For the present, we still suggest that you go ahead and clean out old nesting material. That helps ensure that any parasites lurking in the houses won't survive to bedevil your birds next year. However, we may be giving different advice in the future.
New research suggests that at least some birds prefer their houses with the old nests left intact.
All very interesting, but inconclusive. Banner Golden-cheeked Warbler photo copyright 1988 Greg Lasley. All rights reserved. Travis Audubon Society. All rights reserved.