Razorbill Alca torda

Status;  International importance;  Population estimates;  Distribution;  Annual abundance/ productivity; Phenology/diet/survival

Description

The following has been 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.

Conservation status

Razorbill 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)

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 was 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.

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).

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 razorbill 1986-2011 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. Between 2005 and 2010, the index declined, 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. However, in autumn 2007, a ‘wreck’ of adult razorbills in the Skagerrak and North Sea, most of which originated from Scottish colonies (see Scotland section), may also have contributed to the declining trend. The index climbs again in 2011 although wide confidence intervals suggest this apparent increase should be treated with caution. While predictions of future population trends are uncertain, the observed low productivity in recent years may lead to continued declines.

Productivity

Figure 2: Trend in UK productivity (no. of chicks fledged per pair) of razorbill 1986-2011. 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 the Isle of May, 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 a decline in the productivity of sandeels may be linked in complex ways to warming sea temperatures².

Recent analysis of the SMP dataset by Cook and Robinson³ found the mean breeding success of razorbill at monitored nests was 0.55 and declined at a rate of 0.013 chicks per nest per year. This equates to a decline in success of 26% over the period 1986-2008. The quality of the dataset meant a change in breeding success greater than 25% would be detected with confidence. However, the data do not have sufficient power to detect a change in breeding success of 10% or less. Population viability analysis (using available life history information on population size, clutch size, age at first breeding and survival rates of different age classes) predicted that were this rate of breeding success to be sustained, razorbill abundance would decline by only around 4% over 25 years. Were breeding success to drop below 0.50, populations would decline by 25% over 25 years. Success would have to half again for a 50% decline over 25 years to be observed.

Population estimates and change 1969-2002 (census data)

* Ind = Individuals

Breeding abundance

Figure 1: Trend in abundance index (solid line) of razorbill in Scotland, 1986-2011 with 95% confidence limits (dotted lines; drawing of upper limit restricted to preserve detail in the abundance index). Based on SMP data; view the methods of analysis (PDF 158 kb).

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 shows an increasing trend until 2004 but declines thereafter so that in 2010 the abundance index was almost on a par with 1986. In autumn 2007, a ‘wreck’ of adult razorbills in the Skagerrak and North Sea, most of which originated from Scottish colonies, may have contributed to the already declining trend. Counts on Handa, once the largest Scottish colony, are typical of that recorded at other colonies over the previous decade with substantial declines in razorbill numbers; 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%. The increase in the index in 2011 may be due to the counts on Mingulay where razorbill numbers more than doubled between 2010 and 2011 from 2,237 to 5,691 individuals. The reason for the increase at this colony is unknown but could be due to unreported methodological differences although survey dates between the two years are similar.

Productivity

Figure 2: Trend in productivity (no. of chicks fledged per pair) of razorbill at Scottish colonies, 1986-2011. Based on SMP data; view the methods of analysis (PDF 158 kb).

Data collected at colonies in Scotland indicate declining productivity since the early 1990s although the decline has not been constant. 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)

* 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. However, at Bempton Cliffs SPA, counts in 2008 found 14,927 individuals, an increase of 138% since 2000 when 6,282 individuals were counted for Seabird 2000 and indeed several thousands higher than the national population at that time. The reasons behind such a large increase are currently unknown but could be due to differences in count methodology; it is unlikely increases have come about due to increased productivity or immigration.

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 from 1996 to 2011.

Population estimates and change 1969-2002 (census data)

* Ind = Individuals

Breeding abundance

Figure 1: Trend in abundance index (solid line) of razorbill in Wales, 1986-2011 with 95% confidence limits (dotted lines; drawing of upper limit restricted to preserve detail in the abundance index). 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 although the index in 2011 almost equals it. 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, 1986-2011. 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. No data was collected in 2011. With productivity falling, and low rates of survival recorded in Wales in recent years (see below) it would be no surprise if abundance also fell but this does not appear to be happening at present (abundance in Wales is climbing) although declines may be recorded in the near future.  

Population estimates and change 1969-2002 (census data)

* 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. A repeat survey in 2011 recorded 22,975 individuals - more than double that in 2007 - making it the largest colony in the UK. Obviously, given the increase that occurred afterward the numbers of razorbills on Rathlin in 2007 were unusually low. However, there is a lack of detail from Rathlin and other colonies in the vicinity of the island from which to form any conclusions.

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)

* 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 numbers from colonies surveyed in 2005-11 were similar to that recorded at the same suite of colonies in 1998-2002 suggesting little change in numbers overall. 

Productivity

Very few systematic productivity data have been collected for razorbills in the Republic of Ireland as part of the SMP. On average, razorbills fledged 0.60 chicks per pair per year at six monitored colonies between 2006 and 2011.

Population estimates and change 1969-2002 (census data)

* 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 at the largest colony had declined by half in 2007 but this trend was entirely reversed in 2011. Combined numbers from colonies surveyed in 2005-11 are similar, perhaps slightly higher, to that recorded at the same suite of colonies in 1998-2002 suggesting little change in numbers overall. 

Productivity

Very few systematic productivity data have been collected for razorbills throughout Ireland as part of the SMP. On average, razorbills at monitored colonies fledged 0.61 chicks per pair per year at six colonies throughout Ireland between 2006 and 2011.

Population estimates and change 1969-2002 (census data)

* 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, possibly due to differences in methodology, so no clear trend is discernable. No data was received in 2011.

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)

* 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 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 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 of May birds). Return rates on the Isle of May between 2009 and 2011 are the highest recorded there. There appears to be no relationship between the UK population trend (nor the trends in Scotland and 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 in the Skagerrak and North Sea during autumn 2007. Ringing recoveries indicated birds had mainly originated from northern or eastern Scotland⁴.

Figure 3. Annual return rate of razorbills breeding on the Isle of May (SE Scotland), 1987-2011.

Figure 4. Annual survival rate of razorbills breeding on Skomer (SW Wales), 1987-2010.

References

1 Wanless, S., Harris, M.P., Redman, P. and 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

3 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.

4 Heubeck, M., Aarvak, T., Isaksen, K., Johnsen, A., Petersen, I.K. and Anker-Nilssen, T. 2011. Mass mortality of adult Razorbills in the Skagerrak and North Sea area, autumn 2007. Seabird 24: 11-32.

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