NY Times article
here.

Each summer, 500,000 wildebeests die along the treacherous
migration from the Serengeti National Park in Tanzania to the Masai Mara
National Reserve in Kenya. And with death come the scavengers, none more
important than the vulture.

But the birds that once feasted on that misfortune, the janitors that clean the
grassy plains, are collapsing — part of a broader decline in vulture populations
that throws off ecosystems and illustrates how far-reaching the effects of
poaching, poisoning and other human interventions can be.

In some parts of Africa, vultures are targeted by poachers who poison carcasses
hoping to kill the birds so they will not circle overhead and signal park
rangers. A vulture can spot a dead elephant in less than 30 minutes, but it can
take a poacher more than an hour to hack off ivory tusks. No vulture, no
warning.

Here on the Mara, one of the greatest natural strongholds left on the planet,
the vultures are not directly targeted but are the unintended victims of
poisoning of carcasses that is meant to kill large carnivores, like hyenas, in
an effort to protect livestock.

Across Africa, the threats to wildlife are myriad, but much of the attention is
focused on the stately animals of the savanna, like lions and elephants.

Vultures do not make for pretty postcards, and the local authorities are already
stretched thin trying to protect the animals that tourists come to see.