Horned grebe (Podiceps auritus)

Description

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Horned grebe fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
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Horned grebe description

Also known as the Slavonian grebe, the horned grebe (Podiceps auritus) is a small waterbird that is named for the distinctive golden-yellow patches of feathers behind its eyes, which resemble short horns ^{(2) (3) (4) (5)}. These “horns” can be erected or lowered, and are only present during the breeding season ^{(3) (4)}.

The horned grebe is also recognised by its straight, stubby bill and rather large, flat-topped head that is peaked at the rear ^{(3) (5) (6)}. In its breeding plumage, this species has a glossy black head, a chestnut neck and flanks, a dark brown or blackish back, and a white belly. In flight, the horned grebe usually shows a small white mark on the shoulder and white secondary feathers on the wing ^{(3) (5)}.

Outside of the breeding season, the horned grebe is much less striking, being mainly dark greyish above and white below. The dark grey crown contrasts with white cheeks that extend to the back of the neck, where the white is divided by a narrow black line ^{(3) (5) (6)}. The neck is usually white, but may have a slightly greyish wash ^{(3) (6)}.

The horned grebe’s bill is black, with a whitish tip. Its eyes are a striking scarlet, with a fine white ring around the pupil, and there is a dusky pink stripe between the eye and bill ⁽³⁾. Like all grebes, the horned grebe has large feet with peculiar, lobed toes ⁽⁷⁾, which in this species are blackish-brown, or blue to grey-green during the breeding season ⁽³⁾.

Male and female horned grebes are similar in appearance, but the male is slightly larger than the female and has brighter breeding plumage ^{(3) (7)}. The juvenile horned grebe resembles the non-breeding adult, but has dark striping or mottling on the side of the head and a less distinct border between the dark crown and white cheeks. Horned grebe chicks have stripy down, particularly on the head and neck ^{(2) (3)}.

Two subspecies of horned grebe are usually recognised: Podiceps auritus auritus and Podiceps auritus cornutus ^{(2) (3) (7)}. P. a. cornutus is generally slightly paler and greyer than P. a. auritus, and has lighter buff “horns” ⁽³⁾. Some scientists have also suggested a third subspecies, Podiceps auritus arcticus ^{(3) (8)}, although this is not recognised by all ⁽³⁾.

The horned grebe is most easily confused with the closely related black-necked grebe (Podiceps nigricollis), but has a thicker, straighter bill and a more slender neck. It is also distinguished by its reddish rather than black neck during the breeding season, and by its lighter face in winter ^{(2) (3) (4)}.

The calls of the horned grebe include a long, squealing trill and a loud, nasal ‘aaarrh’, which descends in pitch and ends in a rattle or trill ^{(3) (4) (5)}.

Also known as

Slavonian grebe.

Synonyms

Colymbus auritus.

Size

Length: 31 - 38 cm ^{(2) (3)}

Wingspan: 55 - 64 cm ⁽⁴⁾

Weight

300 - 570 g ^{(3) (4)}

Horned grebe biology

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⁾.

Horned grebe range

The horned grebe is widespread across Europe, Asia and North America ⁽⁹⁾. The subspecies P. a. auritus breeds from Iceland, Scandinavia and the United Kingdom, east to the Pacific coast of Russia, while P. a. cornutus breeds in southern Alaska, western and central Canada, and into the northern United States ^{(2) (3) (4) (7) (9)}.

A migratory species, the horned grebe moves south for the winter, typically to coastal waters. P. a. auritus winters in the North, Adriatic, Black and Caspian Seas, as well as south to the Mediterranean, in the Arabian Gulf, and along the coasts of Japan, China and Korea. P. a. cornutus winters in the coastal United States, as far south as California in the west and Texas in the east ^{(2) (3) (7) (9)}.

Horned grebe habitat

During the breeding season, the horned grebe is typically found on small, shallow freshwater pools and marshes, as well as in secluded parts of larger lakes and rivers and sometimes areas of brackish water ^{(2) (3) (9)}. Its preferred habitats have patches of open water as well as plentiful submerged and emergent vegetation ^{(3) (6) (9)}.

In winter, the horned grebe moves to coastal inshore waters, such as bays, lagoons and estuaries, and occasionally the open sea. Smaller numbers can also be found inland on large lakes, reservoirs and rivers ^{(2) (3) (6) (9)}.

Horned grebe status

The horned grebe is classified as Least Concern (LC) on the IUCN Red List ⁽¹⁾.

Horned grebe threats

Although the horned grebe has an extensive range and is generally common, its population appears to be declining and its range contracting in some areas ^{(3) (4) (7) (9)}.

One of the main factors thought to be affecting this small waterbird is habitat degradation, due for example to agricultural activities and pesticides that affect water quality and reduce insect abundance ⁽³⁾. Fluctuating water levels and changes to water systems as a result of afforestation are also likely to affect the horned grebe ^{(2) (3) (9)}, and this species is particularly vulnerable to oil spills in its winter marine habitat ^{(2) (3) (7) (9)}.

Other potential threats to the horned grebe are human disturbance at its nesting and roosting sites, which can cause it to abandon an area ⁽³⁾, and the stocking of lakes with rainbow trout (Oncorhynchus mykiss), which compete with the horned grebe for insect prey ^{(2) (9)}. The horned grebe is also sometimes caught accidentally in fishing nets and drowned ^{(2) (3) (9)}.

During the 19th century, the horned grebe was shot for its feathers, but shooting and hunting are not currently thought to be significant threats to this species ⁽³⁾.

Horned grebe conservation

Conservation measures targeted at the horned grebe have so far included efforts to provide suitable nesting habitat, for example by extending sedge beds at a breeding lake in Scotland ⁽⁹⁾. This species is listed on Appendix II of the Convention on Migratory Species (CMS or Bonn Convention), which aims to protect migratory species across their range ⁽¹⁰⁾, and is listed under the African-Eurasian Waterbird Agreement (AEWA), which calls upon parties to protect and conserve species that are dependent on wetland habitats ⁽¹¹⁾.

Further recommendations to address the declines in this species include identifying key sites at which it occurs, and surveying and closely monitoring its populations. The horned grebe is considered to be a good indicator of wetland quality, and could therefore be used as a focal species for wetland conservation in the regions it inhabits ^{(3) (7)}.

Find out more

Find out more about the horned grebe and its conservation:

• BirdLife International - Horned grebe:
  http://www.birdlife.org/datazone/speciesfactsheet.php?id=3640
• Birds of North America Online - Horned grebe:
  http://bna.birds.cornell.edu/bna/species/505
• O’Donnel, C. and Fjeldså, J. (1997) Grebes: Status Survey and Conservation Action Plan. IUCN/SSC Grebe Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:
  http://data.iucn.org/dbtw-wpd/edocs/1997-058.pdf

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Glossary

Afforestation

The establishment of forest by natural succession (progressive changes in the vegetation over time) or by the planting of trees on land where they did not grow formerly.

Brackish

Slightly salty water, usually a mixture of salt and freshwater, such as that found in estuaries.

Crustaceans

Diverse group of animals with jointed limbs and a hard chitinous exoskeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.

Emergent

Aquatic plants whose stems and leaves extend beyond the water’s surface.

Incubate

To keep eggs warm so that development is possible.

Molluscs

A diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.

Monogamous

Having only one mate during a breeding season, or throughout the breeding life of a pair.

Parasite

An organism that derives its food from, and lives in or on, another living organism at the host’s expense.

Secondary feathers

The shorter flight feathers projecting along the inner edge of a bird’s wing.

Subspecies

A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Territory

An area occupied and defended by an animal, a pair of animals or a colony.

References

1. IUCN Red List (February, 2012)
   http://www.iucnredlist.org/
2. del Hoyo, J., Elliott, A. and Sargatal, J. (1992) Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona.
3. Stedman, S.J. (2000) Horned grebe (Podiceps auritus). In: Poole, A. (Ed.) The Birds of North America Online. Cornell Lab of Ornithology, Ithaca. Available at:
   http://bna.birds.cornell.edu/bna/species/505
4. The Cornell Lab of Ornithology: All About Birds - Horned grebe (February, 2012)
   http://www.allaboutbirds.org/guide/Horned_Grebe/id/ac
5. Peterson, R.T., Mountfort, G. and Hollom, P.A.D. (1993) Collins Field Guide: Birds of Britain and Europe. HarperCollins Publishers, London.
6. Dunne, P. (2006) Pete Dunne’s Essential Field Guide Companion: A Comprehensive Resource for Identifying North American Birds. Houghton Mifflin Company, New York.
7. O’Donnel, C. and Fjeldså, J. (1997) Grebes: Status Survey and Conservation Action Plan. IUCN/SSC Grebe Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:
   http://data.iucn.org/dbtw-wpd/edocs/1997-058.pdf
8. Fjeldså, J. (1973) Distribution and geographical variation of the horned grebe Podiceps auritus (Linnaeus, 1758). Ornis Scandinavica, 4(1): 55-86.
9. BirdLife International - Horned grebe (February, 2012)
   http://www.birdlife.org/datazone/speciesfactsheet.php?id=3640
10. Convention on the Conservation of Migratory Species of Wild Animals (February, 2012)
    http://www.cms.int/
11. Agreement on the Conservation of African-Eurasian Migratory Waterbirds (February, 2012)
    http://www.unep-aewa.org/