Do Highly Modified Landscapes Favour Generalists at the Expense of Specialists? An Example using Woodland Birds

Abstract

Demands on land use in heavily populated landscapes create mosaic structures where semi-natural habitat patches are generally small and dominated by edges. Small patches are also more exposed and thus more vulnerable to adverse weather and potential effects of climate change. These conditions may be less problematic for generalist species than for specialists. Using insectivorous woodland birds (great tits and blue tits) as an example, we demonstrate that even generalists suffer reduced breeding success (in particular, rearing fewer and poorer-quality young) and increased parental costs (daily energy expenditure) when living in such highly modified secondary habitats (small woods, parks, farmland). Within-habitat heterogeneity (using the example of Monks Wood NNR) is generally associated with greater species diversity, but to benefit from heterogeneity at a landscape scale may require both high mobility and the ability to thrive in small habitat patches. Modern landscapes, dominated by small, modified and scattered habitat patches, may fail to provide specialists, especially sedentary ones, with access to sufficient quantity and quality of resources, while simultaneously increasing the potential for competition from generalists.

Key Words:

• Airborne remote sensing
• habitat fragmentation
• marsh tit
• parkland
• phenology