Grey Coupland

The ratios of the stable isotopes of carbon and nitrogen (13 C/ 12 C and 15 N/ 14 N) were measured in samples of hair collected from tammar wallabies (Macropus eugenii) between July 2005 and February 2006 to determine the long-term diet of three subpopulations from Garden Island, Western Australia. These populations were living on HMAS Stirling Naval Base, located at the southern end of the island, and in native bushland at the northern and southern ends of the island. The stable isotopic signatures of hair samples were compared with those of 12 plant species known to be consumed by tammar wallabies from previous dietary studies to test the hypothesis that the subpopulation living on the base would be relying heavily on the grasses from its ovals and lawns, resulting in higher δ 13 C and δ 15 N values in their tissues than in those of wallabies living in native bushland. We also expected that the δ 13 C and δ 15 N value of hair collected in summer, the period of reduced food availability, would be higher than that of hair collected during winter/spring. The δ 13 C value of hair from tammar wallabies caught on the base was higher than that of wallabies from the northern and southern subpopulations (p < 0.05). In addition, tammar wallabies from the northern subpopulation had higher δ 15 N values than those from the southern subpopulation (p < 0.05). These differences reflected the consumption of irrigated C 4 grasses (e.g. Cynodon dactylon) found on the base and demonstrate the long-term reliance of these tammar wallabies on this artificial source of food. The δ 15 N value of hair did not differ between seasons (p = 0.861) but hair samples collected in December were lower in 13 C than hair collected in July and September (p < 0.05). Our findings demonstrate that tammar wallabies living on the base rely mainly on introduced grasses as a source of food. Limiting access to this source of food might be adopted to manage this population.