The week in wildlife - in pictures

Ice-coated tree branches in Pennsylvania's Rothrock state forest. February marked the start of the UN international year of forests, to raise awareness of management, conservation and sustainable development of all types of forests Photograph: Jim Lo Scalzo/EPA

Hundreds of monarch butterflies line a tree in the Pedro Herrada butterfly sanctuary, on a mountain in the Mexican state of Michoacan. Every year thousands of these black and tan coloured butterflies fly up to 3,000 miles south from their home in the Rocky Mountains to spend the North American winter in the warmer climates of Mexico and southern California. But illegal deforestation and habitat destruction in the highland fir forests of Mexico that are essential to the monarchs' survival has led to a drop in numbers Photograph: Stringer/Reuters

A bird hangs on a tree in Karachi, Pakistan. Many cities in Pakistan are experiencing unusual cold weather conditions Photograph: Rehan Khan/EPA

A close view of a the 'eyelash viper' (Bothriechis schlegelii) in San Jose, Costa Rica. Scientists at the Instituto Clodomiro Picado have been studying snake's poison in order to create better antidotes for it Photograph: Jeffrey Arguedas/EPA

Moorhen in Bodsar wetland in Pampore, in Indian-administered Kashmir. Wetlands in the valley are under sever threat from encroaching human settlements and agricultural land Photograph: Yawar Nazir/Getty Images

A snow-covered pine tree on a cliff in the Yellow Mountain (Huang Shan Mountain), Anhui province, east China. This week saw the start of the new Chinese year of the rabbit Photograph: KeystoneUSA-ZUMA/Rex Features

A bison forages for food underneath the snow in Yellowstone national park, Wyoming. An estimated 368 bison have been captured over the last week while attempting to migrate to lower elevations in Montana in search of food. Yellowstone workers and state livestock agents are trying to halt the animals' exodus from the snow-packed park under a controversial programme meant to guard against the spread of the disease brucellosis to livestock. Those animals that test positive for exposure to brucellosis are slated to be shipped to slaughter Photograph: Anonymous/AP

Deer at Skånes Djurpark, near Höör, in southern Sweden Photograph: Yves Herman/REUTERS

One of the four elephants 'held hostage' in Casablanca, Morocco, following European Union travel restrictions that prevent wild animals coming from Africa from entering the EU. But having spent more than six months in Morocco 'under European rules they have technically acquired the nationality of the country where they are,' the EU said last month. Morocco, however, has no regulations on animal health compatible with EU rules and also suffers from foot and mouth disease. The elephants left France on tour in 2005 Photograph: Abdelhak Senna/AFP/Getty Images

Snow monkeys bathe in hot springs at Jigokudani monkey park, Nagano, Japan. These monkeys live in the icy Japanese highlands, farther north than any other species of monkey in the world. With their double layer of thick fur, that resembles a furry hooded top on the younger members, they are able to withstand temperatures as low as -15C. According to an official at the wildlife park, the bathing ritual of the monkeys did not begin until 1964, when a young monkey jumped into the hot pool chasing chestnuts, liked the feel, and stayed to bathe. Many other youngsters followed and were soon followed by the adults. With the freezing winter, the naturally heated bathes were soon adopted as part of monkey life Photograph: Sinopix / Rex Features/Sinopix / Rex Features

The common water flea, Daphnia pulex, has more genes than any other animal known - including humans - scientists have discovered Photograph: Dr. Paul D.N. Hebert, University/PA

A wood turtle (Glyptemys insculpta) endemic to North America. Turtle conservation groups together with Partners in Amphibian and Reptile Conservation (Parc), have designated 2011 as the Year of the Turtle. They say turtles are disappearing from the planet faster than any other group of animal and nearly 50% of turtle species are identified as threatened with extinction Photograph: Steven Kirchbaum/Pacific Northwest Research Station/USDA

A white rhinoceros in the Pilanesberg national park, South Africa. The chief executive officer of South African National Parks, David Mabunda, said this week South Africa had lost 21 rhinoceros to poaching during January. The country lost 333 rhinos to poaching in 2010, the highest annual loss to date Photograph: JON HRUSA/EPA

A lbaby Siamang gibbon (Symphalangus syndactylus) and his mother at Noah's Ark zoo farm, near Wraxall, Bristol. Siamang gibbons are tree-dwelling primates native to the rainforests of Malaysia, Thailand and Sumatra. The palm oil trade, habitat destruction and the illegal pet trade have caused huge losses to wild populations and they are classified as 'threatened' on the IUCN 'red list' of endangered species Photograph: Ben Birchall/PA