Olfaction-based Detection Distance: A Quantitative Analysis of How Far Away Dogs Recognize Tortoise Odor and Follow It to Source

Adapting an ant colony metaphor for multi-robot chemical plume tracing

We consider chemical plume tracing (CPT) in time-varying airflow environments using multiple mobile robots. The purpose of CPT is to approach a gas source with a previously unknown location in a given area. Therefore, the CPT could be considered as a dynamic optimization problem in continuous domains. The traditional ant colony optimization (ACO) algorithm has been successfully used for combinatorial optimization problems in discrete domains. To adapt the ant colony metaphor to the multi-robot CPT problem, the two-dimension continuous search area is discretized into grids and the virtual pheromone is updated according to both the gas concentration and wind information. To prevent the adapted ACO algorithm from being prematurely trapped in a local optimum, the upwind surge behavior is adopted by the robots with relatively higher gas concentration in order to explore more areas. The spiral surge (SS) algorithm is also examined for comparison. Experimental results using multiple real robots in two indoor natural ventilated airflow environments show that the proposed CPT method performs better than the SS algorithm. The simulation results for large-scale advection-diffusion plume environments show that the proposed method could also work in outdoor meandering plume environments.

Collective odor source estimation and search in time-variant airflow environments using mobile robots

This paper addresses the collective odor source localization (OSL) problem in a time-varying airflow environment using mobile robots. A novel OSL methodology which combines odor-source probability estimation and multiple robots' search is proposed. The estimation phase consists of two steps: firstly, the separate probability-distribution map of odor source is estimated via Bayesian rules and fuzzy inference based on a single robot's detection events; secondly, the separate maps estimated by different robots at different times are fused into a combined map by way of distance based superposition. The multi-robot search behaviors are coordinated via a particle swarm optimization algorithm, where the estimated odor-source probability distribution is used to express the fitness functions. In the process of OSL, the estimation phase provides the prior knowledge for the searching while the searching verifies the estimation results, and both phases are implemented iteratively. The results of simulations for large-scale advection-diffusion plume environments and experiments using real robots in an indoor airflow environment validate the feasibility and robustness of the proposed OSL method.

Spatial and behavioral changes by red foxes (Vulpes vulpes) in response to artificial territory intrusion

Urine marking is thought to play a pivotal role in territory demarcation by red foxes ( Vulpes vulpes (L., 1758)), but little is known about how individuals respond to alien scent marks, and whether there are sex-related differences in territorial defense. We radio-tracked dominant male and female urban foxes before and after synthetic fox urine was applied to approximately a third of their territories and compared spatial and behavioral reactions both before and after scent application and with foxes on territories where no urine was applied. Home-range boundaries of male foxes shifted towards the scent-marked area, but this change did not affect the total territory size. Larger males shifted their home ranges to a greater degree than small males. Scent application did not affect total activity, but males spent more time in the scent-marked area. Behaviors such as distance moved per night and speed of movement did not differ before and after application, but foxes searched a greater percentage of their home range each night following scent marking. Females showed no significant spatial or behavioral response to the synthetic scent marks. Overall, responses of foxes to synthetic scent marks were male-biased and related to changes in space use rather than movement behaviors.

The success of using trained dogs to locate sparse rodents in pest-free sanctuaries

Context. Better techniques to detect small numbers of mammalian pests such as rodents are required both to complete large-scale eradications in restoration areas and to detect invaders before they become abundant or cause serious impacts on biodiversity. Aims. To evaluate the ability of certified rodent dogs (Canis familiaris) to locate Norway rats (Rattus norvegicus) and mice (Mus musculus) or their scent trails at very low densities in field conditions. Methods. We experimentally tested two rodent dogs by releasing small numbers of laboratory rats and mice in a 63 ha rodent-free forest sanctuary and then determining if the dogs and their handlers could find the rodents and their scent trails. We divided the enclosure into two halves, east and west of the midpoint, and alternated releases daily between the two areas to minimise residual scent between consecutive trials. Radio-tagged rats or mice were released a total of 96 times at random locations that were unknown to handlers, followed for 50–100 m, then caught and either placed in hidden cages at the end of the scent trail or removed from the forest. Handlers and their dogs had up to 6 h to search for rodents. Key Results. Despite the extremely low density of rodents in the effective research area of 32 ha, both dogs were highly successful at finding rodents, together locating 87% of rats and 80% of mice. Handlers reported few false positive detections. We found that well-trained dogs can effectively cover 30–40 ha of steep forested habitat in half a day (6 h). Conclusions. Despite the limitations of our study design, we conclude that well-trained rodent dogs may be able to locate wild rodents at low densities in forest situations. Implications. Our results support the ongoing use of certified dogs to detect rodent survivors and invaders in conservation areas in New Zealand and elsewhere. Additional research is required to trial dogs on experimentally released wild rodents and to compare the cost-effectiveness of dogs with other detection methods.