OMAHA, Neb. (AP) – Zoos across North America are moving their birds indoors and away from people and wildlife as they try to protect them from the highly contagious and potentially deadly avian influenza.

Penguins may be the only birds visitors to many zoos can see right now, because they already are kept inside and usually protected behind glass in their exhibits. Nearly 23 million chickens and turkeys have already been killed across the United States to limit the spread of the virus.

Zoos are working hard to prevent any of their birds from meeting the same fate. Birds spread the virus through droppings and nasal discharge. Experts say it can be spread through contaminated equipment, clothing, boots and vehicles carrying supplies.