The Tern Story
Terns have a long history on the Copeland Islands with great variations in abundance over the years. Their story is both interesting and complex. It is not always possible to be sure why populations have waxed and waned. One thing is certain, the Copelands were a very important colony in the not too distant past.
Much of the information presented here has been extracted from the Annual Reports of the Copeland Bird Observatory, particularly from an article by Ernie Donaldson in the 1981 Report.
Donaldson, in his 1981 article, reports records going back to 1827 including one by J.R. Garrett in 1849,
Terns were in great abundance at the Mew Island today. I endeavoured to estimate their number and considered that there were not less than two thousand within sight.
William Thompson recorded Common Terns on the Copelands in 1843 and Arctic Terns breeding on the Copelands in 1833. Roseates were breeding on Mew in 1827 when the island was described as a low rocky place with short pasture affording food to cattle.
By the second half of the nineteenth century most, if not all, of the terns had disappeared from Mew and the Copelands, mostly, it is recorded, because of intense shooting and egg-collecting.
Records are sparse between 1889 and 1930, but thereafter, and despite extra disturbance caused by the construction of the new Lighthouse on Mew, the terns became well established with all four species breeding in good numbers.
Mid 20th Century onwards
In June 1941 Ken Williamson, Denis and Nial Rankin and H.C. Jones visited Mew and Lighthouse Islands to count the breeding terns. They were amazed by the huge numbers present.
They carried out counts over the eight larger sections divided by narrow channels and identified on the map in Figure 1. The counts are shown in Table 1.
Figure 1 Identity of sub-divisions on Mew for counts by Williamson et al.
(The Lighthouse lies at the northern end of section D)
|D & E||1,100|
|D (NW side)||500|
|A & B||2,000|
Table 1. Numbers of all terns breeding in each section of Mew Island and on Lighthouse Island
Unfortunately, the group did not have sufficient time to count the numbers of each species on each section of Mew. They did complete an accurate count of the nests on section C, which was judged to have an average density of nests and also contained the main colony of Roseate Terns.
Arctic Terns occupied the southern part of H and, almost exclusively, the whole of A. There were also some in fair numbers on B and C, part of the east coast of D and the west and northwest of H, but in these sections the Common Tern was the more dominant.
Common Terns occurred abundantly on C, were present on E and the only tern breeding on the northwest and west sides of D. Section F was full to capacity but on G and H nests were less concentrated.
The main Sandwich Tern colony was on D with a small number on C.
The main colony of Roseate Terns was on C.
The Lighthouse island colony was on the western side of the island and contained about 5000 birds, predominantly Common Terns.
The nest counts for section C were: Common and Arctic 1147 nests, Roseate 207 nests and Sandwich 10 nests.
Arnold Benington visited the island in July 1947 and sketched the location of the terneries. His map shows 3,000 pairs of Common Terns on the west of Lighthouse Island, and 100 pairs of Roseate Terns on the east of section D with a “few” in section C. Other tern colonies are marked but no counts are recorded. By this time there were 500 pairs of Herring Gulls and 800 pairs of Black-headed Gulls on Lighthouse Island and 1,000 pairs of Black-headed Gulls on Mew Island.
Between 1941 and 1956 the numbers of terns on the two islands fell from around 17,400 to 2,000 to 3,000. Donaldson speculates that this reduction of about ten percent per year was caused by a combination of circumstances including increases in the breeding populations of the large gulls and environmental pollution. After 1956 the numbers of terns continued to fall and Donaldson reports that there is little doubt that the remarkable increase in gull populations led to this further decline and put an eventual end to tern breeding on the outer Copeland Islands.
Table 2 shows how the numbers of terns breeding on Mew declined between 1958 and 1964. The numbers of gulls breeding on Mew and Lighthouse Islands is also given.
|Common and Arctic Terns||984||630||500||250+||100||nil||50|
Table 2 – Numbers of nests of breeding terns (Mew) and pairs of gulls (Mew and Lighthouse Islands).
Note: n.c. = no count
After 1964 a few Common and Arctic Terns still attempted to breed on Lighthouse and Mew Islands but although some chicks hatched, none survived. By 1966 terns of all four species still arrived at the Copelands and numbers increased from May to July but no breeding occurred. The pattern was similar in 1967 and no terns have bred on the outer two islands since that time.
Recent changes in the populations of breeding gulls and terns on the Copeland Islands
The situation has changed markedly over the past ten years. There have been two particularly important developments.
The first has been the effects of botulism on our population of breeding gulls. The numbers of Herring Gulls breeding on the two outer islands (mostly on Lighthouse Island) have fallen from over 7,000 pairs in 1982 to under 200 pairs in 1995 and only around 100 pairs in 2001. Botulism has also kept the population of Greater Black-backed Gulls in check with counts in recent years of just three or four pairs. There is a small colony of Common Gulls breeding at the southern end of Lighthouse Island. Numbers of pairs vary between ten and twenty, but they too have been reduced recently by botulism. The Lesser Black-backed Gull population appears to be more steady, it has rarely varied outside 200 to 300 pairs in the past 20 years. A few Lessers have been found dying of botulism in recent years but so far this has not had significant effects on the population.
The second important change has been the successful establishment of a colony of breeding Arctic Terns on Big Copeland, the larger, inner island in the group. Arctics settled to breed here in 1987 and, with varying fortunes, have remained since that date. Annual counts and breeding success are shown in Table 3. The colony has been remarkably successful given the relatively high level of disturbance from grazing and from summer visitors to the island and the apparent lack of suitability of the nesting sites which are close to landing stages and in areas much frequented by visitors.
Table 3 Numbers of pairs of Arctic Terns breeding on Big Copeland
In 1995 one pair of Arctic Terns prospected on the shore of Lighthouse Island, but no eggs were laid. The next breeding attempt was in 2001. Another pair of Arctics nested on the south shore of Lighthouse Island. Three eggs were laid and incubated with the parent birds guarding the nest with their customary ferocity. Sadly the eggs failed to hatch. However, there is obviously hope that the terns will return.
The Observatory has signed an agreement with the Commissioners of Irish Lights which will permit us access to Mew Island and to manage the vegetation there to encourage reoccupation by terns. Click HERE for details of recent work on Mew.