This paper reviews the reasons why so many species of birds have declined i
n the eucalypt woodlands and associated habitats across the agricultural zo
ne of southern Australia. The extent of habitat lost, over 90% in some regi
ons, has led to the local extinction of some bird species, simply through r
andom sampling effects. Habitat specialists and those that move sequentiall
y among several habitats, are especially at risk, as some habitats have bee
n lost disproportionally. Fragmentation introduces additional problems by s
ubdividing populations into small, isolated sub-populations. Whereas some o
f the remaining species of birds appear able to move through highly fragmen
ted landscapes, it is possible that they suffer high mortality while doing
so. Some species that have been lost regionally may have had difficulty dis
persing, but there have been few detailed studies of the demography of Aust
ralian birds in fragmented landscapes. Such studies are necessary before we
can assess the value of corridors, or other means, to assist dispersal of
birds. Fragmentation also leads to edge effects, which, when compounded by
habitat degradation, may alter the intensity of a number of ecological proc
esses. There is circumstantial evidence suggesting that loss of nest sites
and increased predation on nests and free-living birds have contributed to
the decline of woodland birds. Increased interspecific competition, for ins
tance with noisy miners Manorina melanocephala, may also have a major impac
t on smaller insectivores and honeyeaters. Effects of parasites and disease
have barely been studied in Australia, though brood parasitism could accou
nt for local losses. Dieback of eucalypts and loss of understorey are commo
n in fragmented and degraded landscapes and are associated with a greatly r
educed diversity of birds. The effect of fragmentation and degradation on f
ood has received minimal attention. We propose further research that tests
the importance of some of these ecological processes in causing the decline
and loss of bird species in agricultural woodlands. Although management sh
ould proceed immediately, including a cessation of any further clearing of
native vegetation, it should be conducted in conjunction with research. We
suggest how the findings of research can inform managers, which will make m
anagement more effective in achieving conservation of regional avifaunas. (
C) 2000 Elsevier Science Ltd. All rights reserved.