Keeping abreast of bird numbers
Monday, July 16, 2012
CORNCRAKES, barn owls, and their likes, are the ‘sick men’ among Irish birds.
Conservationists worry about them, as they should.
In contrast, the species common to gardens and the countryside are taken for granted and receive little attention.
As Milton said, ‘they also serve who only stand and wait’; we should not neglect Joe Soap. How have upheavals in the environment affected the familiar tits and thrushes? The Celtic Tiger changed our landscape. Housing estates, finished and unfinished, mushroomed in unlikely places, new motorways sliced through the countryside and windmills appeared on the skyline. Two recent winters were severe. Temperatures rose globally, droughts in North Africa making life difficult for migrant birds.
There are winners and losers among our feathered friends in these turbulent times, according to the Countryside Bird Survey, organised by BirdWatch Ireland with the support of the National Parks and Wildlife Service. Changes in bird numbers are not easy to detect but scientists devised a ‘cunning plan’.
The work covers 1998 to 2010. Two hundred people participated and during the breeding season, 400 1km squares, selected at random, were visited twice. The first visit took place in April or early May, when birds were starting to breed and residents and early migrants were easy to observe. The areas were surveyed again at least four weeks later, by which time the later migrants had arrived.
Starting between six and seven in the morning, when birds are most active, a pre-arranged route was walked through each square, all adult birds seen or heard being counted. Of course, some will have been missed, but total numbers are not the issue; it is the overall trends in the population that matter. By surveying the squares year after year, and combining the results from all of them, changes in bird numbers can be detected.
The approach, the authors say, has its limitations. Waders and gulls, for example, can’t be adequately monitored. Nor is it easy to census colonial nesters. For a ‘trend analysis’ to be carried out, a species has to be recorded in at least 30 squares; 53 species qualified for this.
Under a ‘traffic light’ classification, devised in 1999 by BirdWatch and the Royal Society for the Protection of Birds, ‘red-listed’ species are those in need of urgent action to survive, while ‘amber’ ones are declining less critically. ‘Green-listed’ birds are holding their own. Three of the 25 or so Irish red-listed species qualified for analysis during the survey, as did 13 on the amber list.
In all, 150 species were recorded. Wrens, robins, blackbirds and chaffinches are Ireland’s most widely distributed birds. They were found in 90% of squares. A further 17 species were seen in half of all squares.
Overall, 17 species increased their numbers during the 12-year period, 13 declined, while 23 remained stable. There was an average of 32 rooks in the squares, the highest number for any species. Starlings, jackdaws and wrens were also numerous.
Goldfinches, redpolls and bullfinches are doing well; their numbers have risen significantly. The blackcap population increased five-fold. Woodpigeon and willow-warbler numbers are also rising. Great tits are holding their own in four out of five regions. Yellowhammer numbers have declined in the southeast, the region in which this ‘red-listed’ species has been strongest traditionally. The greatest losses were among swifts, grey wagtails, kestrels and greenfinches. Meadow pipit numbers fell in two out of three regions.
Fifteen species recorded their lowest-ever figures following the cold winter of 2009/10.
The indices for stonechat, long-tailed tit, and meadow pipit dropped by over 50%. The goldcrest, Europe’s smallest bird, is highly susceptible to cold.
Its index fell by more than 30% as did those for sparrowhawk, sand martin, meadow pipit, wheatear, song thrush and raven.
* Countryside Bird Survey Report 1998-2010. www.birdwatchireland.ie