the zoo de Servion, in Servion, Switzerland, Friday, April 27, 2012. (AP Photo/Keystone, Laurent Gillieron)

Photo: Laurent Gillieron, Associated Press

A one day-old American bison cub and its mother enjoy a sunny day... Photo-2869422.42205 - SFGate

Image 7 of 15

In this April 20, 2012 photo, Vail Academy fourth-grader Rylan Sander hangs out in a compactor's wheel during a tour of the Eagle County Landfill with his class in Wolcott, Colo. (AP Photo/The Vail Daily, Kristin Anderson) less

In this April 20, 2012 photo, Vail Academy fourth-grader Rylan Sander hangs out in a compactor's wheel during a tour of the Eagle County Landfill with his class in Wolcott, Colo. (AP Photo/The Vail Daily, ... more

Afghan men attend an organised ram fight in Kabul on April 27, 2012. Spring marks the start of theafter scattered showers fell throughout the Orange County earlier in the morning. (AP Photo/The Orange County Register, Mark Rightmire) MAGS OUT; LOS ANGELES TIMES OUT less

The sky begins to clear as the Great Park Balloon goes up for a test flight to check the wind in Irvine, Calif. Thursday morning, April 26, 2012, after scattered showers fell throughout the Orange County ... more

Photo: Mark Rightmire, Associated Press

The sky begins to clear as the Great Park Balloon goes up for a... Photo-2869425.42205 - SFGate

Image 10 of 15

An Indian shepherd woman carries a lamb as she walks across a dried pond on the outskirts of Hyderabad, India, Thursday, April 26, 2012. (AP Photo/Mahesh Kumar A.)

An Indian shepherd woman carries a lamb as she walks across a dried pond on the