Huw Cordey / Mexican free-tailed bats (Tadarida brasiliensis) emerging from Bracken Cave, Texas. Over 15 million bats are thought to live in this cave, making it the greatest concentration of mammals on the planet...

Karine Aigner / Woman with arms in air enjoying emergence of millions of Mexican free-tailed bats (Tadarida brasiliensis) at dusk. Bracken Bat Cave, San Antonio, Texas. June 2016.

Karine Aigner / Mexican free-tailed bat (Tadarida brasiliensis) on a glove. Bracken Cave Preserve, San Antonio, Texas, USA, July.

Karine Aigner / Park ranger Niki Lake poses as 'Batty the Clown' alongside her friend 'Ellie the Moth' in San Antonio where a bachelor colony of Mexican free-tailed bats (Tadarida brasiliensis) live under the bridge....

Karine Aigner / Park ranger Niki Lake poses as 'Batty the Clown' in San Antonio in San Antonio where a bachelor colony of Mexican free-tailed bats (Tadarida brasiliensis) live under the bridge. San Antonio, Texas, U...

Karine Aigner / Park ranger Niki Lake poses as 'Batty the Clown' alongside her friend 'Ellie the Moth' in San Antonio where a bachelor colony of Mexican free-tailed bats (Tadarida brasiliensis) live under the bridge....

Karine Aigner / Park ranger Niki Lake poses as 'Batty the Clown', teaching child to do the 'Bat handshake', in San Antonio where a bachelor colony of Mexican free-tailed bats (Tadarida brasiliensis) live under the...

Karine Aigner / Park ranger Niki Lake poses as 'Batty the Clown' alongside her friend 'Ellie the Moth' in San Antonio where a bachelor colony of Mexican free-tailed bats (Tadarida brasiliensis) live under the bridge....

Karine Aigner / Tourists viewing Mexican free-tailed bats (Tadarida brasiliensis) leaving maternity colony at night to feed. This viewing is organized by Bat Conservation International. Bracken Cave, San Antonio, Tex...

Karine Aigner / Tourists viewing Mexican free-tailed bats (Tadarida brasiliensis) leaving maternity colony at night to feed. This viewing is organized by Bat Conservation International. Bracken Cave, San Antonio, Tex...

Karine Aigner / Tourists viewing Mexican free-tailed bats (Tadarida brasiliensis) leaving maternity colony at night to feed. This viewing is organized by Bat Conservation International. Bracken Cave, San Antonio, Tex...

Karine Aigner / Children learning about Mexican Free-tailed bats (Tadarida brasiliensis), and make 'bat masks' while waiting for the bats to emerge at Bracken Cave. Bracken Cave Preserve, San Antonio, Texas, USA. Jul...