News for November 2000, Bird Populations
Bird On! News
15th November 2000
Bird populations are rarely stable: most rise and fall for a variety of reasons, ranging from the weather to the availability of food and habitat. Through the BTO/JNCC/RSPB Breeding Bird Survey a pretty good idea can be obtained of the fluctuating fortunes of Britain's breeding birds. The survey was launched in 1994 and uses what is known as a line transect method to record birds in randomly selected 1km squares. Two surveys are undertaken during each breeding season.
BTO News, the newsletter of the British Trust for Ornithology, has just published the results of the Breeding Bird Survey (or BBS) for 1999. It reveals some intriguing population trends. Farmland birds such as grey partridge, turtle dove, linnet, bullfinch and corn bunting are all continuing to decline. Grey partridge numbers, for example, have fallen by 43% since the survey started in 1994 and bullfinches by 28% over the same period. However, certain farmland birds that have been declining for some years now seem to be stabilising. These include tree sparrow, spotted flycatcher, reed bunting and song thrush. However, it should be remembered that their numbers are now considerably lower than they were a quarter of a century ago.
House martins, Swallows and swifts all seem to have declined in my area but, according to the survey, numbers are increasing throughout the UK. House martins in particular have enjoyed considerable increases in Scotland and Wales. Both pied and grey wagtails have also increased but the migratory yellow wagtail is declining. So too is the meadow pipit, particularly in Scotland, but populations in both Wales and Northern Ireland are flourishing. Curiously, the pattern for the very similar tree pipit is the reverse with significant increases in Scotland and declines in England.
Most woodland birds are doing well and my own observations agree with the BBS that birds like great spotted woodpecker, nuthatch and treecreeper are flourishing. This makes the marked fall in numbers of our two species of black-headed tits - marsh and willow - difficult to understand. Willow tits have now disappeared from my local woods, reflecting a 42% fall in numbers since the BBS started in 1994.
Other birds that have declined significantly since 1994 include cuckoo, kestrel, shelduck, oystercatcher, curlew, redshank, common sandpiper, lapwing and (surprisingly) both black-headed and great black-backed gulls. According to the BTO, the decline in waders (something particularly evident in Scotland) is mainly due to loss and deterioration of upland and farmland habitats. The problems for these birds include increased grazing activity, drainage and afforestation.
Of course it's not all bad news. Counts of buzzard, heron, moorhen and coot have all increased significantly. So, too, have numbers of both greylag and Canada geese though these two species often create problems when they become too numerous. Collared doves first arrived in Britain in the mid 50s and soon established themselves across the length and breadth of the country. There was a period when their numbers looked set to stabilise but the BBS shows that this dynamic species is still increasing, while numbers of stock doves and wood pigeons remain stable. Magpies - arguably Britain's least-popular breeding bird - are also showing signs of stabilising after several years of increase but carrion crow and jackdaw numbers continue to grow.
By monitoring our bird population so carefully it is far easier to recognise problems at any early stage and for conservation measures to be implemented.
Declining goose numbersAs its name makes clear, the BBS is concerned only with nesting birds. There are several other surveys that look at populations of our wintering birds. One of the most interesting is the annual national census of pink-footed geese and Icelandic greylag geese in Britain and Ireland. This long-running survey is undertaken by the Wildfowl and Wetlands Trust. In 1960 26,500 greylags were counted, rising to 65,000 in the 70s. Numbers continued to grow for the next 10 years, reaching 100,000 in 1984. This population was maintained until 1990 when numbers started to fall again.
Last year's count was the 40th consecutive census and it found that greylag numbers had declined by 8.7% on the previous year's estimate, with a count of 75,866 birds. The cause of the decline is unknown but an increased annual bag by hunters in Iceland may be the reason. A number of sporting agencies now offer goose-shooting holidays in Iceland so the geese are certainly coming under increasing shooting pressure.
The fall in numbers is not yet worrying. However, if the annual kill of geese starts to exceed the recruitment of young birds into the flock, then international action may be needed to help the birds. Though the geese may breed in Iceland, they spend a much greater proportion of their lives in Britain, so their population is a joint responsibility.
Siberian blue robin: a potential first for BritainThere's nothing a twitcher likes more than a rare bird, but the most attractive bird of all is one that has never been recorded in Britain before. There was a stampede of twitchers to the RSPB bird reserve at Minsmere when a Siberian blue robin was reported there at the end of October but it was only seen on one day and the 1,000 twitchers who arrived the next day failed to see it.
There was only one previous record of a Siberian blue robin in northern Europe: a first-winter female was trapped on the island of Sark, in the Channel Islands, on 27th October 1975. Though Sark may be part of the United Kingdom, birds recorded in the Channel Islands don't qualify for the British List, the official list of birds recorded in Great Britain, Northern Ireland and the Isle of Man. This list is maintained by the British Ornithologists' Union, which is the body that considers all records of new birds.
The BOU has just published its most recent updated list. Since the previous update, a year before, there has been a number of additions and deletions. The most interesting of the former is short-toed eagle following the appearance of a wandering juvenile on the Isles of Scilly in October last year. This individual was well photographed so there was no doubting its identity. The three other additions - green-winged teal, Iberian chiffchaff and lesser redpoll - are all taxonomic splits. The North American green-winged teal is now regarded as a separate species to the very similar European teal (the drakes are easy to tell apart, but the ducks virtually impossible) while the Iberian chiffchaff has a different song to the common chiffchaff but is almost identical in appearance. The lesser redpoll has long been regarded as a recognisable sub-species of the mealy redpoll but the two now gain full specific status.
Twitchers call these new additions "arm-chair splits" as many will gain extra species on their life-lists as a result of these decisions. Few twitchers are likely to disagree with the two deletions to the British list. All records of North American hooded mergansers are now regarded as likely to have been escapes from captivity. North American ducks can and will travel across the Atlantic but the attractive hooded merganser is only a short-distance migrant and it is thought highly unlikely that it would undertake such a movement.
The other deletion is an interesting old record of two griffon vultures at Ashbourne, Drebyshire on 4 June 1927. This is the only British record of this species that breeds commonly in Spain and elsewhere around the Mediterranean but which rarely wanders north of its breeding grounds. The BOU committee has reconsidered the old record and has now decided that it is unlikely that the observer really did see the vultures.
These days, with a wealth of excellent field guides, identifying a big bird like a griffon vulture is relatively easy. In addition, many British birders have seen grifffons during their travels. In 1927 there were no field guides and relatively few observers had even seen the birds in the wild. Thus it's not surprising that on reconsideration the record has been thrown out. However, I wonder what the two birds in Ashbourne were if they weren't vultures?
A new guide to North American birdsEurope is spoilt for choice when it comes to field guides as we have the best selection in the world. Most serious birdwatchers now use the new Collins Bird Guide with its superb illustrations by Killian Mullarney and Dan Zetterström and comprehensive text by Lars Svensson and the late Peter Grant. Until now there hasn't been a North American guide to compare with the Collins Bird Guide but the recently published North American Bird Guide is equally impressive.
Remarkably it is all the work of one man, David Sibley. He researched it by travelling the length and breadth of the USA and Canada gaining field experience of virtually every one of the 810 species he covers. It took him a further five years to paint the 6,600 individual illustrations and to write the accompanying text.
The result is a handsome volume that should enable any competent birdwatcher to identify virtually any bird they encounter in North America. Each species is allotted its own half page and is illustrated perched as well as flying with most plumage variations also shown. In addition there is a brief, one-sentence description of the bird plus a more detailed note on the voice and a coloured distribution map. For anyone birding in North America, this is the book to have.