http://boisestatepublicradio.org/post/why-vultures-are-being-celebrated-boise

Elephant poachers have been poisoning vultures, according to
National Geographic - “Poachers lace the discarded elephant carcass with cheap
poisons to kill vultures in mass. Why? Because vultures circling in the sky
alert wildlife authorities to the location of poachers’ activities.”

http://www.vultureday.org/2013/index.php