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. 1. Introduction Knowledge of species abundance and distribution must underpin rational conservation and management decisions [1]. However, acquiring such critical information is far from a trivial undertaking [2, 3]. This is particularly true for cryptic animals (especially when they occur at low densities) [4], for which there is often a need to use indirect survey methods [5]. These indirect methods include, but are not limited to, sign surveys [6, 7]; of which scat (fecal pellet) survey is one of the oldest and most widely used indirect methods [8, 9]. More specifically, scat surveys are often used to determine habitat preferences and predict habitat quality (e.g., [10, 11]) and are thus commonly used for monitoring endangered wildlife [12] or managing game species [13]. However, variability of both scat detectability and decay rate has led to the expression of concerns regarding the reliability of such surveys [14]. Some sources of biases due to detectability and decay have been widely studied, and methods have been developed to compensate for them. For instance, scat detectability varies between observers but can be standardized by
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