Stephen T. Garnett - Queensland Parks and Wildlife Service, and Gabriel M. Crowley - Birds Australia
Environment Australia, 2000
ISBN 0 6425 4683 5
Threats facing each taxon were assessed on the basis of the recovery outlines and the taxon summaries. Impacts of threats on habitat (Table 5.1), food (Table 5.2) and demographic factors (Table 5.3) were assessed and summarised separately from the threatening processes (Table 5.4).
Both impacts and processes were summarised for all extinct, threatened and near threatened taxa.
Habitat loss, fragmentation and/or degradation has affected nearly two-thirds of all the birds considered. Over half these are birds from temperate or subtropical woodlands or mallee, the habitats that have been most widely cleared for agriculture. A fifth of the taxa have been affected by loss of rainforest. Most of these are from Christmas or Norfolk Is.
Seeds and terrestrial invertebrates are the foods most likely to be in short supply as result of threatening processes, although food shortage is considered a problem of only a quarter of the taxa.
Most threatening processes reduced the probability of survival after birds have become independent. For over a third of threatened taxa, however, threatening processes also operated to reduce nest success, either because nest site availability has been reduced or because nests fail. An incapacity of birds to cross hostile habitat that now surrounds them as a result of habitat modification has affected nearly a fifth of the birds considered.
In Table 5.4 the processes that resulted in extinction are separated from those processes that pertain to extant taxa. For these processes, a temporal analysis was undertaken. Many processes which operated in the past are no longer operating, usually as a result of successful conservation management, so are listed as historical. Others are not operating now but may in the future, so are potential threats. Some threatening processes could resume if conservation management is relaxed, hence some processes are judged to be both historical and potential. Most processes are affecting taxa at the moment, so are current. This can include the effects of clearing in the past. Although the clearing has stopped, its effects continue as a result of habitat fragmentation and continued degradation.
Land clearing and grazing by sheep and/or cattle are each currently affecting about a quarter of the threatened or near threatened birds. Predators continue to be a major problem on islands and an altered fire regime is also thought to be having a long-term detrimental effect on nearly a fifth of the taxa.
|Habitat type||No. of taxa|
|Tropical and subtropical woodland||28|
|Food type in short supply||No. of taxa|
|Effect||No. of taxa|
|Lack of nest sites||23|
|Reduced adult survival||235|
In Table 5.4 taxa are grouped by principal habitat or location; groupings are mutually exclusive. Threats are divided into those that have affected extinct taxa (extinct) or extant taxa in the past (historical), those currently operating (current) and those that may affect taxa in the future (potential). A taxon may be threatened by several processes.