A child looks at a polar bear swimming under a water in its enclosure on a hot summer day at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A newly born Silvery Gibbon baby is held by its mother Alangalang at Prague Zoo, Czech Republic, July 30, 2015. The baby of endangered Silvery Gibbon was born on Tuesday and it is the first one born in captivity in the Czech Republic, according to the zoo. (Photo by David W. Cerny/Reuters)

A newly born Silvery Gibbon baby is held by its mother Alangalang at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A child looks at a polar bear swimming underwater in its enclosure on a hot summer day at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A newly born Silvery Gibbon baby is held by its mother Alangalang at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A newly born Silvery Gibbon baby is held by its mother Alangalang at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A Siberian tiger growls in its enclosure on a hot summer day at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A newborn Silvery Gibbon baby is held by its mother Alangalang at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A newborn Silvery Gibbon baby is held by its mother Alangalang at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A newborn Silvery Gibbon baby is held by its mother Alangalang at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A polar bear swims underwater in its enclosure on a hot summer day at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A polar bear swims underwater in its enclosure on a hot summer day at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A newborn Silvery Gibbon baby is held by its mother Alangalang as it eats a tomato at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A Silvery Gibbon named Alangalang eats a tomato in its enclosure at Prague Zoo, Czech Republic, July 30, 2015. The baby of Alangalang, an endangered species, was born on Tuesday and it is the first one born in captivity in the Czech Republic, according to the zoo. (Photo by David W. Cerny/Reuters)

A newborn Silvery Gibbon baby is held by its mother Alangalang at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A polar bear swims in its enclosure on a hot summer day at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)

A polar bear jumps into the water in its enclosure on a hot summer day at Prague Zoo, Czech Republic, July 30, 2015. (Photo by David W. Cerny/Reuters)