In 1990 during a cold rainy weekend in May, Keith Radel lost 63 Bluebird chicks in nest boxes with vent holes. He was certain they perished from the cold wet weather and the resulting lack of insects. Ever since, Keith has closed the vent holes during the first nesting in an effort to help the female Bluebird keep her chicks warm and enable her to spend more time out of the nest box foraging for insects. After the first clutch fledged, he opened the vent holes for the second and third nesting attempts. As an experiment in 2005, he left the vent holes closed on a few nest boxes for the entire season. He observed no chick’s deaths from heat in those boxes.

In 2006, he did a much larger study. He had 39 second and third nesting on his Bluebird trail, 23 were in boxes with vent holes closed. There were 19 in Gilbertson PVC, one in a Peterson and one in a modified Gilwood, two in the VanErt plastic Troyer style box, 16 were in boxes with vent holes open.  There were 13 in Gilbertson PVC, two in Peterson’s, and one in the VanErt plastic Troyer style box.

STUDY RESULTS
23 non-vented boxes – 97 eggs – 88
hatched 90.7% - 88 fledged – 100%
16 vented boxes – 68 eggs – 63 hatched
– 92.6% - 62 fledged – 98.4%

One small chick disappeared in one of the vented boxes when it was about a week old. Keith believes it died and was carried out by one of the parents.

In Rice County Minnesota where the study was conducted, there were more than two weeks where the temperature was 90 degrees including in July there were two days where the temperature was in the 100’s. This past July, dew points were in the 70’s and 80’s during that hot weather. The weekly checking was purposely done in the late afternoon. No chick deaths were recorded from the heat in either group of boxes. In addition, the chicks did not seem heat stressed when they were checked, no matter what age they were. But while checking the boxes, Keith remembered he was certainly heat stressed.

This past summer was one of the three hottest summers since he started his trail 21 years ago.

One added advantage of closed vent holes, or no vent holes was discovered by Gary Gaard of the Bluebird Restoration Association of Wisconsin. He had many deaths of Bluebird chicks from black fly (gnat) bites in vented boxes, but none in the non-vented Gilwood box. Black fly or gnat problems in Minnesota are rare, but Keith did have 35 deaths of baby Bluebirds from their bites in late June and early July of 1993. Keith thinks there is a good chance those deaths would not have occurred if he had not opened the vents holes for the second and third nesting.

Keith plans to have all vent holes closed for the entire season of 2007.