2019-03-12 P&E Agenda - Item 5 - Attachment 2 - Koala Infrastructure & Feasibility Report

3.3.4.          Managing Koalas
Thought must be given to the management of koalas not only long-term through the planning and
implementation of road mitigation measures but also during construction and operation of those measures.
AMBS (2012) provides recommendations for koala management that can be incorporated into construction
and operational management plans.

3.3.5.          Predator-prey interactions
The prey-trap hypothesis theorises that predators exploit the predictability of prey movement afforded by
crossing structures. The hypothesis predicts that predation events occur closer to a highway after the
construction of fences and crossing structures and that prey species' use of crossings increases the probability
that predators will attack prey (Ford & Clevenger 2010). However, Little et al. (2002) conclude that evidence
for the existence of prey-traps is scant, largely anecdotal and tends to indicate infrequent opportunism rather
than the establishment of patterns of recurring predation. More recent studies, such as Ford & Clevenger
(2010) and Dupuis-Desormeaux et al. (2015), found no support for the prey-trap hypothesis at their study
sites.

The Handbook of Road Ecology (Mata et al. 2015) suggests the potential relevance of this situation should
be assessed on a case-by-case basis because:

1. Wildlife crossing structures will be less effective for prey if their use is adversely influenced by predator-
   prey interactions;
2. The outcome of predator-prey interactions at wildlife crossing structures may depend on the degree of
   co-evolution between them;
3. Our knowledge of specific interactions between predators and prey at crossing structures is scarce, and
   research is urgently needed; and
4. Roads and crossing structures should be designed to minimise potentially deleterious predator-prey
   interactions.

The increased road safety and wildlife connectivity benefits provided by wildlife crossing structures for a wide
range of species are positive, with little evidence for predators using crossing structures in a systematic way
to increase hunting effectiveness (Mata et al. 2015). However, measures to reduce the risk of predation
should be considered during the design and operation of crossing structures.

3.3.6.          Further investigation – proving effectiveness
New designs of road-crossing structures for wildlife are typically based on some learning from a previous
project. They are rarely tested for suitability before they are permanently installed as part of a new road
project (Goldingay & Taylor 2016). However, knowledge of the use of structures is available for only a
relatively small number of species. Thus, ongoing monitoring and analysis is critical to gather a sound
knowledge of the most appropriate structures, structure density and location in a landscape to enable design
of effective mitigation measures.

Ree et al. (2007) reviewed 123 studies in the refereed scientific literature, conference proceedings and
consultant reports and found all but two found an effect at the level of the individual animal. Those two
studies demonstrated a positive effect for the population. The effectiveness of mitigation measures at
reducing the risk of population extinction remains unclear. A clear distinction must be made between “use”
and “effectiveness” of a wildlife crossing structure: the use of a structure may be broadly defined as the rate
of detections of individuals or species, while effectiveness relates to a specific question or the goal of
mitigation (Ree et al. 2007). A large amount of effort has conclusively shown that crossing structures are used
by many species of wildlife, however, the long-term success of mitigation measures depends on their
effectiveness.
Koala Infrastructure Audit & Feasibility Report                                                           Page 18

Noosa Council
17SUN-0087/1700860