"Timing Issues" by Nick Baker
By the time you read this, several of your neighbourhood birds – particularly the thrushes, blackbirds and robins – will have already got their first brood out of the way. Equally, there are other species around that haven’t even started to think about nest building.
The whole process of breeding essentially boils down to throwing as many chicks as you can out into the world, while maximising the number who can stick around long enough to breed themselves. It’s a stressful time.
The majority of British garden birds are what we call multi-brooded, knocking out a second and even a third family in the space of a year. In fact surprisingly few species are regularly single-brooded when nesting in and around gardens.
It’s thought that the reason birds don't put all their eggs in one basket comes down to the risk of predation. And if you’re a cavity nester – like blue and great tits – this danger might not be quite as high.
These two species are also cunning strategists. The timing of their chicks’ arrival matches a natural peak in the availability of certain species of moth caterpillars. And this in turn synchronises their hatching with spring’s unfurling of leaves on deciduous trees.
Interestingly, species like the closely-related coal tit are much more inclined to be multi-brooded in coniferous evergreen forests, where leaves are always available and food species tend to have a more protracted availability. Therefore the coal tit’s under far less pressure to get its timings just right.