Hybridisation and competition with the European polecat In the early 20th century, northern Europe underwent a warm climatic period which coincided with an expansion of the range of the European polecat. The European mink possibly was gradually absorbed by the polecat due to hybridisation. Also, competition with the polecat has greatly increased, due to landscape change favouring the polecat. There is one record of a polecat attacking a mink and dragging it to its burrow. Polecat-mink hybrids are termed khor'-tumak by furriers and khonorik by fanciers. Such hybridisation is very rare in the wild, and typically only occurs where European minks are declining. A polecat-mink hybrid has a poorly defined facial mask, yellow fur on the ears, grey-yellow underfur and long, dark brown guard hairs. Fairly large, the males attain the peak sizes known for European polecats (weighing and measuring in length), and females are much larger than female European minks (weighing and measuring in length). The majority of polecat-mink hybrids have skulls bearing greater similarities to those of polecats than to minks. Hybrids can swim well like minks and burrow for food like polecats. They are very difficult to tame and breed, as males are sterile, though females are fertile. The first captive polecat-mink hybrid was created in 1978 by Soviet zoologist Dr. Dmitry Ternovsky of Novosibirsk. Originally bred for their fur (which was more valuable than that of either parent species), the breeding of these hybrids declined as European mink populations decreased. Studies on the behavioural ecology of free-ranging polecat-mink hybrids in the upper reaches of the Lovat River indicate the hybrids will stray from aquatic habitats more readily than pure minks, and will tolerate both parent species entering their territories, though the hybrid's larger size (especially the male's) may deter intrusion. During the summer period, the diet of wild polecat-mink hybrids is more similar to that of the mink than to the polecat, as they feed predominantly on frogs. During the winter, their diets overlap more with those of polecats, and will eat a larger proportion of rodents than in the summer, though they still rely heavily on frogs and rarely scavenge ungulate carcasses as the polecat does. Predation Predators of the European mink include the European polecat, the American mink, the golden eagle, large owls and the red fox. Red fox numbers have increased greatly in areas where the wolf and Eurasian lynx have been extirpated,