Doug Gimesy / Greater crested tern (Thalasseus bergii) flies over breaking waves on a stormy day, with a rainbow in the background, Apollo Bay, Victoria, Australia.

Doug Gimesy / Greater crested tern (Thalasseus bergii) flying over a breaking waves on a stormy day, with a rainbow in the background, Apollo Bay, Victoria, Australia. Cropped.

Doug Gimesy / Crested terns (Thalasseus bergii) flying over a coastal rock shelf in the early morning with waves breaking in the background. Long exposure. Skenes Creek, Victoria, Australia. July 2016

Terry Whittaker / Greater crested tern (Thalasseus bergii) flock perched on posts in Pangalanes Canal, Palmarium Reserve. Lake Ampitabe, Madagascar.

Doug Gimesy / Crested tern (Thalasseus bergii) in flight. Ricketts Point, Beaumaris, Victoria, Australia

Doug Gimesy / Crested tern (Thalasseus bergii) standing on intertidal rocks, water in the background. Port Philip Bay shoreline, Sandringham, Victoria, Australia.

Doug Gimesy / Crested tern (Thalasseus bergii) in flight, holding an Australian sardine (Sardinops sagax) in its mouth. Ricketts Point, Beaumaris, Victoria, Australia. May.

Tony Wu / Greater crested tern (Thalasseus bergii) feeding on Sardine, Tonga.

Steven David Miller / Australian sea lion (Neophoca cinerea) male basking on beach with Great crested terns (Thalasseus bergii) in foreground. Seal Bay Conservation Park, Kangaroo Island, South Australia.

Ann & Steve Toon / Swift terns (Thalasseus bergii) Luderitz, Namibia.

Jiri Lochman / Crested tern (Sterna bergii) juvenile entangled in a fishing line, likely cut off by a fisherman after the bird swallowed the hooked bait. Australia.

Jiri Lochman / Crested tern (Sterna bergii) juvenile, entangled in a fishing line, likely cut off by a fisherman after the bird swallowed the hooked bait Australia.

Franco Banfi / Greater crested terns (Thalasseus bergii) on a strip of sand with the MV Atlantis Azores liveaboard boat in distance, Tubbataha Reef Natural Park, UNESCO World Heritage Site, Sulu Sea, Cagayancillo...

Franco Banfi / Greater crested terns (Thalasseus bergii) on a strip of sand with the MV Atlantis Azores liveaboard boat in distance, Tubbataha Reef Natural Park, UNESCO World Heritage Site, Sulu Sea, Cagayancillo,...

Charlie Summers / Greater crested tern (Thalasseus bergii) flying against a backdrop of the South Atlantic Ocean. Lambert's Bay, South Africa.

Oriol Alamany / Greater crested terns (Thalasseus bergii) along shore of Seventy Five Mile beach, Fraser Island UNESCO World Heritage Site. Queensland, Australia, November.

Hanne & Jens Eriksen / Greater crested tern (Thalasseus bergii) walking in shallow water, Oman, May

Hanne & Jens Eriksen / Greater crested tern (Thalasseus bergii) in flight and with fish, Oman, August

Robin Chittenden / Greater Crested tern (Thalasseus bergii) Goa India

Juergen Freund / Flock of Crested terns (Sterna bergii) on the sand bar of Bird Islet, Tubbataha Reefs, Sulu Sea, Philippines.

Juergen Freund / Flock of Crested terns (Sterna bergii) on the sand bar of Bird Islet, Tubbataha Reefs, Sulu Sea, Philippines.

Brent Stephenson / Great crested tern (Thalasseus bergii) in non-breeding plumage, perched on a post. Mataiva, Tuamotus, French Polynesia. November.

Doug Perrine / Greater crested / Swift tern (Thalasseus / Sterna bergii) large flock in flight, Turu Cay, Torres Straits, Queensland, Australia. October.

Doug Perrine / Greater crested / Swift tern (Thalasseus / Sterna bergii) large breeding colony on shoreline, rising spring tide floods across the cay, threatening the breeding colonies, Turu Cay, Torres Straits, Que...

Doug Perrine / Greater crested / Swift tern (Thalasseus / Sterna bergii) large breeding colony on shoreline, rising spring tide floods across the cay, threatening the breeding colonies, Turu Cay, Torres Straits, Que...

Doug Perrine / Greater crested / Swift tern (Thalasseus / Sterna bergii) adult with creche of chicks on shoreline, Turu Cay, Torres Straits, Queensland, Australia. October.

Doug Perrine / Greater crested / Swift tern (Thalasseus / Sterna bergii) chicks starting to swim across a pond formed as rising tide floods the interior of Turu Cay, Torres Straits, Queensland, Australia. October....

Brent Stephenson / Portrait of a Great Crested Tern (Thalasseus bergii) in non-breeding plumage perched on a channel marker. Mangareva, Gambier Islands, French Polynesia, September.

Brent Stephenson / Great Crested Tern (Thalasseus bergii) in breeding plumage, standing on a fishing bouy. Bora Bora, French Polynesia, November.

Brent Stephenson / Great Crested Tern (Thalasseus bergii) in non-breeding plumage. Papeete, Tahiti, October.

Steven David Miller / Crested tern (Sterna bergii) Point Quobba, Carnarvon region, Western Australia

Steven David Miller / Crested tern (Sterna bergii) Point Quobba, Carnarvon region, Western Australia

Steven David Miller / Flock of Crested tern (Sterna bergii) Point Quobba, Carnarvon region, Western Australia

Hanne & Jens Eriksen / Crested / Swift tern (Thalasseus bergii) pair in courtship display, Masirah, Oman.

Pete Oxford / Crested Tern (Sterna / Thalasseus bergii) Moreton Bay, Queensland, Australia

Hanne & Jens Eriksen / Swift / Crested Tern {Thalasseus bergii} Nafoon, Oman.

Richard Du Toit / Crested tern {Thalasseus / Sterna bergii} flying landing with fish, Dyer Is, South Africa

Mark Yates / Crested & Lesser crested terns nesting {Thalasseus bergii & bengalensis} Persian Gulf, Iran

Dave Watts / Crested tern {Thalasseus bergii} on nest with chick, Australia

Hanne & Jens Eriksen / Flock of Crested terns {Thalasseus bergii} taking flight, Khor Dirif, Oman, June

Hanne & Jens Eriksen / Crested tern portrait {Thalasseus bergii} Salalah, Oman, June

Staffan Widstrand / Crested tern colony {Thalasseus bergii} Lady Eliot Island, Australia

Rob Drummond/ BIA / Greater Crested Tern (Thalasseus bergii) juvenile flying, Victoria, Australia

Greg Oakley / Greater Crested Tern (Thalasseus bergii) calling, Victoria, Australia

Ralph Martin / Greater Crested Tern (Thalasseus bergii), Oman

Ralph Martin / Greater Crested Tern (Thalasseus bergii), Oman

Jan Wegener / Greater Crested Tern (Thalasseus bergii) with a caught fish, Victoria, Australia