IOWA CITY, Iowa (AP) — Federal prosecutors are defending their use of an obscure law to indict two recreational Iowa pilots whose low flying may have disturbed thousands of resting migratory birds.

Paul Austin and Craig Martin are charged with violating the Airborne Hunting Act.

Prosecutors say they flew separate small planes 20 feet above Saylorville Lake last November, causing a large group of waterfowl and white pelicans to take flight. The two were not hunting, but prosecutors say they violated the law, which prohibits using an aircraft to harass animals.

Austin and Martin have asked a judge to dismiss the indictment, arguing the law is unconstitutional. They question how pilots are supposed to know whether birds feel harassed.

Prosecutors said last week that harassment is like pornography: you know it when you see it.

(© Copyright 2012 The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.)