Winters deadly for lively long-tailed tits

THIS winter a small flock of long-tailed tits has become a regular visitor to my bird feeding station.

They’ve rapidly become favourites. It’s not just the way they look — the tiny, walnut-shaped body, the absurdly long, thin tail and the faint flush of pink on the underparts — it’s also the way they behave. They’re acrobatic, full of vitality and display impeccable manners in their interactions with other birds.

Another reason I’m delighted to see them is that they suffer very high mortality in severe winters, up to 80%, and because our previous two winters were so bad I was afraid they might have declined in numbers. But they lay large clutches of eight to 12 eggs, occasionally up to 15, which means the population can bounce back quite rapidly.

They’re not actually tits. They used to be, but scientists now place them in a separate family which has no other European members, although there are various races and colour variants of the long-tailed tit in Europe and Asia.

There are two reasons why they die in such large numbers in bad winters. One is that they’re very small and more likely to die of hypothermia. The other is that they’re quite strictly insectivorous, with a strong preference for the eggs, caterpillars and pupae of small moths and butterflies. This kind of food is hard to find in winter, which is why they’ve had to resort to the balls of fat and seeds on my feeding station.

Wrens are also very small, very insectivorous and uncommon visitors to bird tables. Both species adopt the same strategy on very cold winter nights. They roost communally, huddling together in a ball. Thermodynamically this turns them into the equivalent of a much bigger bird, which means they lose less body heat during a long night.

For most of the year long-tailed tits form small flocks, sometimes mixing with coal tits or blue tits. The long-tailed tits in the flock all tend to be related to each other — last year’s young along with parents and a few uncles and aunts. These flocks will be breaking up in the next couple of weeks as the birds pair up for nesting. The flocks will form again in late summer.

Their nests are extraordinary constructions, shaped like miniature rugby balls standing on end with an entrance hole at or near the top. They weave an elastic material out of the silk from the egg cocoons of spiders held together by tiny pieces of moss. This is camouflaged on the outside by up to 3,000 individual flakes of lichen and lined on the inside with around 2,000 small feathers. They usually manage to find enough feathers lying around but have been observed plucking dead birds. The end result is a beautifully insulated and camouflaged structure which can expand as the young birds grow bigger. Despite all this there is a very high failure rate among nests, many being destroyed by magpies or squirrels. One study found that only 17% of nests were successful.

If a nest fails the pair often decide that they can’t face all the hard work involved in making a new one. Instead theyhelp another pair with a viable nest to rear their young. Nests with four ‘parents’ instead of two have a much higher success rate.

The winter flock which is now based in my garden is formed of parents, offspring and foster parents. These winter flocks can sometimes number up to 30 birds, though they’re normally smaller and I think there are less than 10 in the one I’ve been observing lately.

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