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Biogeography

Movement patterns of koalas in remnant forest after fire

Matthews, A, Lunney, A, Gresser, S & Maitz, W 2016, Australian Mammalogy, vol. 38, pp. 91-104.

With greater fragmentation of remnant, fire-prone forest across eastern Australia, prevailing koala populations are becoming increasingly susceptible to disturbance events. This study investigated the dispersal of koalas after a large wildfire on the central coast of New South Wales. Radio-tracking over three years revealed a wide variety of patterns, with rehabilitated and unburnt koalas demonstrating both localised and long-range movement exceeding 20km.

  The study area in Port Stephens, New South Wales consisted of 7000 hectares of remnant forest, approximately 35% of which was burnt in January 1994. Seventeen koalas that sustained injuries during the fire were captured and rehabilitated, to be radio-tracked after release. Twenty-seven unburnt koalas within the study area were also captured and fitted with radio transmitters for comparison. Movement patterns varied considerably, with koalas exhibiting great variation in home range size and location, as well as dispersal distance. On average, koalas travelled 189m each day and males were shown to travel significantly further than females. During the breeding season, daily movements were markedly greater. Monthly displacement was higher in individuals which subsequently died, and increased significantly during the breeding season. Dispersal distances over 600m were demonstrated by 15 koalas (both rehabilitated and unburnt), 13 of which departed the study area during the breeding season. Accordingly, dispersal is unlikely to have resulted wholly from rehabilitation. Significantly larger home-range and core areas were occupied by males, with overall home-range size (average 39.5 ha) not influenced by use of burnt trees.

  The findings of this study indicate that koalas are highly mobile; an advantageous trait, allowing individuals to respond to disturbance events, choose preferred food trees and recolonise rehabilitated habitat. Such behaviours were displayed in this study, in which koalas quickly re-established core home-ranges throughout burnt forest areas, efficiently adapting to the post-fire environment. It is thus apparent that, for koalas, resource loss resulting from bushfires has only a short-term impact. Furthermore, with most movement occurring during the breeding season, this study supports the prevailing view that large-scale dispersal patterns are prompted by social factors. It was shown that individuals that travelled greater distances were more vulnerable to threats, with koalas that died during the study exhibiting larger monthly displacements than those that survived. Reported home-ranges are noticeably greater than reported in previous studies; a possible manifestation of the large, burnt areas that no longer offered suitable habitat/resources, forcing koalas to disperse more widely. Importantly, rehabilitated koalas maintained similar survival and reproductive rates to unburnt koalas, highlighting the efficacy of koala rehabilitation and reintroduction as a recovery technique for isolated populations.

  Although bushfires pose a significant risk to koala populations, the recolonisation of burnt forest in the face of large-scale habitat fragmentation is a  far greater and more complex issue. Planners and policy makers must appreciate the dispersal patterns of koalas, as the daily movements of koalas through an urban matrix where threats such as dogs and cars are prolific can only be made safer by an increase in habitat connectivity.

 

Summarised by Julian Radford-Smith

 

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