BTO: Early starters already on the nest

Tawny owl (Strix aluco). Picture by Jill Pakenham ANL-150216-110238001
Tawny owl (Strix aluco). Picture by Jill Pakenham ANL-150216-110238001
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There are signs of the approaching spring, even though winter has yet to release her grip. A growing dawn chorus of song thrush, woodpigeon and great tit underlines that many of our resident birds have already started to establish breeding territories.

Others are prospecting for suitable nest sites and many garden nest boxes will have been visited by blue tits and other nest box using species. Tradition has it that St Valentine’s is the day on which birds select their mate. While this is an overly romantic notion, not based in fact, some species will already be well into their first nesting attempt of the year.

A few species regularly nest very early in the year and will already have eggs or chicks in the nest. Tawny owls, for example, establish their breeding territories in early winter, their hooting calls echoing across the dark evenings of October and November. Most tawny owls will only now be producing their first eggs but some will have laid eggs at the tail end of December. One pair, nesting near Ramsey in Cambridgeshire, had their first egg hatch on January 9 – the box has a video camera installed – and the two chicks reared were ringed in early February. Other early nesters include crossbill, raven and grey heron.

The timing of these early nesting attempts is, of course, influenced by the weather but food availability may also be important. We know, for example, that female tawny owls need to lay down sufficient fat reserves through the winter months if they are to produce a clutch of eggs. In those years when small mammal populations are low, then the females cannot lay down enough reserves and so are unable to make a breeding attempt.

In addition to those birds that always start early there will be a few early nesting attempts by species that normally nest a bit later in the year. Blackbird, woodpigeon, robin, collared dove and song thrush are species for which the British Trust for Ornithology (BTO) normally receives records of active nests ahead of St Valentine’s Day. Many of these reports come from urban areas, perhaps because there are more human observers in these areas to find and report the nests or perhaps because urban areas offer increased opportunities for early nesting. If a bird has access to bird table fare like suet and mealworms then it might be able to breed that much earlier.

Even though the breeding season has already started for some it is not too late to put up a nest box in your garden. You won’t be alone in doing this; National Nest Box Week (NNBW) runs through until February 21 and many people will be using the advice on the NNBW website to provide opportunities for nesting birds in their gardens.