Killdeer (Charadrius vociferus)
Owing to its noisy behavior, tendency to nest near people, nearly ubiquitous range, and relative abundance, the Killdeer is one of North America’s most familiar shorebirds. Moreover, it has probably done more to instruct humans (albeit unintentionally) about distraction displays (the “broken-wing act”) and the meaning of onomatopoeia than has any other bird. The Killdeer is somewhat of an outlier among shorebird species. For starters, it often nests and feeds far from water. Too, it seldom travels in compact flocks, unlike many Arctic-nesting waders. It is tame and approachable and quite at home in human-dominated landscapes such as gravel parking lots, grazed pastures, golf courses, airports, and athletic fields. Last, like many plovers it is a visual forager that is most active during the day; however, recent evidence suggests it routinely forages during moonlit nights, probably to avoid diurnal predators and to take advantage of increased prey availability after sundown (Eberhart-Phillips 2017).
Killdeers occur in Montana year-round, although many that overwinter here probably come from nesting grounds in Canada. They commonly winter in the southern half of the U.S. south through Mexico and Central America to Colombia and Venezuela. Historically, Killdeers nested along the rocky shores of streams and lakes. Nowadays, however, the typical nest is on a gravel parking lot or road shoulder, pasture, rural yard or garden, or pebbly roof of a building. Because Killdeers often put their nests in areas where people walk and drive, their eggs and hatchlings are highly vulnerable to human-induced disturbance and mortality. Indeed, the Killdeer’s ready acceptance of degraded habitats is a big factor in the general lack of concern that has been directed toward its conservation.
The latest global population estimate is 1 million birds (Morrison et al. 2006). The accuracy of this estimate is difficult to assess, but it suggests that Killdeers are fairly abundant. Without question, however, population trends are mostly negative and point to declining numbers in much of the species’ range. The best method for assessing population trends is the Breeding Bird Survey (BBS), which is conducted annually in North America by skilled volunteer birders and biologists. Biometricians at the U.S. Geological Survey’s Patuxent Wildlife Research Center analyze the data and provide estimates of population trends in the form of a proportional change in the average number of individuals detected along a BBS route (each of which is 24.5 miles long, with survey points every half mile) for a given species and geographic area. The most recent long-term summary of BBS data is for the 50-year period from 1966 to 2015 (Sauer et al. 2017).
During this time span, Killdeer numbers declined significantly in 31 of the 57 U.S. states and Canadian provinces for which adequate data were available. The data indicated a survey-wide decline in numbers of 1.09% per year, with the highest drops in Canada and the western U.S. For example, numbers detected on surveys declined by an average of 3.6% per year in British Columbia, 4.8% in Quebec, 3.2% in Colorado, and 3.2% in Utah. Closer to home, Killdeer numbers in Montana (for which data were first obtained in 1968 versus 1966) sank by an average of 2.15% per year, which translates to a drop in numbers of 63.6% from 1968 to 2015 (see Figure 1). To put this into perspective, using the decline rate measured in Montana, a hypothetical population of 25,000 Killdeers in 1968 would consist of only 9,101 individuals by 2015. On balance, all indications from the BBS point to wholesale trouble for Killdeer populations.
The causes behind the alarming decline in Killdeer numbers are not fully understood, nor is it known whether major problems are occurring on the breeding grounds, wintering grounds, or during migration. Loss and degradation of habitat, human disturbance at nests, mortality from collisions with cars and encounters with roving house pets, and exposure to toxic chemicals are likely factors (Sanzenbacher and Haig 2001). The Killdeer’s habit of nesting along roads and near human settlements results in many nests being destroyed by cars and trucks, and countless numbers of young being killed by cats and dogs. Too, because Killdeers feed on lawns, athletic fields, and golf courses, they are exposed to a variety of chemical pollutants that humans apply to the landscape to control insect pests and undesirable plants, sometimes with tragic results. In one case, a researcher counted 175 dead Killdeers following application of the organophosphate insecticide Azodrin to a field in Florida (Fisk 1976). Two other Killdeers died from wheat seeds treated with strychnine in California (Warnock and Schwarzbach 1995).
Only a few states consider the Killdeer to be a species of conservation concern, and no formal management guidelines have been proposed for it. At the local level, homeowners and birders can help protect the nests they find by keeping pets indoors and avoiding driving over nests along roadsides. Small barriers that deter driving near nests surely can help, but they also make nests more conspicuous to visual predators like corvids. Discouraging or banning pesticide use in areas frequented by Killdeers also would help, although such efforts often will not be successful.
Despite unanswered questions about why its numbers are declining, one thing is certain: the Killdeer’s plight is not likely to get better until more people are aware of it. The attention generated by a public education campaign might inspire new investigations into causes of population declines, and ultimately could result in management guidelines that would benefit the species throughout its range.
Eberhart-Phillips, L. J. 2017. Dancing in the moonlight: Evidence that Killdeer foraging behaviour varies with the lunar cycle. Journal of Ornithology 158: 253-262.
Fisk, E. J. 1976. A deadly rain of robins. Florida Naturalist 49(2): 13-14.
Morrison, R. I. G., B. J. McCaffery, R. E. Gill, S. K. Skagen, S. L. Jones, G. W. Page, C. L. Gratto-Trevor, and B. A. Andres. 2006. Population estimates of North American shorebirds, 2006. Wader Study Group Bulletin 111: 67-85.
Sanzenbacher, P. M., and S. M. Haig. 2001. Killdeer population trends in North America. Journal of Field Ornithology 72: 160-169.
Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski, Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link. 2017. The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. Patuxent Wildlife Research Center, Laurel, Maryland.
Warnock, N., and S. E. Schwarzbach. 1995. Incidental kill of Dunlin and Killdeer by strychnine. Journal of Wildlife Diseases 31: 566-569.