Common Birds CensusA survey organised annually by the British Trust For Ornithology in which observers plot the positions at which song of common birds is heard on large scale maps so that the territory of each pair can be roughly worked out, thus giving an indication of numbers and population density for the census areas. Population trends can thus be monitored when results are compared from year to year. Farmland and woodland are the main habitat types covered by the survey.
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver