Sustained evaluation of the effectiveness of detector dogs for locating brown tree snakes in cargo outbound from Guam

Abstract

The accidental introduction of the brown tree snake Boiga irregularis to Guam has resulted in the extirpation of most of the island's native terrestrial vertebrates, has created a health hazard to infants and children, and has resulted in economic losses. The high brown tree snake population densities on Guam, the species' adaptations for successful dispersal, and Guam's position as a focal point for commercial and military cargo shipments have created a high level of concern that brown tree snakes could spread from Guam to colonize other vulnerable locations. Cargo inspections using teams of handlers and their detector dogs form the last line of defense for preventing brown tree snake dispersal from Guam. We assessed the efficacy of the teams of handlers and their dogs during 1998 and 1999 for locating stowed brown tree snakes by planting live brown tree snakes (in escape-proof containers) in cargo without the knowledge of the handlers inspecting the cargo. Many of these inspections were monitored by a concealed observer to determine the reason if a planted snake was not located by the dog teams. For 1998 and 1999, we found similar efficacies of 61% and 64%, respectively. When the snakes were not located by the dogs, we found that twice as many were missed because the dog did not change its behavior in response to the snake rather than because the handler did not conduct an adequate search pattern. During daytime inspections we found a greater efficacy for outdoor inspections than for indoor inspections. We found that the average efficacy of 62% for the 1998-99 period was lower than the baseline efficacy of 70% established in 1997. Sustained evaluation of the effectiveness of detector dogs for locating brown tree snakes in cargo outbound from Guam Richard M. E n g e m a n a . * , Daniel S. viceh, Darryl Yorka, Kenneth S. Gruver" AbstractThe accidental introduction of the brown tree snake Boiq<~ irr.c~qu1uri.s to Guam has resulted in the extirpation of most of the island's native terrestrial vertebrates, has created a health hazard to infants and children, and has resulted in economic losses. The high brown tree snake population densities on Guam, the species' adaptations for successful dispersal, and Guam's position as a focal point for commercial and military cargo shipments have created a high level of concern that brown tree snakes could spread from Guam to colonize other vulnerable locations. Cargo inspections using teams of handlers and their detector dogs form the last line of defense for preventing brown tree snake dispersal from Guam. We assessed the eficacy of the teams of handlers and their dogs during 1998 and 1999 for locating stowed brown tree snakes by planting live brown tree snakes (in escape-proof containers) in cargo without the knowledge of the handlers inspecting the cargo. Many of these inspections were monitored by a concealed observer to determine the reason if a planted snake was not located by the dog teams. For 1998 and 1999, we found similar efficacies of 6196 and 64'36, respe...

The Influence of Habitat Type and the Presence of an Invasive Wetland Plant (Phalaris arundinacea) on Capture Rates of Sympatric Rare and Common Gartersnake Species (Thamnophis butleriandThamnophis sirtalis)

“…Researchers have successfully used detector dogs to locate chelonians (Cablk and Heaton 2006) and there may be promise in using these animals to find snakes (Engeman et al 2002). There are a myriad of methods and techniques for catching and studying snakes (Fitch 2001;Dorcas and Willson 2009) and the cumulative or comparative efforts of different techniques employed intensively are likely to be useful in raising detection rates.…”

Objectives and integrated approaches for the control of brown tree snakes: An updated overview

“…The interaction between dog and handler is complex making it impossible to precisely determine in the latter case whether: 1) the snake wasn't detected by the dog, 2) the dog detected the snake but did not respond, or 3) the handler did not recognize the dog's response. Continued testing found fewer missed snakes were due to insufficient search patterns (Engeman et al, 2002). As training has progressed over the intervening years, training tests with planted BTS have seen steady improvements in detection rates to 81%e93%.…”

“…The efficacy of dog teams for locating stowed BTS was investigated by planting live BTS (in escape-proof containers) in cargo without the knowledge of handlers responsible for inspecting the cargo (Engeman et al, 1998d(Engeman et al, , 2002. This percentage was likely a conservative estimate for detection of BTS naturally entering cargo for a couple reasons.…”

“…Similarly, facility workers and managers have expressed increased confidence and interest in the abilities of handlers and dogs, leading to proactive snake control efforts by employees at inspected facilities (Engeman et al, 1998d). Consistent, relevant training is crucial, and all handling teams on Guam undergo periodic proficiency training and are tested annually.…”

Training of a dog for the monitoring of Osmoderma eremita

“…Several authors suggest that the best parameters to describe the ability of conservation dogs in correctly locating their target are the overall percentage of correct indications and the percentage of correctly detected targets for the total number of targets (Wallner and Ellis 1976,Welch 1990, Engeman et al 2002, Brooks et al 2003, Cablk and Heaton 2006, Long et al 2007, Richards et al 2008, Gsell et al 2010, Lin et al 2011, Waters et al 2011, Suma et al 2014, Hoyer-Tomiczek et al 2016. Although these parameters are often characterised by different names, for this work, the definition used by Allouche et al (2006) was adopted in relation to the assessment of presence-absence predictive models i.e.…”