Sergey Gorshkov / Snow geese (Chen caerulescens caerulescens) two landing,Wrangel Island, Far Eastern Russia, June.

Sergey Gorshkov / Snow geese (Chen caerulescens caerulescens) group calling and landing, Wrangel Island, Far Eastern Russia, June.

Sergey Gorshkov / Snow goose (Chen caerulescens caerulescens) in flight, Wrangel Island, Far Eastern Russia, June.

Sergey Gorshkov / Arctic fox (Vulpes lagopus) stealing Snow goose (Chen caerulescens caerulescens) with Snow geese mobbing it, Wrangel Island, Far Eastern Russia, May.

Sergey Gorshkov / Snow goose (Chen caerulescens caerulescens) mobbing Arctic fox (Vulpes lagopus) trying to steal eggs, Wrangel Island, Far Eastern Russia, May.

Jussi Murtosaari / Siberian flying squirrel (Pteromys volans) baby feeding on leaves, central Finland, June.

Jussi Murtosaari / Siberian flying squirrel (Pteromys volans) adult female in a pine tree eating flowers, central Finland, May.

Jussi Murtosaari / Siberian flying squirrel (Pteromys volans) juvenile, central Finland, June.

Jussi Murtosaari / Siberian flying squirrel (Pteromys volans) adult female, central Finland, May.

Sue Flood / Crested auklets (Aethia cristatella) large flock cal in flight above Yankicha Island in the Kuril Island chain, Russian Far East, June.

Gerrit Vyn / Lesser Sandhill cranes (Grus canadensis) riding thermals in migration along the Alaska Range near Mt. McKinley. These birds are from the mid-continent population that nest across Northcentral Canada t...

Bryan and Cherry Alexander / Russian Mi-2 helicopter from the Kapitan Khlebnokov flying past glaciers in the Gerlache Strait. Antarctica, October 2006.

Bryan and Cherry Alexander / Russian Mi-2 helicopter flying over icebergs on ice reconnaisance in Erebus & Terror Gulf. Antarctica, October 2006.

Nature Production / Russian Flying Squirrel (Pteromys volans) resting on branch, Hokkaido, Japan, February

Nature Production / Russian Flying Squirrel (Pteromys volans) foraging in tree, Hokkaido, Japan, March

Neil Lucas / Helicopter landing on the deck of the Russian ice breaker ship, Kapitan Khlebnikov, Ross Sea, Antarctica, November 2008

Neil Lucas / People disembarking from a Russian ice breaker ship, Kapitan Khlebnikov, amongst sea ice on a Quark expedition, Helipcopter flying in background, Ross Sea, Antarctica, November 2008

Nature Production / Siberian / Russian Flying Squirrel {Pteromys volans} gliding from tree to tree in snow, Hokkaido, Japan

Nature Production / Siberian / Russian Flying Squirrel {Pteromys volans} eating snow off tree trunk, Hokkaido, Japan

Nature Production / Siberian / Russian Flying Squirrel {Pteromys volans}feeding on winter buds in tree, Hokkaido, Japan

Nature Production / Siberian / Russian Flying Squirrel {Pteromys volans}feeding on winter buds in tree, Hokkaido, Japan

Konrad Wothe / Russian Flying Squirrel (Pteromys volans), Ural mountains, Pechora-Ilych Reserve, Komi, Russia

Konrad Wothe / Russian Flying Squirrel (Pteromys volans), Ural Mountains, Pechora-Ilych Reserve, Komi, Russia

Jan Vermeer / Helicopter landing on the deck of the Russian icebreaker Kapitan Khlebnikov, Antarctica

Jan Vermeer / Helicopter landing on the deck of the Russian icebreaker Kapitan Khlebnikov, Antarctica

Tony Wu / Japanese dwarf flying squirrel (Pteromys volans orii) perched on a small branch, just after a major snowstorm. Hokkaido, Japan. February.

Tony Wu / Japanese dwarf flying squirrel (Pteromys volans orii) gliding through forest canopy during light snowfall. Hokkaido, Japan. February.

Tony Wu / Japanese dwarf flying squirrel (Pteromys volans orii) gliding through forest canopy during light snowfall. Hokkaido, Japan. February.

Tony Wu / Japanese dwarf flying squirrel (Pteromys volans orii) gliding towards its nest in snowy forest. Hokkaido, Japan.February. This image shows the squirrel on its final approach to the nest. The squirrel...

Tony Wu / Japanese dwarf flying squirrel (Pteromys volans orii) in the split second before landing on a tree after gliding in snowy forest. Hokkaido, Japan. February. The Sakhalin fir trees in the background a...

Tony Wu / Siberian flying squirrel (Pteromys volans orii) peeking out from its nest just after major snowstorm. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) gliding back to its nest after foraging at the top of 20m tall Japanese elm trees (Ulmus davidiana var. japonica), carrying branch with fresh elm buds b...

Tony Wu / Siberian flying squirrel (Pteromys volans orii) eating fresh needles of Sakhalin fir tree (Abies sachalinensis) during light snowfall. Hokkaido, Japan. February.

Tony Wu / Female Siberian flying squirrel (Pteromys volans orii) feasting on branch cut from nearby Sakhalin fir tree (Abies sachalinensis). Hokkaido, Japan. February.

Tony Wu / Portrait of Siberian flying squirrel (Pteromys volans orii) taken moments before launching from tree. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii)l gliding through forest. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) gliding through forest in early morning. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii), usually nocturnal, gliding through forest. Diurnal activity like this is not common, probably adaptation to presence of pair of Ural owls. Hokkaido, Ja...

Tony Wu / Siberian flying squirrel (Pteromys volans orii) often have favored locations for defecation. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) peeking out of entrance of its nest prior to emerging to forage, surveying its surrounding. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) consuming snow for moisture. Behavior taking place most often after foraging. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) sitting in favorite spot during overcast winter morning. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) scratching. Hokkaido, Japan. February.

Tony Wu / Close-up view of Siberian flying squirrel (Pteromys volans orii) finishing eating meal of male catkins from Erman's birch tree (Betula ermanii). Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) consuming male catkins from Erman's birch tree (Betula ermanii). Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) sitting in favorite perch used to sit, eat or stopover before gliding to forage. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) consuming male catkins from Erman's birch tree (Betula ermanii). Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) eating male catkin from Erman's birch tree (Betula ermanii) on snowy day. Hokkaido, Japan. February.

Tony Wu / Female Siberian flying squirrel (Pteromys volans orii) sitting at entrance to nest. Hokkaido, Japan. February.

Tony Wu / Male Siberian flying squirrel (Pteromys volans orii) sitting at entrance to nest. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) inside nest has brought few sticks of Japanese elm (Ulmus davidiana var. japonica) back at end of foraging to enjoy before going inside. Sensing opportu...

Tony Wu / Siberian flying squirrel (Pteromys volans orii) carrying sticks of Japanese elm (Ulmus davidiana var. japonica) back to nest; enjoying eating one before entering nest. Hokkaido, Japan. February.

Tony Wu / Two Siberian flying squirrel (Pteromys volans orii), just emerged from nest, taking moment prior to foraging. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) consuming snow for moisture after extended period of foraging. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) consuming fresh buds of small branch from Japanese elm tree (Ulmus davidiana var. japonica). Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) eating male catkins of Erman's birch tree (Betula ermanii). Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) plucking out and consuming male catkins of Erman's birch (Betula ermanii) from stashed food in unused bird's nest. Unusual behaviour. Hokkaido...

Tony Wu / Siberian flying squirrel (Pteromys volans orii), split-second prior to landing on tree trunk, stretching forward to brace for impact. Hokkaido, Japan. February.

Tony Wu / Female Siberian flying squirrel (Pteromys volans orii) consuming small branches of Erman's birch tree (Betula ermanii) that it has brought back to nest as takeaway meal. Hokkaido, Japan. February...

Tony Wu / Male Siberian flying squirrel (Pteromys volans orii) making appearance in late afternoon, just before heading up into treetops to forage. Hokkaido, Japan. February.

Tony Wu / Male Siberian flying squirrel (Pteromys volans orii) sitting in favorite spot on sunny day, looking down upon his surroundings. Hokkaido, Japan. February.

Tony Wu / Composite image showing landing sequence of Siberian flying squirrel (Pteromys volans orii), covering distance of about four meters in less than half a second. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) consuming meal of Japanese elm buds (Ulmus davidiana var. japonica) while perched more than 20m above the ground. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) pausing in favored spot after emerging from its nest, just prior to ascending to treetops to forage. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) leaning down to consume snow for moisture. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) looking down from tree at sunset. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) gliding through trees. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) gliding through canopy on a sunny day. Hokkaido, Japan. March.

Tony Wu / Pair of Siberian flying squirrel (Pteromys volans orii) emerging from nest at dusk. The female seated above is entering estrus. The male is checking her readiness for mating. Hokkaido, Japan. March.

Tony Wu / Male Siberian flying squirrel (Pteromys volans orii) attempting to enter nest with female inside during reproductive season but stopped mid-way then rejected. Hokkaido, Japan. March.

Tony Wu / Silhouetted Siberian flying squirrel (Pteromys volans orii) perched on small branch moments after emerging from nest after sunset to forage at night. Hokkaido, Japan. March.

Tony Wu / Male Siberian flying squirrel (Pteromys volans orii) pushed out of nest by female. Male dragging some soft nesting material along with him. Hokkaido, Japan. March.

Tony Wu / Frequent and repeated defecation by Siberian flying squirrel (Pteromys volans orii) in favored locations results in accumulated droppings. As winter snow melts, embedded droppings dissolve, dripping d...

Tony Wu / Siberian flying squirrel (Pteromys volans orii) resting in secure spot in late afternoon. Hokkaido, Japan. March.

Tony Wu / Male Siberian flying squirrel (Pteromys volans orii) looking into entrance of nest with female inside, in hope of mating opportunity. Hokkaido, Japan. March.

Tony Wu / Male Siberian flying squirrel (Pteromys volans orii) inside nest heat-butting potential rival male that was looking into nest with objective of gaining access to female inside. Hokkaido, Japan. March.

Tony Wu / Pair of Siberian flying squirrel (Pteromys volans orii) mating. Copulation occurs multiple times over extended period of time. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) peeking out from its nest, just before emerging for evening of foraging in treetops. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) peeking out from its nests prior to exiting. Hokkaido, Japan. March.

Tony Wu / Composite image showing Siberian flying squirrel (Pteromys volans orii) defecating for duration of about twenty seconds after emerging from nest to forage. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) carrying small branch of Japanese elm (Ulmus davidiana var. japonica) back to its nest. This branch is take-away meal for enjoyment back home. Hokkaido,...

Tony Wu / Split-second prior to Siberian flying squirrel (Pteromys volans orii) landing on tree, adjusting its attitude in mid-flight toward relatively vertical position to reduce speed and folding its wings in...

Tony Wu / Siberian flying squirrel (Pteromys volans orii) gliding through forest early in morning. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) perched at top of twenty meter Japanese elm tree (Ulmus davidiana var. japonica) early in morning. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) scratching his face on branch while grooming himself early in morning. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) enjoying early morning scratch. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) enjoying good scratch in early winter morning. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) making its final approach back to nest, a narrow crack in Erman's birch (Betula ermanii) tree, Hokkaido, Japan. March.

Tony Wu / Four Siberian flying squirrel (Pteromys volans orii) emerging from single nest at same time, just before foraging. Simultaneous appearances like this are relatively uncommon. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) gliding through forest early in morning. Hokkaido, Japan. March.

Tony Wu / Head-on view of Siberian flying squirrel (Pteromys volans orii) gliding through forest. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) gliding through forest on early winter morning. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) flying directly over photographer. Hokkaido, Japan. February.

Tony Wu / Male Siberian flying squirrel (Pteromys volans orii) defecating while perched in safe place on cloudy and overcast day. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) gliding through forest. Hokkaido, Japan. February.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) cleaning its whiskers while grooming itself. Hokkaido, Japan. February.