Livestock grazing effects on riparian bird breeding behaviour in agricultural landscapes

Abstract

Globally, many bird species that rely on native woodland or forest environments are declining due to vegetation clearing for livestock pastures and cereal cropping. In many landscapes, woodland remnants are restricted to waterways and roadsides in narrow, sometimes degraded patches, and not all patches can necessarily provide the resources required to support bird populations. This study investigated the influence of livestock grazing and vegetation characteristics on bird breeding activity in riparian zones in northern Victoria, Australia, where much of the landscape is used for production and has experienced significant loss of woodland. Birds were broadly categorised as ‘woodland’ or ‘non-woodland’ species, based on dependency on woodlands for breeding. The majority of woodland species detected were relatively common, and where riparian zones were heavily grazed, there was significantly lower woodland bird breeding activity compared to non-woodland bird breeding activity (the latter increasing with grazing intensity). Woodland and non-woodland birds had consistently opposite responses to grazing intensity, vegetation and landscape characteristics, suggesting that the factors influencing breeding differ markedly between these two groups. Thus, where riparian zones are intensively grazed, the bird community shifts from predominantly woodland to largely non-woodland species. This has implications for the conservation of both rare and common woodland bird species in southern Australia. Simple changes in land management, for example, livestock exclusion from important breeding habitat, may confer large gains for population persistence of woodland bird species.