The use of fynbos fragments by birds: Stepping-stone habitats and resource refugia

摘要

Fynbos habitats are threatened by fragmentation through land use and anthropogenic changes in fire regimes, leading to a loss of suitable habitat for birds. We investigated the response of fynbos-typical avifauna to fragmentation and postfire vegetation age in order to better understand the consequences of these processes for bird communities. Vegetation composition and bird inventory data were collected along wandering transects in three South Outeniqua Sandstone Fynbos habitat configurations: fragmented patches (associated with anthropogenically driven habitat loss 150 years ago), naturally isolated fynbos islands (formed through climate-driven forest expansion in the Holocene) and extensive areas of relatively pristine habitat known as ‘mainland'. The latter configurations served as references against which to investigate bird and vegetation responses to more recent habitat fragmentation. Linear regressions were used to compare the relationships of a number of bird and plant species to areas between each habitat configuration. Bird attribute frequency data were compared between habitat configurations using chi-square tests. Birds and plants showed significant species–area relationships in natural island and mainland sites, but no such relationship occurred in artificial fragments for birds, where the surrounding anthropogenic land uses are likely to have contributed generalist or colonist species. Avifaunal migratory groups were not affected by isolation distances of 10 km in this study and their frequencies were the same across the three habitat configurations. Certain feeding guilds did, however, respond to postfire vegetation age, with nectarivore species twice as likely to occur in oldgrowth mainland fynbos. Fragmentation can alter fire disturbance regimes, which in turn alter the availability of resources in a habitat, so the impacts of fragmentation on birds are probably indirect through changes in the vegetation component.Conservation implications: Fragments of South Outeniqua Sandstone Fynbos have value as resource refugia and ‘stepping-stone' reserves for avifauna. Fragments should be managed for vegetation age to ensure that at least some patches sustain high levels of nectarproducing plant species. Fire management should, however, factor in both plant and bird requirements.Keywords: Avifauna; Agricultural Mosaic; Cape Floristic Region; Conservation; Habitat Fragmentation; Species-Area Relationships