Hi everybody -
Marjorie Wisby's enquiry about definitions of conservation status terms
raises problems of what criteria to use with regard to threatened taxa.
Political boundaries bedevil bird conservation within Australia (and
certainly between countries elsewhere). A state may have its own criteria
and list of birds threatened on a statewide basis, even though birds listed
as threatened may in fact be vagrants or have undergone a minor range
contraction and be abundant and secure elsewhere. Conversely, a bird may be
in drastic decline in one state (as with the Grey-crowned Babbler and Bush
Stone-curlew in Victoria) and not further north largely because the
processes leading to local extinction began, and reached fruition, earlier
in the south.
Birds with restricted distributions may be much more at risk from random
events or catastrophes than those with wider distributions. An island
national park may hold an endemic species in (from the human perspective)
perpetuity - until a pregnant rat swims ashore from a fishing boat.
Taxonomy matters quite a lot in bird conservation management, usually
because money is short and taxon-priority allocation criteria mean that
threatened subspecies will not receive anywhere near the same level of
attention as a recognised species (unless there are other considerations
such as being a state emblem or particularly pretty or charismatic).
These include population size, degree of ecological or behavioural
specialisation, evolutionary history and the quirky side-effects of human
technological development. Who would have thought that the invention of the
disposable plastic cigarette lighter might lead to increased mortality in
already vulnerable albatross species through ingestion and subsequent
starvation or stomach rupture?
So, categorising birds by degree of threat (and probability of extinction
within defined times) is complicated and often arbitrary. A good
publication to look at is 'Birds to Watch 2 - The World List of Threatened
Birds' by N.J.Collar, M.J.Crosby and A.J.Stattersfield; and published by
BirdLife International. This attempts to set out new criteria, which are
more objective, numerical and accountable than previous ones, to categorise
birds at the species level and in a global context. The basic ones are
(with examples taken from Australasian birds listed):
Extinct (Paradise Parrot)
Extinct in the Wild (Kakapo)
Critical (Night Parrot)
Endangered (Golden-shouldered Parrot)
Vulnerable (Short-billed Black-Cockatoo)
Conservation Dependent (Red-lored Whistler)
Near Threatened (Turquoise Parrot)
Of Less Concern (not listed)
Abundant (not listed)
(no birds listed as such from Australia or New Zealand, but with many in the
south-west Pacific region).
Many of the considerations noted above were taken into account in the
population viability analysis (PVA) of each species. Those with an
unfavourable PVA fall into the THREATENED category with the estimated
probability of extinction as follows:
Critical: >50% within 5 years.
Endangered: >20% within 20 years.
Vulnerable: >10% within 100 years.
Birds Australia Conservation & Liaison,
Australian Bird Research Centre,
415 Riversdale Road,
Hawthorn East, VIC 3123, Australia.
Tel: +61 3 9882 2622. Fax: +61 3 9882 2677.
Web Homepage: http://www.vicnet.net.au/~birdsaus