Estimating population size using capture-recapture encounter histories created from point-coordinate locations of animals

Abstract

Summary1. Estimating population size is a fundamental objective of many animal monitoring programmes. Capture-recapture methods are often used to estimate population size from repeated sampling of uniquely marked animals, but capturing and marking animals can be cost prohibitive and affect animal behaviours, which can bias population estimates. 2. We developed a method to construct spatially explicit capture-recapture encounter histories from locations of unmarked animals for estimating population size with conventional capturerecapture models. Prior estimates of the maximum distance individuals move in the population is used to set a summary statistic and process subsequent capture-recapture survey data. Animal locations are recorded as point coordinates during survey occasions, and the parameter of interest is abundance of individual activity centres. 3. We applied this method to data from a point-coordinate capture-recapture survey of burrowing owls Athene cunicularia in the Imperial Valley of California, USA. We also used simulations to examine the utility of this technique for additional species with variable detection probabilities, levels of home range overlap and distributions of activity centres within a survey area. 4. The estimates from empirical and simulation studies were precise and unbiased when detection probabilities were high and territorial overlap was low. 5. This method of estimating population size from point locations fills a gap in non-invasive census and long-term monitoring methods available for conspicuous species and provides accurate estimates of burrowing owl territory abundance. The method requires high detection probabilities, low levels of home range overlap and that individuals use activity centres. We believe that these requirements can be met, with suitable survey protocols, for numerous songbird and reptile species.

Estimating densities for sympatric kit foxes (Vulpes macrotis) and coyotes (Canis latrans) using noninvasive genetic sampling

“…To evaluate the effectiveness of management strategies intended to maintain harvested populations, control nuisance species, or conserve imperiled species, managers require reliable estimates of population density or abundance (Williams et al 2002;Solberg et al 2006;Brøseth et al 2010;Granjon et al 2017). Capture-recapture techniques can provide reliable estimates of abundance (Williams et al 2002;Efford and Fewster 2013), but conventional methods of capture and recapture (e.g., live capture) are often challenging and cost-prohibitive for long-term monitoring (Pollock et al 2002;Manning and Goldberg 2010). Capture-recapture analyses based on noninvasive genetic sampling (NGS) provide alternative strategies that have seen rapid technological advancements (Lukacs and Burnham 2005;Miller et al 2005;Schwartz et al 2007;Thompson et al 2012) and increased use by practitioners (Brøseth et al 2010;Stenglein et al 2010b;Russell et al 2012;Granjon et al 2017).…”

Population Estimation Methods for Free-Ranging Dogs: A Systematic Review

“…In Ecology, the term “population” defines a group of organisms of one species that interbreed and live in the same place at the same time [ 1 ]. Plenty of estimates of abundance have been obtained, especially for populations of wild animals, for example, elephants [ 2 ], frogs [ 3 ], birds [ 4 ], wales [ 5 ], insects [ 6 ] and foxes [ 7 ]. In relation to dogs, although a great percentage of them are domiciliary and restricted animals, there is still a great percentage of animals continuously circulating on the street [ 8 ] forming specific population groups which are named free-roaming, stray, wandering, not domiciled or unrestricted.…”

A broader definition of occupancy: Comment on Hayes and Monfils

“…Hayes and Monfils (2015) question their use for analyzing avian point count data based on purported violations of model assumptions incurred by avian mobility. Animal mobility is an important consideration, not just for occupancy models, but for a variety of population and habitat models (Boyce 2006, Royle et al 2009, Manning and Goldberg 2010, Dormann et al 2013, Renner et al 2015. Nevertheless, we believe the ultimate conclusions of Hayes and Monfils are shortsighted mainly due to a narrow interpretation of occupancy.…”