Words: Kate Risely, of the British Trust for Ornithology (BTO)
I started watching birds in the early seventies, when Tree Sparrows were common. They nested in a tree near my home in suburban Birmingham, we ringed a small number of broods in Edgbaston Park, just three miles from the city centre, and several flocks of 100 or more birds could be found in the surrounding countryside during the winter-time.
I vividly remember a flock of 250 birds at Bodymoor Heath, in Warwickshire, mixed in with Linnets and other finches. Checking BirdTrends on the BTO website, I see that numbers were already in decline by 1970, reaching their lowest ebb at about the same time that the Breeding Bird Survey was launched by the BTO, JNCC and RSPB in 1994.
That’s the sort of context that one needs to be aware of when reading, in the latest BBS report, that numbers increased by 55% between 1995 and 2008. Based on population estimates from Denis Summers-Smith, this change would represent a rise of just 30,000 pairs, following a loss of 850,000 since 1965. Who would have thought, in 1970, that such a rapid decline was even possible – and across the whole of the United Kingdom? That’s why it’s worth keeping an eye on common birds; sometimes things change.
Tree Sparrows in the UK are mostly fairly sedentary but there is more dispersal of juveniles and movement between breeding and wintering areas than there is for House Sparrows. When population levels were higher, there were a few reported exchanges between the UK and countries on the other side of the North Sea.
Far fewer are caught and ringed these days and there has been less evidence of international travel. There are regular movements of birds along the coast, for instance at Spurn Bird Observatory but, as Tree Sparrows living in other parts of Europe are equally unlikely to migrate, these are probably British birds.
Looking at the summary of ringing information for 2009, on the ringing section of the BTO website, I see that there were five movements of over 100 km and that four of these had a Humberside connection.
They have always been colonial by nature and patchy in their distribution, as one can read in the first Breeding Atlas (1968-72) “Thus, although there will be many 10-km squares with more than 1,000 breeding pairs, some others on the fringe of its range may hold only a handful”. When coupled with the fact that birds will readily use nest-boxes, a local recovery programme becomes possible.
Detailed research, largely by RSPB, has shown that ‘first aid’ for Tree Sparrows consists of supplementary winter feeding and locating nest-boxes close to areas where adults can find aquatic insects with which to feed their youngsters. In these wetland fringes, productivity is high enough to support the expansion of the species.
By targeting help in this way, many conservation organisations, local farmers, water companies etc. are making a real difference for Tree Sparrows. If only thinly-distributed species such as Willow Tit, Hawfinch, Spotted Flycatcher and Wood Warbler could be so readily supported.
So what does the future hold for Tree Sparrows? BBS results for 2009 indicate a continued increase since 2008, of about 10% – which is good news – but it will be interesting to see how the species coped with last winter’s hard weather.
Potentially, Tree Sparrows may have fared better than other species because of their preparedness to seek out new feeding sites and of local efforts to provide supplementary seed to promote population growth.
We shall get another ‘health bulletin’ when the 2010 results are released next year. In the medium term, there are three reasons for some optimism; historically, Tree Sparrow numbers have fluctuated wildly, there are a lot of conservationists working hard to develop strong breeding colonies and we know that young birds do disperse from these source populations.
Birdwatchers then have a major part to play, by looking out for Tree Sparrows in new areas and trying to persuade land owners to create the conditions in which this new nucleus can turn into a successful breeding population.