Magnitude of the impact of illegal poisoning on biodiversity revealed

Red kite ( Milvus milvus ) recorded by automatic photo-trapping cameras on simul
Red kite ( Milvus milvus ) recorded by automatic photo-trapping cameras on simulated baits placed in an experimental study to determine biodiversity exposed to wildlife poisoning / Olea et al 2022.

A study in which the Autonomous University of Madrid (UAM) is participating has managed to estimate the number of species that are actually affected by the illegal use of poison. The magnitude of this threat had remained unknown until now due to the low detection of poisoning cases in the wild.

A study carried out by researchers from the Universidad Autónoma de Madrid (UAM), Instituto Mixto de Investigación en Biodiversidad (IMIB) and the Instituto de Investigación en Recursos Cinegéticos (IREC), in collaboration with the Portuguese NGO Palombar and the Monfragüe National Park, has estimated for the first time the biodiversity actually exposed to illegal poisoning.

The work, published in the journal Biological Conservation, is based on a large-scale field experiment with simulated baits distributed throughout the main ecosystems of the Iberian Peninsula.

The results will help to understand the true extent of the impact of wildlife poisoning on ecosystems, to improve the inspection of baits and poisoned animals in the natural environment and to combat more effectively this serious threat to biodiversity.

Poaching and poisoning

Millions of animals from thousands of species are poached annually, which is driving iconic species such as tigers, elephants, rhinos and vultures to the brink of extinction. Illegal wildlife poisoning, along with firearms and the use of traps and snares, is one of the most common methods used by poachers.

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

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 to be one of the major drivers of global biodiversity loss.

Baits placed in the natural environment are not selective and act indiscriminately, and can directly or indirectly (by secondary poisoning) affect 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%) occurring in the wild are detected. Although this high cryptic mortality was suspected, its magnitude had not been accurately estimated, i.e. the number of species and individuals that may actually be affected in ecosystems or in each poisoning event.

Field experiment

The researchers conducted a large-scale field experiment using nearly 600 simulated baits distributed throughout the main ecosystems of the Iberian Peninsula, monitored with photo-trapping cameras.

The data obtained were analyzed using statistical techniques based on cryptanalysis to estimate, from the observed biodiversity, the fraction of undetected biodiversity, 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 vertebrate species are susceptible to poisoning in the Iberian Peninsula, ranging from small rodents such as mice and dormice, and reptiles such as lizards and snakes to large predators such as wolves, bears and large eagles.

Twenty-five percent of the species observed consuming the baits are listed as nationally or internationally endangered. The species that most frequently consumed the simulated baits, and therefore are more susceptible to poisoning, were fox, crow, griffon vulture, marten and marten, several species of mice, wild boar and dog.

In addition to revealing the identity of fauna susceptible to poisoning, the study develops statistical models capable of predicting the number of species and individuals affected in a poisoning event according to 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 placed influence the identity of species susceptible to poisoning.

Iberian wolf (Canis lupus) recorded by automatic photo-trapping cameras during the study / Olea et al 2022.

Bibliographic reference:

Olea, P. P., Fernández-García, M., López-Bao, J. V., Viñuela, J., Valente e Santos, J. P., Rodríguez-Pérez, J., Sotelo, L., Cortizo, C., Sazatornil, V., Planella Bosch, A., Gutiérrez, I., Pereira, P., Luna Aguilera, S. J., Rivas, Ó., Suárez, E., Lema, F. J., del Rey, M. G., Martínez-Delgado, A., Mateo-Tomás, P. 2022. Unraveling the real magnitude of illegal wildlife poisoning to halt cryptic biodiversity loss. Biological Conservation. DOI: 10.1016/j.biocon.2022.109702

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