Hardheads were formerly widespread throughout their range but the populations have become fragmented with the populations in many of the mainstreams of the rivers being extirpated, leaving foothill populations isolated. This has been caused by habitat alteration which makes the stream unsuitable for this specialised species. In one stream which seems to be largely unaltered, the Cosumnes River, hardheads are absent with an invasion of redeye bass (Micropterus coosae) being seen as the probable cause of their extirpation. Hardheads are largely absent from reservoirs where there are extreme annual variations in water level, although they have been found to survive in small numbers in hydroelectric reservoirs where water levels are more stable.
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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 prefer larger lakes, swamps and rivers with deep, still water, but are often seen in smaller streams, flooded grasslands, and shallow pools.
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The common types of fish are mackerel, sardines, hardheads and prawns. Fishing is done from land with nets or from boats such as pandy (motor launch) and dhoni (dug out canoes). There is also mechanised trawling. The brackish water of the Kali estuary is suitable for prawn farming.
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They also appear to be vulnerable to invasive predatory fish in reservoirs, generally impoundment and damming do not favour hardheads and tend to favour introduced fish species. Hardheads seem to be especially vulnerable to the introduction of predatory bass from the family Centrarchidae. They are also vulnerable to pollution from agricultural runoff and their presence in midden sites of native peoples in the Sacramento and San Joaquin basins show that they were previously much more abundant and widespread than they are currently. In general, the simplification of water regimes, pollution and introduction of exotoc fish have caused declines in this species which was also persecuted as a competitor to more desirable game fish species.
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The site has been identified by BirdLife International as an IBA because it has supported significant numbers of freckled and pink-eared ducks, grey teals, hardheads, Australian pelicans, banded stilts, red-necked avocets and Caspian terns. It also supports populations of Eyrean grasswrens, black honeyeaters, banded whitefaces, chirruping wedgebills and cinnamon quail-thrushes.
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Plagioscion is a genus of hardheads, ray-finned fish in the family Sciaenidae. They are found in tropical and subtropical South America where they inhabit fresh and brackish waters. Some species (notably P. squamosissimus and P. surinamensis) are important food fish and support major fisheries. Depending on the exact species, they reach up to about in length.
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The lake is important for freckled and blue-billed ducks which are listed as threatened in Victoria. Waterbirds, waders and rails which have bred at the lake include black swans, hardheads, musk ducks, Australasian and hoary-headed grebes, darters, little pied and little black cormorants, dusky moorhens, purple swamphens, Eurasian coots and black-fronted dotterels. It is also a roosting site for hundreds of cormorants and ibises.
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From 1997-2001, 361,022 hardhead catfish were harvested within 200 miles of the shore in the IRL region. Hardheads are also harvested for industrial purposes in commercial bottom-trawling operations. Annual harvests vary greatly, but from 1987–2001, 1.04 million pounds of marine catfishes (including both the hardhead catfish and the gafftopsail catfish) were harvested in the IRL region. The harvest was valued at $777,497.
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"Hardheads" believe that peace and stability can only be established under one rule — theirs. The planar faction known as the Harmonium is actually just a small part of a much larger political entity which rules over the entirety of the Prime Material world of Ortho. In Sigil, they serve as the city's police force, and their headquarters is the City Barracks. They are related to present day authoritarianism, particularly religious evangelicalism and fundamentalism.
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Hardhead are apparently unable to recolonize areas they have been extirpated from and among the suggested measures to conserve the species are the artificialrestocking of suitable areas where it was formerly found. It has been also suggested that managing water flows to suit this species, and other native species, and disadvantage non native species should be researched and put into practice together with measures to mitigate impoundments and canalisation of the streams used by hardheads.
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As a general rule, they avoid coastal waters. They rarely come to land and never perch in trees. Hardheads are small by duck standards, usually not much more than 45 cm long but reaching 60 cm sometimes, 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 the duck is in the water).
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Some 2262 km2 of the lake system and its surroundings have been identified as an Important Bird Area by BirdLife International because it has significant breeding colonies of the letter-winged kites and over 1% of the world populations of plumed whistling- ducks, grey teals, hardheads, little black cormorants, Australian pelicans, straw-necked ibises, Eurasian coots, Oriental plovers, Australian terns and flock bronzewings. It also provides habitat for Australian bustards. When fully inundated, it may support up to a million waterbirds.
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The hardhead (Aythya australis) (also white-eyed duck) is the only true diving duck found in Australia. 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 the islands of the Pacific, where they can remain for some time, even breeding for a season or two.
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These twopenny placks are known as "hardheads" today.David Masson, Register of the Privy Council of Scotland: 1585-1592, vol. 4 (Edinburgh, 1881), pp. 317, 326; Nicholas Holmes, Scottish Coins: A History of Small Change in Scotland (Edinburgh, 1998), pp. 49-51. The coin appears in the old song: :A’ that e’er my Jeanie had, :My Jeanie had, my Jeanie had, :A’ that e’er my Jeanie had ::Was ae bawbie :There’s your plack, and my plack, :And your plack, and my plack, ::And Jeanie’s bawbie.
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Centaurea nigra - MHNT Illustration small heath butterfly on knapweed Centaurea nigra is a species of flowering plant in the daisy family known by the common names lesser knapweed, common knapweed and black knapweed. A local vernacular name is hardheads. It is native to Europe but it is known on other continents as an introduced species and often a noxious weed. Although the plant is often unwanted by landowners because it is considered a weed by many, it provides a great deal of nectar for pollinators.
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The site has been identified as an Important Bird Area (IBA) by BirdLife International because it supports regular numbers of orange- bellied parrots, and over 1% of the world populations of blue-billed, musk, freckled and pink-eared ducks, Australian shelducks, chestnut teals, Australasian shovelers, hoary-headed grebes, red-necked stints and sharp- tailed sandpipers. Other waterbirds that use the site in substantial numbers include banded stilts, curlew sandpipers, red-capped and double-banded plovers, black-fronted dotterels, pied oystercatchers, red-necked avocets, black swans, hardheads, Pacific black ducks and great crested grebes.
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They will infrequently take plankton and surface insects and, in Shasta Reservoir they were recorded feeding on cladocerans. Hardheads of less than mainly prey on benthic invertebrates, in particular the larvae of mayflies and caddis flies, as well as small snails. Larger fish grazed on filamentous algae, as well as preying on crayfish and other large invertebrates. As the fish mature their tooth structure changes; the juveniles have hooked teeth for catching insects and as they mature they develop more molar-like crushing teeth better adapted to grind plant material and larger invertebrates.
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A plack () was an ancient Scottish coin of the value of four Scots pence or by 1707 one third of an English penny.SND: plack On 3 March 1574 Regent Morton issued a proclamation to "cry down" or devalue unofficial placks and lions or hardheads (two pence pieces) made in the time of Mary of Guise. These placks would now be current at two pence, and the lions at one penny. The coins were to be returned to the mint, and if found lawful marked with a Douglas heart and returned to the owner.
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Hardheads from the Feather River which had grown to were aged at 9–10 years old, and it is considered that older and larger fish may occur in the Sacramento River. Hardhead found in smaller streams rarely reach longer than while old records suggest that this species attained total lengths of up to . Hardhead reach sexual maturity after their second year and spawn in April and May when the adults migrate upstream into the smaller tributary streams. Females have been found with mature eggs in March and specimens of both sexes examined in July and August had spent gonads.
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The site has been identified by BirdLife International as an Important Bird Area (IBA) because, when conditions are suitable, it supports up to 400,000 waterbirds with over 1% of the world populations of black swans, freckled and pink-eared ducks, grey teals, Australasian shovelers, hardheads, red-necked avocets, white-headed and banded stilts, sharp-tailed sandpipers and red-capped plovers. It supports regionally significant numbers of Australian pelicans, Eurasian coots and whiskered terns. It also holds populations of inland dotterels, Caspian terns, Bourke's parrots, grey-headed, black and pied honeyeaters, slaty-backed thornbills, Hall's babblers, chirruping wedgebills and chestnut-breasted quail-thrushes.
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The core of the wetland system has been identified as an Important Bird Area (IBA) by BirdLife International because it supports over 200,000 waterbirds when extensively flooded. It has periodically supported over 1% of the world populations of Australian pelicans and straw-necked ibises, their breeding colonies being among the largest recorded in the Australian tropics. Other birds which have bred in the IBA in relatively large numbers include freckled ducks, great and intermediate egrets, glossy ibises, Australian terns, magpie geese, plumed whistling-ducks, grey teals and hardheads. Nationally vulnerable Australian painted snipes bred at Tarrabool in 1993.
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A pair of brolgas amongst other waterbirds in the Northern Territory The lake serves as a major migratory stop-over area for a variety of shorebirds. It also provides a major breeding habitat of several species of water birds, including cormorants and terns. It has been identified by BirdLife International as an Important Bird Area (IBA) because it supports over 1% of the world populations of hardheads, grey teals, pink-eared ducks, little black cormorants, brolgas, sharp-tailed sandpipers. It sometimes supports similarly important numbers of magpie geese, Pacific black ducks, freckled ducks and Oriental plovers, as well as providing habitat for Australian bustards.
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Hardhead are mainly bottom feeders, foraging on invertebrates and aquatic plant material from the stream bed although they will also eat drifting insects and algae from higher in the water column. They will infrequently consume plankton and insects taken from the surface and in Shasta Reservoir the fish found there were observed to feed on cladocerans. They can attain in standard length after a year and by the end of the second year lengths of and by the end of their third year. In the American River hardheads can reach by the age of four but in the Pit River and the Feather River fish only reach this size at age 5 or 6.
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The lake, with its associated seasonal claypans and the nearby Barrolka Lakes to the north-east, has been identified by BirdLife International as a Important Bird Area (IBA) because it has supported over 1% of the world populations of plumed whistling-ducks, sharp-tailed sandpipers and Australian pelicans, as well as providing habitat for Australian bustards. A large colony of Australian pelicans breeds on an island at the north-eastern end of the lake. The Barrolka Lakes hold several cormorant colonies. Other birds recorded in substantial numbers include hardheads, white-headed stilts, glossy ibises, grey teals, black-tailed nativehens, Australian pratincoles, whiskered terns and Pacific black ducks, with smaller numbers of freckled ducks and white- winged black terns.
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The two ladders are funded by nearly $10 million in grants from several agencies, including $5.36 million from the California Wildlife Conservation Board and $3 million from the California Natural Resources Agency. When those projects are completed in 2021, steelhead will be able to migrate upstream to spawning habitats in the Sunol Valley for the first time in a half-century. California's archaeological record has contributed to knowledge of the prehistoric distribution of fishes in Alameda Creek and its tributaries including Sacramento perch (Archoplites interruptus), Sacramento suckers (Catostomus occidentalis occidentalis), Tule perch (Hysterocarpus traskii), Hitches (Lavinia exilicauda), Hardheads (Mylopharodon conocephalus), Sacramento blackfish, and Sacramento pikeminnow (Ptychocheilus grandis). Many of these fishes still occupy the creek, although the number of introduced exotic fishes continues to increase.
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Aerial view at southern end The lake, with its surrounding mudflats and grasslands, has been identified by BirdLife International as an Important Bird Area (IBA) because it supports about 150,000 waterbirds with twelve species being represented in large enough numbers to be considered internationally significant. The mud flats and grasslands are the natural habitat of eight wader species also represented in internationally significant numbers, along with a healthy population of Australian bustards which are considered a "near threatened" species. Birds for which the lake has global importance include magpie geese, wandering whistling-ducks, green pygmy-geese, Pacific black ducks, hardheads, black-necked storks, white-headed stilts, red-capped plovers, Oriental plovers, black-fronted dotterels, long-toed stints and sharp-tailed sandpipers. Common larger-bodied bird species found at the lake include the Australian pelican, black swan, eastern great egret, royal spoonbill, osprey and wedge-tailed eagle.
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It has been estimated that the spawning occurs at different times based on location, with juvenile recruitment suggesting that hardhead spawn by May–June in the streams of the Central Valley but at higher altitudes it may extend into August, for example in foothill streams. The adults may migrate more than from larger rivers and reservoirs may to spawn in smaller tributary streams while fish from in smaller waters will migrate short distances, either upstream or downstream, from their home pool to breed, seldom more than from their home pool. Although the spawning of hardheads in the wild has never been observed it is thought that it is probably similar to the spawning of the closely related Lavinia exilicauda and Sacramento pikeminnow, both species which lay their fertilized eggs in sand or gravel substrates in well oxygenated water such as riffles, rills, or faster flows at upper ends of pools. The breeding success of hardhead appears to be highest when the highest flows of a river occur between April and June.
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