Evaluating the Breeding Bird Survey for producing national population size and density estimates. Newson, S., Woodburn, R., Noble, D., Baillie, S., & Gregory, R. Bird Study, 52(1):42–54, Roy. Soc. for the Protect. of Birds, The Lodge, Sandy, Bedfordshire, SG19 2DL, United Kingdom, 2005.
abstract   bibtex   
Capsule: The BBS has potential for producing better estimates of habitat-specific densities and population sizes for many UK bird populations than those available previously. Aims: To examine the use of the Breeding Bird Survey (BBS) in providing unbiased national population and habitat-specific density estimates of British birds. Methods: Line transect data collected by volunteers in 1998 from 2287 1-km squares across the UK were analysed using distance sampling methods to calculate habitat-specific density and abundance estimates. For each species, the habitat-specific decline in detectability with distance from a transect line was modelled and applied at a regional level to incorporate variation in sampling intensity in different areas of the country. Results: National population and density estimates calculated here were at a magnitude expected for at least seven species in this study. However, national population size estimates were higher than expected for Starling Sturnus vulgaris, House Sparrow Passer domesticus, Blackbird Turdus merula, Greenfinch Carduelis chloris, Jackdaw Corvus monedula, Whitethroat Sylvia communis, Woodpigeon Columba palumbus and Linnet Carduelis cannabina and lower than expected for Skylark Alauda arvensis, Dunnock Prunella modularis, Song Thrush Turdus philomelos and Corn Bunting Miliaria calandra. These differences are likely to be related to differences in sampling design and survey methods. For example, Starling, House Sparrow, Blackbird, Jackdaw, Greenfinch and Wood Pigeon, which have considerable populations in urban areas, were undoubtedly underestimated by the Common Birds Census (CBC). The counts of species that flock during the breeding season, or are not strongly territorial (e.g. Linnet, Jackdaw and Wood Pigeon) could be biased if detectability is strongly related to flock size. National population estimates of Skylark and Corn Bunting are lower than those based on CBC, but higher, or similar, to targeted national surveys of these species. Possible reasons for the differences between these estimates are considered. Conclusions: This study highlights the strength of the BBS over previous data sources in producing national estimates of density and abundance at the habitat and national level. More research on the sex ratio and status of birds counted during surveys, and on the reliability of the detectability functions derived from distance sampling is needed to improve the interpretation of population estimates derived from BBS data. © 2005 British Trust for Ornithology.
@ARTICLE{Newson2005,
  author = {Newson, S.E. and Woodburn, R.J.W. and Noble, D.G. and Baillie, S.R.
	and Gregory, R.D.},
  title = {Evaluating the Breeding Bird Survey for producing national population
	size and density estimates},
  journal = {Bird Study},
  year = {2005},
  volume = {52},
  pages = {42--54},
  number = {1},
  abstract = {Capsule: The BBS has potential for producing better estimates of habitat-specific
	densities and population sizes for many UK bird populations than
	those available previously. Aims: To examine the use of the Breeding
	Bird Survey (BBS) in providing unbiased national population and habitat-specific
	density estimates of British birds. Methods: Line transect data collected
	by volunteers in 1998 from 2287 1-km squares across the UK were analysed
	using distance sampling methods to calculate habitat-specific density
	and abundance estimates. For each species, the habitat-specific decline
	in detectability with distance from a transect line was modelled
	and applied at a regional level to incorporate variation in sampling
	intensity in different areas of the country. Results: National population
	and density estimates calculated here were at a magnitude expected
	for at least seven species in this study. However, national population
	size estimates were higher than expected for Starling \textit{Sturnus
	vulgaris}, House Sparrow \textit{Passer domesticus}, Blackbird \textit{Turdus
	merula}, Greenfinch \textit{Carduelis chloris}, Jackdaw \textit{Corvus
	monedula}, Whitethroat \textit{Sylvia communis}, Woodpigeon \textit{Columba
	palumbus} and Linnet \textit{Carduelis cannabina} and lower than
	expected for Skylark \textit{Alauda arvensis}, Dunnock \textit{Prunella
	modularis}, Song Thrush \textit{Turdus philomelos} and Corn Bunting
	\textit{Miliaria calandra}. These differences are likely to be related
	to differences in sampling design and survey methods. For example,
	Starling, House Sparrow, Blackbird, Jackdaw, Greenfinch and Wood
	Pigeon, which have considerable populations in urban areas, were
	undoubtedly underestimated by the Common Birds Census (CBC). The
	counts of species that flock during the breeding season, or are not
	strongly territorial (e.g. Linnet, Jackdaw and Wood Pigeon) could
	be biased if detectability is strongly related to flock size. National
	population estimates of Skylark and Corn Bunting are lower than those
	based on CBC, but higher, or similar, to targeted national surveys
	of these species. Possible reasons for the differences between these
	estimates are considered. Conclusions: This study highlights the
	strength of the BBS over previous data sources in producing national
	estimates of density and abundance at the habitat and national level.
	More research on the sex ratio and status of birds counted during
	surveys, and on the reliability of the detectability functions derived
	from distance sampling is needed to improve the interpretation of
	population estimates derived from BBS data. © 2005 British Trust
	for Ornithology.},
  address = {Roy. Soc. for the Protect. of Birds, The Lodge, Sandy, Bedfordshire,
	SG19 2DL, United Kingdom},
  owner = {eric},
  subdatabase = {distance},
  timestamp = {2006.11.05}
}

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