Who’s who in pecking order

RESULTS of last winter’s BirdWatch Ireland Garden Birds Survey have been published.

Almost 1,000 people kept an eye out for the birds visiting their gardens and sent their records to the survey coordinator. The methodology used is standardised, so comparisons can be made year-on-year, giving an indication of trends in numbers. There are interesting findings.

Writing in Wings magazine, Oran O’Sullivan notes last winter’s temperatures were above normal and rainfall levels were below average, at least in the southern half of the country. The three preceding winters had been very severe and birds suffered accordingly. Songbirds, however, recover quickly from disasters. They produce lots of chicks, most of which die in a normal year. However, following a cold winter, adult numbers are down, competition for resources is reduced and more youngsters survive.

The garden survey, however, doesn’t track changes in numbers; it just ranks the species seen. Eighteen out of 34 common birds improved their position compared to the previous year, while nine others showed no change. The top four continue to hold their own.

The robin remains the most ubiquitous garden bird; it visited 98.6% of locations. It’s not necessarily the most abundant species, however. Both males and females hold territories in winter. You’ll find groups of robins together only on Christmas cards; this species is thinly distributed. Tits and finches, on the other hand, gather into flocks; the chaffinch, fourth in the rankings, is probably our most abundant garden bird. The blackbird and blue tit took the silver and bronze awards, with appearances in 98.3% and 98% of gardens respectively. The unpopular magpie came sixth.

The only bird of prey to have genuine ‘garden bird’ status is the sparrowhawk; it came 25th in the listings. Kestrels, a bird of more open country, rose seven places to 34th position. The buzzard, whose numbers have increased greatly in Ireland, has applied for membership of the club, appearing in 6% of locations. Another exotic newcomer, the great spotted woodpecker, ranks 63rd.

I ringed both song and mistle thrushes in my garden this week. Catching a mistle thrush is a bit special; this bird of open parkland seldom wanders into a mist net. Both species, thought to be declining, fared particularly badly in last winter’s survey, a development which Oran O’Sullivan describes as ‘worrying’. Our commonest thrush, the blackbird, didn’t lose rank but it fell five places in the abundance league.

Interpreting the thrush results is tricky. When severe weather afflicts Europe, huge numbers of birds flee to Ireland. Oran reports that, in previous years, thrushes ‘undertook a mass westerly movement, desperate to find a food source, and many perished flying west out to sea along our Atlantic seaboard’. Our winter visitors are mostly fieldfares, redwings and blackbirds. Song thrushes come here too but in smaller numbers. Visits by mistle thrushes are rarer still, although not unknown. In October 1959, for example, 300 visited Cape Clear and, in October 1961, about 600 flew in from the sea at Malin Head. Ringing, however, shows that mistle thrush movements are few.

With milder conditions in Europe last winter, there was no incentive to migrate and this may account for some of the decline in numbers. There may also be a ‘visibility’ factor. Thrushes like to feed in the fields. In very cold weather the soil freezes and they can’t catch worms or leatherjackets. When all available berries are eaten out, garden bird-tables become a vital lifeline. In a mild winter, like last year’s, thrushes tend to remain in the countryside; there is little need to visit gardens. The poor showing of these birds in the survey may, to some extent, be a refection of weather conditions.

However, in the case of the song thrush, a genuine decline is suspected. According to BirdWatch, the numbers breeding each summer are also falling. The species was found in only 62% of gardens, the lowest percentage since 1994 and a drop of ten points in the league table compared to a slippage of four for the mistle thrush.

Small bodies lose heat more quickly than large ones, so the smaller a bird the greater its vulnerability to cold. A song thrush weighs about 80 grams whereas a blackbird might exceed 100 and the mistle thrush 120. Small size, however, is unlikely to be a major factor in the species’ decline.

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Saturday, January 23, 2021

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