Britain's Queen Elizabeth visits the new Asiatic lion enclosure at London Zoo, March 17, 2016. REUTERS/Arthur Edwards/Pool TPX IMAGES OF THE DAY

Britain's Queen Elizabeth visits the new Asiatic lion enclosure at London Zoo, March 17, 2016. REUTERS/Arthur Edwards/Pool

Britain's Queen Elizabeth visits the new Asiatic lion enclosure at London Zoo, March 17, 2016. REUTERS/Arthur Edwards/Pool

Britain's Queen Elizabeth visits the new Asiatic lion enclosure at London Zoo, March 17, 2016. REUTERS/Arthur Edwards/Pool

Britain's Queen Elizabeth visits the new Asiatic lion enclosure at London Zoo, March 17, 2016. REUTERS/Arthur Edwards/Pool

Britain's Queen Elizabeth visits the new Asiatic lion enclosure at London Zoo, March 17, 2016. REUTERS/Arthur Edwards/Pool

Britain's Queen Elizabeth visits the new Asiatic lion enclosure at London Zoo, March 17, 2016. REUTERS/Arthur Edwards/Pool

Britain's Queen Elizabeth visits the new Asiatic lion enclosure at London Zoo, March 17, 2016. REUTERS/Arthur Edwards/Pool

Britain's Queen Elizabeth visits the new Asiatic lion enclosure at London Zoo, March 17, 2016. REUTERS/Arthur Edwards/Pool

Two fourteen-week old Barbary lions (Panthera leo leo), a male named Ramzes and a female named Zara, are seen after a naming ceremony at the Bojnice Zoo April 4, 2015. REUTERS/Radovan Stoklasa

One of two fourteen-week old Barbary lions (Panthera leo leo), a male named Ramzes and a female named Zara, during a naming ceremony at the Bojnice Zoo April 4, 2015. REUTERS/Radovan Stoklasa

Two fourteen-week old Barbary lions (Panthera leo leo), a male named Ramzes and a female named Zara with their mother named Gina, are seen after a naming ceremony at the Bojnice Zoo April 4, 2015. REUTERS/Radovan Stoklasa

Ono of two fourteen-week old Barbary lions (Panthera leo leo), a male named Ramzes and a female named Zara, plays with a ball after a naming ceremony at the Bojnice Zoo April 4, 2015. REUTERS/Radovan Stoklasa

Ono of two fourteen-week old Barbary lions (Panthera leo leo), a male named Ramzes and a female named Zara, tastes a meat cake after a naming ceremony at the Bojnice Zoo April 4, 2015. REUTERS/Radovan Stoklasa

Two fourteen-week old Barbary lions (Panthera leo leo), a male named Ramzes and a female named Zara, play with ball after a naming ceremony at the Bojnice Zoo April 4, 2015. REUTERS/Radovan Stoklasa

Two fourteen-week old Barbary lions (Panthera leo leo), a male named Ramzes and a female named Zara, are seen after a naming ceremony at the Bojnice Zoo April 4, 2015. REUTERS/Radovan Stoklasa

Ono of two fourteen-week old Barbary lions (Panthera leo leo), a male named Ramzes and a female named Zara, plays with a ball after a naming ceremony at the Bojnice Zoo April 4, 2015. REUTERS/Radovan Stoklasa

Two fourteen-week old lion cubs, a male named Ramzes and a female named Zara, are seen during a Christening ceremony at the Bojnice Zoo April 4, 2015. The two cubs are Barbary lions (Panthera leo leo), local media reported. REUTERS/Radovan Stoklasa

Two fourteen-week old lion cubs, a male named Ramzes and a female named Zara, are seen with godparents TV host Dana Strculova (3rd L) and Jan Meciar (3rd R) during a Christening ceremony at the Bojnice Zoo April 4, 2015. The two cubs are Barbary lions (Panthera leo leo), local media reported. REUTERS/Radovan Stoklasa

Two fourteen-week old lion cubs, a male named Ramzes and a female named Zara, are seen with godparents TV host Dana Strculova (L) and Jan Meciar (R) during a Christening ceremony at the Bojnice Zoo April 4, 2015. The two cubs are Barbary lions (Panthera leo leo), local media reported. REUTERS/Radovan Stoklasa

Two fourteen-week old lion cubs, a male named Ramzes and a female named Zara, are seen with their mother, Gina, after a Christening ceremony at the Bojnice Zoo April 4, 2015. The two cubs are Barbary (Panthera leo leo) lions, local media reported. REUTERS/Radovan Stoklasa

A male South African white lion sits in an enclosure after his arrival at Karachi Zoological Garden July 17, 2012. A pair of Bengal tiger and white lion was unveiled to the public during a ceremony on Tuesday, Pakistan's Express News reported. REUTERS/Akhtar Soomro (PAKISTAN - Tags: ANIMALS)

African white lions female Agata (C) and male Almaz (R), both aged one year and a half, and Khan, a 2-year-old male Bengali white tiger look out from their open-air cage at the Royev Ruchey zoo in Russia's Siberian city of Krasnoyarsk, January 11, 2012. REUTERS/Ilya Naymushin (RUSSIA - Tags: ANIMALS SOCIETY)

African white lions female Agata (L) and male Almaz , both aged one year and a half, walk in their open-air cage at the Royev Ruchey zoo in Russia's Siberian city of Krasnoyarsk, January 11, 2012. The lions were bought in South Africa and delivered to Siberia about a year ago, according to the zoo representatives. REUTERS/Ilya Naymushin (RUSSIA - Tags: ANIMALS SOCIETY)

Iblis, an Asiatic lion plays with a recycled Christmas tree in his enclosure at Chester Zoo, northern England December 29, 2010. The Zoo has been using unsold Christmas trees given to them by a local supplier as part of their animal enrichment programme. REUTERS/Phil Noble (BRITAIN - Tags: ANIMALS ENVIRONMENT)

One of two ten-week-old Asiatic Lion cubs explores its outside enclosure for the first time at London Zoo August 13, 2009. The two cubs are the first to be born at the zoo for over ten years to their mother Abi who was the last cub to be born at the zoo in 1999. REUTERS/Stephen Hird (BRITAIN ANIMALS ENVIRONMENT SOCIETY)

A lion (Panthera Leo) rests at the National Zoo in Managua October 2, 2007. REUTERS/Oswaldo Rivas (NICARAGUA)

A Barbary Lion drinks water inside its cage at Madrid's zoo August 8, 2007. REUTERS/Sergio Perez (SPAIN)

A Barbary Lion yawns inside its enclosure at Madrid's zoo August 8, 2007. REUTERS/Sergio Perez (SPAIN)

A lion, a Leon Africano (Panthera Leo), eats a meal in a zoological park in Managua July 5, 2007. REUTERS/Oswaldo Rivas (NICARAGUA)

Two African lions (Panthera Leo) roar while mating in Kenya's Maasai Mara game reserve March 23, 2006. The lions' mating take place at most times of the year when the dominant male and the female in heat leave the pride and mate every 15-30 minutes for several days in a row. Picture taken March 23, 2006.

Two African lions (Panthera Leo) roar while mating in Kenya's Maasai Mara game reserve March 23, 2006. The lions' mating take place at most times of the year when the dominant male and the female in heat leave the pride and mate every 15-30 minutes for several days in a row. Picture taken March 23, 2006. REUTERS/Radu Sigheti

Two African lions (Panthera Leo) roar while mating in Kenya's Maasai Mara game reserve March 23, 2006. The lions' mating take place at most times of the year when the dominant male and the female in heat leave the pride and mate every 15-30 minutes for several days in a row. Picture taken March 23, 2006. REUTERS/Radu Sigheti

An African lion resting August 21, 2005. REUTERS/Adeel Halim AH/AD/CN

African lions resting August 21, 2005. REUTERS/Adeel Halim PP05080208 AH/AD/CN

African lions resting. August 21, 2005. REUTERS/Adeel Halim AH/AD/CN

- FILE PHOTO TAKEN JUL04 - A lion cub is seen walking in the grass at Nairobi animal orphanage in Kenya in this July 2004 file photo. Even the King of the Jungle needs a hand staying alive on his own turf. That is what the government of Kenya thinks as far as the majestic African lion, a symbol of the continent and one of its most feared predators, is concerned. The Kenya Wildlife Service is pushing the Convention on International Trade in Endangered Species (CITES), to give the African lion, panthera leo, its most protected status. Current conservative estimates place the African lion population at 23,000, Kenya wrote in its proposal.

- FILE PHOTO TAKEN MAR04 - Two lions are seen resting in the shadow of a tree in Kenya's national park Masai Mara in this March 2004 file photo. Even the King of the Jungle needs a hand staying alive on his own turf. That is what the government of Kenya thinks as far as the majestic African lion, a symbol of the continent and one of its most feared predators, is concerned. The Kenya Wildlife Service is pushing the Convention on International Trade in Endangered Species (CITES), to give the African lion, panthera leo, its most protected status. Current conservative estimates place the African lion population at 23,000, Kenya wrote in its proposal. Picture taken on March 2004.

- FILE PHOTO TAKEN MAR04 - A lion is seen passing in front of a zebra in Kenya's national park Masai Mara in this March 2004 file photo. Even the King of the Jungle needs a hand staying alive on his own turf. That is what the government of Kenya thinks as far as the majestic African lion, a symbol of the continent and one of its most feared predators, is concerned. The Kenya Wildlife Service is pushing the Convention on International Trade in Endangered Species (CITES), to give the African lion, panthera leo, its most protected status. Current conservative estimates place the African lion population at 23,000, Kenya wrote in its proposal. Picture taken on March 2004.

- FILE PHOTO TAKEN MAR04 - A lion rests in in the shadow of a bush in Kenya's national park Masai Mara in this March 2004 file photo. Even the King of the Jungle needs a hand staying alive on his own turf. That is what the government of Kenya thinks as far as the majestic African lion, a symbol of the continent and one of its most feared predators, is concerned. The Kenya Wildlife Service is pushing the Convention on International Trade in Endangered Species (CITES), to give the African lion, panthera leo, its most protected status. Current conservative estimates place the African lion population at 23,000, Kenya wrote in its proposal. Picture taken on March 2004.

A lion cub is seen walking in the grass at Nairobi animal orphanage in Kenya in this July 2004 file photo. Even the King of the Jungle needs a hand staying alive on his own turf. That is what the government of Kenya thinks as far as the majestic African lion, a symbol of the continent and one of its most feared predators, is concerned. The Kenya Wildlife Service is pushing the Convention on International Trade in Endangered Species (CITES), to give the African lion, panthera leo, its most protected status. Current conservative estimates place the African lion population at 23,000, Kenya wrote in its proposal. Picture taken on March 2004. REUTERS/Radu Sigheti RSS/

A lion cub is seen on the shoulder of a keeper at Nairobi animal orphanage in Kenya in this July 2004 file photo. Even the King of the Jungle needs a hand staying alive on his own turf. That is what the government of Kenya thinks as far as the majestic African lion, a symbol of the continent and one of its most feared predators, is concerned. The Kenya Wildlife Service is pushing the Convention on International Trade in Endangered Species (CITES), to give the African lion, panthera leo, its most protected status. Current conservative estimates place the African lion population at 23,000, Kenya wrote in its proposal. Picture taken on March 2004. REUTERS/Radu Sigheti RSS/THI

A lion rests in in the shadow of a bush in Kenya's national park Masai Mara in this March 2004 file photo. Even the King of the Jungle needs a hand staying alive on his own turf. That is what the government of Kenya thinks as far as the majestic African lion, a symbol of the continent and one of its most feared predators, is concerned. The Kenya Wildlife Service is pushing the Convention on International Trade in Endangered Species (CITES), to give the African lion, panthera leo, its most protected status. Current conservative estimates place the African lion population at 23,000, Kenya wrote in its proposal. Picture taken on March 2004. FEATURE MATCHER REUTERS/Radu Sigheti RSS/THI

Two lions are seen resting in the shadow of a tree in Kenya's national park Masai Mara in this March 2004 file photo. Even the King of the Jungle needs a hand staying alive on his own turf. That is what the government of Kenya thinks as far as the majestic African lion, a symbol of the continent and one of its most feared predators, is concerned. The Kenya Wildlife Service is pushing the Convention on International Trade in Endangered Species (CITES), to give the African lion, panthera leo, its most protected status. Current conservative estimates place the African lion population at 23,000, Kenya wrote in its proposal. Picture taken on March 2004. FEATURE MATCHER REUTERS/Radu Sigheti RSS/THI

A lion is seen walking in Kenya's national park Masai Mara in this March 2004 file photo. Even the King of the Jungle needs a hand staying alive on his own turf. That is what the government of Kenya thinks as far as the majestic African lion, a symbol of the continent and one of its most feared predators, is concerned. The Kenya Wildlife Service is pushing the Convention on International Trade in Endangered Species (CITES), to give the African lion, panthera leo, its most protected status. Current conservative estimates place the African lion population at 23,000, Kenya wrote in its proposal. Picture taken on March 2004. FEATURE MATCHER REUTERS/Radu Sigheti NO RIGHTS CLEARANCES OR PERMISSIONS ARE REQUIRED FOR THIS IMAGE RSS/THI

A lion is seen passing in front of a zebra in Kenya's national park Masai Mara in this March 2004 file photo. Even the King of the Jungle needs a hand staying alive on his own turf. That is what the government of Kenya thinks as far as the majestic African lion, a symbol of the continent and one of its most feared predators, is concerned. The Kenya Wildlife Service is pushing the Convention on International Trade in Endangered Species (CITES), to give the African lion, panthera leo, its most protected status. Current conservative estimates place the African lion population at 23,000, Kenya wrote in its proposal. Picture taken on March 2004. FEATURE-MATCHER REUTERS/Radu Sigheti NO RIGHTS CLEARANCES OR PERMISSIONS ARE REQUIRED FOR THIS IMAGE RSS/THI