Failure to account for behavioral variability significantly compromises accuracy in indirect population monitoring

Abstract

Indirect wildlife population surveying largely depends upon counts of artifacts of behavior (e.g., nests or dung). Likelihood to encounter these artifacts is derived from both artifact production and decay, and variability in production behavior is considered to contribute minimally to inaccuracy in wildlife estimation. Here, we demonstrate how ignoring behavioral variability leads to significant population misestimation, using an example of an endangered ape, the bonobo (Pan paniscus). Until now, a single estimate of nest construction rate has been used to extrapolate bonobo densities, assumed to be broadly representative of bonobo sign production behavior. We estimated nest construction rates across seasons and social groups at the Kokolopori Bonobo Reserve, Democratic Republic of the Congo, and find nest construction rates in bonobos to be highly variable across populations as well as seasonal within populations. Failure to account for this variability led to degradation in the accuracy of bonobo population density estimates, accounting for a likely overestimation of bonobo numbers by 34%, and at worst as high as 80%. With this example, we demonstrate that failure to account for inter-and intrapopulation behavioral variation compromises the ability to estimate both relative and absolute wildlife abundances. We argue that variation in sign production is but one of the several potential ways that behavioral variability can affect conservation monitoring, should be measured across contexts whenever possible, and must be considered in population estimation confidence intervals. With increasing attention to behavioral variability as a potential tool for conservation, conservationists must also account for the impact that behavioral variability can have upon wildlife population estimation. Our results underline the importance of observational research to wildlife monitoring schemes as a critical component of conservation management. We discuss the avenues through which behavioral variability is likely to impact wildlife monitoring accuracy and precision and propose potential approaches for accounting for behavioral variability in wildlife monitoring.

Habitual ground nesting in the Bugoma Forest chimpanzees (Pan troglodytes schweinfurthii), Uganda

“…Therefore, here, we provide the following nesting data: GPS location, approximate age (1 day, 2 days, under a week, over a week), the nest type (ground, tree), and the number of ground and tree nests in the nesting site from August 2019 to June 2022. Nest decay rates vary substantially between populations and are shaped by local ecological and seasonal factors (Morgan et al, 2016; Wessling & Surbeck, 2021). We followed Romani et al (2023); who recently described nest stages and decay rates for the Bugoma Central Forest Reserve.…”

“…Full nests—night or day—are distinguished in their construction from other flimsier resting structures such as “day beds” and “cushions,” which involve only 1–2 bent branches, loosely interwoven, and may be as simple as a single small sapling bent over or a clump of ferns (Boesch, 1995; Brownlow et al, 2001; Furuichi & Hashimoto, 2000; Koops et al, 2007). Nests are constructed each evening for overnight use, but they are also built during the day for a range of reasons from sleeping, to play, or sexual solicitation (Boesch, 1995; Brownlow et al, 2001; Fruth & Hohmann, 1996; Fruth et al, 2018; McGrew, 2010; Plumptre & Reynolds, 1997), with bonobos also regularly constructing additional full nests during the day (Wessling & Surbeck, 2021).…”

Habitual ground nesting in the Bugoma Forest chimpanzees (Pan troglodytes schweinfurthii), Uganda

“…Therefore, here, we provide the following nesting data: GPS location, approximate age (1 day, 2 days, under a week, over a week), the nest type (ground, tree) and the number of ground and tree nests in the nesting site from August 2019 to June 2022. Nest decay rates vary substantially between populations and are shaped by local ecological and seasonal factors (Morgan et al, 2016; Wessling & Surbeck, 2021). We followed Romani and colleagues (2023); who recently described nest stages and decay rates for the Bugoma Central Forest Reserve.…”

Decay rates of arboreal and terrestrial nests of Eastern chimpanzees (Pan troglodytes schweinfurthii) in the Bugoma Central Forest Reserve, Uganda: Implications for population size estimates

“…The use of this method, despite its practicality, has some disadvantages. Because rates of chimpanzee nest production decay vary significantly between populations and depend on a complex array of ecological and seasonal factors (Morgan et al, 2016), locally‐acquired nest decay and production rates should be used whenever possible (Kühl et al, 2008; Laing et al, 2003; Wessling & Surbeck, 2022). These data are, however, often not available, in which case a range of values from other sites is typically used to provide an estimate (e.g., Hicks et al, 2014).…”