Razorbill Alca torda
Status; International importance;
Population
estimates; Distribution; Annual abundance/
productivity; Phenology/diet/survival
Description
The following was adapted from
original text by Oscar J. Merne & P. Ian Mitchell in
Seabird Populations of Britain and Ireland (with
permission from A&C Black, London).
The razorbill is a bird of the temperate North Atlantic and
adjacent parts of the Arctic Ocean. They breed on both sides of the
Atlantic and in the east they breed as far south as Brittany
(France), north to Svalbard and east to the White Sea in north-west
Russia. Razorbills breeding in the British Isles winter along the
Atlantic coast of Europe from southwest Norway to Iberia and North
Africa, and into the western Mediterranean. Immatures move
significantly further away from their natal colonies than do adults
and generally further south, though occasionally they stray west as
far as Greenland and the Azores.
Razorbills breed mainly on small ledges or in cracks of rocky
cliffs and in associated screes, and on boulder-fields. Rarely,
colonies have been found up to 300m inland. Razorbills are usually
associated with colonies of other seabirds, and small numbers
scattered among large concentrations of common guillemots and
black-legged kittiwakes can easily be overlooked. Razorbill 'nest'
sites are usually hidden from view, but the presence of a colony is
clearly indicated by the attendance of off-duty birds standing
close by. Since it is not usually possible to count occupied sites,
the species is difficult to census. Hence, prior to Operation
Seafarer (1969-70), very little was known about its numbers and
population trends in the UK. Furthermore, interpreting differences
between Operation Seafarer (1969-70) and the SCR Census
(1985-88) is difficult, since most counts in Operation Seafarer
were expressed as pairs, while the SCR Census counted the number of
individuals. Despite methodological differences between the two
censuses, during 1969-1988, there appeared to be an increase in the
total number of razorbills breeding. For example, in Shetland,
where individual birds were counted in both censuses, numbers of
razorbills doubled between 1969 and 1988.
Conservation status
Razorbill is currently identified as a conservation priority in
the following:
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)
International importance
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)
The count unit for razorbills is individuals (on suitable
breeding ledges), which may include off-duty adults, non-breeders
and immatures as well as - where nests are visible - brooding and
incubating birds. At a few sites it is possible to count apparently
occupied sites or nests (AOS or AON). However, in order to compare
counts between between years, all counts of AOS and AON were
divided by 0.67 to estimate the equivalent count of individuals. In
Seabird 2000, only 3% of the population estimate (in terms of
birds) was converted from counts of AOS and AON, comparable to the
SCR Census when converted counts comprised 5% of the total
estimate. In contrast, 78% of the total population estimate of
razorbills in Operation Seafarer were expressed as pairs (i.e. AOS
or AON). However, it is unclear how surveyors
determined 'pairs' present in each colony. Therefore
comparisons of Operation Seafarer data with subsequent counts
of individuals should be treated with caution.
During Seabird 2000 and the SCR Census survey, methods
prescribed counting razorbills between 1 and 21 June, to coincide
with the late incubation and main nestling period, and during 08:00
to 16:00 hrs (BST) to coincide with the periods of most consistent
attendance by birds at the colony. This may not necessarily
coincide with the maximum numbers of birds attending the cliffs
during a season, but instead provides the most comparable measure
of attendance when using one-off counts. In Seabird 2000, 43% of
counts were conducted during this period and time, with a
further 21% in the prescribed period, but either outwith the
correct time or the time was not noted. During the SCR
Census, only 37% of counts were conducted on the correct dates
but actual time was never recorded. These count
windows were not prescribed during Operation Seafarer and
so some counts were carried out later in July or even early
August when many successful adults would have left with their
chicks and when failed breeders would have deserted resulting in an
underestimate.
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| UK Population estimate (Individuals) |
132,734 |
154,219 |
187,052 |
| % change since previous census |
N/a |
+16 |
+21 |
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 razorbill found in different regions, and a
map showing where colonies are found and how large they are is
provided in the Seabird 2000 razorbill
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
Breeding abundance
Figure 1: Trend in UK abundance index (solid
line) of razorbill 1986-2010 with 95% confidence limits
(dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
Like the common guillemot, the UK population
index for razorbill has increased over the reporting period.
Over the longer term, census results show that the UK razorbill
population increased by 13% between 1969-70 and 1985-88. After a
period of stability between 1986 and 1991 the index increased
fairly steadily until 2005 when the index peaked at 87% above the
value in 1986. The reasons for these increases are not known. Since
2005, the index has again fallen, possibly as a result of
so-called 'density-dependent' effects, where growth at
the densest colonies slowed or reversed when competition
for space and food reached critical levels. While predictions of
future population trends are uncertain, the observed low
productivity in recent years may lead to continued declines,
though this could be buffered if relatively small increases in
adult survival were to occur.
Productivity
Figure 2: Trend in UK productivity (no. of
chicks fledged per pair) of razorbill 1986-2010. Based
on SMP data; view the methods
of analysis (PDF 158 kb).
Razorbill productivity was fairly
stable from 1986 to1993 but declined thereafter, with four
particularly unproductive seasons during the last seven
years. The decline coincides with food shortages, especially
notable at colonies in the north and east of the UK and, at one
colony, a decrease in the energy content of fish brought to
chicks1. The association of years of
low razorbill productivity with rising sea surface
temperatures (SST) due to climate
change is uncertain, though there are indications
that declines in the productivity of sandeels may be linked
in complex ways to warming sea temperatures2.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
111,038 |
123,586 |
139,186 |
| % change since previous
census |
N/a |
+11 |
+13 |
* Ind = Individuals
Breeding abundance
Figure 1:
Abundance of razorbill on Handa, 1986-2010.
In Scotland, the number of razorbills increased between
Operation Seafarer and Seabird 2000. Numbers during the
Seabird Colony Register were 11% higher than in 1969/70 and
had increased again, by 13%, during Seabird 2000. The
abundance trend extrapolated from colonies sampled for the SMP was
found to be unrepresentative, as it didn’t agree with that shown by
census data. However, 17 colonies covered in 2010 held
14,529 individuals compared to 26,766 individuals during Seabird
2000. Although this is a small sample of colonies it does suggest
numbers have fallen with the more frequently monitored
colonies indicating the decline began near the start of this
century. Counts on Handa, once the largest Scottish colony,
are typical of that recorded at other colonies where razorbills
have declined substantially (Figure 1); 12,925 individuals
were recorded in 2006 which represented a fall of almost 24%
since 2001 with numbers declining again by 2010 to 7,709
individuals - a further fall of 40%.
Productivity
Data collected at colonies in Scotland indicate there is no
statistically significant variation in the productivity of
razorbills over time. On average 0.49 chicks were
fledged per pair each year. Some colonies have recorded low
levels of success in recent years; on Fair Isle
near complete breeding failure has occurred in three of the
last four years.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
5,405 |
10,101 |
11,144 |
| % change since previous
census |
N/a |
+87 |
+10 |
* Ind = Individuals
Breeding abundance
Razorbill numbers in England almost doubled between Operation
Seafarer and the Seabird Colony Register to 10,101 individuals. By
the time of Seabird 2000 a further increase of 10% had occurred.
Few colonies of any great size are monitored regularly so the
current trend is unknown. However, at Bempton Cliffs, counts in
2008 found 14,927 individuals, an increase of 234% since 2000
when 4,463 individuals were counted for Seabird 2000. The reasons
behind this increase are unknown but could be due to recent
good breeding seasons at the colony and/or immigration rather
than errors due to count methodology.
Productivity
Productivity data have only been collected at one colony in
England, on the Farne Islands. There was no statistically
significant variation over time; on average approximately 0.68
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 (Ind*) |
9,316 |
9,501 |
12,638 |
| % change since previous
census |
N/a |
+2 |
+33 |
* Ind = Individuals
Breeding abundance
Figure 1: Trend in abundance index (solid
line) of razorbill in Wales, 1986-2010 with 95% confidence
limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
The trend in abundance for razorbills at Welsh colonies has
generally been upward since 1986, with a peak in 2005.
National census data show numbers were stable between Operation
Seafarer and the Seabird Colony Register, but then increased by 33%
by the time of Seabird 2000, a trend which has continued
to the present.
Productivity
Figure 2: Trend in productivity (no. of
chicks fledged per pair) of razorbill in Wales, 1986-2010.
Based on SMP data; view the methods
of analysis (PDF 158 kb).
Productivity of razorbills was not collected at Welsh
colonies prior to 1993. Although productivity has varied
between years there is a sharply declining trend which
appears to have steepened in recent years. The three lowest values
recorded have occurred during 2008-2010.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
6,975 |
11,031 |
24,084 |
| % change since previous
census |
N/a |
+58 |
+118 |
* Ind = Individuals
Breeding abundance
Razorbill numbers in Northern Ireland have been on the increase
since Operation Seafarer according to national census data. The
Seabird Colony Register recorded 58% more than during the first
census, which was followed by a large
increase at Seabird 2000; numbers more than doubled
to over 24,000 individuals. Few colonies are monitored frequently
but most of the national population (87% during Seabird 2000) is
found on Rathlin Island where a count in 2007 recorded 10,684
individuals - a severe decline of 49% since Seabird
2000. Clearly, given the importance of this colony in
a national context, the overall population in Northern
Ireland will have fallen too, although numbers are
probably still higher when compared with that
recorded during the SCR.
Productivity
Very few systematic productivity data have been
collected for razorbills in Northern Ireland as part of the
SMP.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
33,989 |
20,987 |
27,446 |
| % change since previous
census |
N/a |
-38 |
+31 |
* Ind = Individuals
Breeding abundance
In contrast to Northern Ireland, razorbill numbers in the
Republic of Ireland were found to have declined by 38% between
Operation Seafarer and the Seabird Colony Register. Although a
subsequent increase had occurred by Seabird 2000, the
population was still slightly below that recorded during the first
census, again in contrast to changes in Northern Ireland where
razorbill numbers doubled over the same period. Colonies
monitored since Seabird 2000 are few but may give some
indication of current population trend. On Lambay, 6,399
individuals were recorded in 2009, an increase of 47% since
1999, making it the largest colony in the country
replacing the Cliffs of Moher where numbers fell from 7,700
individuals to 3,547 apparently incubating birds in 2005
(approximately 5,320 individuals). Numbers at several smaller
colonies had changed little since the last census. Combined
counts from colonies surveyed in 2005-10 were close to
those recorded in 1998-2002 suggesting no overall change.
Productivity
Very few systematic productivity data have been
collected for razorbills in the Republic of Ireland as part of
the SMP.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
40,964 |
32,018 |
51,530 |
| % change since previous
census |
N/a |
-28 |
+61 |
* Ind = Individuals
Breeding abundance
The razorbill population for the whole of Ireland was 51,530
individuals during Seabird 2000, 61% higher than during the
Seabird Colony Register when numbers were found to have declined by
28% since Operation Seafarer. Few colonies are monitored
frequently in either Northern Ireland or the Republic of Ireland so
any information as to the current trend must be taken
from counts at the larger colonies covered periodically. In the
Republic of Ireland, increases at some colonies are offset by
decreases at others so there has probably been little change
in numbers over the last decade. In Northern Ireland, numbers on
the largest colony have declined by half to 10,684 individuals in
2007. Overall, these changes would indicate the current population
now lies closer to that recorded during Operation Seafarer but
still well above that of the Seabird Colony Register.
Productivity
Very few systematic productivity data have been
collected for razorbills throughout Ireland as part of the
SMP.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
897 |
848 |
1,524 |
| % change since previous
census |
N/a |
-5 |
+80 |
* Ind = Individuals
Breeding abundance
Figure 1: Abundance of razorbill on the
Calf of Man, 1986-2010.
Between Operation Seafarer and the Seabird Colony Register the
number of razorbills on the Isle of Man was relatively stable. By
Seabird 2000 the population had increased by 80% to 1,524 birds.
With few colonies surveyed since then the status of the species is
unknown. On the Calf of Man, which held between one quarter
and one fifth of the population during the previous two
censuses, numbers in 2010 were close to the peak
count recorded in 1999. However, counts in both these
years are far above that usually recorded at this colony so no
clear trend is discernable.
Productivity
Very few systematic productivity data have been
collected for razorbills on the Isle of Man as part of the
SMP.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
63 |
81 |
65 |
| % change since previous
census |
N/a |
+29 |
-20 |
* Ind = Individuals
Breeding abundance
The small population of razorbills nesting on the Channel
Islands numbered just 65 individuals during Seabird 2000, almost
the same as that recorded by Operation
Seafarer. Razorbills were slightly more numerous during the
Seabird Colony Register, when 81 individuals were counted. There
are no recent counts for the archipelago so the species' current
status is unknown.
Productivity
No systematic data on productivity have been collected as part
of the SMP.
UK phenology, diet, survival rates
Phenology
No systematic data on phenology (timing of life-cycle events)
have been collected as part of the SMP.
Diet
No systematic data on razorbill diet have been
collected as part of the SMP.
Return rate and survival rate
Important notes on interpretation: Estimation
of razorbill adult return 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 in 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 2010
presented here for Isle of May need to be treated as minimum
estimates of survival of birds seen in 2009. In contrast, survival
estimates do take into account birds that are not seen one
year but which re-appear in following years.
Figures 3 and 4 show that annual return rate/survival rate of
razorbills has shown no clear trend over the period monitored,
though low rates have been recorded in recent years (in 2007 for
Skomer birds and in 2008 for Isle if May birds). In 2009 and 2010
survival was the highest recorded on the Isle of May. There
appears to be no relationship between the UK population trend (nor
the trend in Wales) and survival/return rates at the
two colonies where this is measured. The low return rate at
the Isle of May in 2008 follows a post-breeding wreck of adult
birds during 2007.
Figure 3. Annual return rate of razorbills
breeding on the Isle of May (SE Scotland), 1987-2010.
Figure 4. Annual survival rate
of razorbills breeding on Skomer (SW Wales),
1987-2009.
References
1 Wanless, S., Harris, M. P., Redman, P. & Speakman, J. R.
2005. Low energy values of fish as a probable cause of a major
seabird breeding failure in the North Sea. Mar. Ecol. Prog. Ser.
294: 1-8.
2 Heath, M., Edwards, M., Furness, R.,
Pinnegar, J., and Wanless, S. (2009) A view from above: changing
seas, seabirds and food sources in Marine Climate Change
Ecosystem Linkages Report Card 2009. (Eds. Baxter JM, Buckley PJ
and Frost MT), Online science reviews, 24pp. www.mccip.org.uk/elr/view
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 razorbill appears courtesy of Ian
Rendall ©, is subject to international copyright law and may not be
reproduced in any form whatsoever.