Birds are very useful indicators for other kinds of biodiversity
The evidence suggests that a network of sites selected as important for birds will capture most other biodiversity and that they are very useful (although still imperfect) indicators of species richness and endemism patterns. Changes in bird populations can also provide a useful indication of broader environmental change.
The expense of comprehensively assessing biodiversity is enormous. One estimate is that an all-taxa inventory of just one hectare of tropical forest might take 50-500 scientist years to accomplish (Lawton et al. 1998). This has led to much interest in finding proxy taxa that can act as indicators for biodiversity as a whole.
There is no perfect indicator taxon, but some are much better than others. The kind of indicator taxon that works best depends on whether the purpose is to track environmental changes, or clarify biodiversity patterns; on the scale involved; and on the kind of habitat being looked at.
Birds score very highly on many of the broad criteria defined for selecting indicator taxa (Pearson 1995). Their most significant advantage is that we have, relatively speaking, so much information about them, and their biology and life-histories are so well understood. Birds are also taxonomically well-known and stable, and their populations are readily surveyed and manipulated. Birds are widespread, occurring almost everywhere in the world. Bird families and genera often occupy a breadth of habitats and have broad geographical ranges, yet many individual species are specialised in their requirements and have narrow distributions. Birds are mobile and responsive to environmental changes. There are enough bird species to show meaningful patterns, yet not so many as to make identification itself a challenge. Birds have real economic importance in their own right-a useful attribute in an indicator.
However, birds are generally less specialised within micro-habitats than, say, insects or plants. Importantly, the extent to which they reflect patterns in unrelated taxonomic groups remains disputed. The evidence so far suggests that:
- on a local scale, patterns of bird distribution may not always match well the distribution patterns of other taxa (Prendergast 1993, Pearson 1995, Lawton et al. 1998); nevertheless a network of sites selected as important for birds will capture most other biodiversity (Howard et al. 1998, Brooks et al. 2001). Birds are likely to work better as biodiversity indicator taxa in terrestrial habitats (especially well-vegetated ones) than in either freshwater or marine habitats
- on a larger scale, birds are very useful (although still imperfect) indicators of species richness and endemism patterns (Bibby et al. 1992, Burgess et al. 2002)
- changes in bird populations tend to integrate a set of ecological factors. Given adequate ecological knowledge, they can provide a useful indication of environmental change (Bennun and Fanshawe 1997, Donald et al. 2001, Gregory et al. 2003). For instance, the UK government has adopted an index based on wild bird populations as one of its 15 headline Quality of Life indicators.