Birds have been repeatedly assessed since 1988 by Birdlife International
. Assessments were carried out in 1988, 1994, 2000, and 2004. Since 1988, the number of species threatened with extinction has continued to rise.
The Red List Index for birds, indicates that the number of species threatened with extinction continues to grow. The 2007 Red List update for birds revealed that 12% of birds are now considered to be threatened with extinction, compared to 10% in 1988.
In the recent red list update, vultures were highlighted as species of particular concern with five more species 'uplisted' into threatened categories. Vultures are becoming increasingly threatened owing to habitat loss and degradation, loss of breeding sites, and poisoning by the veterinary drug diclofenac.
Habitat loss and degradation now threatens 86% of all threatened bird species.
Albatrosses and petrel species are currently exhibiting the greatest rate of decline when compared to migratory species and waterfowl. This is largely attributed to increases in fishing effort particularly within the longline fishery which regularly takes these species as bycatch.
Many island species, such as the hihi found in New Zealand, are increasingly threatened by the introduction of mammalian predators.
However, a number of species were downlisted on the recent red list update following successful conservation programs. One such example is the Christmas Island Hawk-owl which was downlisted from Critically Endangered in 2000, to Vulnerable since a program was implemented to control the Yellow Crazy Ant which was known to feed on nestlings.