Monitoring indicates greater resilience for birds than for mammals in Kakadu National Park, northern Australia

Context A previous study reported major declines for native mammal species from Kakadu National Park, over the period 200109. The extent to which this result may be symptomatic of more pervasive biodiversity decline was unknown. Aims Our primary aim was to describe trends in the abundance of birds in Kakadu over the period 200109. We assessed whether any change in bird abundance was related to the arrival of invading cane toads (Rhinella marina), and to fire regimes. Methods Birds were monitored at 136 1-ha plots in Kakadu, during the period 200104 and again in 200709. This program complemented sampling of the same plots over the same period for native mammals. Key results In contrast to the decline reported for native mammals, the richness and total abundance of birds increased over this period, and far more individual bird species increased than decreased. Fire history in the between-sampling period had little influence on trends for individual species. Interpretation of the overall positive trends for bird species in Kakadu over this period should be tempered by recognition that most of the threatened bird species present in Kakadu were unrecorded in this monitoring program, and the two threatened species for which there were sufficient records to assess trends partridge pigeon (Geophaps smithii) and white-throated grass-wren (Amytornis woodwardi) both declined significantly. Conclusions The current decline of the mammal fauna in this region is not reflected in trends for the region's bird fauna. Some of the observed changes (mostly increases) in the abundance of bird species may be due to the arrival of cane toads, and some may be due to local or regional-scale climatic variation or variation in the amount of flowering. The present study provides no assurance about threatened bird species, given that most were inadequately recorded in the study (perhaps because their decline pre-dated the present study). Implications These contrasting trends between mammals and birds demonstrate the need for biodiversity monitoring programs to be broadly based. The declines of two threatened bird species over this period indicate the need for more management focus for these species.