Biases in the Detection of Intentionally Poisoned Animals: Public Health and Conservation Implications from a Field Experiment

Abstract

Intentional poisoning is a global wildlife problem and an overlooked risk factor for public health. Managing poisoning requires unbiased and high-quality data through wildlife monitoring protocols, which are largely lacking. We herein evaluated the biases associated with current monitoring programmes of wildlife poisoning in Spain. We compared the national poisoning database for the 1990–2015 period with information obtained from a field experiment during which we used camera-traps to detect the species that consumed non-poisoned baits. Our findings suggest that the detection rate of poisoned animals is species-dependent: Several animal groups (e.g., domestic mammalian carnivores and vultures) tended to be over-represented in the poisoning national database, while others (e.g., corvids and small mammals) were underrepresented. As revealed by the GLMM analyses, the probability of a given species being overrepresented was higher for heaviest, aerial, and cryptic species. In conclusion, we found that monitoring poisoned fauna based on heterogeneous sources may produce important biases in detection rates; thus, such information should be used with caution by managers and policy-makers. Our findings may guide to future search efforts aimed to reach a more comprehensive understanding of the intentional wildlife poisoning problem.

Models of poisoning effects on vulture populations show that small but frequent episodes have a larger effect than large but rare ones

“…So, consistent with intuition and experience, a substantial initial group size is needed to offset mortalities due to poison baiting, consistent with the predictions of many demographic and genetic studies demonstrating that the persistence time of a colony increases with initial size (Shaffer, 1987;Griffith et al, 1989;Allen et al, 1992). Specifically, if poisoning events of impact D (i.e., the number of dead vultures) happen every T years and the species has a yearly growth rate r, the colony size should always be well in excess of D/(rT ) birds in order to have a sustainable population.…”

“…Vulture reintroduction or restocking projects (the latter applies when local populations are not extinct but are not yet able to recover alone) have been applied with exceptionally positive results due to certain aspects of vulture biology, such as passive behavior, easy reproduction in captivity, and simple post-release food management through controlled feeding and easy adaptation in natural habitat through collective foraging with wild conspecifics (Houston, 2006). In the last few decades, reintroductions and restocking projects have been popular as a management tool for the restoration of vulture populations in Europe, Asia and America (Griffith et al, 1989;Wilson and Stanley Price, 1994;Bustamante, 1998;Terrasse et al, 2004;Sarrazin, 2007;Stoev et al, 2016;Stoynov et al, 2016;Colomer et al, 2020).…”

How do invasive predators and their native prey respond to prescribed fire?

“…Moreover, the use of lures with camera traps can influence animal behaviour, which may complicate the interpretation of their response to fire (Gil‐Sánchez et al., 2021 ; Johnson et al., 2021 ). For instance, da Rocha et al.…”

“…Lures are commonly used when surveying for cryptic predators—especially felids and canids—to increase detection probability and analytical power, particularly when cameras are set off trails (Cove et al., 2014 ; Ferreras et al., 2018 ; Rees et al., 2019 ; Satterfield et al., 2017 ). We acknowledge, however, that lures may alter space use and local movement patterns of nearby animals, potentially causing an over‐ or underestimate of certain species' presence (Da Rocha et al., 2016 ; Gil‐Sánchez et al., 2021 ; Johnson et al., 2021 ). We incorporated lure age into our analytical framework due to its potential to influence detectability (Stobo‐Wilson, Brandle, et al., 2020 ; see Section 2.3 ), and we suggest that these factors be considered when interpreting the results.…”

“…Moreover, the use of lures with camera traps can influence animal behaviour, which may complicate the interpretation of their response to fire (Gil-Sánchez et al, 2021;Johnson et al, 2021). For instance, da Rocha et al (2016) found that lures had no effect on carnivore capture rates in Brazil, but likely reduced prey species capture rates.…”