BTO Surveys

By Harry Green, BTO Regional Representative for Worcestershire.

Common Bird Census (CBC) and Breeding Bird Census (BBS)

The main survey which has accurately followed trends in breeding bird numbers for many year has been the Common Bird Census (CBC). This survey started in 1962 after trials the previous year It is based on a mapping technique in which a census plot of around 70 acres is visited ten times during the breeding season and all the birds seen and especially those heard singing are plotted on a visit map. This information is transferred to species maps and used to estimate the number of breeding territories of each species on the census plot. The CBC has mainly concentrated on farmland and woodland plots. The method does not accurately count all the birds on the plot (for instance, some are more conspicuous than others) and the important point is to register changes from year to year while the survey methodology remains constant. The results are analysed using standardised methods by BTO scientific staff and the results from all plots are combined to produce an annual estimate of change for each species by year on year comparisons. The CBC gives excellent results but there are various problems. The method is time-consuming for both field workers and BTO staff, and its expensive to run. Also the sites are self-selected by the surveyor and tend to be sites which are good for birds. There is also a bias towards SE England where most census plot are situated.

To overcome some of these problems the BTO (with funding from both RSPB and JNCC) started the Breeding Bird Survey in 1994. This survey is based on randomly selected (by BTO computer) 1-km squares of the national grid. The survey method is by walking two (out and back) 1 km transects in each square twice in the breeding season, and recording the birds encountered. All-important habitat details are also recorded. The results are again analysed by BTO scientists using standard methods. This survey is now running well with over 2000 1-km squares surveyed each year, and it is providing information from all over UK

Changes in funding now mean that JNCC will not support the CBC after the year 2000. However the overlap between the two surveys is being managed and integrated in such a way that long-term trends will still be revealed. It is hoped that CBC will continue on some plots for specific purposes such as monitoring in relation to management, and in integral study plots alongside bird ringing and other studies.

The demise of the CBC is in many ways is a sad thing because through these surveys we have made a difference which should help conserve birds, especially on farmland! However, the BBS is even more exciting as it will provide monitoring of many more habitats and many more species over a much greater area, and this is very important. For instance recent research is showing that heavy over-grazing of upland grasslands by huge numbers of sheep (and red deer in Scotland) is seriously affecting bird populations. Lapwings, hard-hit by intensive lowland farming, are now being hit on northerly and upland grasslands. BBS will help monitor these and other changes barely touched by CBC.

A small number of CBCs are currently running in Worcestershire (less than five I think). As I reported in Worcestershire Record No 5 we have 51 BBS 1-km squares in Worcestershire and most of these are covered each year. We have yet to achieve 100% coverage - some disaster always strikes! I thought we'd hit it in 1999 but sadly two squares were not covered and I am still waiting for results for two others. Perhaps in 2000 we shall hit the jackpot! Within the national pot we are now monitoring birds over about 50 square kilometres in Worcestershire compared with a few hundred acres covered by CBC.

Wintering Farmland Birds Survey

This new survey is attempting to find out how many (how few!) birds feed on farmland in winter and which types of fields or crops they are using.

Starting this winter (November to February) and running for three years, the survey is at three levels.

First: Field by field survey. Based on randomly selected 1-km squares including many of the BBS and Winter Skylark Survey squares and a few new ones. The aim is to survey all farmland fields in the square for certain birds on three occasions during the winter (mid-November to mid-February).and to record some habitat information. BTO provides a map of the square, forms and instructions. This is the major part of the survey and nationally about 1500 squares have been taken on this winter. I've been a bit slow getting started and so far I have eight squares covered - the aim for Worcestershire is about 25 squares. If anyone is interested in taking part in this survey please contact me as soon as possible as its not too late to make a start this winter.

Second: Winter Walks. The aim of this survey is to collect records during a regular winter walk of at least 1 km on farmland and. Observations are to be entered on a form with minimum data on habitat and activity.

Third: Casual records of significant flocks above a certain size of certain species are also required. Observations are to be entered on a form with some information on habitat and activity.

Which species are to be recorded? The species included in the main survey and the winter walks are: Grey Partridge, Golden Plover, Lapwing, Snipe, Curlew, Stock Dove, Woodlark, Skylark, Meadow Pipit, Pied Wagtail, Stonechat,. Fieldfare, Song Thrush, Redwing, Mistle Thrush, Starling, House Sparrow, Tree Sparrow, Chaffinch, Brambling, Greenfinch, Goldfinch, Linnet, Twite, Redpoll, Bullfinch, Snow Bunting, Yellowhammer, Reed Bunting, Corn Bunting

For the casual records the species and flock size criteria are:

100 or more plovers (Golden Plover, Lapwing)
20 or more other waders (Snipe, Curlew)
100 or more thrushes and starlings (Fieldfare, Song Thrush, Redwing, Mistle Thrush, Starling)
20 or more partridge or doves (Grey Partridge, Stock Dove)
20 or more small passerines (Skylark, Meadow Pipit, Pied Wagtail, House Sparrow, Chaffinch , Brambling, Greenfinch, Goldfinch, Linnet, Redpoll, Bullfinch, Yellowhammer)
All scarce passerines (Woodlark, Stonechat, Tree Sparrow, Twite, Snow Bunting, Reed Bunting, Corn Bunting)

Which habitats are to be surveyed?
This is a survey of farmland habitat patches - fields, hedges and farmyards. Woods, gardens and other non-agricultural habitats are ignored. If anyone would like to take part in these surveys please contact me for information, forms, etc.

Countryside Survey 2000

This is a small scale but very important survey of breeding birds in spring and summer 2000. It is linked to the 1-km squares which are nationally subject to very detailed habitat and land use surveys by ITE (Institute of Terrestrial Ecology). The methodology will be similar to BBS - transects - but with minimal collection of habitat data as this is being done in detail by ITE. The survey will probably be repeated about every ten years.

It is estimated that Worcestershire's allocation will be about five squares and I should very much like to hear from anyone who might wish to participate.

Naturalised Goose Survey 2000

The aim of this survey is count swans and naturalised geese within randomly selected tetrads (2x2 km squares) on two visits, one between mid-April and mid-May, the other between mid-June and mid-July. Main target species are Mute Swan, Canada Goose and Greylag Goose, with others Pink-footed Goose, Barnacle Goose, White-fronted Goose, Egyptian Goose, and hybrid farm geese breeding in the wild.

The tetrads allocated to Worcestershire are SO74E, SO76R, SO83Q, SO83T, SO84M, SO85S, SO86E, SO93C, SO95L and SP04V

This is a straightforward survey. In many of these tetrads it will be quite difficult to find water bodies, never mind about swans and geese, and the target species are easy to identify - a useful identification guide will be supplied with the survey instructions and forms. In many cases the tetrad will be easy to search from public rights of way as the target species and habitats are quite big!

Again anyone interested in taking part should contact me as soon as possible as BTO want to know by end of December 1999 - They'll be lucky!

Other surveys

On-going surveys include the Heronries Census (undertaken in Worcestershire by Shaun Micklewright) , Nest Records Scheme, Waterways Birds Survey, several important investigations associated with bird ringing, and Garden BirdWatch. The latter is amazingly successful with over 11,000 people taking part nationally, and some fascinating data is emerging.

WBRC Home Worcs Record Listing by Issue Worcs Record Listing by Subject