In general, managers prefer to use activity indices of murid rodent abundance rather than methods that give absolute population density estimates because index techniques are easier to use in the field. We have shown here that in places with high rodent densities footprint tracking tunnels and wax blocks should be used together as their sensitivity to changes in density differ and are complementary. Moreover, Kaukeinen (1979) recommends that a minimum of two independent census techniques should be used in each evaluation and Blackwell et al. (2002) also argue that the use of more than one index increases the confidence in population trends, and the quality and quantity of information gained.
We make the following recommendations for the deployment of these indices in New Caledonian forests.
(i) Index techniques: tracking-tunnels should be run for a single night and Waxtags© for three consecutive nights.
(ii)Environment conditions: as recommended by Blackwell et al. (2002) and Morgan et al. (2009), the index techniques should always be used to compare populations directly in the same habitat type only; the density index will then more accurately reflect differences in actual abundance than differences due to activity levels.
(iii) Number and spacing: tracking tunnels are commonly spaced every 50 m in New Zealand, though Blackwell et al. (2002) considered that such close spacing may risk the effects of contagion through multiple tracking of tunnels by the same individual. A greater spacing (100 m) would mean a lower number of tunnels overall, but for larger home range sizes it may increase the reliability of the index. Taking into account current information pointing to smaller home range sizes for New Caledonian species, a 50-m spacing for tracking tunnels in New Caledonian forests is recommended. However, further investigations of rodent home ranges for each species are
needed. The wax block technique (Waxtags©) was developed in New Zealand by Thomas et al. (1999). They used a 10-m spacing on five separate lines. As seen previously, Waxtags© are easy to use and more can be deployed in the field, increasing both accuracy and precision (Brown 2002). We used a 50-m spacing here, but for the reasons given above and to increase the reliability, we recommend a 25-m spacing be used in future studies.
5.5 Acknowledgements
All the work on Isle of Pines reported here was funded by the Direction de
l’Environnement de la Province Sud and by the Institut Agronomique Néo- Calédonien
(IAC); work in dry forest was funded by the Programme de Conservation des Forêts Sèches. We thank Vincent Koteureu and Raphael Nédia for helping with fieldwork.
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CHAPTER 6
IMPACT OF THE INVASIVE LITTLE FIRE ANT (WASMANNIA AUROPUNCTATA) ON NEW
CALEDONIAN PLACOSTYLUS (MOLLUSCA:GASTROPODA:BULIMULIDAE) IN SEMI-