Razorbill (Alca torda)

Figure 1. Trends in abundance index of razorbill 1986–2019. UK (red), Scotland (blue) and Wales (orange). Further details, including 95% confidence limits, can be found in the sections below. Based on SMP data; view the methods of analysis.

The razorbill abundance trend indices for all three countries declined slightly after monitoring began in 1986 but had recovered by 1992 (Figure 1). Since then, they have remained at, or above, the baseline. After 2005, all three indexes underwent a period of decline, which was most pronounced in Scotland, However, for much of the last decade, the indices have been increasing, and in Wales markedly so. Since 2017, the Scotland and England indices have been in decline, although Wales has continued to increase.

The number of colonies monitored frequently by the SMP are only sufficient to allow meaningful abundance trends to be produced for the UK, Scotland and Wales.

Productivity

Figure 2. Trend in UK breeding productivity (no. of chicks fledged per pair) of razorbill 1986–2019. UK (red) and Scotland (blue). Further details can be found in the sections below. Based on SMP data; view the methods of analysis.

A large proportion of the razorbill sites monitored for productivity are based in Scotland and, as such, the UK and Scotland trends are closely matched. Both trends were relatively stable between 1986 and 1998, after which they declined to a low point in 2008. Since then, they have increased, although have not reached the level they were at in the 1990s.

The number of colonies monitored frequently by the SMP are only sufficient to allow meaningful productivity trends to be produced for the UK and Scotland.

Figure 3. Trend in UK abundance index (solid line) of razorbill 1986–2019 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis.

Census results show that the UK razorbill population increased by 16% between 1969-70 and 1985-88, and a further 21% by Seabird 2000 (1998–2002) to over 187,000 individuals. After a period of stability between 1986 and 1991, the SMP trend index (Figure 3) increased steadily until 2003, when it was 91% above the baseline. Between 2005 and 2010, the index declined, possibly as a result of so-called 'density-dependent' effects, where growth at some colonies slowed or reversed when competition for space and food reached critically high levels. In autumn 2007, a ‘wreck’ of adult razorbills in the Skagerrak (the strait between Denmark, Norway and Sweden) and North Sea, most of which originated from Scottish colonies (see Scotland section), may also have contributed to the declining trend. The index has risen since 2010, with 2017 recording the highest index value to date (143% above), although the wide confidence intervals mean this apparent increase should be treated with caution. The trend has declined since then and was 95% above the baseline in 2019.

Table 1 below shows how numbers have changed at some of the most important UK and Republic of Ireland colonies within the Special Protection Area (SPA) network in the period since they were surveyed for Seabird 2000. The largest declines have been at SPAs in northern and western Scotland, while those in England and Wales have all increased.

Figure 4. Trend in UK productivity (no. of chicks fledged per pair) of razorbill, 1986–2019. Based on SMP data; view the methods of analysis.

Razorbill productivity in the UK was relatively stable from 1986 to 2001 but then declined to a low point in 2008, when only 0.38 chicks were fledged per pair. Between 2010 and 2017, however, there was a steep upward trend to 0.65 chicks fledged per pair. In 2019, an average of 0.63 razorbill chicks were fledged per pair (Figure 4).

Productivity at several colonies monitored in Scotland and Wales has been particularly poor in recent years compared to that recorded in England. The decline in productivity coincided 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 between years of low razorbill productivity with rising sea surface temperatures (SST) due to climate change is uncertain, although there is evidence that a decline in sandeel stocks may be linked to rising sea temperatures^2,3.

Figure 5. Trend in abundance index (solid line) of razorbill in Scotland, 1986–2019 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.

In Scotland, census data show that the razorbill population during the Seabird Colony Register was 11% higher than in 1969-70 and had increased again, by 13%, by Seabird 2000. The SMP annual abundance trend (Figure 5) increased between 1992 and 2003, then underwent a period decline until 2010, when the index was equal to the 1986 baseline. The index then increased to a peak of 106% above the baseline in 2017, although declined rapidly thereafter to 26% above the baseline in 2019. Wide confidence throughout much monitoring period mean, however, that the Razorbill abundance index trend should be treated with caution.

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 dip in the trend between 2007 and 2009⁴. Whole-colony counts submitted to the SMP from 52 sites indicate that these sites held 28,493 razorbill individuals in 2018, an increase of 28% compared to the total from the same sites counted during Seabird 2000.

Productivity

Figure 6. Trend in productivity (no. of chicks fledged per pair) of razorbill at Scottish colonies, 1986–2019. Based on SMP data; view the methods of analysis.

The razorbill productivity trend declined overall between 1986 and 2008, although has increased since then. Some colonies recorded consistently low levels of productivity between 2009 and 2019. At these colonies, in the years when chicks fledged, success has only been above 0.25 on Papa Westray five times (mainly from 2014 onwards); and on Fair Isle only above 0.5 five times (again from 2014 onwards but not during 2017)⁵. The few data available from Sumburgh Head suggest low productivity has been widespread in the Northern Isles in recent years⁶. Mingulay (Western Isles), where productivity monitoring began in 2013, had poor breeding seasons in 2013 (0.23), 2014 (0.28) and 2015 (0.30). In contrast, the frequently monitored colonies at North Sutor and on the Isle of May (both east coast of Scotland) were relatively successful between 2009 and 2019, fledging an average of 0.49 and 0.57 chicks per site respectively, with neither colony recording complete failure.

Figure 7. Abundance of razorbill at Flamborough Head and Bempton Cliffs, 1986–2019.

Razorbill numbers in England almost doubled between Operation Seafarer and the Seabird Colony Register, from 5,405 to 10,101 individuals. By the time of Seabird 2000, a further 10% increase had occurred. Few colonies of any great size are monitored in England regularly from which to draw firm conclusions about trends since Seabird 2000. However, available data strongly suggest an increase may have occurred. For example, in 2017 and 2018, 24 monitored colonies held 33,000 individuals compared to 10,000 during Seabird 2000. Data from the largest English colony, at Flamborough Head and Bempton Cliffs (Figure 7), found a substantial increase with 27,967 individuals being recorded in 2017, an increase of 230% since the Seabird 2000 census (8,463 individuals), and more than double the English population recorded during that census. In 2019, data from only a few smaller colonies were submitted to the SMP.

Productivity

Productivity data have been collected in England from the Farne Islands since 1996 and Bempton Cliffs since 2009. On average, razorbills fledged 0.64 chicks for both sites combined between 2009 and 2019.

Figure 8. Trend in abundance index (solid line) of razorbill in Wales, 1986–2019 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.

National census data show numbers were stable between Operation Seafarer and the Seabird Colony Register but, by Seabird 2000, had increased 33% - a trend which has continued to the present. Almost 75% of Welsh razorbill colonies (n=51) were surveyed in 2018, with numbers totalling 15,992 individuals, 26% more than recorded in the whole country during Seabird 2000. The trend in abundance index for razorbills at Welsh colonies (Figure 8) has increased since 1986, with a new peak being reached in 2019, at 186% above the 1986 baseline. However, due to the wide confidence intervals, this recent increase should be treated with caution.

Productivity

Figure 9. Trend in productivity (no. of chicks fledged per pair) of razorbill on Skomer, 1986–2019. Based on SMP data.

Although productivity on Skomer Island has varied between years, there was an overall decline between 1999 and 2012 (Figure 9). Since then, productivity has begun to rise and, in 2019, was 0.67 chicks fledged per pair. Since 2017, all recorded productivity values have been higher than the historical average of 0.53 chicks fledged per pair between 1993 and 2019⁷. Razorbill productivity data were not collected at any Welsh colonies prior to 1993.

Figure 10. Abundance of razorbill on the Calf of Man, 1986–2019.

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. A seabird census of the Isle of Man in 2017 recorded a total of 682 individual razorbills, a 54% decrease since Seabird 2000⁹. On the Calf of Man, which held between 20–25% of the razorbill population during the SCR and Seabird 2000 censuses, numbers have shown considerable variation over time (Figure 10). However, differences in the method used to collect data makes it difficult to draw any conclusions from the trend.

Productivity

Data submitted to the SMP on the productivity of razorbills on the Isle of Man are sparse; thus, no meaningful average productivity value can be provided.

Figure 11. Annual return rate of razorbills breeding on the Isle of May, 1987–2019.

The annual return rate of razorbills from the Isle of May (Figure 11) shows fluctuation over time with a recent increase¹¹, with rates between 2009 and 2012 and in 2017 among the highest recorded there. After a steep decline in 2008, return rate increased overall until 2018 when it was equivalent to the 1987 value (92.1%) when monitoring began. The return rate in 2019 was 87.2%. In contrast, the survival rate on Skomer (Figure 12) does not show any clear trend over the monitoring period, although fluctuation has become more pronounced in recent years, with much lower rates being recorded in 2007 and 2014⁷. In recent years, Skomer survival rates returned to the high levels recorded at the beginning of this long-term study. Survival across the Skomer study (1987–2018) averages 0.87, and in 2017-18 was 0.817.

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 on the Isle of May in 2008 followed a post-breeding 'wreck' of adult birds in the Skagerrak (the strait between Norway, Denmark and Sweden) during autumn 2007. Ringing recoveries indicated birds had mainly originated from northern or eastern Scotland⁴. A further 'wreck' off the east coast of Scotland and northern England during winter 2012/13, when many adult and juvenile guillemots and razorbills died, may have been the cause of low return rates on the Isle of May during the 2013 breeding season.

In addition, the winter of 2013/14 saw a succession of severe storms from late January to the beginning of March result in a large 'wreck' of seabirds along Atlantic coasts from England and Ireland to Spain. A minimum of 54,000 seabirds, mostly auks, were washed ashore dead or dying. Examination of many corpses revealed birds were emaciated with empty stomachs indicating starvation as the main cause of death although a small proportion showed signs of oil contamination¹². Overall, about 10% of casualties were razorbills¹². However, in Cumbria, 70% of the 850 seabirds washed ashore dead or dying during this 'wreck' were razorbills¹³. Biometric data from 43 corpses recovered from Cumbrian beaches indicated birds were of the subspecies islandica which breeds in Britain and Ireland, France and Iceland. Rings recovered from razorbill corpses (from beaches in England and in France) also indicated birds originated from colonies around the UK and Ireland¹³. The majority of birds examined were found to be adults. The total mortality will be much higher than reported because not all beaches were checked, birds were washed ashore over a number of weeks and many birds will be lost at sea¹².

On Skomer, after collecting sufficient data to observe the effect of the above event on long-term population parameters (scientists require two years’ data following a winter to be confident of survival estimates), a considerable drop in the survival of adult breeding razorbills was clear (Figure 12), after a period of steady increase over the last 30 years. The survival of breeding adult razorbills after the seabird wreck in the winter of 2013-14 was just 0.59, more than 30% below the study average of 0.90 (1970–2014)¹⁴.

Figure 12. Annual survival rate of razorbills breeding on Skomer, 1986–2019.