Within its vast northern breeding range, the Horned Grebe selects small ponds and lake inlets containing a mixture of emergent vegetation and open water, which are used to good advantage: its cryptic, floating nest is usually concealed in the vegetation, and its intraspecific visual signals, including stereotyped breeding displays such as the unique Weed Rush, are presented in the open water. Monogamous and intensely territorial, the Horned Grebe usually nests solitarily or in loose aggregations, occasionally in small colonies. The young are subprecocial and must be fed and kept warm by a parent for several days after hatching.
Known to most field observers in its contrasting dark-and-white Basic (nonbreeding) plumage, the Horned Grebe acquires chestnut in the neck, breast, and flanks during prealternate molt in spring and performs intricate courtship displays in its breeding habitat. Its Holarctic distribution and approachability during the nesting season have resulted in many intensive life-history studies in both the New World and Old World, making it among the better-known breeding species of the Northern Hemisphere. Breeding studies in North America include those of Ferguson (1, 2), Faaborg (3), Riske (4), Sugden (5), Ferguson and Sealy (6), Heglund et al. (7), and Fournier and Hines (8); European breeding studies of note include those of Fjeldså (9, 10, 11), and Ulfvens (12, 13, 14, 15). Food preferences in North America were investigated early on by McAtee and Beal (16), Wetmore (17), and Munro (18). The foremost behavioral study in North America is that by Storer (19).
Although the Horned Grebe is among the most abundant grebe species in North America, knowledge of the status and trends of populations in the New World is somewhat limited relative to knowledge of populations in Europe. Most breeding populations in North America occur in low densities at high latitudes, making it difficult to obtain population estimates. The Horned Grebe is also widely distributed within its North American overwintering range, rendering population assessment at that season equally difficult. This gap in knowledge is significant because North American Breeding Bird Survey (BBS) and Christmas Bird Count (CBC) results have suggested a long-term decline in population since the mid 1960s. Although BBS results suggest an increase numbers from approximately 2005 to 2015, broader survey efforts are needed to generate better population estimates for conservation planning.