Introduction

Birds are among the easiest of animals to census. They are often brightly coloured, highly vocal at certain times of the year and relatively easy to see. They are also very popular, with the result that high-quality field guides are available in most parts of the world and there are many professionals and amateurs with a high level of identification skills. Because of this popularity, they are undoubtedly the most frequently surveyed of all taxonomic groups. The widespread involvement of volunteers in many schemes makes bird surveys an extremely cost-effective way of monitoring the overall health of the environment, as demonstrated by the inclusion of an indicator based on wild-bird population trends in the UK Government's list of headline indicators of sustainable development (Gregory et al. 2003, 2004c; Anon 2005; http://www.sustainable-development.gov.uk/indicators/headline/h13.htm) and among the European Union's structural and sustainability indicators (Gregory et al. 2005; http://epp.eurostat.cec.eu.int/portal/page?_pageid=1090,30070682,1090_33076576&_dad=portal&_schema=PORTAL).

Before you start counting

Before undertaking a survey you must decide on your objectives and plan accordingly. The temptation at this stage is often to be too ambitious, so careful thought should be given to your key objectives and priorities (see also Chapter 1). You may be interested in an inventory of a site, the population size (i.e. total or absolute numbers) of a species or set of species in a particular area, or a population index (i.e. relative numbers). In many instances, your aim may well be to estimate the total numbers of a particular species in an area.