Macropod studies at Wallaby Creek. 6. A validation of the use of dung-pellet counts for measuring absolute densities of populations of macropodids

Abstract

Densities of red-necked wallabies Macropus rufogriseus banksianus and eastern grey kangaroos M. giganteus at Wallaby Creek were estimated from dung-pellet counts, and these estimates were compared with the actual densities, known from censuses of individually recognisable animals. Rates of pellet accumulation were measured by clearing and re-surveying permanently marked plots. Trials measured the rates at which pellets disappeared, and defaecation rates were measured in a concurrent study. Pellets disappeared quickly during warm, moist conditions (and at rates which varied with habitat), but survived well in cold, dry conditions. Winter is considered to be the most appropriate season to run dung-pellet surveys in this or similar environments. Dung-pellet surveys estimated red-necked wallaby density with consistent accuracy, regardless of whether counts of individual pellets or counts of pellet groups were used. Counts of individual pellets underestimated grey kangaroo density, but counts of pellet groups returned more accurate estimates. Inaccuracies in previous estimates of macropodid density derived from dung-pellet surveys appear to have been due to the inappropriateness of defaecation rates measured on captive animals.