A study conducted by the Ethology and Animal Welfare Unit of Cardenal-Herrera University examined 1,568 animal houses in 63 Spanish zoos and concluded that there is potential for animals in zoos to escape due to insecure housing or by getting through physical barriers surrounding their enclosures.

In this research, scientists found that birds were the most likely animals to escape Spanish zoos, but lions, bears, monkeys, crocodiles, and other animals were also potentially at risk for escape. Such escapes could pose environmental risk, as these zoos may become entry channels for exotic or non-indigenous species.

According to lead researcher Maria Fabregas,”of the 1,568 animal houses studied, 221 were insecure against the threat of the species housed in them escaping, 167 housed non-indigenous species (potentially dangerous to the environment), and of these 21 housed invasive species.” These invasive species are one of the leading causes of loss of biodiversity, and can also have detrimental effects on human health, agriculture and the economy.