Australian bush birds are in decline. Both bird abundance and species numbers have fallen in many southern Australian agricultural regions, especially where woodlands have been cleared. Australia could lose half of its terrestrial bird species in the 21st century. The main cause is the loss, fragmentation and degradation of habitat due to human activities. This also influences predation, competition and the availability of nest sites. Community groups have become active but land clearing continues. Ecologists argue that land clearing, especially in already heavily cleared regions of southern Australia, should cease immediately. They have also called for fencing off and active management of remnant patches of vegetation.