Journal of the Royal Society of Western Australia, 86:133-137, 2003 
Effects of short-term drought on the avifauna of Wanjarri Nature Reserve: 
What do they tell us about drought refugia? 
MD Craig 1 * 3 & A Chapman 2 ' 4 
’Zoology, School of Animal Biology M092, University of Western Australia, Crawley WA 6009 
department of Conservation and Land Management, Kalgoorlie WA 6430 
3 Present address: 5 Monument Street, Mosman Park WA 6012 
4 Present address: PO Box 264, Ravensthorpe WA 6346 
E mcraig@myrealbox.com; fishyboy@ivn.com.au 
(Manuscript received November 2002; accepted November 2003) 
Abstract 
A bird survey in the Wanjarri Nature Reserve in the Goldfields of Western Australia at the end 
of a year long drought revealed two responses to the short-term dry spell. Firstly, many bird 
populations were present in very low numbers. Secondly, areas of groving and creekline mulga 
supported a significantly higher number of bird species and individuals than other habitats. This 
was thought to be due to the greater foliage cover in groving and creekline mulga, probably as a 
consequence of soil structure, greater water availability and higher soil fertility. These areas of 
groving and creekline mulga may be important as drought refugia for resident bird species. Our 
results need to be confirmed by a more comprehensive study but the identification of drought 
refugia is of fundamental importance in the conservation of birds in the arid-zone of Australia, so 
we believe that the conservation of these groving and creekline mulga areas should be given a high 
priority. 
Keywords: birds, drought refugia, mulga, spinifex, foliage cover, conservation, landscape 
Introduction 
Arid habitats, especially those in Australia, are 
characterised by the unpredictable nature of resource 
availability. Rainfall is spatially and temporally erratic 
and this leads to large fluctuations in faunal biomass and 
productivity in any particular area (Stafford-Smith & 
Morton 1990). Birds in the arid-zone adapt to the 
ephemeral nature of available resources in two ways. The 
first group, characterised by many honeyeaters, are 
highly mobile and cover large areas in their search for 
suitable habitats. Their strategy is to be mobile enough so 
that they can always find areas of recent rainfall, hence 
high biomass and productivity, no matter where they 
occur (Davies 1986). The second group, characterised by 
thornbills and robins, are resident and relatively non- 
mobile. Their strategy is to eke out an existence in 
drought refugia during periods of low rainfall. After 
heavy rains, populations in the drought refugia increase 
and move out into previously unsuitable habitat to take 
advantage of the increased productivity (Davies 1986). 
During drought, most populations die out and only those 
located in drought refugia persist. Their survival strategy 
approximates a "core-satellite" population model 
(Boorman & Levitt 1973; Hanski 1982) where some 
habitats that support populations which persist for long 
periods of time are surrounded by habitats that are 
occupied only part of the time, usually when conditions 
are favourable (Harrison 1991). 
Conservation and management of the first group of 
highly-mobile birds within a reserve system is difficult 
due to the unpredictable nature of their occurrence, both 
© Royal Society of Western Australia 2003 
temporally and spatially. Reservation of a particular area 
will seldom satisfy their conservation needs because the 
areas they cover are so large. Members of the second 
group of resident birds are easier to conserve and 
manage within a reserve system because all their needs 
can be provided within a relatively small area. One of the 
main objectives in conserving and managing relatively 
non-mobile species is to locate and identify their refugia. 
Drought refugia are likely to be of fundamental 
importance because they provide the only suitable 
habitat for these species during dry conditions, so the 
loss of these areas will lead to local extinction (Davies 
1986). It has been postulated that the degradation of 
relatively fertile drought refugia was largely responsible 
for the extinction of almost all medium-sized mammals 
in the arid-zone of Australia (Morton 1990). 
In September 1994, we examined patterns of habitat 
use by birds during a short drought at Wanjarri Nature 
Reserve (27° 25’ S, 120° 40' E; 500 m asl) in the Goldfields 
region of Western Australia. Wanjarri (53 248 ha) is 
located within the Murchison Interim Biogeographic 
Regionalisation for Australia (IBRA) Region (formerly the 
Austin Vegetation District), which is the second largest 
IBRA Region in WA (Thackway & Cresswell 1995). Its 
vegetation, soils and fauna have been affected by pastoral 
activity. Although the reserve was relinquished as a 
pastoral lease in 1971, the effects of grazing were still 
apparent; 75% of the reserve was in 'good' resource 
condition, 23% in 'fair' and 2% in 'poor' in 1992 (Pringle 
1995). Wanjarri is ideal for studies of drought refugia 
because it is located well within the arid-zone, so patterns 
found here are likely to be applicable to other arid areas, 
and results have relevance to both pristine and grazing 
affected vegetation in the arid-zone. While our results do 
not provide unequivocal evidence, we believe that the 
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