INHS Reports May-June 1999

Deer in the Suburbs of Chicago

The management of overabundant deer populations in suburban areas continues to be one of the most immediate and frustrating problems facing conservation and wildlife professionals nationwide. As rapid development encroaches on the remaining open landscapes surrounding most metropolitan areas, wildlife is forced into ever-shrinking islands in a sea of development. This concentration of wildlife into smaller and smaller areas causes intraspecific competition for the remaining available resources. In particular, overabundant white-tailed deer can cause severe impacts to ecosystems through excessive browsing, and they also pose threats to public safety through deer-vehicle collisions and the potential spread of wildlife-borne diseases. The solutions to managing overabundant deer in suburban settings are often controversial, posing new challenges to managers. The traditional method of population control, recreational hunting, is unacceptable to urbanites. Additionally, despite the proliferation of literature published about deer, little research has focused on the biology of this species in its newly exploited suburban environment. Basic life history information is crucial to managers attempting to reduce and then maintain ecologically responsible suburban deer populations using alternative management techniques.

Fawn in suburban Chicago.

With funding from the Forest Preserve Districts of Cook and DuPage counties, Cook County Animal Control, and Chicago Wilderness, we are developing a model to predict population trends in suburban deer and documenting the recovery of native plant communities as deer populations are reduced.

Work to document life history information for deer from the Forest Preserve Districts of Cook and DuPage counties began in winter 1995. More than 130 deer have since been captured and radio-collared. Deer were monitored for survival and radio-tracked to document movements within the suburbs of Chicago. Additionally, reproductive information was collected from more than 4,000 deer removed from forest preserves during culling operations designed to reduce overabundant populations. Collection of vegetation data began in DuPage County forest preserves in 1991, two years prior to the initiation of deer culling operations. This summer will represent the ninth year for collection of this important information.

Life history information to support our model includes classic deer biology as well as unique behaviors for suburban deer. In general, suburban does are homebodies living out their lives in the same general area as their mothers. Bucks, however, are gregarious, often dispersing during their second summer. Suburban deer often existing at extremely high densities (>150 deer/mile²) continue to have high fecundity (>1.6 offspring per adult doe) even when understory vegetation is severely depleted. Populations at these extreme densities are checked somewhat by reduced breeding by younger does and by higher fawn mortality.

White-tailed deer, a common site in Chicago suburbs.

Overall survival for adults is greater than 80% annually, which is similar to survival reported for deer living on refuges in the Midwest. As might be expected, auto-deer and train-deer collisions account for more than 60% of annual deer mortalities with a few hunting and poaching losses accounting for the remainder. Unlike elsewhere in Illinois spring, not fall, is the time of year when most suburban deer are killed by cars. We have also documented a potential adaptive strategy used by suburban deer to cross roads during heavy rush-hour traffic. Adult deer will patiently watch cars drive by and wait for a lull in traffic when they can sprint across untouched. Considering the high reproductive potential and high survival of suburban deer, it's easy to see how this species continues to thrive even in the potentially harsh suburban environment.

Results from the vegetation study are encouraging for the recovery of ecosystems heavily impacted by overabundant deer. In most cases we have observed an increase in native plant species composition, plant height, and overall ground cover as deer populations have been reduced from more than 100 deer/mile² to less than 40 deer/mile². We have also documented the appearance and resurgence of several rare native plant species in forest preserves where deer populations have been greatly reduced. Some notable species include Michigan lily, upland boneset, and great flowering trillium.

This research will assist managers from the Chicago region and potentially nationwide in better managing overabundant suburban deer, restoring depressed native ecosystems, and reducing human-deer conflicts.

Dwayne R. Etter, Department of Natural Resources and Environmental Sciences, University of Illinois, and Timothy Van Deelen, Center for Wildlife Ecology.

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