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1.1 The BTO's monitoring of breeding birds in the UK

The Integrated Population Monitoring Programme has been developed by the BTO, under a BTO/JNCC contract, to monitor the numbers, breeding performance and survival rates of a wide range of bird species. It has the following specific aims (Baillie 1990, 1991):

  (a) To establish thresholds that will be used to notify conservation bodies of requirements for further research or conservation action.
  (b) To identify the stage of the life cycle at which demographic changes are taking place.
  (c) To provide data that will assist in identifying the causes of such changes.
  (d) To distinguish changes in population sizes or demographic rates induced by human activities from those that are due to natural fluctuations in abundance.

The programme brings together data from several long-running BTO schemes.

  • Changes in numbers of breeding birds are measured by:
    • The Common Birds Census (CBC) - which ran from 1962-2000. This scheme mapped the territories of common birds on 2-300 farmland and woodland plots measuring, on average, about 60 and 20 ha respectively.
    • The Waterways Bird Survey (WBS) - which began in 1974 and maps the territories of birds on rivers, streams and canals on 1-300 plots, each covering, on average, 4.5km.
    • The Constant Effort Sites Scheme (CES) - which began in 1983 and is based on bird ringing at over 100 sites. The catching effort is kept constant at each site during each year, so that changes in numbers of birds caught are likely to reflect population changes and not variation in catching effort.
    • The BTO/JNCC/RSPB Breeding Bird Survey (BBS) - which began in 1994, has replaced the CBC as the major monitoring scheme for landbirds. It is based on 2300 1-km squares, in which bird-watchers count and record birds along a 2 km transect walked in a standardised manner within each square. All habitats and regions are well covered by the survey because the squares are chosen randomly by computer.
  • Changes in breeding performance are measured by:
    • The Nest Record Scheme - which began in 1939 and collates standardised information on up to 35,000 individual nesting attempts per year. This allows the measurement of
      • Laying dates
      • Clutch sizes
      • Brood sizes
      • Nesting success over egg and chick stages
    • The CES provides information on overall productivity for a range of species by measuring the ratio of the numbers of juveniles to numbers of adults caught each year.
  • Changes in survival are measured by:
    • The National Ringing Scheme - which provides information on the finding circumstances and longevity of ringed birds found dead by members of the public.
    • The CES can provide information on survival rates based on the recapture of ringed birds at CES sites.

An overview of the way in which the schemes fit together is shown in the diagram below, which also demonstrates the way in which the BTO aims to combine all this information to understand the mechanisms behind changes in population sizes (using "population models").


Next Section - 1.2 The value of combining results from different monitoring schemes

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This report should be cited as:
Baillie, S.R., Crick, H.Q.P., Balmer, D.E., Beaven, L.P., Downie, I.S., Freeman, S.N., Leech, D.I., Marchant, J.H.,
Noble, D.G., Raven, M.J., Simpkin, A.P., Thewlis, R.M. and Wernham, C.V.
(2002) Breeding Birds in the Wider
Countryside: their conservation status 2001. BTO Research Report No. 278. BTO, Thetford. (

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