Counting the unmarked: Estimating animal population using count data


Understanding population parameters are important tools for wildlife management, and one of the key objectives of the ecological research. Motion sensor cameras are a widely used tool to estimate abundance and densities of species that are identifiable based on the natural markings on their bodies. Though camera trapping provides information such as count data, on species that are not individually identifiable, estimating population size using conventional capture-recapture methodologies is not possible hindering estimating population information of several wildlife species. However, recent methodologies help use camera trapping data to bridge this gap. Here we extend the model of Chandler and Royle (2013), with suitable modifications, and used camera trap detection data to estimate abundance and density of eight wild-prey, and five domestic prey species of leopards (Panthera pardus fusca). In this context, a new procedure has been proposed, based on grouping of the count data, which is useful in cases of large encounters.

The current model should apply widely to a range of other unmarked wildlife species such as dholes, lions, golden jackal, Indian fox, ratel, to name a few, that could help understand prey-predator relationships, competition, trophic interactions, species interactions and other similar ecological questions. The methodology could also reduce costs, and maximise the utilisation of existing camera trapping data. The methodology helps understanding population parameters of several endangered, unmarked species to draw up conservation strategies whose estimates are currently largely based on educational guess.

DOI Code: 10.1285/i20705948v12n3p604

Keywords: Abundance estimation, camera-trapping, count data, density, ungulates, unmarked species


Bagchi, S., Goyal, S. P., and Sankar, K. (2004). Herbivore density and biomass in a semi-arid tropical dry deciduous forest of western India. Journal of Tropical Ecology, 20(4):475-478.

Biswas, S. and Sankar, K. (2002). Prey abundance and food habit of tigers (Panthera tigris tigris) in Pench national park, Madhya Pradesh, India. Journal of Zoology, 256(3):411-420.

Campbell, S. P., Clark, J. A., Crampton, L. H., Guerry, A. D., Hatch, L. T., Hosseini, P. R., Lawler, J. J., and O'Connor, R. J. (2002). An assessment of monitoring efforts in endangered species recovery plans. Ecological Applications, 12(3):674-681.

Carbone, C., Christie, S., Conforti, K., Coulson, T., Franklin, N., Ginsberg, J., Griffths, M., Holden, J., Kawanishi, K., Kinnaird, M., et al. (2001). The use of photographic rates to estimate densities of tigers and other cryptic mammals. In Animal Conservation forum, volume 4, pages 75-79. Cambridge University Press.

Carbone, C., Pettorelli, N., and Stephens, P. A. (2010). The bigger they come, the harder they fall: body size and prey abundance influence predator-prey ratios. Biology Letters, page rsbl20100996.

Champion, F. W. (1992). With a camera in tiger-land. Chatto and Windus.

Chandler, R. B. and Royle, J. A. (2013). Spatially explicit models for inference about density in unmarked or partially marked populations. The Annals of Applied Statistics, 7(2):936-954.

Dave, C. and Jhala, Y. (2011). Is competition with livestock detrimental for native wild ungulates? a case study of chital (Axis axis) in Gir forest, India. Journal of Tropical Ecology, 27(3):239-247.

Garshelis, D. L., Joshi, A. R., and Smith, J. L. (1999). Estimating density and relative abundance of sloth bears. Ursus, pages 87-98.

Gopal, R., Qureshi, Q., Bhardwaj, M., Singh, R. J., and Jhala, Y. V. (2010). Evaluating the status of the endangered tiger Panthera tigris and its prey in Panna tiger reserve, Madhya Pradesh, India. Oryx, 44(3):383-389.

Gopalaswamy, A. M. (2006). Estimating sloth bear abundance from repeated presence-absence data in Nagarahole-Bandipur National Parks, India. Ph.D. thesis, University of Florida.

Griffths, M. and Van Schaik, C. (1993). Camera-trapping: a new tool for the study of elusive rainforest animals. Tropical biodiversity, 1(2):131-135.

Jathanna, D., Karanth, K. U., and Johnsingh, A. (2003). Estimation of large herbivore densities in the tropical forests of southern India using distance sampling. Journal of Zoology, 261(3):285-290.

Karanth, K. U. and Nichols, J. D. (2000). Ecological status and conservation of tigers in India. Final Technical Report (February 1995 to January 2000). Centre for Wildlife Studies.

Karanth, K. U., Nichols, J. D., Kumar, N. S., Link, W. A., and Hines, J. E. (2004). Tigers and their prey: Predicting carnivore densities from prey abundance. Proceedings of the National Academy of Sciences of the United States of America, 101(14):4854-4858.

Kumara, H. N., Rathnakumar, S., Sasi, R., and Singh, M. (2012). Conservation status of wild mammals in Biligiri Rangaswamy Temple wildlife sanctuary, the western ghats, India. Current Science, 933-940.

Madhusudan, M. and Karanth, K. U. (2002). Local hunting and the conservation of large mammals in India. AMBIO: A Journal of the Human Environment, 31(1):49-54.

Owen-Smith, N. and Mills, M. G. (2008). Predator-prey size relationships in an African large-mammal food web. Journal of Animal Ecology, 77(1):173-183.

Ramsey, D. S., Caley, P. A., and Robley, A. (2015). Estimating population density from presence-absence data using a spatially explicit model. The Journal of Wildlife Management, 79(3):491-499.

Royle, J. A., Chandler, R. B., Sollmann, R., and Gardner, B. (2013). Spatial capture-recapture. Academic Press.

Sreekumar, P. and Balakrishnan, M. (2002). Seed dispersal by the sloth bear (Melursus ursinus) in south India. Biotropica, 34(3):474-477.

Varman, K. S. and Sukumar, R. (1995). The line transect method for estimating densities of large mammals in a tropical deciduous forest: An evaluation of models and field experiments. Journal of Biosciences, 20(2):273-287.

Full Text: pdf

Creative Commons License
This work is licensed under a Creative Commons Attribuzione - Non commerciale - Non opere derivate 3.0 Italia License.