Sharp decline in some bird numbers

THE British Trust for Ornithology, normally called the BTO, publishes a Garden Bird Feeding Survey and it makes for interesting reading.

Of course, our own BirdWatch Ireland does the same thing and their results are more relevant to us because there are some differences between British and Irish bird populations and subtle differences in bird habitat.

But what makes the British results interesting is that they are distilled from a much larger number of gardens and they have 40 years of information, the oldest database of its kind in the world. Some of the changing trends in bird populations over 40 years are quite dramatic and unexpected.

But these trends have to be interpreted with caution. Most of the data is based on birds that visit bird tables or feeders in gardens. Over 40 years the industry that supplies wild bird food and feeders has developed and changed.

New feeder designs and new products like nyger seed and sunflower kernels can alter the behaviour of different species and skew the results.

Song thrushes and starlings have each declined by 75%. Tree-creepers, which would be an unusual species in an Irish garden, have gone down by 71% and the humble house sparrow by 70%. British mistle thrush numbers have declined by 63%. I have certainly noticed the long-term decline of house sparrows in my garden, but this appears to have been offset by a dramatic increase this year. I put this down to a very successful breeding season resulting from good summer weather and plenty of insect food.

A 42% decline in blue tits is surprising. I feel it may be due, at least in part, to the fact that new species are now elbowing the little blue tits off the prime feeders. A 29% decline in greenfinches is more likely the result of the disease trichomonosis reducing their numbers.

But some of the increases are even more dramatic than the declines. The most outstanding one is the goldfinch, up by a staggering 17,333%. This is obvious in my own garden as well, but only if I put out oil-rich seeds like nyger seed, though the birds will settle for peanuts as a second choice. I’ve only been using nyger seed for the past couple of years – before that goldfinches were rather rare visitors to the garden.

Wood pigeons have increased by 3,026% and long-tailed tits by 1,825%. Both are probably examples of how an increasing number of people putting out bird food can seduce a farmland bird into a garden. There seems to be a ‘tipping point’ at which the density of feeders and bird tables in an area makes it worthwhile for a bird species to change its behaviour.

Magpies have, rather predictably, increased by 570% in British gardens, but rather surprisingly their shy relation, the jay, has also increased by 448%. The surveys are carried out over the winter months so they include two winter migrant members of the thrush family – fieldfares were up 518% and redwings by 840%.

Forty years ago almost all the blackcaps in Britain and in Ireland would have migrated south in the winter. But an increase in the numbers that are now resident all the year round is reflected in the figures at +359% The figures that I got off the website only show the top 10 increases and decreases.

* dick.warner@examiner.ie


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