Experimental Evaluation of Koala Scat Persistence and Detectability with Implications for Pellet-Based Fauna Census

Abstract

Establishing species distribution and population trends are basic requirements in conservation biology, yet acquiring this fundamental information is often difficult. Indirect survey methods that rely on fecal pellets (scats) can overcome some difficulties but present their own challenges. In particular, variation in scat detectability and decay rate can introduce biases. We studied how vegetation communities affect the detectability and decay rate of scats as exemplified by koalas Phascolarctos cinereus: scat detectability was highly and consistently dependent on ground layer complexity (introducing up to 16% non-detection bias); scat decay rates were highly heterogeneous within vegetation communities; exposure of scats to surface water and rain strongly accelerated scat decay rate and finally, invertebrates were found to accelerate scat decay rate markedly, but unpredictably. This last phenomenon may explain the high variability of scat decay rate within a single vegetation community. Methods to decrease biases should be evaluated when planning scat surveys, as the most appropriate method(s) will vary depending on species, scale of survey and landscape characteristics. Detectability and decay biases are both stronger in certain vegetation communities, thus their combined effect is likely to introduce substantial errors in scat surveys and this could result in inappropriate and counterproductive management decisions.

Accuracy and efficiency of detection dogs: a powerful new tool for koala conservation and management

“…With the detection dog off-leash, the accuracy reached 100%. Comparing the detection dog results to a previous study on human survey scat detection11 revealed that in an experimental setting, the dog was as accurate but much more efficient than a human being (Table 4). In fact the detection dog was on average 350 times quicker.…”

“…In fact the detection dog was on average 350 times quicker. This comparison has some limitations, as the previously mentioned experimental survey11 was extremely thorough (up to 49 minutes for a 5 m 2 plot), whereas consultancy projects would be more limited by working within budget constraints which undoubtedly limits search time. In order to test the performance of the detection dog in a more realistic field survey, we compared its performance to that of a human-only team under a commonly used scat survey method.…”

“…The search was focused on the base of up to 30 trees per location, and was stopped when koala scats were found or the 30 trees had been assessed, with no time limit on the search11.…”

“…Such a high number of repeated visits can make many surveys logistically unfeasible. Scat surveys, while heavily relied upon, are unfortunately not exempt from false negatives11. In particular, detection of scats can be difficult as researchers surveying for scats rely on their eyesight and scats are easily obscured by ground cover.…”

“…In particular, detection of scats can be difficult as researchers surveying for scats rely on their eyesight and scats are easily obscured by ground cover. For example, the koala, a cryptic arboreal Australian marsupial often found at low densities, produces small sized scats (1.5 by 0.5 cm) which are easily hidden from view in dense ground vegetation or covered by leaves, are usually difficult to locate, and whose detectability by humans decreases as the complexity of ground cover increases11. However, the scat's odour persists and dogs, due to their high olfaction ability, represent a potentially powerful alternative method for scat survey12.…”