Professor Tim Birkhead, of the University’s Department of Animal and Plant Sciences, first visited Skomer Island – situated off the cost of west Wales – in 1972 and since then he has returned every summer, gaining invaluable information about guillemots.
He will visit the island again on June 21 2012 for 10 days, marking his 40th breeding season studying the guillemots, conducting an annual census and ringing the birds to see how old they are when they start to breed and how long they live.
Professor Birkhead said: “It has been an invaluable investigation, for example it is clear that climate change has had a huge effect on the guillemots as they now breed two weeks earlier than they did in the 1970s. We also know a huge amount more about guillemot biology than we did 40 years ago, and we can use changes in guillemot numbers to tell us what is happening in the seas surrounding the island.
“Long term studies like this are few and far between but remain vital for understanding changes taking place in the environment. It’s been a constant challenge both to secure funding and to carry out the work itself as the birds breed on the sea battered cliffs of a remote island.”
Home to about half a million seabirds, including the guillemots, razorbills and puffins, uninhabited Skomer Island is a natural nature reserve, specially protected and a site of scientific importance.
Technological advances throughout the four decades have enabled Professor Birkhead to gain even more information about the birds.
Guillemots on the island
He added: “Using new tracking technologies, like GPS and geolocators, we now have a very complete picture of where guillemots go to forage. During the breeding season they forage within about 60 km of Skomer in the south Irish Sea, but in winter they travel huge distances moving between the Bay of Biscay and the far north of Scotland.
“We also know from guillemots research elsewhere around the UK coast that Skomer is extremely fortunate to be enjoying an increasing population. At other colonies the lack of fish has caused massive breeding failures, reduced survival and decreasing populations.”
During the early stages of the pioneering study, Professor Birkhead came up with innovative ways to overcome the many technical challenges he faced. In 1972 no one knew how to conduct a census of guillemots as it had never been tried before.
The second task was to determine how many chicks were produced each year and whether it was enough.
In 1972 when Professor Birkhead began his studies the guillemot population breeding on Skomer was just 2,000 individuals, yet pictures of the island thirty years earlier showed that there were around 100,000 guillemots then. In 2011 numbers were up to 20,000 individuals.
By marking birds individually with colour rings Professor Birkhead was able to measure their breeding success, see how old they are when they first start to breed and see how long the birds live.
Adult guillemots have an annual survival rate of 95 per cent and equivalent of an average life span of 25 years. On average about 80 per cent of guillemot pairs successfully rear a chick to fledging, and of these around half survive to breeding age, which is seven years old. This high survival of immature birds more than off-sets the natural mortality of the adult birds, so the population has increased.
Oil spills and climate change double the mortality rate of British seabirds
New research from the University of Sheffield has shown that major oil spills and a changing climate have had a far greater impact on populations of British sea birds than was previously thought.
A team led by Professor Tim Birkhead from the Department of Animal and Plant Sciences at the University of Sheffield, has shown for the first time that major oil spills double the mortality rate of adult guillemots in Britain, even though the pollution occurs hundred of miles from the birds’ breeding grounds. The research, which is to be published in the November issue of Ecology Letters also shows a direct link between a warmer climate in the North Atlantic and a higher mortality rate among British guillemots.
Professor Birkhead’s long-term guillemot study has been carried out on Skomer Island, Wales, since 1972. The length of the ongoing study has allowed the research team to study the effects of a number of serious winter oil spills on the guillemot population. Their findings show that highly publicised oil spills in southern Europe, such as the Prestige oil tanker disaster off the coast of Galicia, Spain, in November 2002, have far-reaching consequences on seabirds breeding far from the scene of the initial pollution.
The study has also found that consistently high values of the North Atlantic Oscillation (NAO) index (an annual measure of a large scale climatic phenomenon affecting winds, temperature and rainfall) for the past 30 years, has had a negative effect on the guillemot population of Skomer Island.
Professor Tim Birkhead of the University of Sheffield said: “Prior to our investigation of the guillemot population of Skomer Island, the impact of oil pollution on seabird mortality rates at a particular colony was difficult to quantify as oil spills usually occur in wintering areas where birds from many different colonies may be distributed over a wide area. However, our long-term monitoring of individually marked birds on Skomer Island has enabled us to see a direct correlation between major oil pollution events and a twofold increase in winter mortality rates of common guillemots.
“Our research has also shown that the NAO index has had a significant effect on the guillemot population. The consistently high values of this climatic phenomenon for the past 30 years may be due to human-induced global climate change. If this is the case, it would mean that seabirds are vulnerable to human activities on two counts: oil pollution from tanker spills and changes to the ecosystem as measured by the NAO index and caused by global climate change from man’s burning of fossil fuels.”
News release from Sheffield University – 25 October 2005
Guillemots nest in dense, noisy colonies with many birds crowding together. Mainly nesting on ledges on near vertical cliffs, they are also present on the top of sea stacks in a few sites.
Guillemots are found in very large numbers on the south coast at Castlemartin, especially at Elegug Stacks, where the well known colonies provide a thrilling and easily observed wildlife spectacle. Skomer has the largest island colony, but there are quite significant colonies on St Margaret’s Island, on Skokholm, and on Ramsey. A small number breed on Grassholm and on the north coast of the county there are scattered colonies of a few hundred birds.
The overall population has been increasing steadily for 40 years and although there have been minor “blips” in the rate of increase this trend is echoed at all colonies. The main study colonies and the detailed whole island counts on Skomer, suggest an average annual rate of increase of 5.7%, the colony increasing from 2,400 birds in 1970 to 17,700 in 2008. In the period between the two atlases of 1984–88 and 2003-07, the overall county population grew from around 16,000 to over 30,000 birds.
The number of Guillemots is currently at its highest level since counting seabirds became a regular annual priority for conservationists and ornithologists, but there is some evidence from comments made by Lockley et al (1949) that pre war populations were higher, perhaps much higher, on the basis of some photographs of colonies. It was surmised that during the war years the high level of marine pollution caused the deaths of many thousands of Guillemots.
Guillemots are very vulnerable to marine pollution incidents as they spend most of their time “rafting” (floating on the surface) and shallow-diving. The Sea Empress incident at the entrance to Milford Haven in February 1996, followed by the Erika incident off the French coast in January 2000, killed many birds from the Pembrokeshire colonies. The Sea Empress spill killed mainly adults and there was a subsequent 60% decline in breeding numbers on St Margaret’s Island. The effects at other coastal and the major island colonies was less clear but subsequent research has shown that such incidents do manifest themselves in reduced survival rates in the years following the incident. However, because there are so many immature birds trying to establish themselves in the colonies the effect has been masked. (Votier et al 2005). The Erika incident mainly affected immature birds less than 6 years old and there was no discernable subsequent effect on numbers at any of the colonies.
Both Mathew (1894) and Lockley et al. (1949) reported that Guillemots nested on all of the islands and at various mainland cliffs. Egg collecting used to be prevalent; Howells (1968) noted that Ivor Arnold took 500 Guillemot eggs from Ramsey in 1908.
It is difficult to census Guillemots accurately as the number of birds present on the breeding ledges varies with the season and time of day. A single count does not necessarily equate with the number of nests present. However, Lockley (1958) estimated that 5,000 Guillemots were present on the Skomer cliffs, resolved as “approximately that number of pairs”. The same assumption has apparently been made by many other observers over the years. This means that the numbers quoted here should not be taken literally, though they should be comparable enough to detect broad trends.
Lockley et al. (1949) noted a decrease in numbers during the second World War and Lockley (1958) used photographs of the occupied ledges at the Wick, Skomer, taken in 1939, 1946 and 1958 to demonstrate a further decline. He was inclined to attribute the decrease to fouling by oil pumped from passing ships. Numbers continued to diminish and the Operation Seafarer survey of 1969 revealed just over 6,000 pairs. They were dealt a further blow by the Irish Sea seabird wreck that same autumn: 15,000 dead or dying Guillemots were accounted for in the Irish Sea but many more must have gone undetected, and Saunders (1976) speculated that as many as 35,000 could have perished. The effects can be judged by a decrease at the Skomer colony from 5,000 in 1966 to 3,000 in 1974.
Pembrokeshire numbers appear to have stabilised during the 1970s and to have increased since, despite temporary setbacks caused by oiling during the wrecks of the Christos Bitas (1978) and the Bridgeness (1985). The Seabird Register survey of 1985-1987 assessed the total county population as about 14,000 pairs, the main colonies being at Skomer (6181), Elegug Stacks, Flimston (3,462), Ramsey (1757), Stackpole Head (980) and Skokholm (160).
Although Guillemots continue to increase conservationists are concerned about disturbance that could be caused by an increasing popularity of rock climbing, particularly on the limestone of the southwest peninsula. The exploration for and possible extraction of oil and gas from our adjacent sea areas also poses potential threats.
Young Guillemots leave the breeding ledges before they are able to fly. The single chicks are accompanied by males and swim to traditional feeding areas, presumably where suitable fish are plentiful. Whilst the young are growing to the fledging stage the adults moult into a state of flightlessness. Only one such regularly used area has been found off Pembrokeshire to date, the sea off Strumble Head, where 300-500 gather each year. After fledging/moulting Guillemots become very mobile. Ringing has shown that while some remain in Pembrokeshire waters other adults journey to Scotland and immature birds into the English Channel, to the North Sea, to France and Spain and into the Mediterranean.
One of the great spectacles of the autumn is the large passage of line after line of Guillemots speeding low across the sea on their way out of the Irish Sea past the north coast of Pembrokeshire between late September and early December, first recorded by Lloyd as long ago as 1936. In more recent times attempts have been made to estimate peak numbers by taking sample counts for 15 minutes in each
hour and extending the results over the duration of the movement. By such means totals of 24,000 were calculated to have passed Strumble Head on 17 October 1983, 26,000 on 13 November 1987 and 35,000 on 20 October 1984.
Small numbers are scattered around the bays and tide races of the coast during the winter, with increased numbers during onshore gales. Large numbers occasionally visit the colonies on fine days in winter when they noisily occupy the ledges and take to the wing for massed whirling flights.
Northern Guillemots subspecies aalge/ hyperborea have been detected on several occasions at passage times and during the winter.
Mathew says it nested on all islands and various mainland cliffs, especially the Stack Rocks, which are today a “tourist” attraction in south Pembs – charabancs run regularly from Tenby during July, and park within a stonethrow of these striking pinnacles of detached rock, and the Guillemots and Kittiwakes seem little disturbed by human sightseers. Breeds from Cemmaes Head to Caldey on suitable cliffs and stacks. Decreased during the war. Approximately 0.5% of the Guillemots on Skokholm and Skomer were estimated in 1946 to be of the “bridled” form.
The Common Guillemot is the well-known “Eligoog” of Pembrokeshire; the Stack Rocks, on which they nest in such numbers as almost completely to cover them, being often called “the Eligoog Stacks.” What we have written above with respect to the Razorbill, applies almost in so many words to the present species. It is to be found upon all the islands, on some of them, as upon Ramsey, in extraordinary numbers, and upon some of the cliffs of the mainland.
Three parts of the year the Guillemots, as well as the other cliff birds, are dispersed upon the open sea. They only resort to the islands and cliffs for the summer months for the purpose of rearing their young. We have visited the Stack Rocks in the early spring before the birds had arrived upon them, only to find a few Herring Gulls and Kittiwakes perched on their ledges, a Shag or two on the rocks just above the sea level, and a pair of otters disporting themselves among the waves that lapped their base. A few weeks later, and there would have been a transformation scene! The Stacks would have been white with birds, the waters in their neighbourhood would have been dotted over by little parties diving and fishing, and there would have been an almost deafening noise proceeding from the multitude of birds.
The Stacks are two in number, distant some sixty or seventy yards only from the shore, and reach in height almost to the level of the cliff on whose top the spectator stands. The largest of them is said to be only about thirty yards across on the summit, and they both present the appearance of rocky towers rising out of the water. The birds cover them from top to bottom, and are huddled together on their tops as close together as they can pack, but as the spaces after all are small, the total number of birds cannot be large, and there is not on these Stacks and on the cliffs in their neighbourhood, any more than a mere fraction of the immense numbers to be found on Ramsey or Skomer, where the birds are distributed over a great length of cliffs. But even on these two islands the birds are not found everywhere, having their favourite cliffs, which are densely thronged with them, while others are quite destitute of birds. Mr. Dix rowed round the Stack Rocks one day, to discover that the Guillemots were more numerous on their ledges fronting the sea than they were on those turned towards the land, although even on these the numbers were astounding.
Like the other diving birds that pursue the fish beneath the water, the Guillemots use their wings, and may be said to fly under the waves. One is able to form some idea of the vast myriads of fish the seas around our coasts must contain, when we consider the millions of birds that are daily feeding upon them. No amount of netting by fishermen is likely to produce any impression upon the shoals of fish ; the only injury that man can inflict upon them is in dredging the spawning beds. If only these could be left in quiet, there would be no danger of our fish supply becoming exhausted, however persistent and united the attacks made upon it by larger fish, seals, birds, and fishermen.
The variety called the Bridled Guillemot (once held to be a distinct species, and called Lomvia lacrymans), that has a white line curving a short distance down the neck on either side from the eye, occurs occasionally among the other Guillemots, but is rare; Mr. Mathias includes it in his list. On each of our visits to the breeding stations of the birds, we have kept a close watch for it, but among the thousands of Guillemots we have closely approached on their ledges, we have never succeeded in detecting one.
The eggs of the Common Guillemot are well known for their beauty, and one or two are generally carried away by visitors to the Stacks as ” curios.” Some very beautiful varieties may be picked out from among them, and we are not a little proud of our own series procured from Ramsey and Lundy. The farmers around St. David’s are said to feed their calves in the summer with a custard made from the “Eligoogs'” eggs obtained on Ramsey.
In the winter time we have seen numerous Common Guillemots far up the Bristol Channel, off Clevedon and Portishead, and often when we have been crossing the ferry to Port Skewet, in company with Razorbills.