Blue Duck Hymenolaimus malacorhynchos Scientific name definitions

53–54 cm; male 820–1077 g, female 680–870 g (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Generally slate-blue with greenish gloss on head , neck and back, chestnut spots on breast , outer secondaries tipped white and narrow black margins to inner secondaries and tertials (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Female averages smaller and has less breast spotting . Bare parts: bill pink-white with black flap at tip; legs and feet dark grey with black at joints; irides yellow (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Juvenile  lacks or virtually lacks breast spotting, and has no gloss on head and back; bill grey, irides dark brown (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Subspecies hymenolaimus darker above.

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Mountain streams and small, narrow rivers of clear, fast-flowing waters in well-vegetated areas, usually on steep gradient in forested areas (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ); rarely visits estuaries (3 Miskelly, C.M., Crossland, A.C., Sagar, P.M., Saville, I., Tennyson, A.J.D. and Bell, E.A. (2013). Vagrant and extra-limital bird records accepted by the OSNZ Records Appraisal Committee 2011-2012. Notornis. 60(4): 296–306. Close ). Structured analysis of habitat, based on multi-area survey throughout New Zealand, found that sections of river supporting the species had significantly greater physical stability, channel gradient (>12 m km ^-1) and elevation (82–1050 m), narrower widths (8–60 m), coarser bed substrata (particularly more boulders) and more native riparian forest (> 50% of vegetation on average) than sections where it was absent (4 Collier, K.J., Moralee, S.J. Wakelin, M.D. (1993). Factors affecting the distribution of Blue Duck Hymenolaimus malacorhynchos on New Zealand rivers. Biological Conservation. 63(1): 119–126. Close ). Also recorded at alpine tarns and lakes, occasionally farm pools, but does not breed in such areas (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ) and perhaps most frequently observed in such areas during dispersal (5 Harding, M.A. (1994). Blue Duck dispersal at Arthur’s Pass. Notornis. 41(4): 293–295. Close ) (see Movements). For roosting, a recent study found that stable undercut banks are most commonly used (42%), followed by log jams along stream banks (25%), and large woody debris is a component of 50% of sites (6 Baillie, B.R. and Glaser, A.B. (2005). Roost habitat of a North Island blue duck (Hymenolaimus malacorhynchos) population. Notornis. 52(1): 1–5. Close ).

Mainly sedentary, adult birds occurring within breeding territory (c. 0·7–1 km linear section of river) throughout year and for life (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ), unless displaced by adverse weather in winter; however, several transalpine movements of up to c. 25 km (mainly by juveniles) have been reported from the Southern Alps in the Arthur’s Pass region (5 Harding, M.A. (1994). Blue Duck dispersal at Arthur’s Pass. Notornis. 41(4): 293–295. Close ). Territories apparently highly fixed, even with changes of pairings due to death or displacement of one partner (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Although (as noted above) juveniles may wander extensively within, and sometimes beyond, natal catchment during first year of life, they generally return to same area and attempt to establish territory nearby (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ); tendency for juvenile males to move farther than young females, with a study in Fiordland National Park revealing that 87% of females remained in their natal catchment, moving a mean 3·84 ± 0·6 km, whereas only 40% of juvenile males remained in their natal catchment and a mean dispersal distance of 8·77 ± 2·05 km (7 Whitehead, A.L., Edge, K.-A., Smart, A.F., Hill, G.S. and Willans, M.J. (2008). Large scale predator control improves the productivity of a rare New Zealand riverine duck. Biological Conservation. 141(11): 2784–2794. Close ). Recent genetic study found that Tongariro R supports what is now a ‘sink’ population solely dependent upon immigration from several different source populations, rather than local production, although scale of movements necessary to support this is generally unknown (8 King, T.M., Williams, M. and Lambert, D.M. (2000). Dams, ducks and DNA: identifying the effects of a hydro-electric scheme on New Zealand’s endangered blue duck. Conservation Genetics. 1(2): 103–113. Close ).

Aquatic invertebrates, mainly insect (chironoid and cased caddis fly) (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ) larvae, but extensive range recorded (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ); also some algae and berries of streamside plants (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ) (e.g. Coprosma rugosa, C. depressa, Phyllocladus alpinus, Muehlenbeckia axillaris, Luzula crinita) (9 Harding, M.A. (1990). Observations of fruit eating by Blue Duck. Notornis. 37(2): 150–152. Close ), and also consumes some silt and periphyton (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). In one study, 37 taxa of aquatic invertebrates were identified within this duck’s diet, of which 45% were Chironornidae (samples ranged from 19–76%), 28% Trichoptera (range 11–49%) and 16% Ephemeroptera (range 2–42%), with the dominant chironomid Eukiefferiella sp., although Cricotopus spp. were also relatively abundant, and caddis flies were main Trichoptera in all samples; Plecoptera comprised 0–20% of invertebrates in faeces (10 Wakelin, M.D. (1993). Contents of Blue Duck faeces from the Tongariro River. Notornis. 40(3): 205–212. Close ). Another study, along Manganuiateao R, in C North Island, also found that selectivity varied, but Trichoptera larvae of the Hydrobiosidae and genus Aoteapsyche (Hydropsychidae) ranked highly, and cased caddis larvae consistently ranked low, in the diet (11 Veltman, C.J., Collier, K.J., Henderson, I.M. and Newton, L. (1995). Foraging ecology of Blue Ducks Hymenolaimus malacorhynchos on a New Zealand river: implications for conservation. Biological Conservation. 74(3): 187–194. Close ). Fruit-eating presumably most prevalent in autumn and analysis of droppings suggests may be, at least regionally, important dietary constituent at this season, perhaps especially in subalpine zone (9 Harding, M.A. (1990). Observations of fruit eating by Blue Duck. Notornis. 37(2): 150–152. Close ). Young take some foods as adults (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Feeds by probing among, and scraping bill over (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ), rocks, diving ; mainly by head-dipping , upending, dabbling and pecking (12 Collier, K. and Wakelin, M. (1996). Instream habitat use by Blue Duck (Hymenolaimus malacorhynchos) in a New Zealand river. Freshwater Biology. 35(2): 277–287. Close ) in shallow waters, especially at margins of rivers where current’s force dissipated by rocks (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ); ingestion of stonefly and mayfly larvae apparently mainly associated with diving (11 Veltman, C.J., Collier, K.J., Henderson, I.M. and Newton, L. (1995). Foraging ecology of Blue Ducks Hymenolaimus malacorhynchos on a New Zealand river: implications for conservation. Biological Conservation. 74(3): 187–194. Close ). Soft lateral flaps at bill’s tip function to increase surface area from which food is gathered, as well as to protect bill from abrasion (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ); although it had been suggested that these flaps might serve as a tactile method of detecting prey, it appears that most food is detected visually and that the species has a wide binocular field of view (13 Martin, G.R., Jarrett, N. and 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. Close ). Foraging apparently occupies as little as 25% of daylight hours, mainly for 1–1·5 hours during first 1–2 hours after dawn, then another period of similar intense feeding after short break, with further bouts of prolonged feeding in late afternoon until dusk (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ); nocturnal feeding also occurs, especially on rivers with high aggregate loads and generally low aquatic invertebrate densities (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ).

Male gives high-pitched piercing, wheezing whistles in territorial defence or advertisement, with neck stretched forward and upper-neck feathers raised, and also utters a short “whi”or “whio” during interactions with intruders; female has long, low, rasping growl in response to disturbance or threat, and also gives low-pitched staccato rasping during other social interactions (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ).

Starts mostly mid Aug with majority of first nests attempted by late Oct, with repeat laying (following early loss of first clutches) perhaps extending to early Dec (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Monogamous (14 Triggs, S.J., Williams, M.J., Marshall, S.J. and Chambers, G.K. (1992). Genetic structure of Blue Duck (Hymenolaimus malacorhynchos) populations revealed by DNA fingerprinting. Auk. 109(1): 80–89. Close ). In single pairs; nests in damp depression in ground, natural cavity, hollow log (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ), crevice among rocks, in dense vegetation (e.g. fern clump) (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ) or on cliff ledge, usually < 30 m from river edge (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ); only a little down added to ground debris, sometimes with soft grass and twigs added (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ); same site may be reused for up to seven years (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Usually 5–6 eggs  (4–9), white, laid at intervals of at least 24 hours, size 59–70·9 mm × 40·8–46·7 mm, mean mass 62·3 g (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ); incubation  c. 31–35 days (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ), by female alone, with male remaining close by for at least 68% of each day, and female taking two periods off nest per day of 37–48 minutes each, but sometimes does not leave nest for two days prior to hatching (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ); chicks have dark brown down above , white below  ; fledging 70–82 days and young tended by both adults (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Chief causes of nest failure are flooding and predation (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ), especially by stoats (Mustela erminea) that can take eggs, ducklings and regularly adult females (15 Whitehead, A., Edge, K.-A., Smart, A. and Willans, M. (2008). The future of whio in Fiordland National Park: is linear stoat trapping sufficient to ensure persistence? Notornis. 55(1): 51. Close ) (many subpopulations exhibit a male-biased sex ratio as a result) (16 Glaser, A., van Klink, P., Elliott, G. and Edge, K-A. (2010). Whio/Blue Duck (Hymenolaimus malacorhynchos) Recovery Plan: 21161169–211619. Threatened Species Recovery Plan 62. Department of Conservation, Wellington. Close ), as well as by brush-tailed possum (Trichosurus vulpecula) (17 Adams, J., Cunningham, D., Molloy, J. and Phillipson, S. (1997). Blue Duck (Whio) Hymenolaimus malacorhynchos Recovery Plan. Department of Conservation, Wellington. Close ), and two other bird species, namely Weka (Gallirallus australis) and Kea (Nestor notabilis) (7 Whitehead, A.L., Edge, K.-A., Smart, A.F., Hill, G.S. and Willans, M.J. (2008). Large scale predator control improves the productivity of a rare New Zealand riverine duck. Biological Conservation. 141(11): 2784–2794. Close ). Predation pressure greatest in beech mast years, when population of mustelids increases in line with that of rodents, but temporarily remains high as numbers of rodents wane (7 Whitehead, A.L., Edge, K.-A., Smart, A.F., Hill, G.S. and Willans, M.J. (2008). Large scale predator control improves the productivity of a rare New Zealand riverine duck. Biological Conservation. 141(11): 2784–2794. Close ). Other causes of mortality included bacterial infections (17% in one study) and predation by New Zealand Falcon (Falco novaeseelandiae) (also 17%), with two birds being killed by avalanches (7 Whitehead, A.L., Edge, K.-A., Smart, A.F., Hill, G.S. and Willans, M.J. (2008). Large scale predator control improves the productivity of a rare New Zealand riverine duck. Biological Conservation. 141(11): 2784–2794. Close ). In one study, of 61 nests, 33 (54%) successfully hatched ducklings, with early nests being generally more successful (72%) and 92% of eggs hatched in successful nests; thereafter, in one study, only 12% of 33 broods lost and 60% of 55 ducklings that reach river actually fledge (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Average of less than one young per pair reared in one study during five seasons, in another productivity was 1·3 fledglings/pair (n = 58) but varied dramatically between years (0–2·7 per pair) and pairs (0·25–2·3 young/year) over period of 5–9 years (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Sexual maturity at one year, but 50% of yearlings do not attempt to breed, with rest doing so in following or third years (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ). Mean annual survival between fledging and territory establishment 0·44 and of territorial adults 0·86, while mean lifespan after assuming territory is 6·75 years (1 Kear, J., Editor (2005). Ducks, Geese and Swans. Volume 1: General chapters, and Species accounts (Anhima to Salvadorina). Oxford University Press, Oxford, UK. Close ).

ENDANGERED. Previously considered Near Threatened, as numbers very reduced and declining; formerly widespread, now rare or absent in majority of territory, dispersed in small, isolated populations in widely scattered locations in North I and South I. Population currently considered by BirdLife International to be 1200 mature individuals within overall range of 54,800 km², but another recent estimate suggested the presence of 640 pairs on North Island and 700 pairs on South Island, with largest numbers in catchments of Bay of Plenty, C North Island, Northwest Nelson, West Coast and Fiordland, but an exhaustive survey of Arthur’s Pass National Park found only six birds in Feb 2011, down from c. 50 in early 1980s. Very sensitive to slightest modification in the torrents of clear water and thus threatened by hydroelectric schemes (e.g. the Tongariro Power Development scheme on North Island, around which local H. malacorhynchos population is in decline and characterized by low pair density and low annual productivity) (8 King, T.M., Williams, M. and Lambert, D.M. (2000). Dams, ducks and DNA: identifying the effects of a hydro-electric scheme on New Zealand’s endangered blue duck. Conservation Genetics. 1(2): 103–113. Close ) and mining activities. Previously, grazing and clearance of waterside vegetation decreased water quality and led to species’ disappearance from lowland rivers. Breeding success low; suffers high predation from introduced mammals, but in some areas (e.g. Fiordland National Park, where significant declines in Blue Ducks have been reported) (7 Whitehead, A.L., Edge, K.-A., Smart, A.F., Hill, G.S. and Willans, M.J. (2008). Large scale predator control improves the productivity of a rare New Zealand riverine duck. Biological Conservation. 141(11): 2784–2794. Close ) introduced stoats are being trapped, with positive results for nesting productivity (15 Whitehead, A., Edge, K.-A., Smart, A. and Willans, M. (2008). The future of whio in Fiordland National Park: is linear stoat trapping sufficient to ensure persistence? Notornis. 55(1): 51. Close ), e.g. mean annual productivity in areas with no trapping compared to sites where stoats have been heavily trapped is 0·67 ± 0·17 nests, 0·22 ± 0·22 ducklings and no fledglings, versus 0·53 ± 0·07 nests, 1·17 ± 0·28 ducklings and 0·8 ± 0·24 fledglings, respectively (7 Whitehead, A.L., Edge, K.-A., Smart, A.F., Hill, G.S. and Willans, M.J. (2008). Large scale predator control improves the productivity of a rare New Zealand riverine duck. Biological Conservation. 141(11): 2784–2794. Close ). Elsewhere, a 2·8-fold population increase in four years with three fledged young per pair each year and 94% chick survival has been noted, whereas nest failures hit 91% and productivity was 0·64 fledged young/pair at unmanaged sites (16 Glaser, A., van Klink, P., Elliott, G. and Edge, K-A. (2010). Whio/Blue Duck (Hymenolaimus malacorhynchos) Recovery Plan: 21161169–211619. Threatened Species Recovery Plan 62. Department of Conservation, Wellington. Close ). These actions constitute part of two co-ordinated management programmes, Operation Ark and Whio Operation Nest Egg (WHIONE) (16 Glaser, A., van Klink, P., Elliott, G. and Edge, K-A. (2010). Whio/Blue Duck (Hymenolaimus malacorhynchos) Recovery Plan: 21161169–211619. Threatened Species Recovery Plan 62. Department of Conservation, Wellington. Close ). Operation Ark was initiated in 2003 to target species occurring in Nothofagus forest, and initially focused on establishing five viable populations of this duck (each of 50 pairs) with an extensive network of predator traps at each site (18 Williams, M. (2006). Blue Ducks demand, and get, greater attention. Threatened Waterfowl Specialist Group News. 15: 44–45. Close ). WHIONE has very successfully monitored breeding pairs, removed the eggs to hatch in captivity and then returned the young once they are less likely to be predated (16 Glaser, A., van Klink, P., Elliott, G. and Edge, K-A. (2010). Whio/Blue Duck (Hymenolaimus malacorhynchos) Recovery Plan: 21161169–211619. Threatened Species Recovery Plan 62. Department of Conservation, Wellington. Close ), which programme has operated alongside one of large-scale predator control. Furthermore, introduced trout may compete for food, but no studies carried out as yet, while introduced alga Didymo may reduce habitat quality (16 Glaser, A., van Klink, P., Elliott, G. and Edge, K-A. (2010). Whio/Blue Duck (Hymenolaimus malacorhynchos) Recovery Plan: 21161169–211619. Threatened Species Recovery Plan 62. Department of Conservation, Wellington. Close ). Major floods destroy nests and eggs, reduce aquatic invertebrate food resources, and can kill juvenile birds by displacing them from their parents; a population viability analysis has found that the additive effects of population losses due to predation and a rising frequency of floods, as expected from anthropogenic climate change, increases substantially extinction risk (19 Simpkins, C., Perry, G.L.W., Glaser, A., Allerby, T. and Dennis, T.E. (2015). Effects of predation by introduced mammals and mortality due to severe floods on population viability of the endangered Blue Duck (Hymenolaimus malacorhynchos). Emu. 115(2): 146–157. Close ). Little gene flow between neighbouring catchments, with adjacent territorial pairs often closely related and sibling and cousin pairings are common (14 Triggs, S.J., Williams, M.J., Marshall, S.J. and Chambers, G.K. (1992). Genetic structure of Blue Duck (Hymenolaimus malacorhynchos) populations revealed by DNA fingerprinting. Auk. 109(1): 80–89. Close ). Translocation may prove a necessary conservation tool, but requires careful management and it has been suggested that genetic difference between North and South Island populations means that they should be treated as completely separate units for conservation purposes (20 Robertson, B.C., Steeves, T.E., McBride, K.P., Goldstien, S.J., Williams, M. and Gemmell, N.J. (2007). Phylogeography of the New Zealand blue duck (Hymenolaimus malacorhynchos): implications for translocation and species recovery. Conservation Genetics. 8(6): 1431-1440. Close ). Captive population established on North Island where c. 20 young reared annually, with (in 1987 and 1991) 12 birds released at Egmot National Park on Mt Taranaki and further releases annually since, with the result that breeding occurred for the first time in 2005–2006 when five pairs produced two young.