Horned grebe (podiceps auritus)

One of the earliest studies of nesting Horned Grebes occurred in Montana. On 3 June of 1917, Alexander DuBois found a nest on a small wetland near Dutton in Teton County (DuBois 1919). That spring had been “extremely rainy” and followed a winter of above-average snowfall. The wetland in question was in a meadow bordered on three sides by plowed fields. The nest was unusually exposed and in shallow water, which enabled DuBois to visit it often enough to determine timing of egg laying, clutch size, and length of the incubation period. DuBois collected the clutch soon after it was completed, and he inadvertently documented the first known case of renesting when the pair laid a second clutch in a new nest close to the first one.

DuBois’s discoveries about breeding biology were important in their own right, but his observation that the nest was within a landscape that was being “rapidly transformed into grain farms” perhaps is even more significant. Indeed, DuBois concluded his paper by stating “At the present writing this slough is dry; the road which passes through it is traveled every day by automobiles; and the spot where the Grebes established their home a year ago has now been plowed and planted” (DuBois 1919: 180).

The population declines of terrestrial birds that resulted from vast tracts of native prairie being plowed under are well known. Less well-appreciated, however, is the influence of habitat loss on species such as the Horned Grebe, which at the southern edge of its North American range nests almost exclusively on prairie wetlands that are less than 2 ha in size (Faaborg 1976, Ferguson and Sealy 1983). The Horned Grebe is in peril throughout its range. Assessing numbers of breeding pairs is difficult because nests typically are concealed within emergent vegetation and thus easily missed. In fact, a recent three-year survey of nesting waterbirds throughout Montana reported only one pair of Horned Grebes (Wightman et al. 2011). Horned Grebes were not among the focal species of the surveys, but surely many more of them nest in the state, which means that surveys must be tailored especially for them to better understand their distribution and numbers.

Given the difficulty of surveying Horned Grebes and the fact that very little attention has been paid to them, the most recent global population estimate is imprecise: 238,800–582,800 birds, about 80% of them in occurring in North America (Wetlands International 2017). Also, because the wetlands used by nesting Horned Grebes often occur far from roads, the Breeding Bird Survey is not ideally suited for assessing population trends. On the basis of combined information from the Breeding Bird Survey (Figure 1) and Christmas Bird Counts, Horned Grebe numbers are thought to have declined by about 75% in North America since the 1970s (Butcher and Niven 2007, Llimona et al. 2017). In addition, the summer range has contracted north and west such that the species no longer breeds in Utah, Nebraska, Iowa, Wisconsin, and eastern Canada. Horned Grebes also are undergoing a widespread drop in numbers in Eurasia (Llimona et al. 2017). Given these declines, the International Union for Conservation of Nature listed the species as Vulnerable in 2015.

As is often the case for poorly studied bird species, we have lots to learn about why the Horned Grebe is in decline. Major threats include logging and other human disturbances around nesting lakes in the boreal forest, and, perhaps surprisingly, stocking of rainbow trout, which compete with grebes for aquatic invertebrates that make up the bulk of their diet. Oil spills on the wintering grounds also can take a toll, in some cases killing several thousand birds in a single event (Stedman 2000). At least in Montana, we can assume that loss of small prairie wetlands, as witnessed by DuBois in 1917, must have resulted in widespread declines in breeding numbers across the state. With only a scant amount of information on the species’ status in Montana, and with no management guidelines for it anywhere in its range, the immediate need for the Horned Grebe is to establish a formal monitoring program that will shed new light on nesting distribution, numbers, and productivity in the state. The Montana Bird Advocacy is preparing to begin surveys for Horned Grebes in the next year or two. Please contact us if you are interested in participating!

Literature Cited

Butcher, G. S., and D. K. Niven. 2007. Combining data from the Christmas Bird Count and the Breeding Bird Survey to determine the continental status and trends of North America birds. National Audubon Society, New York.

DuBois, A. D. 1919. An experience with Horned Grebes (Colymbus auritus). Auk 36: 170-180.

Faaborg, J. 1976. Habitat selection and territorial behavior of the small grebes of North Dakota. Wilson Bulletin 88: 390-399.

Ferguson, R. S., and S. G. Sealy. 1983. Breeding ecology of the Horned Grebe, Podiceps auritus, in southwestern Manitoba. Canadian Field-Naturalist 97: 401-408.

Llimona, F., J. del Hoyo, J., D. A. Christie, F. Jutglar, E. F. J. Garcia, G. M. Kirwan, and C. J. Sharpe. 2017. Horned Grebe (Podiceps auritus). In J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana  (Eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.

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.

Stedman, S. J. 2000. Horned Grebe (Podiceps auritus). In The birds of North America, No. 505 (A. Poole and F. Gill, Eds.). Academy of Natural Sciences of Philadelphia and American Ornithologists’ Union.

Wetlands International. 2017. Waterbird population estimates.
http://wpe.wetlands.org/

Wightman, C., F. Tilly, and A. Cilimburg. 2011.  Montana’s colonial-nesting waterbird survey: Final report. Montana Department of Fish, Wildlife and Parks, Helena.