Male Magnificent Frigatebird (Fregata magnificens) with inflated gular sac, North Seymour Island, Galapagos National Park, Ecuador, South America

Fresh avalanche debris on Carn nan Sac, 920m, on the hills above Glenshee ski centre in the Cairngorm National Park, Scotland, United Kingdom, Europe

Portrait of male Great Frigatebird (Fregata minor) on Genovesa Island, Galapagos National Park, Ecuador, South America

Male Magnificent Frigatebird (Fregata magnificens) with inflated gular sac, North Seymour Island, Galapagos National Park, Ecuador, South America

Portrait of male Great Frigatebird (Fregata minor) on Genovesa Island, Galapagos National Park, Ecuador, South America

Small cul-de-sac overlooking Pilies Street, Vilnius, Lithuania, Europe

Male Magnificent Frigatebird (Fregata magnificens) with inflated gular sac, North Seymour Island, Galapagos National Park, Ecuador, South America

Male Magnificent Frigatebird (Fregata magnificens) with inflated gular sac, North Seymour Island, Galapagos National Park, Ecuador, South America

View over palm trees, Cul de Sac Du Marin, Martinique, French Overseas Department, Windward Islands, West Indies, Caribbean, Central America

View over palm trees, Cul de Sac Du Marin, Martinique, French Overseas Department, Windward Islands, West Indies, Caribbean, Central America

Cul de Sac Du Marin, Martinique, French Overseas Department, Windward Islands, West Indies, Caribbean, Central America

Maman a 21st century bronze sculpture of a spider, 9.25m high with a sac of 26 eggs, by Louis Bourgeois, in front of the Cathedral and Basilica of Notre Dame built between 1839 and 1885, Ottawa, Ontario, Canada, North America

Man wearing the traditional Berritta Sardinian hat and carring the traditional double Sardinian sac, St. Antioco celebrations, Sant'Antioco,Sardinia, Italy, Europe

White island, Grand Cul de Sac Marin, Basse Terre, Guadeloupe, Caribbean, Central America

Aerial view, White island, Grand Cul de Sac Marin, Basse Terre, Guadeloupe, Caribbean, Central America

White Island, Grand Cul de Sac Marin, Guadeloupe, Caribbean, Central America

Juvenile Northern Bottlenose Whale (Hyperoodon ampullatus) lying on the floor of the post mortem room before examination, close up shot of jaws and melon, SAC, Inverness, Scotland.

Egg sac of Dog Stinkhorn (Mutinus caninus), UK

Anatomy of the cow digestive apparatus. From left to right: mouth and esophagus, the reticulum (brown excrescence on the left), the rumen or composed paunch, from the top to the bottom by the dorsal sac, the cranial sac and the ventral sac. The grey excrescence beneath is the abomasum or velles.

Farmland Green Tree Frog (Rhacophorus arvalis), inflated vocal sac, courtship display, species endemic to Taiwan, Asia

Farmland Green Tree Frog (Rhacophorus arvalis), inflated vocal sac, courtship display, species endemic to Taiwan

Farmland Green Tree Frog (Rhacophorus arvalis), inflated vocal sac, courtship display, species endemic to Taiwan, Asia

Velan Hut, Cabane du Velan, of the Swiss Alpine Club, SAC, at the foot of the Grand Combin Mountain, Valais Alps, Valais, Switzerland, Europe

Phantasmal poison frog (Epipedobates tricolor) in captivity

Tree frog (Rhacophorus arvalis), inflated vocal sac, courtship, endangered species, Taiwan, Asia

Calling Waxy monkey tree frog (Phyllomedusa sauvagei) with vocal sac, Gran Chaco, Paraguay

Eastern giant grey kangaroo (Macropus giganteus), adult, female, mother with young, in pouch, on grassland, social behaviour, Maloney Beach, New South Wales, Australia, Oceania

European robin (Erithacus rubecula) at a feeding bag, winter feeding, Schleswig-Holstein, Germany, Europe

Red-necked wallaby (Macropus rufogriseus), Bennett's kangaroo, albino, adult, female, juvenile, juvenile looking out of pouch, Cuddly Creek, South Australia, Australia, Oceania

Couch's Spadefoot (Scaphiopus couchii), adult at night, calling, vocal sac inflated, Laredo, Webb County, South Texas, USA, America

Fruit in reusable bags, Germany, Europe

Potato, Celtiane variety, in reusable bags, Germany, Europe

Red-necked wallaby (Macropus rufogriseus), Bennett's kangaroo, albino, juvenile, portrait, juvenile looking out of pouch, Cuddly Creek, South Australia, Australia, Oceania

Blue tit (Parus caeruleus) at a feeding bag, winter feeding, Schleswig-Holstein, Germany, Europe

Red-necked wallaby (Macropus rufogriseus), Bennett's kangaroo, albino, juvenile, portrait, juvenile looking out of pouch, Cuddly Creek, South Australia, Australia, Oceania

Eastern grey kangaroo (Macropus giganteus), adult, female, juvenile, looking into pouch, on grassland, Maloney Beach, New South Wales, Australia, Oceania

Lesser Prairie-Chicken (Tympanuchus pallidicinctus), male displaying in prairie, vocal sac inflated, Canadian, Panhandle, Texas, USA

Phantasmal poison frog (Epipedobates tricolor) in captivity

Gauderfest 2008 Festival, Zell am Ziller, Zillertal Valley, North Tyrol, Austria, Europe

Solar collectors for autonomous energy supply to a mountain hut, Velan Hut, Cabane du Velan, of the Swiss Alpine Club, SAC, Valais Alps, Valais, Switzerland, Europe

The futuristic Velan Hut, Cabane du Velan, of the Swiss Alpine Club, SAC, with its six solar panels in front of the summit of Grande Aiguille des Maisons Blanche, Valais, Switzerland, Europe

Eastern Bluebird (Sialia sialis), male in flight with fecal sac, Willacy County, Rio Grande Valley, Texas, USA

Group of hikers arriving at Velan Hut, Cabane du Velan, of the Swiss Alpine Club, SAC, Valais Alps, Valais, Switzerland, Europe

Contratto wine producer in Canelli, the big room called " sac room" devoted to a collection of ancient tools and machines for manufacturing wine, Asti, Piedmont, Italy

A fieldworker sharpens shovels the old fashioned way at the Big Eddy, an Archaeological site on the Sac River in southwestern, MO. Archaeologist Neal Lopinot from Missouri State University has been digging their since 1997 to gain a more complete understanding of the prehistoric record in North America. (Photo by David McLain, Aurora)

Great Frigatebird With Inflated Gular Sac