Wildebeest

Wildebeest gather along the banks of the Mara River as they prepare to cross, in the Maasai Mara Game Reserve in Kenya, Dec. 3, 2013.

Only months after their annual migration south to Tanzania's Serengeti National Park, thousands of wildebeest have been spotted back in the Maasai Mara, a rare occurrence which wildlife officials have said may be the result of drought and insufficient pastureland in Tanzania.

Credit: Rebecca Blackwell/AP

Wildebeest

Wildebeest and zebra cross the Mara River, in the Maasai Mara Game Reserve in Kenya, Dec. 3, 2013.

Credit: Rebecca Blackwell/AP

Wildebeest

Wildebeest cross the Mara River in the Maasai Mara Game Reserve in Kenya, Dec. 3, 2013.

Credit: Rebecca Blackwell/AP

Crocodiles

Crocodiles devour a zebra they killed, as wildebeest and zebra crossed the Mara River, in the Maasai Mara Game Reserve in Kenya, Dec. 3, 2013.

Credit: Rebecca Blackwell/AP

Wildebeest and zebra

Wildebeest and zebra mount the opposite bank after crossing the Mara River, in the Maasai Mara Game Reserve in Kenya, Dec. 3, 2013.

Credit: Rebecca Blackwell/AP

Wildebeest

A wildebeest runs past a zebra that has been killed by crocodiles while crossing the Mara River in the Maasai Mara Game Reserve in Kenya, Dec. 3, 2013.

Credit: Rebecca Blackwell/AP

Wildebeest and zebra

Wildebeest and zebra cross the Mara River, in the Maasai Mara Game Reserve in Kenya, Dec. 3, 2013.

Credit: Rebecca Blackwell/AP

Wildebeest

Wildebeest gather along the banks of the Mara River as they prepare to cross, in the Maasai Mara Game Reserve in Kenya, Dec. 3, 2013.

Credit: Rebecca Blackwell/AP

Wildebeest

Wildebeest run across a plain in the Maasai Mara Game Reserve in Kenya, Dec. 3, 2013.

Credit: Rebecca Blackwell/AP

Wildebeest

Wildebeest walk in line toward the Mara River, in the Maasai Mara Game Reserve in Kenya, Dec. 3, 2013.

Credit: Rebecca Blackwell/AP