Two adult Cuban crocodiles rest inside their enclosure at the Skansen zoo and aquarium in Stockholm, Wednesday April 15, 2015. Zoo director Jonas Wahlstrom says they were originally given as a gift from Fidel Castro to a Soviet cosmonaut four decades ago. The zoo is sending 10 of the pair's hatchlings to Cuba for introduction into the wild. The Cuban crocodile is considered critically endangered. (Photo by David Keyton/AP Photo)

A goldfinch feeds its newly hatched chicks in their nest in Chungju, North Chungcheong Province, South Korea, April 21, 2014. (Photo by Kim Jae-Sun/EPA)

A baby chimpanzee grimaces on its mother Swela at the Leipzig Zoo in Leipzig, central Germany, Thursday, April 23, 2015. The baby, whose gender is not yet known, was born on April 14, 2015. (Photo by Jens Meyer/AP Photo)

A baby chimpanzee relaxes on its mother Swela at the Leipzig Zoo in Leipzig, central Germany, Thursday, April 23, 2015. (Photo by Jens Meyer/AP Photo)

A chimpanzee eats its lunch using a spoon at Villa Lorena animal refugee center in Cali, in this file photo taken October 20, 2009. An animal rights group, in what it says is a worldwide first, has been granted a court hearing in which it will argue that two chimpanzees used in research at a New York state university cannot be held captive. (Photo by Jaime Saldarriaga/Reuters)

A orca lands on the beach to catch a baby sea lion along the shore of Punta Norte, near the Patagonian village of Puerto Piramides, April 21, 2015. The orcas hunt in this manner during this time of the year when baby sea lions are learning to swim. (Photo by Maxi Jonas/Reuters)

A chimpanzee drinks a sweet refreshment as it is sprayed with water on a hot day at Dusit zoo in Bangkok April 22, 2015. (Photo by Chaiwat Subprasom/Reuters)

A white Bengal tiger licks a block of ice during a hot day at Dusit zoo in Bangkok April 22, 2015. (Photo by Chaiwat Subprasom/Reuters)

A chimpanzee enjoys cold fruit juice during a hot day at Dusit Zoo in Bangkok, Thailand, 22 April 2015. The temperature in the Thai capital reached 39.8 degrees Celsius, nearly the hottest recorded since April 1979. (Photo by Diego Azubel/EPA)

Baby giraffe Connie makes her debut at the Montgomery Zoo along with her mother, Ashley, Wednesday, April 22, 2015, in Montgomery, Ala. (Photo by Julie Bennett/AL.com via AP Photo)

A baby bactrian camel enjoying the sunny day at ZSL Whipsnade Zoo on April 20, 2015 in Whipsnade, England. ZSL Whipsnade Zoo has welcomed a pair of bactrian camels into their family recently. The two Bactrian camels named Olaf and Orlagh were born within 48 hours of each other. (Photo by Tony Margiocchi/Barcroft Media)

Wild baby boars seen sleeping with their mother in the sun at the ZSL Whipsnade Zoo on April 21, 2015 in Bedfordshire, England. (Photo by Tony Margiocchi/Barcroft Media)

A moon bear lies inside its sanctuary in Vietnam Bear Rescue Centre, which is operated by international organization Animals Asia, in Tam Dao national park, about 70 kms from Hanoi, Vietnam, 11 April 2015. Animals Asia has rescued more than 500 bears in Vietnam and China, according to media reports. (Photo by Luong Thai Linh/EPA)

Snow leopard Bagheera in a wildlife rehabilitation center in Issyk-Kul, 325 km from Bishkek, Kyrgyzstan, 17 April 2015. The Nature and Biodiversity Conservation Union (NABU, Berlin) and the Republic of Kyrgyzstan in Central Asia have agreed in 2011 on a ten year program to protect the endangered snow leopard. (Photo by Igor Kovalenko/EPA)

An Orangutan plays at Zoo in Chengdu Sichuan province, southwest China 19th April 2015. (Photo by Yong Wang/Cpressphoto/ZUMAPress)

A Golden snub-nosed monkey plays at Zoo in Chengdu Sichuan province, southwest China 19th April 2015. (Photo by Yong Wang/Cpressphoto/ZUMAPress)

A golden monkey born 24 days ago plays in its mother's arms at the Jinan Zoo in Jinan, capital city of east China's Shandong Province, April 22, 2015. A newly-born white-cheeked gibbon and a golden monkey made their debut at the zoo on Wednesday and attracted many visitors. (Photo by Lu Chuanquan/Xinhua/SIPA Press)

New born white lion cubs are pictured with their mother at the zoological park of the eastern French city of Amneville on April 17, 2015. (Photo by Jean-Christophe Verhaegen/AFP Photo)

New born white lion cubs are pictured with their mother at the zoological park of the eastern French city of Amneville on April 17, 2015. (Photo by Jean-Christophe Verhaegen/AFP Photo)

The mother of a 39-day-old giraffe is pictured at the Chapultepec zoo in Mexico City, on April 20, 2015. (Photo by Ronaldo Schemidt/AFP Photo)

Ring-tailed lemurs look at a camera at Zoom Torino, a zoological park in Cumiana near Turin, on April 22, 2015. Zoom Torino is a new immersive zoological park, where animals can be seen without bars or cages, only natural barriers ensure the visit. (Photo by Marco Bertorello/AFP Photo)

African penguins are pictured at Zoom Torino, a zoological park in Cumiana near Turin, on April 22, 2015. (Photo by Marco Bertorello/AFP Photo)

In this Sunday, April 19, 2015 photo a Golden Retriever dog runs past a rape seed field in Hofen, southern Germany. (Photo by Bernd Weissbrod/AP Photo/DPA)

This September 7, 2005 photo released by National Oceanic and Atmospheric Administration shows a humpback whale diving among an aggregation of short-tailed shearwaters in Cape Cheerful, near Unalaska, Alaska. The federal government is proposing removing most of the world's humpback whale population from the endangered species list. National Oceanic and Atmospheric Administration Fisheries announced on Monday, April 20, 2015 that they want to reclassify humpbacks into 14 distinct populations, and remove 10 of those from the list. (Photo by Brenda Rone/National Oceanic and Atmospheric Administration via AP Photo)

Two cows fight during the traditional “Combats de Reines” (“Battle of the Queens”), a cow fight in Yens, western Switzerland, Sunday, April 19, 2015. During the combat, the cows simply push forehead against forehead. They also use their horns in different ways. (Photo by Laurent Gillieron/Keystone via AP Photo)

A Pakistani family sit with their pet cubs in Multan, Pakistan, Sunday, April 19, 2015. An African lioness has given birth to five healthy cubs at a private zoo. Lions normally have litters of two or three cubs. (Photo by Asim Tanveer/AP Photo)

Two month old white tiger cubs play on the ground at the Tobu Zoo in Miyashiro, in Saitama prefecture, north of Tokyo on April 19, 2015. Four male white tigers, born from their mother Cara at the zoo on January 25, will be debut in public on April 22. Only 250 white tigers live in the world. (Photo by Yoshikazu Tsuno/AFP Photo)

Billy, owned by Natasha Jodoin, of Altoona, Iowa, looks on during judging at the 36th annual Drake Relays Beautiful Bulldog Contest, Sunday, April 19, 2015, in Des Moines, Iowa. The pageant kicks off the Drake Relays festivities at Drake University where a bulldog is the mascot. (Photo by Charlie Neibergall/AP Photo)

In this photograph taken on April 14, 2015, a member of Indonesia's Nature Conservation Agency (BKSDA) seizes an endangered slow loris from a pet owner in Banda Aceh in Aceh province as part of campaign to stop the illegal trade of wildlife. Slow lorises are listed as critically endangered primates by the International Union for Conservation of Nature (IUCN) due to forest habitat loss in Indonesia and high demand in the illegal trade of wildlife. (Photo by Chaideer Mahyuddin/AFP Photo)

A woman looks at British Shorthair cat during a cat exhibition in Bishkek on April 19, 2015. Cat lovers from Kyrgyzstan, Kazakhstan and Uzbekistan took part in the exhibition. (Photo by Vyacheslav Oseledko/AFP Photo)

A ring-tailed lemur is pictured at Zoom Torino, a zoological park in Cumiana near Turin, on April 22, 2015. Zoom Torino is a new immersive zoological park, where animals can be seen without bars or cages, only natural barriers ensure the visit. (Photo by Marco Bertorello/AFP Photo)

A monkey looks on as it eats a chapati (flat bread) from a garbage bin in New Delhi on April 24, 2015. (Photo by Chandan Khanna/AFP Photo)

A hippopotamus enjoys a chunk of icy frozen fruit during a hot day at Dusit Zoo in Bangkok, Thailand, 22 April 2015. The temperature in the Thai capital reached 39.8 degrees Celsius, nearly the hottest recorded since April 1979. (Photo by Diego Azubel/EPA)

A hooded vulture is pictured at Zoom Torino, a zoological park in Cumiana near Turin, on April 22, 2015. Zoom Torino is a new immersive zoological park, where animals can be seen without bars or cages, only natural barriers ensure the visit. (Photo by Marco Bertorello/AFP Photo)

Mali the elephant enjoys a shower inside the Manila Zoo in Manila, the Philippines, April 23, 2015. Mali, the lone Asian elephant inside the Manila Zoo, has eight showers a day to beat the heat of summer. (Photo by Rouelle Umali/Xinhua/ZUMA Press)

One of the two Spanish Lynxes from Iberlince programme that was released during a ceremony in Mazarambroz, Toledo, Spain, 24 April 2015. Spain's Queen Sofia attended the event. (Photo by Ismael Herrero/EPA)

A female hippo opens her mouth to catch food at a zoo in Hanover, Germany, 24 April 2015. Hippos are mainly fed with plants. (Photo by Susann Prautsch/EPA)