The state of Minnesota and the city of Oakland, California are the latest governments to pass legislation that mandates bird-friendly building designs.

They join San Francisco - which passed "Standards for Bird Safe Buildings" in 2011 - along with several municipalities in the Chicago area. The city of Chicago has produced voluntary guidelines.

National legislation has been introduced in the House by Illinois representative Mike Quigley. It calls for all public buildings, whether renovated, constructed or acquired to incorporate bird-friendly designs and materials, as well as modify existing buildings to meet these goals.

As many as one billion birds die each year colliding with buildings, one of the leading causes of bird mortality in the US.