Looking for the Perfect Fixer-Upper

Chickadees prefer nest tubes filled with wood shavings more than nest boxes

By Caren Cooper, David Bonter, and Laura Erickson

Black-capped Chickadee by Bruce Echols

If Black-capped Chickadees consulted with real estate agents about their housing needs, they’d be easy to please with regard to neighborhoods, accepting a variety of habitats from pristine forests to suburban backyards and urban parks. But chickadees are fussy about house design and prefer to excavate their own cavities. They’d be drawn to a listing for a “fixer-upper for the do-it-yourself homeowner.”

Scientists have learned a great deal about social interactions, bird personalities, brain neuron regeneration, how ultraviolet plumage color influences mate choice, and other issues by studying Black-capped Chickadees, but there are gaps in our understanding of their basic nesting habits. Chickadee nest cavities have such tiny entrance holes that it’s difficult for researchers to get the inside story except by studying them in nest boxes.

Chickadees prefer birdhouses filled with wood shavings, giving them something to excavate. Standard nest boxes have long been available in Sapsucker Woods but were rarely used by chickadees. Even boxes filled with shavings aren’t as readily accepted as researchers, and bird watchers, would like. So we (Caren and David) set out to learn whether chickadees would more readily accept an “artificial tree snag” made from a PVC tube. We based our design on a model developed by Thomas Grubb and C.L. Bronson in Ohio in the 1990s. The design of their snag and the results of their study were published in Artificial Snags as Nesting Sites for Chickadees, The Condor, November 1995 and are available at elibrary.unm.edu/sora/Condor/files/issues/v097n04/p1067-p1070.pdf.

The authors set out to learn whether chickadees would more readily accept an “artificial tree snag” made from a PVC tube, above.

Starting in 2005, we gave chickadees a choice of nesting options near the Lab of Ornithology in Sapsucker Woods. With a team of helpers, we grouped one artificial snag and one standard nest box at 20 sites in Sapsucker Woods. At each site, the nest box and the snag were filled with wood shavings. We located eight of the sites next to existing unfilled nest boxes. Entrance holes for the structures at each site were oriented in the same direction.

Each year of the study, chickadees excavated 60—70 percent of the artificial snags, but only 40—50 percent of the filled nest boxes. They built nests in 25—30 percent of the snags but in only 15 percent of the filled nest boxes, and seldom nested in empty boxes. Their selection of artificial snags may have been influenced by the higher entrance holes in the snags and/or because the snags were less accessible to mice, but the preference was clear.

Black-capped Chickadee eggs nestled snugly in moss and grasses.

House Wrens and mice compete with chickadees for nest sites. Neither wrens nor mice excavate their own cavities, but they often take over one after chickadees have excavated it. We found that artificial snags were no more likely than boxes to attract wrens, and none were taken by mice, suggesting that the snags may be less susceptible to other climbing predators as well.

Results of our study are published in the Summer 2008 issue of the Journal of Field Ornithology.

Caren Cooper is a research associate in Bird Population Studies. David Bonter is the leader of Project FeederWatch.

For permission to reprint all or part of this article, please contact Laura Erickson, editor, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY, 14850. Phone: (607) 254-1114. email: lle24@cornell.edu