Can the abundance of tigers be assessed from their signs?

Abstract

Summary1. Indices of abundance offer cost effective and rapid methods for estimating abundance of endangered species across large landscapes, yet their wide usage is controversial due to their potential of being biased. Here, we assess the utility of indices for the daunting task of estimating the abundance of the endangered tiger at landscape scales. 2. We use double sampling to estimate two indices of tiger abundance (encounters of pugmarks and scats per km searched) and calibrate those indices against contemporaneous estimates of tiger densities obtained using camera-trap mark-recapture (CTMR) at 21 sites (5185 km 2 ) in Central and North India. We use simple and multiple weighted regressions to evaluate relationships between tiger density and indices. A model for estimating tiger density from indices was validated by Jackknife analysis and precision was assessed by correlating predicted tiger density with CTMR density. We conduct power analysis to estimate the ability of CTMR and of indices to detect changes in tiger density. 3. Tiger densities ranged between 0AE25 and 19 tigers 100 km )2 were estimated with an average coefficient of variation of 13AE2(SE 2AE5)%. Tiger pugmark encounter rates explained 84% of the observed variability in tiger densities. After removal of an outlier (Corbett), square root transformed scat encounter rates explained 82% of the variation in tiger densities. 4. A model including pugmark and scat encounters explained 95% of the variation in tiger densities with good predictive ability (PRESS R 2 = 0AE99). Overall, CTMR could detect tiger density changes of >12% with 80% power at a = 0AE3, while the index based model had 50% to 85% power to detect >30% declines. The power of indices to detect declines increased at high tiger densities. 5. Synthesis and applications. Indices of tiger abundance obtained from across varied habitats and a range of tiger densities could reliably estimate tiger abundance. Financial and temporal costs of estimating indices were 7% and 34% respectively, of those for CTMR. The models and methods presented herein have application in evaluation of the abundance of cryptic carnivores at landscape scales and form part of the protocol used by the Indian Government for evaluating the status of tigers.

Potential for camera-traps and spatial mark-resight models to improve monitoring of the critically endangered West African lion (Panthera leo)

“…In addition, the precision of such estimates can be poor, resulting in large intervals of possible abundances, which can hinder their use in assessing population status and trends. Despite these problems, monitoring of carnivores in Africa still often relies on attempts to locally calibrate counts or indices (Funston et al 2010;Thorn et al 2010;Bauer et al 2014;Henschel et al 2014;Midlane et al 2015), even though there is a strong record of failure with track index validation for multiple species across many regions (Ruscoe et al 2001;Blackwell et al 2002;Jhala et al 2011;Karanth et al 2011;Katzner et al 2011;Watts et al 2011;Sollmann et al 2013a), and especially for carnivores with typically very low detection rates . In Africa in particular, track indices are considered ineffective at estimating absolute abundance (Balme et al 2009;Biodivers Conserv Thorn et al 2010).…”

How much gene flow is needed to avoid inbreeding depression in wild tiger populations?

“…Within the last century, the number of wild tigers has declined rapidly from an estimated 100 000 individuals in the early 1900s [1] to the most recent estimate of 3800-5180 individuals globally [2], with fewer than 1850 tigers in South Asia [3,4]. Tigers now occupy only 7.1% of their historical range [5].…”

Evidences Dependent Population Distribution Patterns of Tiger and Leopard in Similipal Tiger Reserve, Odisha, India

“…Accurate information on copious and gradual alterations in copiousness is highly important for the effective management of endangered species (Gibbs 1999). Assessment of copiousness for any sly species having low density and wide ranging is highly required in terms and resources (Jhala 2011). Today, though the whole world is concerning towards conservation of big carnivores with respect to their ambient ecosystem, but yet no concrete success we have got to check their continual declinations.…”