The spatial and temporal distribution of koala faecal pellets
Ellis, WAH, Sullivan, BJ, Lisle, A & Carrick, FN 1998, Wildlife Research, vol. 25, pp. 663-668.
Faecal pellet counting is a convenient tool to determine the habitat use of vertebrate species, and particularly how individual koalas utilise trees. This study investigates the relationship between koala activity and the temporal and spatial patterns of pellet production by koalas. The authors reported that koala pellet production was at its peak between 6pm and midnight, and that there was a significant relationship between the average length of time spent in a tree by a koala and the time of day at which the koala arrived in the tree.
Faecal pellet counts were carried out in both captive and free-ranging koala populations. To help in the identification and collection of pellets in free-ranging koalas, 8 x 8 m plastic mats were placed underneath trees inhabited by koalas. Koalas are a nocturnal species, which is consistent with the present finding that pellet recovery was greatest between 6pm and midnight. This peak seems to be related to the observed increase in movement and feeding activity among the trees during this time. This pattern of defecation that corresponds to the temporal variation in activity has also been recorded in grey kangaroos and red-necked wallabies. It was reported that total counts of pellets from released rehabilitated koalas equalled 47% of the daily pellet production of their captive counterparts. Captive koalas have been reported to display increased activity when presented with browse, the lack of which in released koalas might explain this result. Furthermore, it has been stated that released koalas spent less time feeding, which may also explain this drop in faecal pellet production. The authors concluded that the density of pellets is disproportionately high adjacent to the trunk of the tree, as 18% of the pellets fell within the 1 x 1 m sampling squares on the mats. Collecting pellets in a close vicinity to the tree thus provides information on 9% of pellets produced daily by koalas.
As no past reports describe the use of a collection mat for koala faecal pellet sampling, this study suggests that the collection of pellets from the base of trees housing koalas will encompass only a small fraction of total faecal deposits, thus highlighting the problems associated with the current analysis and sampling of faecal pellets used to assess koala diet. Our current understandings of diet as a result of this sampling style are thus limited to datasets from small sample sizes. Moreover, these studies rely on the assumption that food is randomly sorted in the gut and defecated, but there is evidence that this may not be the case due to the selective retention of small food particles in the gut as well as potential associations between particular types of activity and the likelihood of defecation.
Overall, the results show that koala faecal pellets found underneath trees are deposited unevenly with respect to time and space. This research is useful in the development of methodologies for studies that utilise faecal pellets to infer information about koala diet and activity patterns.
Summarised by Caitlin Ford
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