UINDEX4

Large-scale surveys of waterbirds (and other wildlife) are typically
afflicted by two problems. Firstly, survey coverage is rarely complete,
especially for widely distributed species. For this reason, inferences
about trends in numbers are drawn from estimates of relative population
sizes, known as index numbers. The second problem is that even within the
set of sites included in a scheme, coverage on any given count occasion
is likely to be incomplete, making comparisons between occasions difficult.
A method which is becoming increasingly used by conservation biologists
is that developed by Underhill (1989) (see also Underhill & Prys-Jones 1994)
which estimates index numbers whilst making most efficient use of the
available information. This has now become the standard method used by
the Wetland Bird Survey in the UK and by IWRB's International Waterfowl
Census.

Underhill, L.G. (1989). Indices for waterbird populations. BTO Research
Report No. 52. British Trust for Ornithology, Tring, UK.
Underhill, L.G. & Prys-Jones, R.P. (1994). Index numbers for waterbird
populations. I. Review and methodology. Journal of Applied Biology,
31, 463-480.

UINDEX4 is a DOS executable programme for the estimation of index numbers
by the Underhill method. Full documentation for the programme is provided
in two files:

- UINDEX4.DOC A WordPerfect 5.1 format document file

- UINDEX4.EPS An Encapsulated Postscript file which may be printed directly
to a Postscript printer

Dr Michael C. Bell
The Wildfowl & Wetlands Trust
Slimbridge
Gloucestershire
GL2 7BT
UK
SL_MCB@VA.WSL.AC.UK