Factors influencing bird species numbers in small woods in south-east England.
Small woods (151) in a 70×30 km agricultural area in Cambridgeshire and S. Lincolnshire, ranging in size from 0.02 to 30 ha and with differing degrees of isolation, were surveyed to determine numbers of breeding birds present over 3 yr (1990-92). Woodland and edge species were analysed separately. Numbers of woodland species showed a strong relation with woodland area, which explained about 70% of the variation in breeding species numbers. Several other features of the woodlands and surrounding landscape also had small additional influences on species numbers. Numbers of edge species were poorly related with woodland area, but perimeter length explained 30-40% of the variation. The number of structural features within a wood and isolation from other woodland also had small additional positive influences of edge species numbers. Small woods held more edge species than equivalent areas of large woods, but tended to hold fewer woodland species than equivalent areas of large woods.