Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) crossing closed road, during annual migration, Christmas Island, Indian Ocean, Australian Territory, November 2009.

Ashley Cooper / Sellafield nuclear power station near Seascale, West Cumbria, UK. February 2013

Doug Wechsler / Diamondback terrapin (Malaclemys terrapin) female ready to lay eggs, trapped on road by barrier, Delaware Bay, New Jersey, USA, July.

Cyril Ruoso / Three European toads (Bufo bufo) moving along a barrier towards an underpass to prevent roadkill during migration, Poncet, Franche-Comte, France, March.

Sebastian Kennerknecht / Highway acts as a barrier for wildlife, Highway 17, Santa Cruz Mountains, Monterey Bay, California

Sebastian Kennerknecht / Highway acting as a barrier for wildlife, Laurel Curve, Highway 17, Santa Cruz Mountains, Monterey Bay, California

Sebastian Kennerknecht / Highway acting as a barrier for wildlife, Laurel Curve, Highway 17, Santa Cruz Mountains, Monterey Bay, California

Paul Williams / Bonnet macaque (Macaca radiata) male standing on road barrier, Vaparai, Tamil Nadu, India, July.

David Woodfall / Flood protection barrier (filled with water) to protect homes during February 2014 flooding. Chertsey, Surrey, England, UK, 16th February 2014.

Michael Quinton / Caribou (Rangifer tarandus) jumping over barrier onto highway during migration, Slana River, Alaska

Mark Carwardine / Barrier across road in Preah Monivong Bokor National Park, Elephant Mountains, south-western Cambodia (formerly Kampuchea)

Philippe Clement / Barrier with buckets for migrating amphibians / toads (Bufo bufo) crossing the road during annual migration in the spring, Belgium, March 2010