Australian Little Grebe
| Australian Little Grebe | ||||||||||
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Australian Little Grebe ( Tachybaptus novaehollandiae ) |
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| Tachybaptus novaehollandiae | ||||||||||
| ( Stephens , 1826) |
The Australian Little Grebe ( Tachybaptus novaehollandiae ) is a species of bird from the family of grebes . He is one of the particularly small representatives of the family. The species occurs in Australia and Tasmania as well as in parts of New Guinea. The species has been introduced in New Zealand since 1969. According to the Clements Checklist of Birds of the World , seven subspecies are assumed today (August 2017).
The exact population of the species is not known. However, it is classified by the IUCN as not at risk ( least concern ).
Appearance
Australian little grebes reach a length of 23 to 25 centimeters. The wingspan is 39 centimeters. The weight varies between 100 and 230 grams. A sexual dimorphism is pronounced only slight. The males are on average slightly larger than the females and have a slightly stronger bill.
In their splendid dress , Australian little grebes have a black, shiny green upper head, the green color extends to the eyes. The black throat patch is large and is bordered by the chestnut brown sides of the head. This brown color extends to the ear covers and the back of the neck. The back of the neck and the top of the body are soot black. The neck is dark gray-brown. The breast is a little lighter gray and has soot-colored speckles. In some individuals there are also beige-brown speckles in the breast plumage. The belly is silvery white. The eyes are orange-yellow, a strong white-yellow line runs in front of the eye, which contrasts strongly with the dark face and beak. The beak is gray-black at the base and brightens whitish at the tip.
In the resting dress, the top of the head is dark gray-brown. The rest of the head is a little lighter with a yellowish brown tone on the ear patches. The rest of the plumage resembles the breeding plumage, but the sides of the body and the flanks are a bit browner. The eyes are orange outside of the breeding season. The beak is bluish white to yellowish at this time. Young birds not yet sexually mature wear plumage that is similar to the resting plumage. Her head, however, is streaked with dark brown and yellowish brown.
There is a possibility of confusion, especially with the poppy diver . Young birds and adults in the plain dress of both species can hardly be distinguished in field observations. In the Australian Little Grebe, the line that separates the dark top of the head from the lighter face runs at eye level, while in the Scorpionfish it runs below the eye. The Australian Little Grebe also has oval nostrils, while those are oblong in the poppy diver. The Maori diver is slightly larger than the Australian Little Grebe and darker on the top of the body in all clothes. It is also strikingly maroon from chin to chest and lacks the yellow eye spot.
distribution and habitat
In addition to Australia, Tasmania and New Guinea, the Australian Little Grebe also inhabits some smaller islands. These include Sepik and Bulol in northern New Guinea, Rennell Island, Vanuatu and the New Hebrides as well as Santa Maria (Gaua), Dolphin, Espiritu Santo and Oba Is as well as Sangihe and Talaud . There are also some sightings on Supul and Timor as well as Java . The IUCN estimates the range to be around 2.96 million square kilometers. The first birds were observed in New Zealand in April 1968, and until the end of the 20th century there were small breeding populations on both the South and North Islands of New Zealand.
The Australian Little Grebe is relatively common and widespread in Australia. The largest stocks on the Australian continent are found in the southeast and east as well as in the southwest. The species makes use of all kinds of wetlands. This ranges from larger cattle troughs to calmly flowing stretches of river and uncrowded water in swamps and marshland to large open lakes. Wetlands that do not offer adequate privacy are mainly used outside of the breeding season. Permanent, nutrient-rich waters are preferred for breeding. The migratory movements of the Australian little diver have not yet been adequately investigated. It is believed to be a resident bird in the east and southwest of Australia, while it is a migratory bird in the north of Australia. In the Australian interior, it probably moves depending on rainfall and water level. In the north of Australia, most of the Australian Little Grebes are observed during the dry season. From the settlement of New Zealand relatively few years ago and the rapid expansion there, one concludes that the Australian Little Grebe is able to migrate far.
Compared to the shaved diver, the Australian little grebe tends to use smaller bodies of water and those with a higher density of vegetation. It is also more frequent at the edge of the water than on the open water. It is far less common in brackish and salt water than the shaved diver. Particularly during the breeding season, it is dependent on extensive floating vegetation.
Food and subsistence
The food spectrum consists mainly of various insects and other invertebrates. This includes water beetles and their larvae and snails. Schnabelkerfen play a particularly large role in the food spectrum . In addition, small fish are also eaten. Australian little grebes prefer clear water for foraging. However, they usually do not dare to venture more than a diving length from a cover consisting of floating plants or the reed belt of the shore to the open water surface. In general, the way they forage varies more than other ragged divers. They dive frequently, but occasionally only dip their heads and necks in the water, pick food from the surface of the water or stalk insects on floating plants. They jump a little forward when diving, dives usually lasting between 8 and 22 seconds. They take breaks of 7 or 8 seconds between the individual dives. Small prey are usually swallowed below the surface of the water. If you catch fish that are more than three centimeters tall, they appear and only then eat the fish. Their hunting methods require that they hunt predominantly individually. Wherever many insects congregate, however, several Australian little grebes are often gathered.
Australian Little Grebes only look for food during the day and start foraging at the earliest half an hour after sunrise.
Reproduction
Little Grebe are monogamous, the pair bond has not yet been fully investigated, but it has many point out that they have a similar behavior as the spread in Eurasia little grebe . Pair bonding is usually maintained for at least one reproductive cycle. However, individual pairs stay together for several reproductive periods and on smaller, permanent bodies of water, the pair bond can last until one of the two partners dies.
During the breeding season, each pair defends a small breeding area. These areas are usually between 1,000 and 2,000 square meters. This can be a smaller pond, but also a bank area of a larger body of water. However, loose colonies can also form in large wetlands. Outside of the breeding season, Australian Little Grebes can often be seen in small flocks of two to seven birds. These can be family groups. Occasionally, however, hundreds of animals gather in loose swarms.
The breeding time depends on the respective distribution area. Often two to three broods are raised in a year. The clutch consists of up to nine eggs. With such large clutches, however, it can never be ruled out that a nest was used by two females as an egg-laying site. Clutches from just one female contain an average of 4.1 eggs. The breeding season is 23 days. The juveniles are usually independent 50 to 60 days after hatching. No data are available on the reproductive rate of the Australian Little Grebe. However, the breeding success is likely to be low. Causes of mortality, in addition to being stunted by predators, are fluctuating water levels and unfavorable weather.
supporting documents
- ↑ Fjeldså, p. 151
- ↑ The Clements Checklist of Birds of the World , August 2017
- ↑ a b BirdLife Factsheet , accessed July 9, 2009
- ↑ a b c Higgins, p. 92
- ↑ Fjeldså, p. 150
- ^ Higgins, p. 93
- ↑ a b c Higgins, p. 94
- ↑ Fjeldså, p. 152
- ↑ Higgins, p. 95
- ↑ a b Higgins, p. 96
- ↑ Fjeldså, p. 153
- ^ Higgins, p. 98
literature
- Jon Fjeldså: The Grebes . Oxford University Press, 2004, ISBN 0-19-850064-5
- PJ Higgins (Ed.): Handbook of Australian, New Zealand & Antarctic Birds , Volume 1, Ratites to Ducks, Oxford University Press, Oxford 1990, ISBN 0195530683
Web links
- Tachybaptus novaehollandiae inthe IUCN Red List of Threatened Species 2013.2. Listed by: BirdLife International, 2012. Retrieved February 6, 2014.