Monday, 2 April 2007

A nest of hair and lichen

There has been something of a totemic presence following my excursions of late. It seems that wherever I go I encounter long-tailed tits; their soft, bubbling contact calls alerting me to their presence.  I have stumbled across them in unexpected places, to the extent that one pair have even been busy building a nest just 20 metres from my office. Perhaps I should not be so surprised; long-tailed tits have been doing rather well of late, their breeding population buoyant after a run of mild winters. As is the case with other similarly diminutive and largely insectivorous birds, long-tailed tit populations can crash following a sudden winter cold snap. The winter of 1962/63, for example, is estimated to have reduced the breeding population to less than 20% of what it had been the previous autumn. No wonder that these tiny birds huddle together in communal roosts during the winter months and forage together in extended family parties, some eight to 20 individuals strong. These foraging groups aggressively defend communal home ranges throughout the winter, but from February onwards they disband to begin nesting.

Long-tailed tit nests are truly amazing, each one an oval-shaped dome made from moss, hair, wool and spider’s webs all carefully woven together within a suitable bush. Of the two nests local to me this spring, one is in gorse (prickly bushes are favoured because they provide additional protection from nest predators) and the other is in a Ceanothus. I am fortunate in having been able to watch the protracted construction of the latter nest over the last two weeks. Such is the complexity of the nest that it can take three weeks to build. As the dome is woven, the tits camouflage it with tiny flakes of lichen. The pair will often add 4,000 or more flakes before turning their attentions to lining the nest. For this, the birds must find as many as 2,000 feathers and it is only once the lining is complete that the birds can get down to the business of laying eggs. Laying can start as early as the first week of March in the south of England but here, in Breckland, it will always be a little later. Interestingly, research has revealed a trend towards earlier laying – a pattern that is most likely linked to global climate change.

Even with the camouflage and choice of nest location, nest losses to predators like jays and crows are high. Pairs that lose their nests in this way will often become helpers at the nests of close relatives, a behaviour that is clearly beneficial because nests with helpers are more productive. Again, this highlights the value of living in an extended family group.

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