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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