Have you, too, been frustrated by putting out nest box after nest box and never finding any tenant to occupy them? You wonder if you have them facing the wrong way, say into the wind, or is it just that there is so much good natural cover that they don't need to bother with your nice little bit of carpentry, even when it's cunningly covered with real bark. Or you think it's cunningly covered. You may get the odd feather in it, as indicating, maybe that birds occasionally use it as a night shelter, but no obvious little brood of blue tits or robins or whatever.
A woman wrote to the BBC Wild- life magazine in dismay. "Throughout April and May," she wrote (that would be last year), "a blue tit visited our birdbox, apparently building a nest and then feeding chicks. But when it stopped visiting, we found no sign of a nest ever having been there. What had it been doing? Chris Mead, an ornithologist, replied that his guess was that that particular bird did not have any chicks that year, but continued to check out potential nest sites - such as the nest box in question. For, and this may come as a surprise to many of us, he said that even short-lived birds such as blue tits, do not necessarily try to breed every year. "Taking a break every now and then can be a sensible strategy, as raising a brood is an exhausting business."
He goes on to say that birds who try to breed every year are likely to produce small broods of weaklings, and may get so worn out that they jeopardise their own survival over winter. Further, he points out that gardens can be a particularly tricky habitat in which to raise young: for, he says, there are often few native trees around to supply the chicks with their staple diet of caterpillars. And by missing a season, the adults can stay in better condition, have more chance of surviving the winter to breed in successive years and produce healthier offspring when they do.
And he says finally that, in the case of blue tits it's usually easy to tell whether nestlings are inside or not, for, when the adults bring food back to the nest, it is carried very visibly in their beaks. What if the nest boxes are in a rural setting with no reason to believe that there is any shortage of caterpillars and other nursery food? Just inability to position the boxes correctly? Too exposed to raids by grey crows or other killers? Boxes that for some reason look too much like a trap? Or just that there are so many other, better places? Y