Tony Wu / Marsh tit (Poecile palustris hensoni) feeding on an icicle formed from the sap of a painted maple tree (Acer pictum) in winter. Hokkaido, Japan.

Danny Green / Willow Tit (Poecile montanus) on a snowy branch. Utsjoki, Finland, February.

Andres M. Dominguez / Siberian tit (Poecile cinctus) perched, Ivalo, Finland. March

Markus Varesvuo / Willow tit (Poecile montanus) on snow covered branch, Kuusamo, Finland, January

Markus Varesvuo / Willow tit (Poecile montanus) on snow covered conifer branch, Kuusamo, Finland, February

Marie Read / Two Black-capped chickadees (Poecile atricapillus) in mid-air fight by a sunflower, New York, USA, February

Wild Wonders of Europe / Zacek / Willow tit (Poecile montanus) on small branch covered in moss, Korouma, Posio, Finland, February 2009

Wild Wonders of Europe / Zacek / Willow tit (Poecile montanus) on small branch, Kitkajoki, Finland, February 2009

Markus Varesvuo / Siberian Tit (Poecile cinctus) on conifer branch, Finland, January

Markus Varesvuo / Siberian Tit (Poecile cinctus) on lichen-covered branch, Kuusamo, Finland, March

David Kjaer / Willow tit {Poecile montanus} perching on snow-covered Pine. Finland.

Hans Christoph Kappel / Marsh Tit in flight, Germany

Donald M. Jones / Black-capped Chickadee (Poecile atricapillus) in winter, Montana

Donald M. Jones / Black-capped Chickadee (Poecile atricapillus) in winter, Troy, Montana

Alan Murphy/ BIA / Boreal Chickadee (Poecile hudsonicus) in pine, Alaska

Alan Murphy/ BIA / Boreal Chickadee (Poecile hudsonicus) during snowfall, Alaska

Alan Murphy / Carolina Chickadee (Poecile carolinensis) landing, Texas

Alan Murphy / Black-capped Chickadee (Poecile atricapillus), Texas

Alan Murphy / Black-capped Chickadee (Poecile atricapillus) during snowfall, Alaska

Alan Murphy / Boreal Chickadee (Poecile hudsonicus) feeding on pine cone seeds, Alaska

Alan Murphy / Boreal Chickadee (Poecile hudsonicus), Alaska

Alan Murphy / Boreal Chickadee (Poecile hudsonicus), Alaska

Steve Gettle / Black-capped Chickadee (Poecile atricapillus), Kellogg Bird Sanctuary, Michigan

Steve Gettle / Black-capped Chickadee (Poecile atricapillus), Kellogg Bird Sanctuary, Michigan

Steve Gettle / Black-capped Chickadee (Poecile atricapillus) on child's hand, Kensington Metropark, Michigan

Steve Gettle / Black-capped Chickadee (Poecile atricapillus), Huron Meadows Metropark, Michigan

Steve Gettle / Black-capped Chickadee (Poecile atricapillus) with berries, North America

Donald M. Jones / Chestnut-backed Chickadee (Poecile rufescens) on Ponderosa Pine (Pinus ponderosa) cone, western Montana

Donald M. Jones / Chestnut-backed Chickadee (Poecile rufescens) in winter on berries, western Montana

Donald M. Jones / Black-capped Chichadee (Poecile atricapillus) in spring, western Montana

Donald M. Jones / Black-capped Chichadee (Poecile atricapillus) perching on snow-covered berries, western Montana

Scott Leslie / Black-capped Chickadee (Poecile atricapillus) flying, Granville Beach, Nova Scotia, Canada

Tom Vezo / Black-capped Chickadee (Poecile atricapillus) in Bayberry bush, Long Island, New York

Fabrice Cahez / Marsh tit (Poecile palustris) with insect prey, France, May.

Jussi Murtosaari / Siberian tit (Poecile cinctus) on snowy tree trunk. Kuusamo, Northern Ostrobothnia, Finland. February.

Tim Laman / Black-capped Chickadee (Poecile atricapilla) perched on tree stump, calling, Massachusetts, USA. April.

Nick Upton / Marsh tit (Parus palustris) pair feeding on peanuts in a bird feeder near Forsythia flowers in the background, Wiltshire, UK, April.

John Cancalosi / Black-capped chickadee (Poecile atricapilla) perched in snow, New York, USA

Danny Green / Siberian tit (Poecile cinctus) perched on a banch, Northern Finland, April.

Erlend Haarberg / Siberian tit (Poecile cinctus), Jokkmokk, Sweden, October.

Erlend Haarberg / Willow tit (Poecile montanus), Muddus National Park, Laponia World Heritage Site, Swedish Lapland, Sweden, November,

Erlend Haarberg / Siberian tit (Poecile cinctus), Muddus National Park, Swedish Lapland, Laponia World Heritage Site, Sweden, November

Erlend Haarberg / Willow tit (Poecile montanus) silhouette with bokeh, Jokkmokk, Sweden, October.

Erlend Haarberg / Siberian tit (Poecile cinctus), Muddus National Park, Swedish Lapland, Laponia World Heritage Site, Sweden, November

Erlend Haarberg / Willow tit (Poecile montanus), Nordherad, Norway, October.

Markus Varesvuo / Siberian Tit (Parus cinctus) with bokeh, Kuusamo, Finland, February.

Markus Varesvuo / Siberian Tit (Parus cinctus) silhouetted at sunset, Kuusamo, Finland, February.

Markus Varesvuo / Siberian Tit (Parus cinctus) and Grey-heades woodpecker (Picus canus), Kuusamo, Finland, January.