The northern flickers have pecked at least 71 holes - from half an inch (1.2cm) to 4in in diameter - in the foam insulation on tank's outside, according to the National Aeronautics and Space Administration.
Mission managers are assessing what damage has been done and how long it will take to fix it before five astronauts take off with a Nasa Tracking and Data Relay Satellite, David Dickinson, for Kennedy Space Centre, said.
The sprayed-on insulation is a few inches thick and helps to keep ice from forming on the fuel tank when it is filled with superchilled propellants.
Dickinson said the woodpeckers' nest was discovered during a routine inspection last Friday, and closed-circuit television cameras caught the little feathered jackhammers in action. Workers brought a flock of great-horned owl decoys to "roost" at the pad to scare them away.
The woodpeckers are not endangered, but "we're protective of every species," Mr Dickinson said. The space centre sits in the middle of the Merritt Island Wildlife Refuge.Reuse content