The alpha male of the bison herd at the European Bison Reserve Valdeserrillas (Valencia) was found beheaded on 16 September. Meanwhile, three others have gone missing and the rest of the herd are believed to be suffering from diarrhoea, prompting investigations into the incident.

The Seprona (Nature Protection Service) of the Spanish Civil Guard is looking into the possibility of whether the herd was poisoned through their water or food. Employees at the Valdeserrillas Reserve found the alpha male's decapitated body but were unable to locate the head.

According to local publication El Paid, Director Carlos Alamo is said to have noticed strange behaviour among the animals last week. When three bisons were noticed to be missing, a search party was sent out across the 365-hectare reserve, which resulted in the discovery of the body of the 800kg alpha bison.

Communications chief of the reserve, Rodolfo Navarro, said that the alpha male was "the largest, healthiest and most beautiful" animal in the herd. Investigators did not find bullet wounds in the body and believe that the alpha male would have ingested the largest amounts of food and, therefore, felt the first effects of the alleged poisoning.

Although the reserve is fenced off to prevent the animals from escaping, Navarro said that it would be relatively easy for strangers to break in due to the large size of it. The Valdeserrillas Reserve was first created in 1972 for the study and preservation of endangered species in the Valencia province.

The 12 specimens of Bison bonasus are considered an endangered species and arrived in Spain between June 2015 and May 2016, following two years of paperwork with the European Union (EU). Those found guilty of killing to animal could face a fine of €600,000.