Improving reliability of scat counts for abundance and distribution estimations of Lumholtz’s Tree-kangaroo (Dendrolagus lumholtzi) in its rainforest habitats.

Abstract

arboreal folivores, such as Lumholtz’s Tree-kangaroo (Dendrolagus lumholtzi) in Far North Queensland, Australia, scat counts seem to be the most promising ecological technique. However, the occurrence of Lumholtz’s Tree-kangaroos in seasonal rainforests with dense understory, a high diversity of coprophagous invertebrates and with sympatric folivores increases the probability of invalidating results based on scat surveys. This study investigates scat production and scat decomposition patterns to select diagnostic traits of Lumholtz’s Tree-kangaroo scats that can, under varying environmental conditions, assist in distinguishing between fresh and old scats to reduce false positive and false negative errors in species presence due to non- or/and misidentification of scats. Scat production rates of six captive Lumholtz’s Tree-kangaroos were highly variable resulting in different scat numbers and masses. Changes in scat size (mass and circumference), pH and the appearance of mould were monitored under different laboratory conditions and in forest trials. Under wet conditions scats gained mass until they reached an apparent plateau of 130% of their original mass. Scats under dry conditions lost up to 90% of their original mass. Changes in mass were accompanied by changes in circumference of scats. By Day 3 scats had developed signs of mould under laboratory conditions and showed an acidic pH. Field trials revealed a high loss of scats due primarily to their consumption by dung beetles (Scarabaeoidea). For studying Lumholtz’s Tree-kangaroos in their rainforest environment, scat surveys should be confined to dry periods to reduce the probability of false negative errors due to activity of coprophagous invertebrates. Additionally, only fresh scats of average size and with an acidic pH should be used to minimize the risk of misidentifying small sized scats from Red-legged Pademelons (Thylogale stigmatica) as tree-kangaroo scats. More studies on species-specific diagnostic traits of Lumholtz’s Tree-kangaroo scats are necessary to validate false negative and false positive errors in scat counts for this species.