Tiger Density Research Articles

The use of photographic rates to estimate densities of tigers and other cryptic mammals: a comment on misleading conclusions

AbstractThe search for easy‐to‐use indices that substitute for direct estimation of animal density is a common theme in wildlife and conservation science, but one fraught with well‐known perils (Nichols & Conroy, 1996; Yoccoz, Nichols & Boulinier, 2001; Pollock et al., 2002). To establish the utility of an index as a substitute for an estimate of density, one must: (1) demonstrate a functional relationship between the index and density that is invariant over the desired scope of inference; (2) calibrate the functional relationship by obtaining independent measures of the index and the animal density; (3) evaluate the precision of the calibration (Diefenbach et al., 1994). Carbone et al. (2001) argue that the number of camera‐days per photograph is a useful index of density for large, cryptic, forest‐dwelling animals, and proceed to calibrate this index for tigers (Panthera tigris). We agree that a properly calibrated index may be useful for rapid assessments in conservation planning. However, Carbone et al. (2001), who desire to use their index as a substitute for density, do not adequately address the three elements noted above. Thus, we are concerned that others may view their methods as justification for not attempting directly to estimate animal densities, without due regard for the shortcomings of their approach.

The use of photographic rates to estimate densities of tigers and other cryptic mammals

AbstractThe monitoring and management of species depends on reliable population estimates, and this can be both difficult and very costly for cryptic large vertebrates that live in forested habitats. Recently developed camera trapping techniques have already been shown to be an effective means of making mark‐recapture estimates of individually identifiable animals (e.g. tigers). Camera traps also provide a new method for surveying animal abundance. Through computer simulations, and an analysis of the rates of camera trap capture from 19 studies of tigers across the species' range, we show that the number of camera days/tiger photograph correlates with independent estimates of tiger density. This statistic does not rely on individual identity and is particularly useful for estimating the population density of species that are not individually identifiable. Finally, we used the comparison between observed trapping rates and the computer simulations to estimate the minimum effort required to determine that tigers, or other species, do not exist in an area, a measure that is critical for conservation planning.

Tiger decline caused by the reduction of large ungulate prey: evidence from a study of leopard diets in southern India

Populations of leopards and tigers in the Kalakad-Mundanthurai Tiger Reserve, India, appear to be declining. To identify the cause of this decline, we examined the diets and the relative densities of leopards and tigers, comparing scat from this park with that from the Mudumalai Wildlife Sanctuary, a park known to have high leopard and tiger densities. Results suggested that the leopard density in Mudumalai was approximately twice that in Mundanthurai. No evidence of tigers was found in Mundanthurai. Prey species found in leopard diets in the two parks was similar; albeit, mean prey weight and the proportion of large ungulates were markedly lower in the Mundanthurai leopard diet. These dietary differences are consistent with the infrequent sightings of large ungulates in Mundanthurai. Analyses of satellite data revealed that large areas of grazing land in Mundanthurai have shifted to thicket, reducing available forage for large ungulates. Since large ungulates constitute important tiger prey, the low density of ungulates in Mundanthurai might explain the apparent absence of tigers. Our findings suggest that the tiger population in the Kalakad-Mundanthurai Tiger Reserve could be enhanced via the application of habitat management for large ungulates.

Estimation of Tiger Densities in India Using Photographic Captures and Recaptures

The tiger (Panthera tigris) is an endangered, large felid whose demographic status is poorly known across its distributional range in Asia. Previously applied methods for estimating tiger abundance, using total counts based on tracks, have proved unreliable. Lack of reliable data on tiger densities not only has constrained our ability to understand the ecological factors shaping communities of large, solitary felids, but also has undermined the effective conservation of these animals. In this paper, we describe the use of a field method proposed by Karanth (1995), which combines camera-trap photography, to identify individual tigers, with theoretically well-founded capture–recapture models. We developed a sampling design for camera-trapping and used the approach to estimate tiger population size and density in four representative tiger habitats in different parts of India. The field method worked well and provided data suitable for analysis using closed capture–recapture models. The results suggest the potential for applying this methodology to rigorously estimate abundances, survival rates, and other population parameters for tigers and other low-density, secretive animal species in which individuals can be identified based on natural markings. Estimated probabilities of photo-capturing tigers present in the study sites ranged from 0.75 to 1.00. Estimated densities of tigers >1 yr old ranged from 4.1 ± 1.31 to 16.8 ± 2.96 tigers/100 km2 (mean ± 1 se). Simultaneously, we used line-transect sampling to determine that mean densities of principal tiger prey at these sites ranged from 56.1 to 63.8 ungulates/km2. Tiger densities appear to be positively associated with prey densities, except at one site influenced by tiger poaching. Our results generally support the prediction that relative abundances of large felid species may be governed primarily by the abundance and structure of their prey communities.

ESTIMATION OF TIGER DENSITIES IN INDIA USING PHOTOGRAPHIC CAPTURES AND RECAPTURES

The tiger (Panthera tigris) is an endangered, large felid whose demographic status is poorly known across its distributional range in Asia. Previously applied methods for estimating tiger abundance, using total counts based on tracks, have proved unreliable. Lack of reliable data on tiger densities not only has constrained our ability to understand the ecological factors shaping communities of large, solitary felids, but also has undermined the effective conservation of these animals. In this paper, we describe the use of a field method proposed by Karanth (1995), which combines camera-trap photography, to identify individual tigers, with theoretically well-founded capture-recapture models. We developed a sampling design for camera-trapping and used the approach to estimate tiger population size and density in four representative tiger habitats in different parts of India. The field method worked well and provided data suitable for analysis using closed capture-recapture models. The results suggest the potential for applying this methodology to rigorously estimate abundances, survival rates, and other population parameters for tigers and other low-density, secretive animal species in which individuals can be identified based on natural markings. Estimated probabilities of photo-capturing tigers present in the study sites ranged from

Estimating tiger Panthera tigris populations from camera-trap data using capture—recapture models

The applicability of capture-recapture models for estimating tiger Panthera tigris numbers from camera-trap data was investigated in a part of Nagarahole National Park, India during 12 months (387 trap-nights) in 1991-92. Camera-traps were placed along regular travel routes of tigers to obtain 31 photographic ‘captures’ of individual tigers in a 15 km 2 study area, during nine sampling occasions. Tigers could be identified unambiguously from photographs, and capture histories of 10 different animals were obtained. The data were analysed in the conceptual framework of capture-recapture theory, using probabilistic models. The results suggest that the closed capture-recapture model M h which allows for heterogeneity of capture probabilities among individual animals was appropriate for estimating tiger population size. The mean tiger numbers and their 95% confidence intervals were estimated at 11 (10–22) and 10 (10–15), respectively, with the M h (Jackknife) and M h (Chao) estimators. Considering the prey biomass available in the study area, the mean tiger densities of 13.3–14.7 adult/subadult tigers per 100 km 2 estimated from the above data appear to be reasonable. Capture-recapture models using camera-trap data offer scope for estimating objectively parameters such as size, density, survival, and recruitment for populations of tigers and other secretive animal species.

The Role of Prey in Controlling Expression of a Trophic Polymorphism in Ambystoma tigrinum nebulosum

1. With only a few exceptions, the potential contribution of heterospecific prey to the evolution of cannibalism and accompanying morphologies in amphibians and other taxa is unknown. In this study we tested the role of invertebrate and vertebrate prey in controlling variation in frequencies of a non-cannibal and an environmentally cued cannibal morph among populations of the Arizona tiger salamander, Ambystoma tigrinum nebulosum. 2. In parts of its range, A. t. nebulosum is syntopic with larvae of the chorus frog, Pseudacris triseriata. Our field measurements revealed a significant positive correlation between the frequency of cannibal morphs in larval tiger salamanders and density of chorus frog tadpoles. Cannibal frequency did not correlate significantly with larval salamander density, although frequency of cannibals varies positively with conspecific density in the laboratory