The conservation value of mesic gullies in dry forest landscapes: Avian assemblages in the box-ironbark ecosystem of southern Australia

Drainage lines and shallow gullies generally have different microclimates and hence flora to surrounding upland ridges and slopes (abbreviated throughout as ‘ridges'). Gullies often have mesic, or at least less xeric, conditions compared with surrounding ridges. Gullies are frequently subjected to greater human impacts, such as clearance for agriculture, logging, grazing-damage and mining for alluvial deposits. We tested the hypothesis that mesic gullies in the generally dry (400–700 mm precipitation p. a.) box–ironbark forests of central Victoria, Australia, harbour a richer and different avifauna to surrounding ridges. Ten pairs of adjacent gullies and ridge sites were surveyed eight times over 1 year. Species richness was one-third greater in gullies than in ridges, while mean total densities of birds were almost twice as great. Assemblage composition also differed significantly, which reflected: (1) significantly different densities of those species common to both gullies and ridges (several more abundant in gullies, some more abundant in ridges); and (2) differences in composition wherein some species occurred only in one or the other habitat, even though pairs of gullies/ridges were only 400–1900 m apart. These results indicate that avian assemblages within gullies are distinct from those in ridges and slopes, and that integrated management is required to conserve the entire avifauna of these dry forests and woodlands. The depletion of gully habitats through human disturbance makes prescriptive management of gullies the highest priority at present.