Woodland Birds May Need A Little Elbow Room

Great Crested Flycatcher Photo by Jim Schultz
of Chicago Zoological Societ

Woodland birds of conservation concern appear to prefer areas with fewer buckthorn and “pole trees” according to data from a Habitat Project study of woodland breeding bird habitat.

Previous studies have found that some bird species prefer managed woodlands over degraded ones, where managed woodlands had lower canopy cover and less dense mid-canopy vegetation compared to degraded woodlands*. Our study looked further at the relationship between woodland birds and the quality and structure of their habitat.

We developed a system that ranks species according to their conservation priority, rather than looking simply at total number of species. Woodland birds of concern such as Northern Flicker, Great Crested Flycatcher, and Yellow-billed Cuckoo (the three most commonly recorded birds of concern in this study) were weighted more heavily in the analysis than other woodland species whose populations are more stable such as Red-eyed Vireo and Hairy Woodpecker (see Table 1). Thus, the results reflect the habitat needs of the species for which we are most interested in managing habitat.

Photo by Lee Ramsey

We found that the quality of the herbaceous layer was not important—breeding birds of conservation concern didn’t seem to notice whether there were weeds or wildflowers on the ground. However, they did seem to notice how many stems of buckthorn and other invasive trees were present. As the number of buckthorn stems increased, the number of bird species of conservation significance decreased (see Fig. 1). Same for pole trees—those trees less than ten-inches in diameter that are crowding our oak woodlands—birds of conservation significance were found less often in areas unnaturally thick with pole trees (see Fig. 2).

The study was conducted during the breeding season in the Cook County forest preserves. Bird monitors and plant monitors both covered the same 43 points, which had been randomly placed within the county’s oak woods. Birders visited each point twice in June and conducted the Bird Conservation Network’s point count protocol. Plant monitors visited each point once and took data on the herbaceous flora, the shrubs, and the trees. The plant data were part of the 2007-2008 Cook County Land Audit, a larger study to assess the condition of the county’s priority conservation lands.

The people who took these data are major contributors to Chicago region conservation. Robert Sliwinski probably spoke for many when he said, “I’m a busy person with work and family, but when I was asked to do bird surveys in the ‘audit’ I took a bunch of sites. It was my chance to be involved in something wonderful and insightful.” Palos monitor Conrad Fialkowski also appreciates the insights gained through monitoring, saying, “The act of surveying takes a person interested in birds to a far better understanding of what birds need.”

The findings are preliminary. The relationships show lots of variation and exceptions, as seen in Figure 1 and Figure 2. We hope to follow up with an experimental study that alters the numbers of pole trees and follows the response of birds. The goal is to provide guidance to stewards and land managers working to provide habitat for species of conservation concern.

Figure 1. As buckthorn stems increased, we found somewhat fewer species of conservation concern.

Figure 2. As the number of“pole trees” increased, we found somewhat fewer species of conservation concern.

High Priority Moderate Priority Low Priority
Northern Flicker Wood Thrush Red-eyed Vireo
Great Crested Flycatcher Rose-breasted Grosbeak Eastern Wood-Peewee
Yellow-billed Cuckoo Eastern Kingbird Hairy Woodpecker


Table 1.The most commonly recorded species in each of three Conservation Priority categories. Categories were developed by the Bird Conservation Network and were based largely on Partners in Flight classifications. Categories also take into account the Chicago Wilderness region’s importance for the species in question - including the species range, trend in the CW region, local population size, and historic status in the area. For more details, please visit Birds of Concern Trends Analysis 2007.

This study was possible because of the time, energy, and expertise of the monitors who collected the data:

Bird Monitors: Al Thomas, Carolyn Fields, Chris and Geoff Williamson, Conrad Fialkowski, Dave Johnson, Dick Riner, Glyn and Sylvia Dawson, Janis Wesley, Jenny Vogt, Jill Anderson, Joan Coster, John Leonard, Judy Pollock, Kim Ramirez, Lee Ramsey, Margaret Mechtenberg, Margo Milde, Mary Anne McLean, Michelle O'Connor, Noel Zak, Robert Sliwinski, Stephen Packard, and Tom Mulcahy.

Plant Monitors:
Alice Brandon, Alison Kerber, Alison Park, Andrew Blackburn, Angela Kerber, Barb Wilson, Barbara Birmingham, Barbara Hill, Bob Claus, Brenda and Joe Occhiuzzo, Briana Goodwin, Brook Herman, Camille Stewart, Carol Howard, Carolyn Faber, Chad Gilson, Cynthia Stone, Dakota Blackburn, Dale Shields, David Wachtel, Diana Krug, Diane Benson, Dick Riner, Don Parker, Doug DeWitt, Duke Riggen, Ed Max, Elizabeth Gilson, Elizabeth Plonka, Erin Faulkner, George Birmingham, Greg Carlson, Greg Rajsky, Helen Marieskind, Helen Mlynarski, Holly Schmaling, James Doss, Jean Sellar, Jeanette Klodzen, Jeff Judycki, Jenna Fahey Heller, Jennifer Boyer, Jerry Fuller, Jessica Valeri, Joe Neumann, John Banaszak, John Berg, John Gipson, John Navin, Juli Mason, Karen Glennemeier, Karen Laskowski, Keith Nowakowski, Ken Schaefer, Kent Fuller, Kirk Anne Taylor, Laura Walsh, Laura Wigren, Laurel Ross, Linda Masters, Lisa Culp, Liz Meyer, Lou Mule, Lynda Behrendt, Maggie Kallai, Marianne Kozlowski, Mark Berninger, Mary Beth Falsey, Mary Busch, Mary Claire Jarvis, Mary Zaander, Melissa Gebien, Michelle Jost, Michelle McNab, Mike Zarski, Nathan Schroeder, Noreen Newton, Otto Roeser, Paul Bollinger, Paul Dolinka, Paul Leffler, Peter Chen, Rebecca Mueller, Rich Hyerczyk, Robbie Sliwinski, Ron Milnarik, Ron Vargasson, Ross Noethling, Ryan White, Scott Namestinik, Stan Fix, Stephanie Frischie, Stephen Packard, Steve Cloutier, Steve Phillips, Sylvia Zarski, Terry Schilling, Thaddeus Cetael, Victor Cassidy, Wally Levenier, and Yone Yu.

* Brawn, J.D. 2006. Effects of Restoring Oak Savannas on Bird Communities and Populations. Conservation Biology, Volume 20, No. 2, pp.460-469.