THE seabird populations of Scotland have declined over the last decade and a report just issued confirms numbers are continuing to fall. According to Scottish Natural Heritage (SNH), there may be 46% fewer seabirds now than there were in 1986 when systematic monitoring began.
Of 11 species assessed in 2012, only two had held their own since the previous estimate. The number of chicks produced per nesting pair has also fallen. It’s down 24% since 2000.
During the breeding season, Scotland and Ireland are hosts to birds from all over the North Atlantic. Huge seabird cities form on islands and mainland cliffs. The gannet colony on St Kilda is the largest in the world. Ornithologists count the birds and measure their reproductive performance. Scotland has 24 breeding species but most are impossible to census accurately. The SNH report covers only species for which reliable figures could be obtained.
The arctic skua is a gull-like pirate which harasses other birds, forcing them to disgorge food they are bringing to their chicks. This predator, with only a foothold in Scotland, recorded the greatest decline of any species. Numbers fell by 5% in the last two years and are down 80% on the 1986 figure. The onset of global warming may have upset this sub-artic breeder and, with fewer victims from which to rob food, a drop in its numbers is only to be expected.
One of the skua’s favourite victims, the kittiwake, nests on cliffs. Visitors to Dunmore East, or the cliffs of Moher, will know this dainty ocean-going gull which comes ashore only to breed. Scottish kittiwake numbers are down by 32% since 1986.
Skuas also harass terns. These elegant little ‘sea-swallows’ nest on shingle-beaches and sandy dunes, locations especially vulnerable to disturbance from foxes, mink and people. Flooding during storms and high tides are an additional hazard. The Arctic tern is probably the world’s greatest traveller, seeing more daylight than any other creature. It spends the winter in the southern oceans, returning north to breed in spring, after a round trip of 40,000km. Arctic tern numbers have dropped by 28% in Scotland.
The common gull and the black guillemot seem to be the only two seabird species holding their own. The black guillemot, a coastal resident, dives for prey off rocky shores and sea-cliffs, visiting harbours in winter where it’s vulnerable to oil-spills. Known as the ‘tystie’ in Scotland, it doesn’t venture out to sea. The common gull, another inshore bird, breeds inland as well as along the coast.
Scientists are cautious as to the causes of the decline. Weather during the crucial months when young are being raised is no worse nowadays than it was prior to 1986. Predation by rats and mink may have increased but this threat has been present for decades. Pollution is a growing problem; between February and April this year, for example, the carcases of 4,000 seabirds were washed ashore on the south coast of England. The birds had been poisoned by a substance used to wash out ships’ fuel tanks at sea. The most important factor in seabird decline, however, seems to be a scarcity of food during the breeding season.
The annual conference of the Pew Fellows took place last month in Malahide; marine fishery scientists from all over the world discussed the state of the oceans. They believe that 75% of the world’s fisheries are over-exploited. Fish are becoming smaller; they don’t survive long enough to reach their full potential. Trawling is not the only problem; climate change is leading to higher sea temperatures.
The waters around Scotland and Ireland are becoming warmer, reducing their oxygen content. ‘Forage fish’, such as the sprat and sand-eels seabirds feed to their chicks, seem to be moving northwards to cooler waters. If the warming trend continues, Scotland and Ireland’s legendary seabird colonies may dwindle — ‘our’ seabirds moving to Norway, Iceland and Greenland. The jury is still out; numbers at some Arctic colonies are also down. This is a very complex issue.
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