Many animals migrate to different and often distant environments, usually on an annual cycle, and often for breeding purposes or to secure food supplies. A number of human activities tend to disrupt such movement; examples are construction of fences, denial of use of island breeding grounds and destruction of wetlands.
A programme, "Captains for Conservation" was launched in 1991. Its goal is to inspire "captains of industry" who own tall skyscrapers to turn off the lights on their buildings during migration season. In bad weather, birds must fly at lower altitudes and the rain/mist/fog can combine with lights to disorient birds, causing them to crash into skyscrapers.
A 2009 audit of Earth’s greatest terrestrial-mammal movements showed that of 24 large species that once migrated in their hundreds to thousands, six migrations have vanished entirely. In Africa, home to some of the most spectacular wildlife migrations, scientists found that of 14 large-mammal species known to migrate en masse, five migrations were already extinct.