A mark-resight survey method to estimate the roaming dog population in three cities in Rajasthan, India

Lex R Hiby John F Reece Rachel Wright Rajan Jaisinghani Baldev Singh Elly F Hiby - A mark-resight survey method to estimate the roaming dog population in three cities in Rajasthan, India Hiby et al. Open Access A mark-resight survey method to estimate the roaming dog population in three cities in Rajasthan, India 1. Abstract Background: Dog population management is required in many locations to minimise the risks dog populations may pose to human health and to alleviate animal welfare problems. In many cities in India, Animal Birth Control (ABC) projects have been adopted to provide population management. Measuring the impact of such projects requires assessment of dog population size among other relevant indicators. Methods: This paper describes a simple mark-resight survey methodology that can be used with little investment of resources to monitor the number of roaming dogs in areas that are currently subject to ABC, provided the numbers, dates and locations of the dogs released following the intervention are reliably recorded. We illustrate the method by estimating roaming dog numbers in three cities in Rajasthan, India: Jaipur, Jodhpur and Jaisalmer. In each city the dog populations were either currently subject to ABC or had been very recently subject to such an intervention and hence a known number of dogs had been permanently marked with an ear-notch to identify them as having been operated. We conducted street surveys to record the current percentage of dogs in each city that are ear-notched and used an estimate for the annual survival of ear-notched dogs to calculate the current size of each marked population. Results: Dividing the size of the marked population by the fraction of the dogs that are ear-notched we estimated the number of roaming dogs to be 36,580 in Jaipur, 24,853 in Jodhpur and 2,962 in Jaisalmer. Conclusions: The mark-resight survey methodology described here is a simple way of providing population estimates for cities with current or recent ABC programmes that include visible marking of dogs. Repeating such surveys on a regular basis will further allow for evaluation of ABC programme impact on population size and reproduction in the remaining unsterilised dog population. 2. Background With the spread of urbanisation throughout the developing world the population of roaming dogs (i.e. dogs that are neither confined nor restricted, sometimes known as street, stray or free-ranging dogs) in urban areas has the potential to increase. Such dogs can suffer from welfare problems and can present a human health risk, most notably rabies, with 99% of human rabies deaths due to rabies transmission from infected dogs [1]. Human mortality from endemic canine rabies has been estimated to be 55,000 deaths per year globally with 19,713 occurring in India [2]. Animal Birth Control (ABC) has been adopted in many Indian cities through sterilisation and vaccination of captured roaming dogs and their release back into their original territories in order to reduce the risk of rabies transmission, stabilise the free roaming dog population and potentially reduce its size. This approach is also outlined in Indian legislation under the Animal Birth Control (Dogs) Rules, 2001. Opinions are divided as to the effectiveness of such programmes in controlling the number of roaming dogs (e.g. [3] and [4]) yet the data needed to assess and optimise their effectiveness are largely lacking. Population surveys may provide information relating to population size and demography that, alongside data relating to rabies incidence, can support evaluation of ABC programme impact. This paper describes a mark-resight survey methodology used in three cities in Rajasthan, India (Jaipur, Jodhpur and Jaisalmer). The roaming dog populations in all three cities were either currently subject to an ABC programme or had been very recently subject to such an intervention. The ABC programme in Jaipur is run by Help in Suffering (HIS) in collaboration with the Jaipur Municipal Council and has spayed and vaccinated 70,000 dogs between 1995 and the end of 2009. The ABC programme in Jodhpur is run by the Marwar Animal Protection Trust (MAPT). The programme started in 2004, up until November 2009 a total of 23,723 females and 25,037 males had been sterilised and vaccinated (for further details see [5], which also considers change in the Jodhpur roaming dog population following the intervention). In May and June 2009, the Tree Of Life For Animals (TOLFA) caught 1,000 male and female dogs for sterilisation and vaccination in Jaisalmer. At the time of sterilisation and vaccination (or vaccination only in the case of adult males in Jaipur) all dogs are earnotched whilst under anaesthetic before being released at the point of capture. It is this ear-notch mark that is then used during the resight stage of the survey. Re-catching is not required as these notches are easily visible on the leading edge of the ear (Figure 1). Resight data was collected using two methods; either during specific surveys to estimate the percentage of ear-notched dogs or opportunistically at the time of capturing dogs for ABC when all dogs Figure 1 Photo of dog in Jaisalmer with ear-notch visible on leading edge of left ear. - All dogs subject to sterilisation and/or vaccination as part ABC projects are ear-notched using a clamp and cauterizer whilst under anaesthetic. An ear-notch provides a permanent and visible mark that the dog is already sterilised and hence avoids them being caught unnecessarily. This photo shows a dog in Jaisalmer with an ear-notch on the leading edge of the left ear. observed are required to be checked for the presence of an ear-notch. Methods for estimating numbers of roaming dogs include questionnaire surveys ([4] and [6]), mark-resight using paint sprays [5], distance methods [7] and exhaustive counts of randomly selected city blocks [8]. Each of these methods has the potential to make an initial estimate of the size of the roaming dog population as required for planning of an intervention. However as a way of monitoring its effects over a large area these methods may need too great an investment of time and resources. We suggest that reliable population monitoring can be achieved with limited resources by exploiting the existence of the large number of marked individuals accumulating as a result of the intervention itself. For example, a previous study [9] was able to estimate the dog population of NDjamena in Chad using household and street surveys to record the percentage of dogs with collars that had been applied during a mass vaccination campaign a few days before. In this paper we extend this idea to dogs ear-notched during an ABC programme over much longer periods by allowing for an estimated rate of mortality in these dogs. We use model Mt [10] to derive the estimator. Thus in common with many other mark-resight surveys we assume that, although sighting probabilities may vary over (...truncated)