132 J. L. Silcock et al.
is capacity for dispersal across cleared valleys. Nevertheless, predation is likely to be elevated in open areas (Lapidge & Henshall, 2001), and remnant habitat between sub- populations probably facilitates dispersal and provides shelter during feeding. A significant change to the habitat within the study area
over the past decade has been the widespread erection of exclusion fences, which are designed to exclude large mac- ropods and dingoes. These fences would be virtually impassable for yellow-footed rock-wallabies, resulting in 25% of the sites surveyed having become isolated when they may once have been contiguous or formed metapopu- lations. Although rock-wallabies are adapted to living in small colonies, somemovement and gene flow between col- onies would be expected, and the long-term effects of these exclusion fences remain unknown (Smith & Allen, 2021). Moreover, if a colony becomes locally extirpated because of predation or goat competition, these fences will prevent recolonization. Introduction of domestic goats within these fences is likely to have detrimental effects on rock- wallaby subpopulations, and the long-term effects of in- creased dingo control are also unknown. Habitat characteristics are the strongest predictor of
P. xanthopus celeris presence and abundance, with shel- tered, complex sites being favoured. These habitats provide protection from predators and temperature extremes as well as relatively diverse foraging environments, and they
are also favoured by P. xanthopus xanthopus (Copley, 1983; Lim & Giles, 1987) and populations of other rock-wallaby speciesacrossAustralia (Telfer etal., 2008;Ruykys, 2017; Turpin et al., 2018). Our results suggest that P. xanthopus celeris may fluctuate in abundance in habitat of low to moderate suitability but remain resident in high-quality habitat (habitat score of 4 or 5). The southern subspecies P. xanthopus xanthopus is restricted to areas close to permanent water (Copley, 1983;Lim &Giles, 1987), but there was no relationship between mean effective distance to water and P. xanthopus celeris occurrence or abundance. The summer-dominated rainfall pattern means there are likely to be ephemeral rock holes and fis- sures available during summer when water requirements by P. xanthopus celeris are higher, thus reducing the reli- ance of the subspecies on permanent water sources (Lapidge & Munn, 2011). In addition, although yellow- footed rock-wallabies in the study area have been observed drinking at dams, springs and rock holes (Sharp, 2011;J.L. Silcock, pers. obs., 2012, 2022), their rates of water turnover in dry conditions are as low as those of any recorded marsupial (Lapidge & Munn, 2011), and they may be able to derive most of their water requirements from their diet. Removal of fleshy chenopod species and other herbage by goats could have a significant impact on P. xanthopus celeris populations (I. Hume, pers. comm., October 2018). Increased water availability in the regional
TABLE 3 Reassessment of conservation status of P. xanthopus celeris using the IUCN Red List criteria (IUCN, 2022). Only records from2010 onwards are included. Extent of occurrence (EOO) and area of occupancy (AOO) values that include Ravensbourne translocations (which will become eligible for inclusion in geographical range calculations in 2025, 5 years post-translocation; IUCN, 2022) are shown in parentheses.
IUCN criterion
A. Population size reduction over three generations (15–18 years)
B. Restricted EOO &/or AOO+ severely fragmented, continuing decline &/or extreme fluctuations
C. Population size & decline
Assessment (TSSC, 2016)
Insufficient data to determine eligibility
Vulnerable (B1ab (ii,iii,v), B2ab(ii,iii,v))
Current (2023) assessment
Not eligible: General stable or increasing trend between 2010 & 2023, including apparent recolonization events, with projected or suspected future population declines likely to be ,30%
Vulnerable (B2ab(iii)): EOO44,876 (45,850) km2, AOO 440 (452) km2, 8 locations (Table 1), not severely fragmented. Continuing decline projected in habitat quality. Fluctuations occur in number of mature individuals in response to rainfall (Sharp & McCallum, 2015), but insufficient evidence that these are of an order of magnitude (IUCN, 2022)
Vulnerable (C2a(i))
Vulnerable (C2a(i)): No reliable estimate of population size, but numbers seen in 2010–2023 surveys suggest , 10,000 mature individuals (C), with projected population decline at numerous sites because of impacts of exclusion fences & introduction of domestic goats observed, projected or inferred (C2) and number of individuals in largest subpopulation , 1,000 (a(i))
D. Number of mature individuals or restricted AOO with plausible future threat
E. Quantitative analysis Not eligible Not eligible
Not eligible: Total population size. 1,000mature individuals and AOO. 20 km2 +. 5 locations, with no plausible threat that could drive the subspecies to Extinct or Critically Endangered in a very short time
Not eligible: No population viability analysis undertaken Oryx, 2025, 59(1), 123–135 © The Author(s), 2024. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605324000760
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