3 A merganser at Auckland Islands, New Zealand MURRAY WILLIAMS School of Biological Sciences, Victoria University, P.O. Box 600, Wellington, New Zealand. E-mail: [email protected] Dedicated to the late Janet Kear, a friend and colleague from afar, whose lifetime work enriched our knowledge and enjoyment of the world’s waterfowl. Abstract The last population of the merganser Mergus australis persisted at Auckland Islands in New Zealand’s Subantarctic until its extermination by specimen collectors in 1902. It is now represented by four duckling specimens, 23 skins of immatures and adults, three skeletons, and a partial cadaver stored in 11 museums. It was the smallest known Mergus, the males weighing c. 660 g and showing little plumage dimorphism from the smaller (c. 530 g) females. Only five published accounts report first-hand observations of its ecology, breeding or distribution. Most likely it occurred as year- round territorial pairs in the larger streams and along the coastal edge at the heads of Auckland Island’s eastern inlets and in Carnley Harbour and fed on both marine and fresh water foods. Its population probably never exceeded 20–30 pairs. The scant records suggest it had a typical summer breeding season. Although its keel area and wing skeleton were reduced relative to its sternum length it was well capable of flapping flight. Key words: Auckland Islands, Auckland Islands Merganser, Mergus australis. A merganser (Family Anatidae, Tribe in 1902 (Alexander 1902; Ogilvie-Grant Mergini) once inhabited the Auckland 1905) was obtained, Polynesians having Islands archipelago, 450 km south of New earlier extirpated the New Zealand Zealand in the subantarctic Southern Ocean and Chatham Island populations. This (Fig. 1). When Polynesians first settled biogeographic oddity, a merganser in New Zealand in the late 13th Century, New Zealand’s waters, is today represented mergansers were also present in New by 27 skins and bones thereof from Zealand (North, South and Stewart Islands) Auckland Islands (Kear & Scarlett 1970; and at Chatham Island 800 km to New Kear 2005a) and a small but increasing Zealand’s east (Holdaway et al. 2001; Worthy collection of bones from midden and & Holdaway 2002). It was from Auckland natural deposits from the other two Islands that the first specimen, in 1840 populations (Worthy 1998a,b, 2004; Millener (Hombron & Jacquinot 1841), and the last, 1999). ©Wildfowl & Wetlands Trust Wildfowl (2012) 62: 3–36 4 A merganser at Auckland Islands Figure 1. The Auckland Islands showing locations referred to in the text. 1= Magnetic Bay, 2 = Maclaren Bay. ©Wildfowl & Wetlands Trust Wildfowl (2012) 62: 3–36 A merganser at Auckland Islands 5 In this paper I review, and where Description of plumage and soft parts appropriate reappraise, existing knowledge of Mergus australis at Auckland Islands, a bird Kear & Scarlett (1970) described the commonly referred to as Auckland Island(s) plumages and soft-parts of the adult, Merganser (e.g. Buller 1882, 1905; Hutton & immature and duckling. The adult Drummond 1905; Kear & Scarlett 1970; description was compiled from the authors’ Kear 2005a; Young & Kear 2006) but also as examinations of three skins in Canterbury Southern Merganser (Tennyson & Museum, Christchurch, New Zealand (CM) Martinson 2006) and New Zealand (see Appendix 1), six skins in the (British) Merganser (Gill 2010). Scattered historical Natural History Museum, Tring, England accounts and documentation of this (NHM), and one skin in the Cambridge merganser were assembled by Kear & University Museum, Cambridge, England Scarlett (1970) to provide a first synthesis. (J. Kear pers. comm.). Livezey (1989) added an appraisal of its Their description was warranted because phylogenetic relationships and of its the original description (Hombron & flightedness. These two publications Jacquinot 1841) had not been referred to in provide the only substantive accounts of M. any publication other than in passing by von australis to date and have been the sources Hugel (1875), and most subsequent for all subsequent accounts (e.g. Marchant & descriptions, commencing with Buller (1882, Higgins 1990; Kear 2005a; Tennyson & 1905), have been incremental modifications Martinson 2006), much as Buller’s (1905) and abbreviations either of von Hugel’s or account was the source for early treatises of Buller’s and have ignored Mathews’ (e.g. Phillips 1926; Mathews 1936; Delacour (1936) substantive re-description (based on 1959). specimens NHM 1901.10.21.57 and NHM Since Kear & Scarlett’s synthesis, a 1901.10.21.58). Similarly, minor changes further skin has been reported in a museum from the initial depiction (Hombron & collection (Sigwart et al. 2004, 2005), a Jacquinot 1853) have resulted in portrayals partial skeleton reported (but erroneously with plumage and soft part colourations that identified; see Appendix 1) from Lyon, differ from original descriptions (e.g. Mathews France (Wood et al. 1982), bones attributed 1936; Shirihai & Jarrett 2002; del Hoyo et al. to mergansers have been located at further 2002; Tennyson & Martinson 2006), and in sites on New Zealand’s main islands the idiom of merganser species familiar to (Worthy 1998a,b, 2004; Worthy & Holdaway the artists (e.g. Fleming 1982). Some are more 2002), and the smaller sizes of bones fanciful (e.g. Flannery & Schouten 2001). found in abundance in a cave on Chatham Depictions based on freshly collected Island prompted Millener (1999) to suggest specimens (e.g. Hombron & Jacquinot 1853; they may constitute a separate taxon. Buller 1905; Fleming 1982) best capture soft Morphometric distinctions between the part and head colouration. A composite of three New Zealand Merganser populations some historic and contemporary illustrations await appraisal. is presented in Colour Plate 1. ©Wildfowl & Wetlands Trust Wildfowl (2012) 62: 3–36 6 A merganser at Auckland Islands Colour plate 1. Historic and contemporary depictions of Mergus australis from: a) Hombron & Jacquinot 1853; b) Buller 1905; c) Fleming 1982; d) Mathews 1936; e) Shirihai & Jarrett 2002; f) Tennyson & Martinson 2006; g) photograph of Otago Museum mount AV1110 (Rod Morris). ©Wildfowl & Wetlands Trust Wildfowl (2012) 62: 3–36 A merganser at Auckland Islands 7 Kear & Scarlett (1970) did not specimen NHM 1904.8.4.1, a female discriminate the ages of the specimens they collected in July 1901 (mid winter), reads examined and, because some were newly- “Iris brown. Bill black on top, red fledged young, their account is amended in underneath. Legs and feet light red”. the descriptions below. Immature Adult This description is of birds newly-fledged Sexes alike but males are larger and have a and identified as such by a terminal notch in longer head crest. Head, crest and neck dark the rectrices or the persistence of the down brown, chin and throat a lighter brown. feather stalk extending from the tip of the Crown and throat more rust-brown in male. rachis (Larson & Taber 1980). Mantle, scapulars, back, rump and tail very Sexes alike. Uniformly dark brownish- dark brownish-black. Rust colouration of black on head, neck and throat. Entire throat may descend onto upper breast dorsal surface, including rump and upper (further in the male than female; Hutton wing, dark grey. Entire ventral surface 1901a). Entire ventral surface a dull grey heavily mottled grey-brown. Developing liberally streaked brown to present an head crest apparent. overall browny-mottled appearance (males Two specimens collected in July 1901 paler on abdomen; Hutton 1901a); flanks (NHM 1904.8.4.1; NHM 1902.8.6.1) whose are uniform dark brown. Wing coverts slate rectrices have terminal notches, show a grey, like the sides of the breast, with the much darker dorsal surface, obvious rufous lower row darker and banded white. Middle on head and throat and conspicuously secondaries white on the outer web and elongated crest feathers. I interpret these as black on the inner web and tips. Primaries having undergone a post-juvenile body and inner secondaries blackish. Males have moult. white sub-terminally on the outer web of The dried legs of immature specimens 3–4 greater coverts to give the impression indicate they were a reddish colour. they have two white wing bars (Falla 1970). Underwing mottled and axillaries white. Duckling Iris dark brown, culmen and tip of lower Description taken from specimen CM mandible black; cutting edge of upper AV1581 (Appendix 1). Dark brown-black mandible and rest of lower mandible above with only a trace of pale wing, yellowish-orange; legs and feet orange; scapular and dorsal rump spots. Chin, throat webs, joints and soles dusky. This and upper breast rusty brown with a spot of description of eye and soft parts is as chestnut beneath the eye (this chestnut may written in F.W. Hutton’s hand on the label represent fading of a darker plumage). of an adult female specimen (NHM Remaining underparts yellowish-white. Bill, 1901.10.21.58) and it is repeated on the label legs and feet dark olive-brown. of the companion male specimen NHM These descriptions indicate that M. 1901.10.21.57 (Appendix 1). The label to australis, like the Brazilian Merganser Mergus ©Wildfowl & Wetlands Trust Wildfowl (2012) 62: 3–36 8 A merganser at Auckland Islands octosetaceus, had little sexual dimorphism in Discriminating sex and age by plumage and the adult nuptial plumage was measurement only a slight enhancement of the juvenile Using measurements of culmen and wing plumage. The patterns of the downy young there was a clear separation between birds were similar to all other mergansers but the labelled as males and females which helped uniformly dark appearance was most similar indicate the likely sex of four unlabelled to M. octosetaceus. skins (Appendix 1). Culmen lengths and Variation in body size wing lengths of males did not overlap those of females and the widths of their nails at A size disparity between males and the bill-tips were wider; in combination any females occurs in all extant mergansers two of these three metrics separated the (Appendix 2).