Environmental officials say they know of three jackals in the Matsalu wetland area in western Estonia, according to a press release. Another has been heard on Hiiumaa island, which experts believe the animal could have reached by crossing the sea ice in winter. There have also been unconfirmed reports of jackals on Saaremaa island and in Viljandi County.

The Environmental Board is now surveying the jackal population in Estonia to determine their number, locations, behavior, and how quickly the population could potentially grow. The agency plans to have an overview by fall and to eliminate the jackals during the next hunting season.

"The purpose of quickly removing a foreign species from the environment comes from the fact that if the population adapts, it can quickly multiply," said Kaja Lotman, a regional director for the Environmental Board.

That can pose a threat to native species, such as birds that nest on the ground, she said.

Lotman said it is improbable that the species was naturally introduced into Estonia.

"There are several regulations on the international level for the event of discovering a new foreign species population. One of the most important principles is that the species should be eradicated as quickly as possible before it becomes a complicated, expensive or impossible process," Lotman said.

As it stands, however, eradication may prove difficult. "We must admit that we are dealing with a very stealthy and clever animal which will not be easy to catch," Lotman said.