Monday, 19 May 2014

Stormy spring troubles

The stormy weather that made an appearance during the second week of May interrupted what had otherwise been an ‘early’ spring. The battering wind, drop in temperature and spells of heavy rain will have caused problems for many nesting birds. Some mistle thrush nests, placed high in deciduous trees, were dislodged and I suspect that the same fate befell a good number of nesting rooks. For some smaller birds, such as the blackcaps nesting in bramble only just beginning to leaf over, the young chicks could quickly chill, while their parents struggled to find sufficient insect food.

Nesting early increases the risk of catching a spell of bad weather, of spring being interrupted, but for many birds it is a risk worth taking. Research has shown that the young from early nesting attempts often do better in the long run, having more of the summer over which to learn their skills and attain independence.

Most small birds feed their chicks on invertebrates, which suggests that breeding birds should time their nesting attempts to deliver chicks at a time when the abundance of invertebrate prey is moving towards its peak. This is particularly true for tits, whose breeding success hinges on them being able to match the peak in their chicks’ demand for food with the peak availability of the caterpillars on which they feed. The caterpillars time their own emergence to match the availability of young leaves on the deciduous trees on which so many of them feed. We know that a changing climate has shifted the timing of bud burst and resulting leaf emergence, something to which the caterpillars have responded. The concern is that although tits and other small birds have shifted their breeding seasons too, they may not be able to keep up with the speed of change being seen in the populations of their caterpillar prey. If the two get out of synch then this could be disastrous for tits and for the security of their populations over the coming decades.

Most of the tits breeding locally now have chicks and the wet and windy weather, which has dislodged caterpillar prey, could have a big impact on the success or otherwise of this breeding season. Let’s hope for better weather ahead.

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