Like other grebes, the horned grebe is a specialised diver, using its large feet to propel and steer its body underwater (3) (7), where it is remarkably agile (2). The feet are set far back on the body, making swimming more efficient but meaning the horned grebe is quite clumsy on land (3) (7). This species mainly dives for food, although it will also take food from the water’s surface, seize insects from the air, or pick prey from aquatic vegetation (2) (3) (4) (7).
The diet of the horned grebe consists of a variety of animal prey, including fish, aquatic insects, crustaceans, molluscs and worms (2) (3) (4). Insects are generally most important in the diet in summer, while fish and crustaceans are the major prey items in winter (2) (3). Interestingly, the horned grebe also regularly eats some of its own feathers, creating a matted plug in the stomach. This may possibly serve as a filter, hold fish bones in the stomach until they can be digested, help in the formation of digestive pellets, or perhaps help rid the grebe of intestinal parasites (3) (4) (7). Adult horned grebes will even feed feathers to their chicks (3) (4).
A monogamous species, the horned grebe usually occurs in solitary pairs during the breeding season, with the pair aggressively defending a territory from other birds. However, where food is plentiful, small, loose breeding colonies may sometimes occur (2) (3) (7) (9). During the non-breeding season, the horned grebe usually forages alone or in small groups, although larger flocks may gather occasionally (3) (9).
The horned grebe breeds between April and August, with egg-laying usually peaking around June (2). Like other grebes, this species has a complex, ritualised courtship display which is performed on open water and involves a number of stereotyped postures and movements (3) (7). Both the male and female horned grebe build the nest (3), which consists of a platform of aquatic vegetation. The nest may float on the water, anchored to emergent vegetation, or it may be built in shallow water from the bottom up, or on a rock sticking out of the water (2) (3) (4). In rare cases, the nest may be built on dry land on the shoreline (3).
The female horned grebe usually lays a single clutch of between three and eight eggs (3) (4), which range from white to brownish or bluish green (4). The eggs are incubated for 22 to 25 days (2), with both the adults sharing in the incubation (3). Although the young horned grebes are well developed at hatching, and are able to swim and dive within the first day (3) (4) (7), they must be kept warm by the adults for the first few days of life and fed for up to 14 days (3). During this time, the chicks are frequently carried on the adults’ backs while they swim, often hidden under their wings (3) (4) (7).
Young horned grebes usually become independent at 19 to 24 days old (3) and can first fly at around 41 to 60 days (2) (3). This species is thought to reach sexual maturity at about two years old (2), and may live for up to five years in the wild (3).