Don't Feed that Chipmunk!

Study finds more nest predators, fewer breeding thrushes in campgrounds

By Ron Rohrbaugh

Nest predators such as chipmunks and gound squirrels were found more often in campgrounds than at survey sites in surrounding forest. Illustration by Evan Barbour

Many of us visit national forests and parks for extended vacations. As birders and naturalists, we are good stewards of the land and try to leave little trace of our forays into the wilderness. We obey signs that ask us to "take only pictures and leave only footprints." But what effects do we really have when participating in low-impact recreational activities such as camping?

A study by the Cornell Lab of Ornithology?s Conservation and Citizen Science programs, in cooperation with the U.S. Forest Service (USFS), investigated how campground development and activities are affecting thrushes in national forests. The results showed that Swainson?s and Varied thrushes were found as often in campgrounds as at control sites in surrounding forest. However, two other species—Hermit Thrushes and Veeries—were less likely to be found in campgrounds throughout the season than in nearby forested areas.

To determine whether campgrounds were affecting thrushes, volunteers collected data at three types of sites: R (campgrounds), E (edge), and C (control).

The data were collected by citizen-science participants at more than 150 campgrounds in 26 National Forests during the 2000, 2001, and 2002 breeding seasons. The sites were located in 7 western and 2 eastern Forest Service regions. Barb Kott and other USFS biologists recruited and trained citizen- science volunteers who dedicated more than 3,900 hours to the project. The volunteers collected data at three types of study points: recreation points located in the campground, edge points located within 500 feet of the campground?s edge, and control points that were 1,500 feet or farther from the campground?s edge. For the three site types, we compared data on breeding thrushes, predators, habitat, and campground characteristics such as the number and sizes of campsites and the presence of trash containers (potential sources of food for predators). (See Figure 1 for survey points.)

Hermit Thrushes and Veeries were less likely to be found on two visits in campgrounds than in nearby forested areas, suggesting that the campsites may have been poorly suited for breeding.

The results showed that campgrounds had little or no effect on the probability of finding Veeries, Swainson?s Thrushes, or Hermit Thrushes on at least one visit. However, on two visits, Hermit Thrushes and Veeries were less likely to be found in campgrounds as they were at control sites (Figure 2).

Apparently, the relatively low-level, local disturbance and small openings created by campgrounds in large contiguous forests did not inhibit the occurrence of these thrushes. However, Varied Thrushes were less likely to be found at large campgrounds. Additionally, since Hermit Thrushes and Veeries were less likely to be found in campgrounds on two visits, fewer of them may have attempted to breed at campground sites, or breeding efforts may have failed more often, resulting in abandoned territories. Negative impacts on breeding thrushes could be due to changes in habitat documented at campgrounds or to increases in predation pressure.

Mammalian and avian predators were more likely to be detected in campgrounds than in nearby forested areas.

Participants detected significantly more mammalian and avian nest predators in campgrounds than in nearby forested sites (Figure 3). The presence of predators was not related to the size of the disturbed zone at campgrounds, but the probability of finding mammalian predators, particularly red or Douglas squirrels, was positively related to the number of campsites. Possibly, larger numbers of campsites have more campers and supplemental food left behind by campers—a finding consistent with other studies that documented increased numbers of small mammals and American Crows in campgrounds and other recreation areas. Thrushes may be more vulnerable to nest predation in areas with abnormally high densities of nest predators.

You may ask, "Why worry about the effects of recreation; isn?t residential and commercial development more threatening to birds?" That?s probably true, but consider this: According to the 2001 National Survey of Fishing, Hunting, and Wildlife-Associated Recreation, 39 percent of United States residents participate in some type of outdoor recreation each year. The USFS is the largest provider of outdoor recreational opportunities for United States citizens and oversees more than 23,000 facilities, including campgrounds, picnic areas, boat ramps, and visitors? centers. According to USFS statistics, there were an estimated 900 million individual visits to USFS lands in 1999 alone. We can?t afford not to pay attention to the effect of recreational activities on wildlife when birds including Veeries have undergone population declines of 30 percent or more since 1966, and Varied Thrushes are in need of long-term stewardship to ensure their numbers remain stable.

So, should you think about canceling that big camping trip that you have planned for next summer? That?s probably not necessary, but in addition to "taking only photographs and leaving only footprints," you may want to heed one more sign often found near campgrounds—"Please Don?t Feed the Wildlife!"

For a complete report on results of the study, visit www.birds.cornell.edu/bfl and click on "Results & Publications."

Ron Rohrbaugh is director of Citizen Science.

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