Patricio Robles Gil / Monarch (Danaus plexippus) butterfly, group backlit on tree in wintering grounds, Monarch butterfly Biosphere Reserve, Michoacan, Mexico

Pete Cairns / Barnacle Geese (Branta leucopsis) feeding on improved pasture on crofting land (used as wintering grounds), Islay, Scotland, UK.

Pete Cairns / Barnacle Geese (Branta leucopsis) feeding on improved pasture on crofting land (used as wintering grounds), Islay, Scotland, UK.

Yva Momatiuk & John Eastcott / Snow Goose (Chen caerulescens) flock flying in formation over wintering grounds, winter, Mattamuskeet National Wildlife Refuge, North Carolina

Thomas Mangelsen / Monarch (Danaus plexippus) butterfly mass at wintering grounds, El Rosario Monarch Butterfly Sanctuary, Mexico

Yva Momatiuk & John Eastcott / Sandhill Crane (Grus canadensis) in pond prior to departure for nesting grounds up north, spring, Bosque del Apache National Wildlife Refuge, New Mexico

Yva Momatiuk & John Eastcott / Snow Goose (Chen caerulescens) flock swimming in lake at sunset with Sandhill Cranes (Grus canadensis) flock flying across full moon, spring, wintering grounds, Bosque del Apache National Wildlife Ref...

Yva Momatiuk & John Eastcott / Snow Goose (Chen caerulescens) flock on lake at sunrise, wintering grounds, early spring, Bosque del Apache National Wildlife Refuge, New Mexico

Yva Momatiuk & John Eastcott / Snow Goose (Chen caerulescens) flocks fly from lake at sunrise, wintering grounds, early spring, Bosque del Apache National Wildlife Refuge, New Mexico

Yva Momatiuk & John Eastcott / Whooping Crane (Grus americana) male stretching wing at wintering grounds, Gulf of Mexico, Aransas National Wildlife Refuge, Texas

Yva Momatiuk & John Eastcott / Whooping Crane (Grus americana) at wintering grounds, Gulf of Mexico, Aransas National Wildlife Refuge, Texas

Yva Momatiuk & John Eastcott / Whooping Crane (Grus americana) at wintering grounds, Gulf of Mexico, Aransas National Wildlife Refuge, Texas