‘Worst breeding season’ for Britain’s migratory birds

THE unusual weather conditions across Britain have taken their toll on the country’s resident and migratory bird populations – of 25 bird species monitored, seven had their worst breeding season ever.

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The British Trust for Ornithology (BTO), which carried out the survey, has been measuring bird productivity for 25 years.

Trained volunteer bird ringers around the country put up the same nets in the same sites on 12 occasions every summer.

By looking at how many adult and how many juvenile birds are caught, they can get a good idea of how successful the breeding season has been.

One of the worst hit species was the blue tit. During the summer, bird ringers were catching only half the number of juvenile blue tits expected in an average year.

The seven biggest losers in 2007 (all with their worst ever productivity) were: blue tit (48 per cent below the long-term average); great tit (33 per cent below normal); reed warbler (27 per cent below normal); whitethroat (25 per cent below normal); willow warbler (19 per cent below normal).

Treecreepers and willow tits were also at their lowest levels (55 per cent and 63 per cent below average) but, as only small numbers are caught, these figures may be unrepresentative.

There is one positive story though: long-tailed tits had their highest ever productivity this year, showing an increase of 48 per cent on the long-term average. They are early nesters – building nests in February and March – and may well have taken full advantage of the great April weather.

Mark Grantham, who runs the scheme, said: “For resident birds, such as blue and great tits, it will be interesting to see how they cope with the poor season.

“Most may well be able to bounce back next year, but it is more serious for the migratory species (reed warbler, whitethroat and willow warbler).

“These are already suffering problems both on migration and in Africa, so a poor breeding season just adds to their plight.”

Some blue tits in southern England fledged before the bad weather started but, from stories told to BTO staff by birdwatchers from around the country, it seems as if most blue tits were not quite this early and that many died in nest boxes.

As Mark explained: “The cold, wet weather over the early summer will have made life incredibly tough for adults that still had hungry youngsters in boxes.

“Each blue tit chick (up to 12 in a box) will need around 100 caterpillars every day, and finding enough caterpillars in the poor weather we’ve seen is no mean feat.”