Black-legged kittiwake Rissa tridactyla
Status; International importance;
Population
estimates; Distribution; Annual abundance/
productivity; Phenology/diet/survival
Description
The following has been adapted
from original text by Martin Heubeck in
Seabird Populations of Britain and Ireland
(with permission from A&C Black,
London).
As well as being the most numerous species of gull in the world,
the black-legged kittiwake is the most oceanic in its habits and
most adapted to nesting on vertical rocky sea-cliffs. In Britain
and Ireland, the largest and most numerous colonies are found along
the North Sea coasts of Britain, around Orkney and Shetland, and
off NW Scotland. Colony size varies from less than ten pairs to
tens of thousands, but the locations of colonies tend to be
traditional over many decades. Although most colonies are on sheer
cliffs, in a few instances man-made structures such as buildings,
bridges, sea walls and even offshore oil installations have been
utilised. During the breeding season black-legged kittiwakes feed
mainly on small pelagic shoaling fish; around the British Isles
these consist of energy-rich species such as sandeels, sprats and
young herring. However, kittiwakes will also scavenge for offal and
discards around fishing boats, which can be an important food
source in years when their preferred prey species are less
abundant. Outside the breeding season the species is essentially
oceanic, and it is probable that populations from many different
breeding localities mix together in the N. Atlantic and North Sea
during winter, with some birds from British and Irish colonies
(especially first-winter and immatures) spending time off the
eastern seaboard of North America.
Conservation status
Black-legged kittiwake is currently identified as a conservation
priority in the following:
EC Birds
Directive - migratory species
Amber listed in Birds
of Conservation Concern 3 (2009 update).
(further information on Conservation Designations for UK Taxa)
Amber listed in
Birds of Conservation Concern in Ireland 2 (2007
update)
OSPAR List of
Threatened and/or Declining Species and Habitats
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 1969-2008
Geographical coverage of known black-legged kittiwake colonies
in the UK was complete during all three national censuses. In some
years, in response to a scarcity of food in spring, nest building
can be delayed by 2-3 weeks. Under such conditions a high
proportion of pairs (up to 40%) may begin nest building but not
complete a structure which qualifies as an apparently occupied nest
(AON), the preferred count unit, or progress to laying. This
phenomenon was documented for Shetland in 2002 but did not affect
counts for Seabird 2000. Counts outwith the recommended count
period (June) may also underestimate figures but, as this applied
to only approximately 5% of UK counts, it is unlikely that such
‘out-of-season’ counts had much influence on gross estimates of
population change.
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| UK Population estimate (AON*) |
407,417 |
504,055 |
378,847 |
| % change since previous census |
N/a |
+24 |
-25 |
*AON = Apparently Occupied Nests
Distribution/abundance
The Seabird
2000 census provides the most comprehensive recent
assessment of the distribution and abundance of breeding seabirds.
Numbers of black-legged kittiwake found in different
regions, and a map showing where colonies are found and how large
they are, is provided in the Seabird 2000 black-legged
kittiwake results page (PDF, 2.0 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
With reference to the regional
accounts below please note the following.
Breeding abundance:
graphs of abundance index with 95% CLs are only shown for a region
where the trend produced has been deemed accurate (see
methods of analysis). Where a trend was thought to be
inaccurate, graphs of abundance at major colonies in a
region may be shown instead, particularly if such colonies
hold greater than 10% of the regional population,
are monitored frequently and may thus help illustrate regional
population fluctuations outwith national censuses.
Occasionally, too few data have been collected regionally to
produce either of these.
Productivity: graphs
of productivity are only shown if analysis of breeding
success data produced a significant result for regional and/or
year effects (again see
methods of analysis). If results were not significant,
then a regional mean productivity value is given.
However, on some occasions too few data are
available from which to provide a meaningful average.
Furthermore, for 11 species where the quality of monitoring data
available was considered high, population viability analysis
was undertaken at the UK level and the results of this are
also reported.
Breeding abundance
Figure 1. Trend in UK abundance index (solid
line) of black-legged kittiwake 1986-2011 with 95%
confidence limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
Figure 1 shows that the UK index of kittiwake abundance has
declined rapidly since the early 1990s, such that by 2011 the
index was just 44% of that in 1986, when the Seabird Monitoring
Programme started, the lowest value in the 26 years of monitoring.
There was a slight increase in abundance in 2010, but such
increases have occurred before only for the index to continue
falling in subsequent years. Over the longer term, combining
census results with the SMP sample indicates that while
black-legged kittiwake numbers increased by around 24% between the
late 1960s and the mid 1980s (see table above), there are probably
now around 40% fewer than in the late 1960s. It is
likely, given recent repeated years of low productivity and
survival (see below), that declines will continue.
Productivity
Productivity of black-legged kittiwakes in the UK has
declined over the course of the Seabird Monitoring Programme
(Figure 2), related to declines in abundance of their sandeel
prey and in certain regions is negatively correlated with sea
surface temperatures1,
which have risen due to climate change. Productivity (and adult
survival) has also been negatively affected by
the presence of a sandeel fishery that operated off SE
Scotland1. Species
such as kittiwakes are particularly vulnerable to food shortages as
they can take prey only when it occurs at or near the surface of
the sea, unlike diving species such as auks, which have access to a
greater variety of prey in the water column. This has exacerbated
the effects of low prey abundance. By 2008, only one chick on
average was fledged from every four nests, compared with close to
one per nest between 1986 and 1995. This low productivity has
probably contributed to the declines in abundance shown above and
would indicate that further declines in abundance are likely in the
coming years, as fewer chicks become recruited to the breeding
population. Although productivity of black-legged kittiwakes
in 2009 was higher than it had been for a number of
years, possibly due to high availability of sandeels in
that year, kittiwakes were less successful in 2010 and again
in 2011.
Figure 2. Trend in UK productivity (no. of
chicks fledged per pair) of black-legged
kittiwake 1986-2011. Based on SMP data; view
the methods
of analysis (PDF 158 kb).
Recent analysis of the SMP
dataset by Cook and Robinson2 found mean breeding success
at monitored nests in black-legged kittiwakes was 0.68 and has
declined at a rate of 0.016 chicks per nest per year. This equated
to a decline in success of 31% over the period
1986-2008. The quality of the dataset meant a
change in breeding success greater than 5% would be detected with
high confidence. Using available life history information
(population size, clutch size, age at first breeding and survival
rates of different age classes) to develop population
viability analysis, it is predicted that
if this level of breeding success is
maintained, then populations of black-legged kittiwakes would be
expected to decline by 35% over 25 years. In order to prevent
such a decline breeding success would need to increase to around
1.50.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
346,097 |
359,425 |
282,213 |
| % change since previous
census |
N/a |
+4 |
-21 |
* AON = Apparently Occupied Nests
Breeding Abundance
Figure 1. Trend in abundance index (solid
line) of black-legged kittiwake in Scotland, 1986-2011
with 95% confidence limits (dotted lines). Based on SMP data;
view the methods
of analysis (PDF 158 kb).
The index of abundance for black-legged kittiwake at Scottish
colonies (Figure 1) has declined steadily since the
late 1980s and in 2011 reached the lowest point yet
recorded. One of the largest declines apparent from
recent data has occurred on Fair Isle where 1,436 AON were recorded
in 2011, 46% lower than the previous count in 2008 (2,688 AON) and
only 7% of the peak count there in 1988 (19,3401
AON). Over the longer term, census results indicate
numbers in Scotland changed little between Operation Seafarer and
the Seabird Colony Register, but fell thereafter so that Seabird
2000 found 21% fewer nests than the SCR. In the Seabird 2000
census, most black-legged kittiwakes were counted in
1999. The abundance index has declined by over half since then
so it is possible Scotland now holds fewer than 150,000
pairs. It seems likely, given the declining trend
in productivity recorded since 1986 (Figure 2) coupled
with a falling survival rate (Figure 4), that the
decline will continue.
Productivity
Figure 2. Trend in productivity (no. of
chicks fledged per pair) of black-legged kittiwake in
Scotland, 1986-2011. Based on SMP data; view
the methods
of analysis (PDF 158 kb).
A sustained decline in productivity has been apparent over
the period monitored, until 2009 when productivity increased
markedly, to reach its highest value since 1996. This
increased production was not sustained in 2010 or 2011, although
birds were still more successful than in some recent
years. Regional differences were apparent in in 2011 with
almost complete failure at monitored colonies in Shetland, Orkney
and North Scotland while success at colonies in regions further to
the south and west approached 0.90 chicks fledged per nest.
Low productivity has probably contributed to the declines in
abundance shown in Figure 1.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
49,676 |
125,819 |
76,281 |
| % change since previous
census |
N/a |
+153 |
-39 |
* AON = Apparently Occupied Nests
Breeding Abundance
Figure 1. Trend in abundance index (solid
line) of black-legged kittiwake in England, 1986-2011
with 95% confidence limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
In England, the peak in abundance index was reached in 1992
(c.f. 1989 in Scotland). A decline is apparent after 1995, but
over the last decade the index has been relatively stable
although fluctuating. The abundance index has not fallen
to the extent seen in Scotland. Other differences between the two
countries is that between Operation Seafarer and the
Seabird Colony Register the English population more than doubled
(although this has been challenged recently3), as opposed to showing
little change, but the proportional size of decline from the
Seabird Colony Register to Seabird 2000 was twice that recorded to
the north. Causes of change are probably the same for both
countries (see under UK) but are clearly having a greater
impact in Scotland (see also below).
Productivity
Figure 2. Trend in productivity (no. of
chicks fledged per pair) of black-legged kittiwake in
England, 1986-2011. Based on SMP data; view
the methods
of analysis (PDF 158 kb).
Productivity at English colonies, usually more successful than
those in Scotland, has been generally decreasing since 1986.
The nadir was recorded in 2004 when productivity averaged just 0.32
chicks per nest, but has improved since. Colonies were
not very productive in 2007 and 2008, but 2009, 2010 and 2011
were three of the more successful recent breeding seasons. The
relatively higher productivity in England compared
with Scotland, despite a declining trend, may explain why
the species' abundance has not fallen to the extent seen in
Scotland.The reasons for higher mean productivity in English
colonies is not clear, though they do not appear
to have encountered the periodic extreme food shortages
that have befallen some Scottish colonies, especially those in the
Northern Isles.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
6,891 |
8,771 |
7,293 |
| % change since previous
census |
N/a |
+27 |
-20 |
* AON = Apparently Occupied Nests
Breeding Abundance
Figure 1. Trend in abundance index (solid
line) of black-legged kittiwake in Wales, 1986-2011 with
95% confidence limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
Compared with Scotland, the abundance index for
black-legged kittiwakes in Wales has been relatively stable since
1986 and is similar to that shown for England,
although with lower peaks and higher troughs. However, in 2010
there was a noticeable drop in abundance with the index falling
slightly below the previous low point in 2004; in both years
the index is some 35% lower than in 1986. National
censuses found that numbers had changed little
between Operation Seafarer and Seabird 2000
but recent measures of abundance suggests the
current population may now be lower than in 1969-70. A slight rise
in index is apparent for 2011 but may prove to be another false
dawn in this species' road to recovery, although factors affecting
colonies at the UK level appear to have less of an impact in
Wales. The reasons for this are not well understood
Productivity
Figure 2. Trend in productivity (no. of
chicks fledged per pair) of black-legged kittiwake in
Wales, 1986-2011. Based on SMP data; view the methods
of analysis (PDF 158 kb).
The productivity of black-legged kittiwakes in Wales has
fluctuated widely over the recording period with no clear trend,
although productivity appears to have been depressed over much of
the last decade. In general, Welsh colonies are less
productive than those in England and there are more years when
productivity falls below 0.50 chicks per
pair compared with both England and Scotland. The
reasons for this are unknown.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
4,753 |
10,040 |
13,060 |
| % change since previous
census |
N/a |
+111 |
+30 |
* AON = Apparently Occupied Nests
Breeding Abundance
There are approximately 13 colonies of black-legged
kittiwake in Northern Ireland but few are monitored regularly.
The largest colony is Rathlin Island which held 76% of
the national population, some 9,917 AON, during Seabird 2000.
In 2007, numbers there were similar, with 9,896
AON recorded but a decline was recorded in 2011 when survey
work found 7,922 AON (a fall of 20%). The small colony on
Muck, also regularly monitored, has also been relatively
stable since Seabird 2000 (240 AON in 2000, 268 AON in
2011). Despite the lack of recent data from other colonies, it
seems that the black-legged kittiwake population of Northern
Ireland has been fairly buoyant since the Seabird Colony
Register compared with those in other countries in the UK
although it is clear that numbers are now on the wane.
Productivity
Figure 2. Trend in productivity (no. of
chicks fledged per pair) of black-legged kittiwake in
Northern Ireland, 1986-2011. Based on SMP data; view
the methods
of analysis (PDF 158 kb).
In Northern Ireland, few data on the productivity of
black-legged kittiwake have been collected as part of the SMP. Data
are too sparse to show any trend and productivity appears to
be extremely variable. Low productivity in several years since 2005
may now be contributing to the fall in numbers recorded at the main
colony on Rathlin Island.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
39,630 |
34,180 |
36,100 |
| % change since previous
census |
N/a |
-14 |
+6 |
* AON = Apparently Occupied Nests
Breeding Abundance
In the Republic of Ireland, Operation Seafarer found 39,630 AON
of black-legged kittiwake. Numbers had decreased slightly by the
second national census, but Seabird 2000 recorded similar
numbers to the Seabird Colony Register. Few sizeable black-legged
kittiwake colonies are monitored frequently so the current
population status of the species is uncertain. However, eight
colonies counted in 2010 (few data were available for 2011)
held 2,941 AON compared with 3,324 AON during
Seabird 2000 suggesting there has been no great change to
the population during the decade since the last national
census.
Productivity
Figure 2. Trend in productivity (no. of
chicks fledged per pair) of black-legged kittiwake in the
Republic of Ireland, 1986-2011. Based on SMP data; view
the methods
of analysis (PDF 158 kb).
Black-legged kittiwakes in the Republic of Ireland have had few
years with high levels of productivity. In most years, productivity
was below 0.80 chicks fledged per pair and often fell below
0.60.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
44,383 |
44,220 |
49,160 |
| % change since previous
census |
N/a |
<-1 |
+11 |
* AON = Apparently Occupied Nests
Breeding Abundance
In the whole of Ireland, Operation Seafarer and the seabird
Colony Register both recorded a little over 44,000 AON of
black-legged kittiwake. Numbers had increased by 11% to 49,160 AON
by the time of Seabird 2000 . Monitoring has only occurred at a few
sizeable colonies since Seabird 2000 but those that have been
counted recently suggest the current population may now lie
closer to that recorded during the Seabird Colony Register.
Productivity
Figure 2. Trend in productivity (no. of
chicks fledged per pair) of black-legged
kittiwake throughout Ireland, 1986-2011. Based on SMP data;
view the methods
of analysis (PDF 158 kb).
The trend in breeding productivity of black-legged
kittiwakes throughout Ireland is similar to that shown for the
Republic of Ireland where most data have been collected. There
are few years when productivity is higher than
0.80 chicks fledged per pair. Particularly poor years were
recorded in 1996 and 2008. Such low levels of productivity may now
be having a deleterious affect on abundance (e.g. see Northern
Ireland).
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (AON*) |
908 |
1,376 |
1,045 |
| % change since previous
census |
N/a |
+51 |
-24 |
* AON = Apparently Occupied Nests
Breeding Abundance
Full censuses recorded 908 black-legged kittiwake AON during
Operation Seafarer, increasing by 50% to 1,376 AON during the
Seabird Colony Register. A decline then occurred with Seabird
2000 recording just over 1,000 nests. Only one colony, the
Calf of Man, has been counted recently and numbers there
have fallen drastically. During Seabird 2000, 182 AON were found in
1999, declining to 104 AON in 2005 but only 8 AON were
recorded there in 2010 (no data were submitted in 2011). In light
of this large drop in numbers, coverage of other colonies in the
region is desirable to ascertain the current population.
Productivity
No data were collected in 2010 or 2011, but up to 2009 there was
no statistically significant effect of year in the breeding
productivity of black-legged kittiwakes nesting on the Isle of
Man; an average of 0.27 chicks per pair were fledged each
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*) |
12 |
34 |
3 |
| % change since previous
census |
N/a |
+183 |
-91 |
* AON = Apparently Occupied Nests
Breeding Abundance
The black-legged kittiwake has only a small breeding presence in
the Channel Islands. Three nests were recorded during Seabird 2000,
34 during the Seabird Colony Register when the population was at
its peak and 12 nests during Operation Seafarer. No data have been
received by the SMP since Seabird 2000.
Productivity
No systematic data on breeding productivity have been collected
as part of the SMP.
UK phenology, diet, return rates and survival rates
Phenology
No systematic data on phenology (timing of life-cycle events)
have been collected as part of the SMP.
Diet
Figure 3. Percentage of sandeels (by weight) in
the diet of young black-legged kittiwakes at the Isle of
May (SE Scotland), 1987-2011.
Sandeels are an energy-rich food source compared with some
alternative prey and the proportion of sandeels by weight may
be used as a measure of 'diet quality' for this colony.
Figure 3 shows that the percentage of sandeel in the diet
has been very low in 2006-2011, excluding 2009; in these years,
sprat Sprattus sprattus, rockling and gadoids
comprised most of the remainder by weight of their diet. Snake
pipefish Entelurus aequoreus were taken in some
abundance between 2005 and 2008, though they contributed very
little in terms of weight and are of low food value4. Sandeels comprised
a high proportion of the diet of Isle of May kittiwake chicks
in 2009 and productivity there and UK-wide was high in that
year.
Kittiwake diet is also sampled at two other of the 'Key Sites'
in the Seabird Monitoring Programme: Canna (Lochaber, Scotland) and
Fair Isle (Shetland, Scotland). At the former site sandeels were
present in most diet samples; sprat and members of the cod family
were also prevalent. No trends in diet composition are evident
over the course of the Seabird Monitoring Programme at Canna. At
Fair Isle, few samples have been obtained in recent years. Pipefish
were prevalent in 2006-7 but not so recently.
Return rates and survival rates
Important notes on interpretation: Estimation
of kittiwake adult return rate and survival rate is
currently undertaken at two sites within the Seabird
Monitoring Programme - the Isle of May in the Firth of Forth, SE
Scotland and Skomer Island, Pembrokeshire, SW Wales. Return
rates are based on sightings of individually colour-ringed birds
and are calculated as the proportion of marked birds present in
year one that is seen in the following
year. Because not every adult alive is seen each year, return
rates for 2011 presented here for Isle of May need to be
treated as minimum estimates of survival of birds seen in 2010. In
contrast, survival estimates - as presented here for Skomer
- do take into account birds that are not seen one year but
which re-appear in following years.
Figure 4. Annual return rate
of black-legged kittiwakes breeding on the Isle of May
(SE Scotland), 1987-2011.
The return rate of black-legged kittiwakes on
the Isle of May (Figure 4) declined between 1986 and 1998 and has
typically fluctuated at a low level since then. Particularly low
rates occurred in 2007-2009 but in 2010 the return
rate (89.0%) was the highest since 1989 and well above
the average for the period prior to this (77.7, 95% CI
=74.5-81.0). Adult survival has been negatively affected by
the presence of a sandeel fishery that operated off SE
Scotland1 between
1990 and 1999.
Figure 5. Estimated adult survival rate
of black-legged kittiwakes on Skomer, Pembrokeshire,
1987-2010.
Survival rates of kittiwakes on Skomer (Figure 5) declined
between 1991 and 1996 then increased up to 2001, after which
another decline is evident. The survival rate in 2007 was
particularly low. There appears to be a degree of correlation
between survival rates on Skomer and return rates on the Isle of
May (Figure 4), suggesting that similar conditions during the
non-breeding season may affect both populations. A recent
study using geolocation data loggers to examine the non-breeding
season distribution of kittiwakes found tagged birds from
Skomer (and Rathlin) remained relatively near the
colony but those from the Isle of May dispersed more
widely and the main areas of use were split between the North Sea
and the Central and West Atlantic5.
References
1 Frederiksen, M., Harris, M.P., Daunt, F., Rothery, P. and
Wanless, S. 2004. The role of industrial fisheries and
oceanographic change in the decline of North Sea black-legged
kittiwakes. Journal of Applied Ecology 41: 1129-1139.
2 Cook, A.S.C.P. and Robinson, R.A. 2010.
How representative is the current monitoring of breeding
success in the UK? BTO Research Report No. 573, BTO,
Thetford.
3 Coulson, J.C. 2011. The Kittiwake. T. and
A.D. Poyser, London.
4 Harris, M.P., Newell, M., Daunt, F., Speakman,
J., and Wanless, S. 2007. Snake pipefish Entelurus
aequoreus are poor food for seabirds. Ibis 150:
413-415.
5 Frederiksen, M. et al. 2012. Multicolony tracking reveals the
winter distribution of a pelagic seabird on an ocean basin scale.
Diversity Distribution 18: 530-542.
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 black-legged kittiwake appears courtesy
of Ian Rendall ©, is subject to
international copyright law and may not be reproduced in any form
whatsoever.