Farmland species of conservation concern (10 December 2005)
The British and Irish ringing scheme has, for a number of years, emphasised the conservation value of the species being studied. Ringers usually pay for their rings, but for some species they are free, and other species attract a rebate for every bird ringed as a recognition of their special importance. Seed-eating birds of farmland have been especially hard-hit by agricultural changes during the last 20 or 30 years, and many of them are now designated species of conservation concern, most of them on the 'Red List' because of rapid population declines of more than 50% in 25 years. Rebates on ring costs are paid for all such species.
Various 'agri-environment' schemes are now available (from DEFRA, the UK Government's Department for the Environment, Food and Rural Affairs) to pay farmers to manage their land in ways that are sympathetic to wildlife, such as leaving uncultivated field margins, creating ponds, leaving hedges untrimmed for two or three years, and so on. Another of the options in the Environmental Stewardship scheme is planting wild bird seed mixtures specifically to benefit the seed-eating species of conservation concern. Areas of up to 0.5ha are planted with small-seed bearing crops such as kale, quinoa, linseed or millet.
We have recently started ringing on one such farm where the conservation-minded farmer has now planted four patches of wild bird crops. A line of mist-nets along a hedge readily catches some of the birds leaving the seed-rich crop, mostly kale in the field shown below:
Yellowhammers Emberiza citrinella apparently prefer the seeds of quinoa. As commented previously, this species can be challenging to age and sex. The head pattern, and tail shape and abrasion, are the main characteristics for ageing Yellowhammers. The extent of yellow is the main feature used for sexing, as with the male (at left below) and female (on the right), both first-year birds:
The mantle and rump can be helpful supporting characters, the male (on the left below) being somewhat brighter and more rusty coloured than the female (on the right):
An old name for Yellowhammer is the Yellow Bunting, and the similarity between Yellowhammer and the congeneric Reed Bunting Emberiza schoeniclus can clearly be seen in this image of two first-year females:
Reed Bunting can be a tricky species to age. Most first-year birds moult all of their greater coverts and the moult limit is usually difficult to see. The tail shape is diagnostic, although we have to beware of those first-year birds that have moulted all of their tail. Classic first-year (left) and adult (right) rectrices, in birds caught on 29 November 2005, are shown here:
Note that the tail of the first-year bird is already quite worn: at this time of year, the degree of feather abrasion can also be quite a helpful guide for ageing. First-year birds fledged around the beginning of June, so their flight feathers are now about six months old. Adult birds underwent a complete moult, finishing between mid-August and the end of September (see here for a bird actively moulting on 23 August) and thus adults have all their feathers only about three months old. As well as being only about half as old, adult-type feathers are physically stronger than the weak juvenile feathers. The difference in wear can often be seen. The first-year bird, on the left, has slightly worn primary tips while the adult bird, on the right, has feathers in pristine condition.
Tree Sparrows Passer montanus also benefit from these seed crops. Their ageing and sexing present no challenge whatsoever to the ringer, as they are impossible to age by plumage, adults and first-year birds having a complete moult in the autumn. There is also no way of distinguishing the sexes outside the breeding season. Sparrows are often thought of as drab, brown birds - the archetypal 'little brown job' - but, in the hand, the mixture of shades of colour is quite stunning:
Flocks of hundreds of Linnets Carduelis cannabina frequented the seed crops.
Males, like this bird, have just a hint of red in the breast during winter. By the breeding season he will have acquired bright red plumage, like the bird shown here.
Another species that apparently found these seed plots to its liking was Dunnock Prunella modularis. This is also on the BTO's 'amber list' of species of conservation concern. It is another difficult species for ringers to age by plumage: most first-year birds do not show an obvious moult limit (60% of Jenni & Winkler's sample in Switzerland had moulted none of their greater coverts - Moult and Ageing of European Passerines, 1994, publ. Academic Press). The colour of the iris is often diagnostic: as with most species, the iris tends to become redder with age. However, this characteristic becomes less useful as the winter progresses and different birds change towards the 'adult' colour at different rates; also, some adult birds never seem to acquire a reddish eye. The iris colour of small passerines can be difficult to photograph, but the two images below, taken on 29 November 2005, show the effect quite well. The top bird is an adult, with a first-year bird (Euring age 3) below:
Note that the bill colour, mentioned by Svensson (Identification Guide to European Passerines, 1992) as an ageing characteristic - 'all dark (blackish)' in adults and 'dark brown with slightly paler base to lower mandible' in most first-years - does not work for these two individuals, and we have a number of retrapped adults on other sites, known from their rings to be more than one year old, whose bills also were not wholly black.
All of the species mentioned above are defined as species of conservation concern, with Tree Sparrow, Linnet, Yellowhammer and Reed Bunting all on the Red List. It is only with hindsight that species can be defined as of conservation concern, because of their drop in population over a period of time. Twenty-five years ago, few ringers would have believed that we would now be receiving a rebate on rings used for House Sparrows Passer domesticus and Starlings Sturnus vulgaris. Although we are now being financially encouraged to study them, it is historical data that are likely to be of most use in teasing out the possible causes for population declines. Such information does exist in the archives of the BTO, and this is one of the advantages of having a ringing scheme in which ringers can, provided they pay for the rings used (and are licensed to do so, of course), study whatever they want.
Many of the birds feeding on the wild bird seed crop on this farm are Chaffinches Fringilla coelebs, a species whose British breeding population has remained stable throughout the declines experienced by other seed-eaters. Chaffinches are amongst my favourite birds, for which I wrote the species text for the BTO's 1981-84 Winter Atlas and the Migration Atlas. Many of these Chaffinches are likely to be migrants from Scandinavia, as are the Bramblings Fringilla montifringilla that accompanied them: maps of Merseyside Ringing Group's overseas recoveries and controls of these two species can be found here.
Most photographs of these finches are of the more spectacularly-coloured males, so these two help to redress the balance, a female Chaffinch (left) and a female Brambling (right):
Finally, any area with high concentrations of birds will attract its fair share of predators, Sparrowhawk Accipiter nisus being the main species that preys on small birds. Several have been seen in the area, but this female was the only one caught. She was easily identified as a first-year bird by the brown fringing on all of the feathers of the wing and mantle, and the pale lemon-yellow iris:
It was not surprising to find female Sparrowhawks in habitat like this. As with all accipiters, the females are much bigger than the males, typically twice their weight in the case of Sparrowhawks. The females tend to hunt in more open areas such as farmland, while the smaller males are usually to be found in woodland.
To finish where we began, British ringers also receive a rebate on the cost of rings used on all top predators. Ringing at this farm is rewarding in more ways than one!