Millions of bird deaths as US hit by avian flu outbreak

A farm near Eagle Grove, Iowa. In Iowa, the state that produces the most eggs, more than 11m of 56m egg-laying hens have died. Photograph: Scott Olson/Getty Images

Millions of birds have died in the US in recent weeks, because of a contagious strain of highly pathogenic avian influenza, popularly known as bird flu.

The bird flu has also led zoos across the US to temporarily close aviary exhibits and move birds away from the public. At zoos from Colorado to Maryland, species ranging from ostriches to penguins have been moved indoors.