Where’s Wallaby? Counting the Uncountable: Animal Arithmetic

The scientists have found a way to adapt a series of formulae for the movement of gas molecules for use with information from camera traps to determine accurately the population density of a species. Population density information is vital for successful conservation but is otherwise impossible to obtain without expensive and time-consuming surveys for species where individuals cannot be easily identified. The research is published today (16th May 2008) in the Journal of Applied Ecology.

Dr Marcus Rowcliffe, ZSL Research Fellow and lead author of the paper, commented: “Most people assume that conservationists know exactly how many animals there are in any given area, but this is actually one of the greatest practical challenges we face, particularly when the animals cannot be individually identified. For example, counting animals in a jungle where there are lots of places to hide is costly and extremely difficult or even impossible. Our new model makes it possible to calculate animal numbers by using the model developed for the movement of gas molecules and applying it to the process of contact rates between animals and cameras.”

The model was tested at one of the Zoological Society of London’s living collections, ZSL Whipsnade Zoo, where known populations of muntjac, wallabies and water deer were camera trapped and the results fed into the model. The estimated densities produced by the model matched the known population counts, demonstrating the efficacy of this approach.

Dr Rowcliffe added, “There are huge numbers of species that will benefit from this research. Pygmy hippos are a great example of a highly secretive species that we know almost nothing about, but which we will be able to calculate the population size of as a result of combining this research with camera trapping work that ZSL is currently undertaking in Liberia. There are many other species which are seldom seen, so we struggle to gain knowledge of them, but which are nonetheless incredibly important parts of our world’s ecosystem.”

Notes to editors

• Founded in 1826, the Zoological Society of London (ZSL) is an international scientific, conservation and educational charity: our key role is the conservation of animals and their habitats. ZSL owns and operates ZSL London Zoo and ZSL Whipsnade Zoo, carries out scientific research at the Institute of Zoology and is actively involved in field conservation in over 40 countries worldwide.

• The Institute of Zoology (IoZ) is the research division of the Zoological Society of London (ZSL). It is a government-funded research institute specialising in scientific issues relevant to the conservation of animal species and their habitats.

• The paper published online on the 16th May 2008: Estimating animal density using camera traps without the need for individual recognition, J. Marcus Rowcliffe (ZSL), Juliet Field (ZSL and University of Leeds), Samuel Turvey (ZSL and Chris Carbone (ZSL), Journal of Applied Ecology 2008.

• ZSL is currently undertaking camera trapping work in Liberia to investigate the surviving population of pygmy hippopotami and obtained the first known camera trap images earlier this year.

• Camera trapping is a method of obtaining images of animals in an area by using cameras that are triggered by movement and is used extensively in conservation research.

Press Contact

Authors Dr Marcus Rowcliffe and Dr Chris Carbone are both available for interview, including onsite at ZSL London Zoo. For further information, a copy of the paper, to set up an interview or to obtain camera trap images, please contact Alice Henchley, alice.henchley@zsl.org (+44) 20 74496361.