Every few years, however, including this one, part of the flock decides to roost downtown. Heyser said that since November the city has received nine crow-related complaints from people who work or live downtown.
Heyser said the only way to get crows from roosting in a particular area is to harass them repeatedly.
This year, the city has lent out four cassette tapes of crows in distress, he said. Residents are advised to play the tapes sporadically for up to 40 seconds at a time over two weeks.
The noise bothers the crows and eventually they move to another area, he said.
Anyone interested in borrowing the tapes may call the city Department of Engineering and Inspections at 301-739-8577, extension 125.
Heyser said that in addition to the tapes, any loud noise will bother the crows and eventually drive them away.
Heyser said the crows generally stop roosting in large groups by April.
"In the summer they scatter over the area, but in cold weather they congregate and roost together," he said.
Over the years, city officials have looked into various ways of ridding the city of crows, including offering a per-crow bounty to hunters and hiring an exterminator, Heyser said.
However, crows are a protected species because they are considered a migratory bird under federal law, Heyser said.
There is, however, a hunting season for crows. It runs from mid-August to mid-March.