The true magnitude of the effects of illegal poisoning on biodiversity

Millions of animals from thousands of species are poached annually, bringing iconic species such as tigers, elephants, rhinos and vultures to the brink of extinction. The illegal poisoning of fauna, together with firearms and the use of traps and traps, is one of the most used methods of poaching.

The practice of poisoning consists of the use of baits — meat, food or animal carcasses — impregnated with toxic substances to kill wild species, which are perceived as a threat to human interests as a result of conservation conflicts such as predation on livestock, damage to agricultural crops or competition for hunting fauna.

In addition, poisoning is used to kill animals that are used in the illegal species trade (such as lions and vultures). This type of wildlife crime is already considered one of the major drivers of global biodiversity loss.

The baits placed in the natural environment are not selective and act indiscriminately, being able to affect directly or indirectly (by secondary poisoning) a large number of animals, triggering a wide cascade of cryptic mortality of species in ecosystems.

In fact, it is estimated that only a very small fraction of poisoning cases (5-15%) that occur in the natural environment are detected. Although this high cryptic mortality was suspected, its magnitude had not been accurately estimated, that is, the number of species and individuals that may actually be affected in ecosystems or in each poisoning event.

A team made up of, among others, Pedro P. Olea and María Fernández-García, both from the Autonomous University of Madrid (UAM) in Spain, has managed to estimate the number of species that are truly affected by the illegal use of poison to kill animals. The magnitude of this threat had remained unknown until now due to the low detection of cases of poisoning in the natural environment.

The study carried out by researchers from the UAM, the Joint Biodiversity Research Institute (IMIB) and the Hunting Resources Research Institute (IREC), in collaboration with the Portuguese NGO Palombar and the Monfragüe National Park in Spain, has estimated in this way and for the first time the biodiversity really exposed to illegal poisoning.

The researchers carried out a large-scale field experiment using almost 600 simulated baits distributed throughout the main ecosystems of the Iberian Peninsula, monitored with camera traps. The animals that consumed the baits were not poisoned but only photographed.

Red kite (Milvus milvus) recorded by automatic photo-trapping cameras on simulated baits placed for study in order to determine the biodiversity exposed to fauna poisoning. (Photo: Olea et al 2022)

The data obtained was analyzed using statistical techniques based on cryptanalysis to estimate, from the observed biodiversity, the fraction of biodiversity not detected, using equations similar to those developed by mathematicians Ian G. Good and Alan Turing to decipher the secret code of the German Army in World War II.

The study recorded nearly 3,100 individuals consuming the baits, and determined that up to 47 species of vertebrates are susceptible to poisoning in the Iberian Peninsula, from small rodents such as mice and dormice, and reptiles such as lizards and snakes, to large predators such as wolves, bears and eagles.

25% of the species observed that consumed the baits are listed as threatened at the national or international level. The species that most frequently consumed the simulated baits, and therefore are more susceptible to poisoning, were fox, raven, griffon vulture, marten and marten, various species of mice, wild boar and dog.

In addition to revealing the identity of the fauna susceptible to poisoning, the study develops statistical models capable of predicting the number of species and individuals affected in a poisoning event depending on the type of bait used and the habitat where it is placed. The study also shows how the type of bait and the habitat where it is found influence the identity of the species likely to be poisoned.

The results of the research will help to discover the true dimension of the impact of fauna poisoning on ecosystems, to improve inspection tasks for baits and poisoned animals in the natural environment, and to more effectively combat this serious threat to biodiversity.

The study is titled “Unraveling the real magnitude of illegal wildlife poisoning to halt cryptic biodiversity loss.” And it has been published in the academic journal Biological Conservation. (Source: UAM)