Dave Watts / Eastern grey kangaroo (Macropus giganteus) with joey in pouch, Australian Capital Territory, Australia, September

DOC WHITE / Blue whale underwater close-up of head and mouth feeding with pouch inflated, Mexico

Mark Carwardine / Aerial view of Fin whale (Balaenoptera physalus) lunge-feeding, with throat pouch distended, southern Sea of Cortez (Gulf of California), Baja California, Mexico.

Mark Carwardine / Aerial view of Fin whale (Balaenoptera physalus) lunge-feeding, with mouth open and throat pouch distended, southern Sea of Cortez (Gulf of California), Baja California, Mexico.

Kerstin Hinze / Black-bellied hamster (Cricetus cricetus) feeding on yew fruits (Taxus baccata), Vienna, Austria, October.

Juergen & Christine Sohns / Swamp Wallaby (Wallabia bicolor) mother and joey, Mount Lofty, South Australia, Australia

Juergen & Christine Sohns / Eastern Grey Kangaroo (Macropus giganteus) mother with joey jumping, Maloney Beach, New South Wales, Australia

Dave Watts / Female Western grey kangaroo (Macropus fuliginosus) rolling with a large joey in her pouch, Kangaroo Island, South Australia.

Dave Watts / Female Tamar wallaby (Macropus eugenii) grazing with a joey in her pouch, Kangaroo Island, South Australia.

Ingo Arndt / Eastern grey kangaroo joey looking out of pouch, Wilsons Promontory NP Australia

Ingo Arndt / Eastern grey kangaroo female with joey peering out of pouch {Macropus giganteus}. Wilson Promontory NP Australia

Sylvain Cordier / Emperor penguin (Aptenodytes forsteri), chick in brood pouch of parent, Snow Hill Island, Antarctic Peninsula