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23-470: Nyroca australis Eyton, 1838 The hardhead ( Aythya australis ), also known as the white-eyed duck , is the only true diving duck found in Australia. The common name "hardhead" has nothing to do with the density of the bird's skull, instead referring to the difficulty encountered by early taxidermists in processing the head. Hardheads are found in wetter, coastal regions of Australia, particularly in

46-611: A counterclockwise pattern. Hurricanes and tropical storms (massive low-pressure systems) spin counterclockwise in the Northern Hemisphere. The shadow of a sundial moves clockwise on latitudes north of the subsolar point and anticlockwise to the south. During the day at these latitudes, the Sun tends to rise to its maximum at a southerly position. Between the Tropic of Cancer and the Equator,

69-620: A seasonal variation in temperatures, which lags the variation in day and night. Conventionally, winter in the Northern Hemisphere is taken as the period from the December solstice (typically December 21 UTC ) to the March equinox (typically March 20 UTC), while summer is taken as the period from the June solstice through to the September equinox (typically on 23 September UTC). The dates vary each year due to

92-418: A soft, wheezy whistle and 'whirr'. Females have a loud rattling 'gaark' call. Diving duck See the text The diving ducks , commonly called pochards or scaups , are a category of duck which feed by diving beneath the surface of the water. They are part of Anatidae , the diverse and very large family that includes ducks, geese , and swans . The diving ducks are placed in a distinct tribe in

115-561: Is a very distinct one however. Although the group is cosmopolitan , most members are native to the Northern Hemisphere , and it includes several of the most familiar Northern Hemisphere ducks. This group of ducks is so named because its members feed mainly by diving, although in fact the Netta species are reluctant to dive, and feed more like dabbling ducks. These are gregarious ducks, mainly found on fresh water or on estuaries , though

138-532: Is evaluated as Least Concern on the IUCN Red List of Threatened Species . Like the other members of the pochard group, hardheads feed by diving deeply, often staying submerged for as long as a minute at a time. They slip under the water with barely a ripple, simply lowering their heads and thrusting with their powerful webbed feet. They eat a broad range of small aquatic creatures, and supplement this with water weeds. Hardheads are usually silent, but males have

161-556: The Coriolis effect . The currents then bend to the right, heading north. At about 30 degrees north latitude, a different set of winds, the westerlies , push the currents back to the east, producing a closed clockwise loop. Its surface is 60.7% water, compared with 80.9% water in the case of the Southern Hemisphere , and it contains 67.3% of Earth's land. The continents of North America and mainland Eurasia are located entirely in

184-460: The Northern temperate zone . The changes in these regions between summer and winter are generally mild, rather than extreme hot or cold. However, a temperate climate can have very unpredictable weather. Tropical regions (between the Tropic of Cancer and the Equator, 0° latitude) are generally hot all year round and tend to experience a rainy season during the summer months, and a dry season during

207-719: The dabbling ducks ; their legs tend to be placed further back on their bodies to help propel them when underwater. Three genera are included in the Aythyini. The marbled duck which makes up the monotypic genus Marmaronetta , however, seems very distinct and might have diverged prior to the split of dabbling and diving ducks as indicated by morphological and molecular characteristics. The probably extinct pink-headed duck , previously treated separately in Rhodonessa , has been suggested to belong into Netta , but this approach has been questioned. DNA sequence analyses have found it to be

230-418: The greater scaup becomes marine during the northern winter. They are strong fliers; their broad, blunt-tipped wings require faster wing-beats than those of many ducks and they take off with some difficulty. Northern species tend to be migratory ; southern species do not migrate though the hardhead travels long distances on an irregular basis in response to rainfall. Diving ducks do not walk as well on land as

253-566: The last glacial period ended about 10,000 years ago. Earth is currently in an interglacial period of the Quaternary , called the Holocene . The glaciations that occurred during the glacial period covered many areas of the Northern Hemisphere. The Arctic is a region around the North Pole (90° latitude ). Its climate is characterized by cold winters and cool summers. Precipitation mostly comes in

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276-620: The Northern Hemisphere, together with about two-thirds of Africa and a small part of South America . During the 2.5 million years of the Pleistocene , numerous cold phases called glacials ( Quaternary ice age ), or significant advances of continental ice sheets, in Europe and North America , occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials which lasted about 10,000–15,000 years. The last cold episode of

299-704: The Sun can be seen to the north, directly overhead, or to the south at noon, depending on the time of year. In the Southern Hemisphere, the midday Sun is predominantly in the north. When viewed from the Northern Hemisphere, the Moon appears inverted compared to a view from the Southern Hemisphere. The North Pole faces away from the Galactic Center of the Milky Way . This results in the Milky Way being sparser and dimmer in

322-402: The difference between the calendar year and the astronomical year . Within the Northern Hemisphere, oceanic currents can change the weather patterns that affect many factors within the north coast. Such events include El Niño–Southern Oscillation . Trade winds blow from east to west just above the equator. The winds pull surface water with them, creating currents, which flow westward due to

345-534: The diving ducks are placed as a subfamily Aythyinae in the family Anatidae which would encompass all duck-like birds except the whistling-ducks . The seaducks commonly found in coastal areas, such as the long-tailed duck (formerly known in the U.S. as oldsquaw), scoters , goldeneyes , mergansers , bufflehead and eiders , are also sometimes colloquially referred to in North America as diving ducks because they also feed by diving; their subfamily (Merginae)

368-536: The duck is in the water). The trailing edges and almost the entire underside of the wings are white. In the male, the eyes are a striking white, in the female, brown. Hardheads are common in the south-east of Australia, particularly in the Murray-Darling Basin , but also in the wetter country near the coasts. They are moderately nomadic in normal years, but disperse widely in times of drought . Significant numbers reach as far afield as New Guinea, New Zealand, and

391-401: The earliest diverging member of the pochard group. The molecular analysis also suggests that the white-winged duck should be placed into a monotypic genus Asarcornis which is fairly close to Aythya and might belong into this subfamily. Northern Hemisphere Due to Earth's axial tilt of 23.439281°, there is a seasonal variation in the lengths of the day and night. There is also

414-630: The form of snow. Areas inside the Arctic Circle (66°34′ latitude) experience some days in summer when the Sun never sets, and some days during the winter when it never rises. The duration of these phases varies from one day for locations right on the Arctic Circle to several months near the Pole, which is the middle of the Northern Hemisphere. Between the Arctic Circle and the Tropic of Cancer (23°26′ latitude) lies

437-453: The islands of the Pacific, where they can remain for some time, even breeding for a season or two. Hardheads prefer larger lakes, swamps and rivers with deep, still water, but are often seen in smaller streams, flooded grasslands, and shallow pools. As a general rule, they avoid coastal waters. They rarely come to land and never perch in trees. Widespread throughout its large range, the hardhead

460-499: The south-east, but are known to disperse as far afield as New Guinea , New Zealand , and the Pacific Islands . Hardheads are smaller than most ducks , usually not reaching much more than 45 cm long but sometimes reaching 60 cm, and noticeably more rounded in overall form than most ducks. Both male and female are a fairly uniform chocolate-brown above, with rufous flanks and white undersides (which are often not visible if

483-476: The subfamily Anatinae , the Aythyini . While morphologically close to the dabbling ducks , there are nonetheless some pronounced differences such as in the structure of the trachea . mtDNA cytochrome b and NADH dehydrogenase subunit 2 sequence data indicate that the dabbling and diving ducks are fairly distant from each other, the outward similarities being due to convergent evolution . Alternatively,

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506-496: The weather patterns that affect many factors within the north coast. For the same reason, flows of air down toward the northern surface of the Earth tend to spread across the surface in a clockwise pattern. Thus, clockwise air circulation is characteristic of high pressure weather cells in the Northern Hemisphere. Conversely, air rising from the northern surface of the Earth (creating a region of low pressure) tends to draw air toward it in

529-482: The winter months. In the Northern Hemisphere, objects moving across or above the surface of the Earth tend to turn to the right because of the Coriolis effect . As a result, large-scale horizontal flows of air or water tend to form clockwise-turning gyres . These are best seen in ocean circulation patterns in the North Atlantic and North Pacific oceans. Within the Northern Hemisphere, oceanic currents can change

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