Editing Blue duck (section)

==Behaviour==
This [[species]] is an [[endemic (ecology)|endemic]] resident breeder in [[New Zealand]], nesting in hollow logs, small caves and other sheltered spots. It is a rare duck, holding territories on fast flowing mountain rivers. It is a powerful swimmer even in strong currents, but is reluctant to fly. It is difficult to find, but not particularly wary when located.

===Diet===
The blue duck feeds almost entirely on aquatic invertebrate [[larva]]e. A study of blue ducks on the Manganuiateao River in the central North Island found the most common prey items were [[Chironomidae]] (midge) and cased [[caddisfly]] larvae, although cased caddisfly were less preferred and were only consumed so much because of their abundance. [[Hydrobiosidae]] (free-living caddisfly) and ''[[Aphrophila neozelandica]]'' ([[crane fly]]) larvae were also frequently eaten. Other prey included [[mayfly]], ''[[Aoteapysche]]'' (net-building caddis) and [[Plecoptera|stonefly]] larvae.<ref>{{cite journal |last1=Veltman |first1=C. J. |last2=Collier |first2=K. J. |last3=Henderson |first3=I. M. |last4=Newton |first4=L. |date=1995 |title=Foraging ecology of blue ducks ''Hymenolaimus malacorhynchos'' on a New Zealand river: implications for conservation |journal=Biological Conservation |volume=74 |issue=3 |pages=187–194 |doi=10.1016/0006-3207(95)00029-4|bibcode=1995BCons..74..187V }}</ref> The blue duck on occasion take berries and the fruits of shrubs.<ref name=iucn/>

===Foraging===
The foraging behaviour of the blue duck is characterised by its reliance on benthic invertebrates in fast-flowing riverine environments. Blue ducks primarily engage in dabbling behaviour where they feed by scouring rocks rather than up-ending or dabbling at the water's surface. Observations indicate that territorial males and females dabble approximately 96% of the time, with juvenile ducks dabbling 86% of the time. During the diurnal cycle, territorial birds exhibit higher foraging in the early morning and late evening, while non-territorial birds tend to forage more at midday. The decrease in dabbling during midday corresponds with an increase in diving behaviour in deeper pools. This pattern suggests that blue ducks capitalise on invertebrate resources that vary in availability throughout the day.<ref name="Eldridge">Eldridge, J. L. (1986). Territoriality in a river specialist: the blue duck. Wildfowl, 37(37), 123-135.</ref> Diving behaviour was seen most frequent in March and July when water levels are higher and prey living on stones and boulders above the water-surface would have been inaccessible using alternative foraging methods.<ref>Veltman, C. J., Collier, K. J., Henderson, I. M., & Newton, L. (1995). Foraging ecology of blue ducks Hymenolaimus malacorhynchos on a New Zealand river: implications for conservation. Biological Conservation, 74(3), 187-194.</ref> Blue ducks’ foraging activities peak during early morning and late afternoon, coinciding with the diurnal activity patterns of invertebrate drift. The reliance on these temporal patterns allows blue ducks to exploit a resource that is continuously recolonising denuded areas in the river.<ref name="Velt">Veltman, C. J., Triggs, S., Williams, M., Collier, K. J., McNab, B. K., Newton, L., ... & Henderson, I. M. (1991). The blue duck mating system: are river specialists any different? Acta XX Congressus Internationalis Ornithologici, 860-867.</ref> Ducks can be seen feeding at other times but often the day and night is spent in hiding or resting.<ref name="Kear">Kear, J., & Burton, P. J. K. (1971). The food and feeding apparatus of the blue duck Hymenolaimus. Ibis, 113(4), 483-493.</ref> Feeding behaviour is influenced by the type of prey available, requiring both tactile and visual foraging techniques. While foraging, blue ducks primarily glean invertebrates from rock surfaces using visual cues for mobile prey such as mayfly larvae. They have forward facing eyes that indicate this visual foraging use, typical of diving ducks, some attribute the evolution of this feature to the special absence of predators.<ref name="Kear"/> Blue ducks also utilise tactile cues to scrape small chironomid larvae from submerged surfaces. <ref name="Martin">Martin, G. R., Jarrett, N., & Williams, M. (2007). Visual fields in Blue Ducks Hymenolaimus malacorhynchos and Pink‐eared Ducks Malacorhynchus membranaceus: visual and tactile foraging. Ibis, 149(1), 112-120.</ref> Changes in water clarity can therefore significantly affect foraging efficiency, particularly for mobile prey. Territoriality in blue ducks is closely linked to the availability of food resources. Although blue ducks occupy large territories, the size is not primarily determined by food abundance; rather, it reflects the overlapping life cycles of benthic invertebrates, which exhibit minimal seasonal variation. <ref name="Velt"/> This indicates that while food resources are critical for blue duck distribution and population structure, they do not necessarily dictate territorial size.<ref name="Godfrey">	Godfrey, J. D., Bryant, D. M., & Williams, M. (2003). Energetics of blue ducks in rivers of differing physical and biological characteristics. Science for Conservation, 214, 35-68.</ref>

===Territoriality===
Blue ducks display territorial behaviours, they are known for their year-round territoriality, with territories typically ranging from 0.5 to 1.5 kilometres along river habitats characterised by alternating pools and rapids. The size and boundaries of these territories depend on resource availability, environmental conditions, and competition with other blue ducks.<ref name="Velt"/><ref name="Eldridge"/> During the breeding season, territory defence becomes critical as breeding pairs protect their territories from intruders. This behaviour secures access to essential resources and optimal breeding sites, enhancing reproductive success.
Both male and female blue ducks cooperate to defend their territories, using a variety of behaviours to deter intruders. Defensive behaviours include head bobbing, vocalisations, and aggressive confrontations. These behaviours communicate their presence and resolve conflicts over territory.<ref name="Eldridge"/><ref name="Williams">Williams, M. (1991). Social and demographic characteristics of blue duck ''Hymenolaimus malacorhynchos''. Wildfowl, 42, 65-86.</ref> The intensity of these interactions varies based on several factors, including the presence of a female during confrontations. When females are present, aggressive behaviours may escalate, highlighting the significance of mate guarding in territory defence. This interaction shows social and environmental factors shaping territorial behaviour.<ref name="Eldridge"/> Territoriality in blue ducks is linked to habitat quality. Research indicates that pairs in higher-quality environments expend less energy on territorial defence, allowing for greater foraging opportunities and improved reproductive fitness.<ref name="Godfrey"/> While pairs defend their territories, extensive areas between them may remain unprotected. Juvenile and unpaired blue ducks exploit these undefended spaces for foraging, indicating that territoriality does not completely limit resource availability for non-breeding individuals.<ref name="Eldridge"/> After the breeding period, blue ducks may adjust their territorial size in response to resource availability, often reducing their territory to focus on the most productive areas. As the breeding season progresses, interactions between neighbouring pairs can intensify, particularly with increasing competition for shared resources. Most aggressive confrontations involve males defending territories against foraging intruders, highlighting male-male competition's role in shaping blue duck social dynamics.<ref name="Eldridge"/><ref name="Williams"/>

===Mating===
Blue ducks exhibit a complex social structure characterised by strong pair bonds and monogamous behaviour, integral to their reproductive success and territory defence in riverine habitats. Typically, blue ducks maintain permanent year-round territories defended by mated pairs, emphasising the significance of monogamy for the successful rearing of offspring. <ref name="Velt">Veltman, C. J., Triggs, S., Williams, M., Collier, K. J., McNab, B. K., Newton, L., ... & Henderson, I. M. (1991). The blue duck mating system: are river specialists any different? Acta XX Congressus Internationalis Ornithologici, 860-867.</ref> Pair members rarely stray far from each other, with individuals often remaining in close proximity throughout the year.<ref name="Williams"/> In blue ducks, synchronous behaviours further enhance the stability of pair bonds, as pairs coordinate their activities, particularly during periods of brood dispersal and moulting. Pairs often forage together, displaying high synchronisation rates during various behavioural activities, which can range from 62% during moult to 81% in the pre-laying phase. <ref name="Velt"/> This synchronised behaviour is said to likely improve foraging efficiency and reduces vulnerability to predation, reinforcing the significance of the social bonds. During incubation, males shift their foraging habits to support female partners and their offspring, highlighting a collaborative approach to parental care. <ref name="Williams"/> Although blue ducks generally exhibit monogamous pair bonding, instances of extra-pair mating may occur, particularly when environmental pressures or territory dynamics shift. <ref name="Velt"/>

===Breeding===
[[File:Blue Ducks.JPG|thumb|Blue duck family in Hawke's Bay]]
Blue ducks nest between August and October, laying 4–9 creamy white eggs. The female incubates the eggs for 31 to 32 days and chicks can fly when about 70 days old.<ref name=hanzab/>

Nesting and egg incubation of four to seven eggs is undertaken by the female while the male stands guard. Nests are shallow, twig, grass and down-lined scrapes in caves, under river-side vegetation or in log-jams, and are therefore very prone to spring floods. For this, and other reasons, their breeding success is extremely variable from one year to the next.<ref name="r8">{{cite web|url=http://www.doc.govt.nz/conservation/native-animals/birds/birds-a-z/blue-duck-whio/|title=Blue duck/whio|website=New Zealand Department of Conservation – Te Papa Atawhai|access-date=13 March 2015|archive-url=https://web.archive.org/web/20150302200701/http://www.doc.govt.nz/conservation/native-animals/birds/birds-a-z/blue-duck-whio/|archive-date=2 March 2015|url-status=dead}}</ref>