 1980s and early 1990s resulted in reduced mortality in
Ghana, these need to be maintained or a resurgence in trapping is
likely1. Food supply in
their wintering grounds is also likely to have affected immature
survival rates. The above conservation measures (and providing
shelter and protection from avian predators in the form of nest
boxes at some colonies) has resulted in the population starting to
recover. However, historical declines were recorded at all
colonies, whilst recovery has mostly been confined to just one
colony and, although numbers are increasing there, full
recovery remains a long way off.
Productivity
Figure 2: Trend in UK productivity (no. of
chicks fledged per pair) of roseate tern 1986-2010.
Based on SMP data; view the methods
of analysis (PDF 158 kb).
Although productivity was low in two
years during the population decline, the number of chicks fledged
in UK roseate tern colonies has generally been high throughout the
reporting period no doubt partly due to increased conservation
effort. Predation of chicks was the likely cause of the earlier
failures in 1987 and 1988 but the cause of low productivity in e.g.
2008 and 2010 was not reported.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
134 |
18 |
14 |
| % change since previous
census |
N/a |
-87 |
-22 |
* AON = Apparently Occupied Nests
Breeding abundance
Figure 1: Abundance of roseate tern on the
Forth Islands, 1986-2010.
The abundance of roseate terns on islands in the Firth of Forth,
the stronghold of the species in Scotland since the Seabird
Colony Register, shows a long-term decline since the late 1980s,
albeit with fluctuations. Three islands held the species although
the largest colony had effectively disappeared by the early 1990s,
due to increased competition for nesting habitat with herring
gulls, and breeding at another isle was sporadic.
Only one colony has been active in recent years but this too now
appears to have died out, due to flooding, predation and
disturbance. Elsewhere in the country, single pairs occasionally
frequent other tern colonies just maintaining its status as a
breeding species in Scotland.
Productivity
Productivity data showed no statistically
significant variation over time although productivity at Scottish
colonies was low, averaging 0.34 chicks fledged per pair
per year.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
355 |
34 |
36 |
| % change since previous
census |
N/a |
-90 |
+6 |
* AON = Apparently Occupied Nests
Breeding abundance
Figure 1: Trend in abundance index of
roseate tern on Coquet, 1986-2010.
In contrast to Scotland, the one extant roseate tern colony in
England, on Coquet Island, has fared better. National census
results show that a large decline occurred between Operation
Seafarer and the Seabird Colony Register both in terms of
numbers and number of colonies. Numbers have generally increased
since then, now essentially confined to Coquet. Increase
was slow at first but more rapid over the last decade but
between 2007 and 2010 numbers have been variable. Active
management on Coquet, via the provision of nestboxes for shelter
and protection from avian predators together with habitat
management, has undoubtedly helped the species thrive there, but
perhaps to the detriment of other nearby colonies as birds abandon
them in favour of Coquet.
Productivity
There is no statistically significant
variation over time in productivity data collected at colonies in
England, which were three times as successful as Scottish
colonies, averaging 1.00 chicks fledged per pair per
year.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
202 |
209 |
2 |
| % change since previous
census |
N/a |
+3 |
-99 |
* AON = Apparently Occupied Nests
Breeding abundance
Figure 1: Abundance of roseate tern at
three colonies in Wales, 1986-2010.
The decline in roseate tern numbers in Wales was steep after the
Seabird Colony Register although prior to this numbers appeared
stable in contrast to the populations of other countries in the
British Isles. By 1991 very few breeding pairs were left and
although there was a slight increase in 1993 and 1994 numbers soon
fell again and have never recovered. Ringing studies showed
the decline was apparently due to terns deserting colonies in Wales
(and Northern Ireland) and emigrating to those in the Republic of
Ireland where active management had created sites of higher
quality. No roseate terns have apparently nested in Wales
during six out of the last seven years.
Productivity
Little information is available on
the productivity of roseate tern at colonies in Wales.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
264 |
62 |
4 |
| % change since previous
census |
N/a |
-76 |
-94 |
* AON = Apparently Occupied Nests
Breeding abundance
Figure 1: Abundance of roseate tern at
three colonies in Northern Ireland, 1986-2010.
In common with Scotland and England, the roseate tern population
of Northern Ireland declined between Operation Seafarer and the
Seabird Colony Register, although the nearby Welsh population was
stable during this period. Then, in conjunction with Welsh
colonies, a steep fall in numbers occurred so that few were left
breeding by 1991. Emigration of birds to higher quality breeding
sites in the Republic of Ireland was at least part of the reason
for the decline. Since then the population has fluctuated without
showing any prolonged recovery but, as of 2003, is once more
declining toward zero.
Productivity
There is no statistically significant
variation over time in productivity data collected at colonies in
Northern Ireland which were slightly more successful than Scottish
colonies. Roseate terns productivity averaged 0.55 chicks
fledged per pair per year.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
1,429 |
227 |
734 |
| % change since previous
census |
N/a |
-84 |
+223 |
* AON = Apparently Occupied Nests
Breeding abundance
Figure 1: Trend in abundance index (solid
line) of roseate tern in the Republic of Ireland, 1986-2010 with
95% confidence limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
After the near ubiquitous decline recorded between Operation
Seafarer and the Seabird Colony Register, roseate tern numbers in
the Republic of Ireland have undergone a healthy increase which
continues to the present. However, breeding is now
confined to two medium to large colonies with only a few pairs at a
third. As on Coquet (England), the provision of nestboxes in
conjunction with other management prescriptions e.g. predator
control, habitat creation, have been of benefit to
the survival of the species.
Productivity
Figure 2: Trend
in productivity (no. of chicks fledged per pair)
of roseate tern in the Republic of Ireland, 1986-2010.
Based on SMP data; view the methods
of analysis (PDF 158 kb).
Roseate terns at colonies in the Republic of
Ireland have generally been quite productive over the years
usually fledging more than one chick per pair each year. However,
in 1997 and 1998 and in 2007 and 2008 at least averages
were lower than usual, largely in response to losses of eggs
and chicks due to poor weather.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
1,693 |
289 |
738 |
| % change since previous
census |
N/a |
-83 |
+155 |
* AON = Apparently Occupied Nests
Breeding abundance
Figure 1: Trend in abundance index (solid
line) of roseate tern throughout Ireland, 1986-2010 with 95%
confidence limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
As few pairs now nest in Northern Ireland the trend shown above
is heavily influenced by the fortunes of the ternaries in the
Republic of Ireland. Active management improving site quality is
key to the continued survival of this species throughout
Ireland.
Productivity
Figure 2: Trend
in productivity (no. of chicks fledged per pair)
of roseate tern throughout Ireland, 1986-2010. Based on
SMP data; view the methods
of analysis (PDF 158 kb).
Unsurprisingly, the trend shown above for All
Ireland closely matches that shown for the Republic of Ireland,
where the majority of data has been collected over the years,
albeit with slightly lower average annual values. The
relatively low values in 1997 and 1998 and in 2007 and
2008 at least were in response to losses of eggs and chicks due to
poor weather.
This species does not breed on the Isle of
Man.
This species does not breed on the Channel
Islands.
UK phenology, diet, survival rates
No data have been collected as part of the Seabird Monitoring
Programme.
References
1
Ratcliffe, N. And Merne, O. 2002. Roseate tern Sterna
dougallii. In: Wernham, C.V., Toms, M., Marchant, J., Clark,
J., Siriwardena, G. and Baillie, S. (eds.) The Migration Atlas:
Movements of the birds of Britain and Ireland. T & A.D.
Poyser, London.
Partners
Data have been provided to the SMP by the generous contributions
of its partners, other organisations and volunteers throughout
Britain and Ireland. Partners to the SMP are: BirdWatch Ireland;
The British Trust for Ornithology; Centre for Ecology and
Hydrology; Countryside Council for Wales; Department of
Agriculture, Fisheries and Forestry (Isle of Man); Department of
Environment, Heritage and Local Government (Republic of Ireland);
States of Guernsey Government; JNCC; Manx Birdlife; Manx National
Heritage; The National Trust; National Trust for Scotland; Natural
England; Northern Ireland Environment Agency; The Royal Society for
the Protection of Birds; Scottish Natural Heritage; Seabird Group;
Shetland Oil Terminal Environmental Advisory Group; Scottish
Wildlife Trust. More about the SMP partners >>
Image of roseate tern appears courtesy
of Ian Rendall ©, is subject to international
copyright law and may not be reproduced in any form
whatsoever.