Worcestershire Record No. 26 April 2009 pp. 43-44

Steve Davies

Following territory mapping for Corn Buntings and breeding season bird counts carried out at Wick Grange Farm at Wick near Pershore in 2007, we wanted to know more about the numbers and species of birds that used the habitat during the winter period October to March. Overwinter stubbles were available on both farms, weed seeds were available in the wildflower margins, and well established hedgerows were present at Wick Grange Farm. There were good areas of game crop on Glenmore land. We were optimistic that the counts would give good returns. Additionally, following my (SD) comments made on the capture and colour ringing of Corn Buntings to identify individual males within the population, and the possibility of tracking their movements in Worcestershire Record 23 (Davies 2007), I was very pleased to receive a response from Peter Holmes offering to set up a ringing scheme at the study site. Peter has a keen interest in farmland birds and has other farmland sites on which he has a ringing scheme. He was also most enthusiastic at the opportunity to ring Corn Buntings. There were now two methods available to us to monitor use of the habitat by birds. Once permission was granted by Tom Meikle, Wick Grange Farm (WGF), and Rob Kings, Glenmore Farm (GF), to carry out these operations on their holdings, we went to work.

Steve Davies

The bird counts would be made in the period October –March avoiding the first and last hour of daylight to reduce the risk of counting birds moving to and from roost sites. Survey visits could be of as long a duration as I had the energy to continue! I would aim to make a walk at least once a fortnight throughout this period. Similar to BTO Atlas methodology I would not have to stick to the same route on each visit, sampling each habitat type was to be the order of the day in a “look-see” type of methodology. Due to the dynamic movements of flocks as resources become depleted, birds could potentially be in different locations on each visit.

Counts were recorded in a field notebook with the location of large concentrations of birds noted so that Peter could make a well-informed choice for placement of his mist nets in areas where there were good concentrations of birds. At the end of the winter period I would be able to highlight the maximum numbers of each species encountered at Wick. Because both farms share a common boundary (see other articles in this issue of Worcestershire Record) and birds will use resources of food and shelter either side of this I have not given a separate treatment to each individual farm but combined counts for the two. After all birds do not recognise such boundaries and seek to find forage and safe refuge wherever it is to be found.

A total of 10 farmland walks to make bird counts were made, including both early and late visits required for the BTO Atlas, during the winter period 2007/8. The duration of visits ranged from one hour twenty minutes and six and a quarter hours, giving a total observer effort of 27 hours and 45 minutes. The longer sessions were on days when ringing was in progress.

Peter Holmes

After an initial assessment, I opened up some existing gaps in the hedge, just wide enough to allow a 6 metre long mist net through. These gaps were in areas where farmland birds, and particularly Corn Buntings, had been congregating. However the first couple of visits in February trapped no individuals of the key farmland species, although I did catch several tits, Robins, Dunnocks and Blackbirds.

Having had no success trapping Corn Buntings in the winter, I got a permit to try tape-luring males in the summer. This was marginally more successful – many days of trying led to a single Corn Bunting captured and colour-ringed! (see Fig. 1)

I again tried baiting in the autumn to see if Corn Buntings were more responsive then. They weren’t! although many Yellowhammers were caught, including several returns from spring 2008.

After a full year of trying, I am no nearer a successful method of catching numbers of Corn Buntings. But the number of other farmland birds, especially Yellowhammers, Linnets and Chaffinches, makes it worth continuing the ringing operation. Linnet numbers are particularly high, and I will more specifically target them next winter. Any Corn Buntings caught will be incidental!

Table 1. Maximum counts of birds derived from winter farmland walks in 2007/8. Maximum counts of individuals from ringing data - bold in parentheses.

The larger species of birds such as wildfowl, raptors, corvids, waders and gulls can be counted on walks with confidence as they are of low population density or are easily detectable due to their size or their foraging behaviour. Therefore, “look-see” counts can be considered accurate for these species.

Conspicuous by their absence from the above list, are nocturnal species: Barn Owl Tyto alba, Tawny Owl Strix aluco, Woodcock Scalopax rusticola. Future winter recording visits will incorporate nocturnal forays to encounter these species.

In the ringing scheme the approach must be tailored to the group of species that you wish to target. Corn Buntings proved to be difficult despite the species being found in flocks of up to 12 individuals and observed associating with other bunting species. It is unlikely that you will trap Skylarks in a net set up through a gap in a hedgerow, although another bird of open grassland, Meadow Pipit, was represented in the dataset by eight individuals.

While farmland bird counts can give a series of “snapshots” of the birds present on each visit, they can never tell us how many birds actually use the habitat throughout the survey period. Here the ringing data can give some quite staggering returns. Peter was surprised at the number of Yellowhammers (see table 1.) he succeeded in capturing and ringing. The same was to be said for Reed Bunting (see Table 1.), both species were more accurately monitored by ringing than by counts. This is almost certainly true for all small graminivorous passerines of flocking habit. These figures could potentially have been a lot higher if the ringing scheme had been started in October.

Both methods on their own merits provide a huge amount of information on farmland birds, but both have obvious limitations. When observer counts and an intensive ringing scheme are used in conjunction at a study site we begin to gain a much more accurate insight into what movements are going on there. These figures at the local level also reinforce the importance of overwinter stubbles, set-aside and game crop as overwinter food resources for farmland gramivores. The habitat quality for wintering birds is quite obvious at this site and is thanks to the efforts of Tom and Rob farming sympathetically for farmland birds. If more landowners could also engage with similar practice surely these “islands” of great biodiversity could expand into the wider countryside and encourage greater dispersal of these species. Will the loss of set-aside in 2008 in the surrounding farmland habitat have a deleterious effect on the birds at this site? We shall have to continue monitoring over the next couple of years to see. Add to this the possibility of future retraps of surviving adults, the value of ringing birds to aid conservation strategy and policy making must never be underestimated.