THOSE OVAL HOLES

Kevin Berner, University of New York, Cobleskill found in past research projects that bluebirds choose a NABS box with the oval hole over a Peterson box, but he was concerned about reports of entry by starlings in the Peterson - holed larger NABS nestbox, even though he felt "starlings rarely use a Peterson box." Kevin and Bobby Cummins tried reducing the holes to 11/4 x 21/4 inches.  Captive starlings could still escape from the boxes, but with far more difficulty.

So Kevin decided to see if bluebirds would use the narrower oval hole on a NABS box.  He paired NABS boxes with the Peterson hole and the narrower oval hole.  He also paired boxes with the narrower hole and with a 1'/2 inch round hole.

Bluebirds showed a strong preference for the Peterson oval hole over the reduced oval hole, with 26 nesting attempts in former, and only four in the smaller holed box.  Swallows often used the smaller hole, but largely because of their later arrival, the larger hole box was occupied by bluebirds.

"Although bluebirds prefer the [Peterson] larger oval hole, when the hole width is reduced, this advantage [over the round hole] is diminished." -- Reported in BLUEBIRD, NABS Journal, Fall 2000 (Ed's note: Dick Peterson did similar experiments several years ago, gradually reducing the width of the oval hole, and found bluebirds preferred his 1'18 x 2114.)

Allen Bower, Britton, MI, believes most of the reports of starlings entering the Peterson box are because the hole was cut too wide.  "Eastern bluebirds like the [Peterson] oval entrance over the round holes because they don't have to duck their heads to get into the box."

His suggestion for saving the oval hole and discouraging the starlings: "Use an exterior glue and glue a 1/16" thick shim by 1'/2" long to the side of the hole; hold it in place with masking or electrical tape until the glue is dry.  Sand or file the square edge off the shim.

If starlings still get in the box, shim the other side of the entrance hole. Bluebirds will use the hole down to 1'/4" wide, but they prefer it wider."

Posted with permission from the February 2001 Bluebird Recovery Program Newsletter "BLUEBIRD NEWS"

10/02/02

Maps