A tiny unborn hummingbird is getting in the way of a big bridge project near San Francisco.

The discovery of a nest and egg in a tree is stalling a $US70 million ($A92 million) upgrade to the Richmond-San Rafael Bridge about 50 km north of San Francisco, officials said on Tuesday. The species, Anna’s Hummingbird, is protected under the Migratory Bird Treaty Act that forbids the removal…