Factors Affecting Efficacy and Methodological Issues

Training

Training is the foundation of CDD performance with several stages including imprinting, indication, search tasks, and discrimination trials. Each has the potential to affect efficacy. In the context of scent detection dogs, imprinting is the process of familiarising the CDD with the target odour and is therefore the basis for conducting CDD work . Given the sensitivity of the canine nose, sample handling during training must be conducted with care . Subtle aspects of sample preparation can lead to the dog learning that another odour is paired with the reward rather than the target itself . Papers often provide only limited information on sample storage and handling so no inference can be made on whether this affected efficacy. Indeed, issues identified regarding sample use include sample contamination with human scent or other non-target scents , poor decontamination procedures like running under hot water rather than sterilisation, dog saliva touching sample containers , and urination and/or defecation by dog during searches which poses a threat to samples and ecosystems . Furthermore, a review of bias in scent detection dog work suggests that over 20% of studies may have used the same samples across training and testing which means the dog may have learnt the specific samples rather than the target odour profile .
Given that CDD are biological systems, their olfactory function is subject to many influences. Factors linked to reductions in olfaction capability include older age, use of certain pharmaceuticals, diseases, dehydration, diet and nutrition, activity levels, temperature, and humidity and precipitation . There is simply no way to know if any internal variables have played a role in CDD efficacy, if details are missing about the dogs used and their care. Furthermore, the target odour which a CDD has been trained to find, can also affect operational search efficacy. It is unclear whether CDD search for complete odour signatures or simply components of the target odour that are present across samples and conditions . Indeed, CDD are very capable of generalising from low scent profiles during training to full specimens in the field and vice versa . However, depending on the samples used to train the dog, different errors may be made in the field. For example, if trained on extremely low concentrations of odour then CDD may alert where no visual sample can be found due to residual scent from past specimen presence. Alternatively, smaller samples may be missed if training involved only high odour concentration samples or failed to simulate any aspect of search environments through field tests and discrimination training, meaning the sample can be masked by non-target scents from wildlife or the environment.
Indication or alerting is how a CDD informs a handler that they have found a target through a distinct and consistent change in behaviour. Indications can be passive (i.e., no interaction with target) or active (i.e., body contact with target) depending on the needs of a project. Passive indication is recommended for CDD work to protect sample integrity and the safety of both the dog and wildlife . However, details and definitions of CDD indications are regularly omitted in the literature. Furthermore, some authors report changes of behaviour (COB) (i.e., notable shifts in CDD behaviour that suggest the dog has found or is tracking a scent) or partial indications as a suitable criteria for a true positive which is far more subjective and open to interpretation and unable to be standardised, thus altering efficacy rates .
Several types of search tasks can be used when training and testing CDD efficacy. Multiple-choice tasks are where the CDD has the option to investigate multiple containers and is rewarded if they alert on the correct one. These can simulate exposure to different scents available in the field and also facilitate discrimination training which is key to ensuring CDD are exposed to commonly encountered scents that should be ignored in favour of the target odour . However, they also provide more sensory interference for the dog and can cause preferences for specific container positions which makes assessing true odour discrimination and indication performance more difficult . Alternatively, yes/no or go/no-go tasks involve presenting the dog with a singular sample and rewarding if they make the correct choice in alerting or ignoring. These allow for a clear examination of where the dog may be making mistakes and whether they are making choices more liberally (i.e., more false positives) or conservatively (i.e., more false negatives . However, requiring the dog to have greater response inhibition during these tasks can make them needlessly challenging . Yes/no tasks have been recommended for CDD , but multiple-choice tasks are commonly seen in the literature. Although this method has benefits, it lacks details on dog performance which can help estimate and explain field efficacy rates.
A vital factor for ensuring efficacy results are reliable is blinding. Single blinding is done to ensure the dog is using olfaction rather than memory to find the target. But double blinding is preferred where both the handler and tester also do not know where the target is . This avoids the ‘Clever Hans effect’ which is an example of a horse seemingly being able to count but instead was reading human behaviour to determine when the correct response was given to receive a reward . Domesticated animals like dogs are highly skilled at reading human behaviour so even in cases where the handler or tester knows the target location and believes that efficacy will be unbiased due to the dog ignoring them for the most part , they may still unconsciously and unintentionally signal the location of the target to the CDD. Indeed, found that within ecological, evolutionary, and behavioural research, only 13.3% of studies susceptible to observer bias, reported use of blinding. IN our own analysis we found that 43% of the studies described in Table 1 used blinding, with 90% of these being double-blinding and 10% single-blinding. In all other cases, it is either unreported or more worryingly not being conducted at all.

CDD Selection and the Handler

Although CDD are used as a tool for detection, unlike analytical devices each individual dog will differ which means the selection criteria of CDD for efficacy is vital. There is little doubt that all dogs with a functioning sense of smell can detect any target that emits odour . This has been demonstrated with pet dogs and their owners that have been trained to perform scent discrimination and search tasks for novel odours similar to CDD teams . However, the breed of CDD is often considered influential in achieving the biological and psychosocial traits necessary for field work. Breeds that have been historically selected for their scent abilities are frequently used under the belief that they will inherently perform well . However individual differences can affect efficacy . Across CDD literature 128 breeds of dogs have been used and minimal differences found in suitability . Furthermore, the assumption that brachycephalic breeds will perform worse is unverified with pugs outperforming German Shepherds in scent discrimination tests , although their ability to physically endure under field conditions is untested.
More important than breed specific differences is individual personality. No standardised measures for conducting personality testing exist and it is unknown when in the dog’s life cycle their ability to work can be determined . Indeed, wastage (i.e., failing training) is a major problem in breeding for CDD as the dog may be unsuited to conservation work . The essential characteristics for CDD are high play and/or food drive, high hunt drive, and low prey drive . However, the lack of quantitative measures means that most assessments of these traits rely on the subjective view of whoever chooses the dog . Moreover, dogs are biological systems and there will always be an amount of variability in performance based on countless internal and external factors throughout their development .
CDD must work as a team alongside a human handler who oversees searches, verifies finds, and reinforces training. As such, the handler also plays a crucial role in CDD outcomes. Similar to dogs, specific skills and traits must be demonstrated to be a handler: ability to direct a search by assessing where the dog has yet to investigate, understanding of animal behaviour, learning, and scent theory, attention to detail, consistency, and endurance for working in field conditions . Handlers can both positively and negatively influence dog performance. The handler’s beliefs about how a search will go or the dog itself , the handler’s behaviour during a search regarding possible finds, the handler’s level of experience , and the handler’s personality can all result in changes to the dog’s behaviour . Furthermore, the bond between a CDD and handler matters for search performance . Dogs working with an unfamiliar handler, display more stress-related behaviours and have reduced search efficacy, if they will even search at all .

Search Environment and Method

Various elements of a search including the area and methods used, also play a role in efficacy. The environment is cited as a part of efficacy variation , but the results for how it can alter CDD performance are mixed . In some cases, detection rates have been seen to have a positive relationship with wind speed and a negative relationship with vegetation density . Precipitation can be a concern as it can wash away or degrade samples . In other cases, no effects for temperature, wind, humidity, or vegetation were found across studies looking for a range of targets including mammalian carnivore scats, bat and bird carcasses at windfarms, scat from different species of quoll, Hermann tortoises, cheetah scat, and bird carcasses infected with avian botulism , and it can be difficult to determine why results differ considering the wide range of climates and locations that these studies took place in.
Regarding search methods, elements that differ include searching on or off leash, operational time, and effective search distance. In terms of how dogs search alongside handlers, it is recommended that CDD perform off-leash searches to avoid handler bias and allow the dog to move freely and make independent decisions regarding following scent trails . This would mean that those who opt for line search where the dog is leashed may be inadvertently altering efficacy. However, line search must be conducted in some circumstances due to safety concerns for the dog regarding the environment or predators, dense vegetation, or safety for wildlife . Traditionally, operational searches occur in 30-minute intervals , but evidence suggests dogs may be able to work continuously for up to two hours if so trained . As such, if the dog has been conditioned poorly for operational searches, they may become demotivated or fatigued too soon into a search which could cause their efficacy to drop. Lastly, CDD have an effective operational search distance from the handler or transect lines. Despite maximum recorded search distances of up to 62.8m , handlers should have continuous visuals of the dog for safety and noticing alerts promptly. In addition, efficacy does appear to be negatively related to search distance . Therefore, the recommendation is usually less than 10m - 15m for the most efficient and productive search , although even this can vary if wind directions and speed are more optimal for the dog which can increase olfaction abilities .

Future Progress

Although there are clearly issues that need to be addressed regarding CDD use, research, and efficacy, the benefits CDD can offer to conservation in this time of worldwide ecological crisis demonstrates the necessity to improve their utilisation for the future. Conservation in general requires more funding to achieve its goals and slow down species decline . If CDD teams had more financial resources, then the budget constraints which prevent some studies from conducting efficacy assessments or deploying CDD on larger scales would be less of a problem. Furthermore, greater communication between CDD practitioners and researchers across institutions could lead to the development of empirical standards of practice with the subsequent following of standards by authors, researchers, and CDD teams globally.