Bird census techniques

Britain has a reputation as a nation of bird-watchers (…did you know that the RSPB has the largest membership of any voluntary organisation in the country?...), and over the last 50 years that passion has been harnessed by major conservation organisations to collect data on Britain’s birds, for ecological analysis at local and national levels.

Questions Ecologists are ALWAYS asking!

Three of the most commonly-asked questions in ecology, and conservation, are:

• What (species exist here)?
• How many (of each species live here)?
• Any change (in numbers of different species and the abundance of each species)?

Two breeding bird survey techniques are commonly used in the UK.

The Common Birds Census (CBC) was a major volunteer fieldwork project of the BTO during almost forty years between 1962 and 2000, funded by JNCC. Its main function of monitoring trends in the UK populations of common breeding birds has now passed to the BTO/RSPB/JNCC Breeding Bird Survey (BBS).

The British Trust for Ornithology, in collaboration with the JNCC, devised the Common Bird Census (“CBC”) as a way of collecting data to answer these questions, and the CBC ran for nearly 40 yrs. It was an intensive data-collection strategy based on mapping territories of breeding birds, and yielded some very valuable data that allowed national population trends to be assessed (go to: http://www.bto.org/survey/cbc.htm if you want more information on what this impressive project achieved…), and is a technique that is still used to collect data at the local scale, in some instances.

The CBC, as a national voluntary fieldwork effort, was replaced with the Breeding Bird Survey (logically, “BBS”) in the mid-1990s. The BBS is a lower-intensity survey that aims to cover a much wider area of the UK (and thus more habitats and species), focusing more on the “what” and “how many” questions, rather than exact territory location and occupancy (go to: http://www.bto.org/bbs/ for more information). Data is still collected by a well-organised army of volunteers, who each survey a specified grid square annually, recording habitat and species present, plus the numbers of individuals seen.

Birds at Malham

As the Malham field station offers a good variety of different habitats we will have a go at working out what the challenges of surveying and censusing birds in each of them is, and you can learn about running a bird-recording transect. What techniques are used? How easy is to it identify and count birds? How does habitat type influence the bird species that you find?

Equipment you will need:

• 1 x pair binoculars (you can borrow these from the equipment store we will take with us)
• 1 x pair ears (unfortunately we have no spares)

[PS: The best time to survey birds is in the morning. Early morning.]

Further Details

Bird Songs

There are a number of websites which have examples of bird songs for you to listen to. These webistes will open in a new window. Close the window to return to this page.

For example:

The RSPB Bird Guide

The Virtual Bird

Common Bird Census Methodology

The survey site is visited ten times between March and July, with visits ideally at ten-day intervals. Visits should be made in the early morning and be timed to coincide with peak times of song / breeding activity. On some sites a couple of evening visits are recommended for nocturnal species such as nightjar, woodcock and owl species. Surveys should not be undertaken in strong wind and rain should be avoided if possible.

Map the boundary of the survey site at a scale of approximately 1:2,500. You will require about a dozen copies of the map - one for each visit and a couple of spares. Walk the survey area at a constant steady pace and choose a route that takes you within 50 metres of every point within the survey boundary. Mark down all breeding registrations on the visit maps along with details of date, weather and visit number. Standard codes are available for all UK breeding species and different symbols are used for different breeding registrations such as singing, alarm calls, adults carrying food etc.

Upon the completion of the ten visits all the visit information is transcribed on to species maps. Ideally a single map should be used for each species, although it is possible to double-up some species where their breeding territories do not overlap. Once the information is transferred to species maps, then clusters of registrations will reveal approximate territories. Actual determination of territories can be open to interpretation, but generally a cluster of registrations will centre on singing males and or nest activity.

Breeding Bird Survey Methodology

The RSPB, BTO and JNCC established the BBS as an annual survey of widespread and abundant terrestrial species in the UK.

This survey is a sample technique and does not require the total survey area to be walked; rather a walk of two 1-km transects selected within randomly allocated 1-km squares. It is therefore better suited for large tracts of land.

Analysis of the collected data is best undertaken by a specialist statistician; ideally the specialist DISTANCE software be used to calculate densities and population sizes.

The survey should be commenced between 0600 and 0700 hrs and no later than 0900 hrs. Three visits are made per transect, one in April to establish the transect route and map the habitats present. The second visits should be in May and June and be four weeks apart. These latter two visits are used to collect the survey data. On each visit the first transect is walked slowly and all birds seen along the route recorded per 200 metres length of the transect. Their relative distance from the transect (within 25 metres of the line, 25 to 50 metres of the transect, over 100 metres from the transect line and those flying over) should also be noted.

Further details of both methods, together with details of species specific monitoring methods are contained in Gilbert, Gibbons and Evans (1998) and on the BTO Web Site http://www.bto.org/survey

References

Buckland ST, Anderson DR, Burnham KP and Laake JL (1993) Distance Sampling: Estimating Abundance of Biological Populations Chapman and Hall. London

Gilbert G, Gibbons DW and Evans J (1998) Bird Monitoring Methods. RSPB Sandy

Gregory RD, Bashford RI, Balmer DE, Marchant JH, Wilson AM and Baille SR (1996) The Breeding Birds Survey 1994-1995. BTO Thetford

Gregory RD, Bashford RI, Balmer DE, Marchant JH, Wilson AM and Baille SR (1997) The Breeding Birds Survey 1995-1996. BTO Thetford

Marchant JH (1983) BTO Common Birds Census Instructions BTO Thetford

Marchant JH, Hudson R, Carter SP and Whittington P (1990) Population Trends in British Breeding Birds BTO Thetford

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