1. Illegal human behaviour such as those affecting natural resource use or resulting from human–wildlife conflicts threaten the sustainable management of ecosystems and the conservation of biodiversity worldwide. However, the frequently scarce and incomplete data owing to the sensitive nature of illegal activities pose a challenge to developing tools to properly understand and prevent those activities.
2. We used species distribution models to identify factors related to a prominent illegal activity, wildlife poisoning, and to produce detailed, spatially explicit maps of the risk of occurrence in NW Spain. We alleviated the constraints of imperfect information and occurrence of absences by using presence-only methods, that is, maximum entropy modelling (MaxEnt). To our knowledge, this is the first time that this method has been used in the context of illegal activities affecting wildlife.
3. A total of 112 poisoning events involving 228 individuals of 25 different species were reported in the study area from 2000 to 2010. Most of the reported deaths (90·8%) were birds of prey (52·6%) and mammalian carnivores (38·2%), of which 95·2% were scavengers. Illegal poisoning affected eleven species classified as endangered at national and/or global level.
4. Our models highlighted the perceived risk of livestock predation by wolves Canis lupus, although not by bears Ursus arctos, as a major motivation for poisoning. The existence of protected areas was positively correlated to this illegal practice, while socioeconomic factors had less influence on predicting its occurrence. Over 56% of the study area was predicted to be under risk of illegal poisoning.
5. Synthesis and applications. We demonstrate a new use for presence-only models, illustrated using MaxEnt, to assist conservation managers dealing with illegal activities. This approach allows the main causes of an illegal practice to be identified and generates spatially explicit risk maps. Managers can take advantage of this modelling approach to allocate the scarce resources available in conservation to key sectors and locations. In our study system, actions against illegal poisoning should aim to resolve the potential conflict existing between cattle-farming and wolves, especially in protected areas.