Birds in woodland fragments - not just who and where, but also what, how many and how good

This paper discusses some of the advantages of quantitative versus qualitative data in the study of bird populations in fragmented habitat on a scale ranging from populations to individuals. Species/area relationships provide good baseline data on species richness and distributions between patches, but breeding species should be distinguished from non-breeders/transients, because the two groups show different relationships with local patch area and with characteristics of the landscape at a larger scale. Distributions based on presence/absence data alone need to be treated carefully because variation in local and/or regional abundance, both within and between species, may have profound effects on species occurrences. Population persistence may also be influenced by the balance between mortality and natality in relation to habitat characteristics. For example, tits breeding in small woods in eastern England breed later and are less successful than pairs in larger woods and may also incur a cost in terms of plumage quality due to later moulting. Individual variation, e.g. in morphology in relation to flight costs, may also influence individual ability to exploit patchy habitat.