VOL. 18 (3) SEP'IEMBER 1999 95 AUSTRALIAN BIRD WATCHER 1999, 18, 95-100 An Apparent Hybrid Royal x Rockhopper Penguin at Macquarie Island

by CINDY L. HULV and ALAN WILTSHIRE2

1 Zoology Department, University of Tasmania, G.P.O. Box 252C, Hobart, Tasmania 7001 (present address: Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, B.C., Canada V5A 1S6) 2 Parks and Wildlife Service, Department of Environment & Land Management, G.P.O. Box 99A, Hobart, Tasmania 7001 (present address: P.O. Box 3061, Launceston Delivery Centre, Tasmania 7250)

Summary Several species of Eudyptes penguins breed in large, mixed colonies on subantarctic islands. However, interbreeding between species has rarely been recorded. This paper provides details of a possible hybrid Royal x Rockhopper Penguin on Macquarie Island, and summarises published records of hybrids and mixed pairs on Macquarie Island and elsewhere.

Introduction There are six species of crested penguins Eudyptes and, at a number of locations, some species breed sympatrically (Warham 1975). Two species of crested penguins, the Royal Eudyptes schlegeli and Rockhopper E. chrysocome Penguin, breed sympatrically on Macquarie Island (54°33'S, 158°54'E ), where there are six mixed colonies of Royal and Rockhopper Penguins (Simpson 1985). An apparent hybrid Royal x Rockhopper Penguin (Plates 23-24) was observed on Macquarie Island in late October 1994. At that time of year, both species had returned to the island to breed after their winter departure. By the end of October, Royal Penguins had laid two eggs (the smaller~ egg', laid first, and the larger 'B egg') and were incubating, while Rockhopper Penguins were preparing to lay (Hull 1997). Within 1 m of the location of the 'hybrid' was an apparently mixed pair of Royal and Rockhopper Penguins (Plate 25). This pair did not have an egg at the time, and were not monitored throughout the breeding season, so their breeding status was unknown.

Methods The 'hybrid' was captured bY. hand, and the following measurements were taken (following Warham 1975, Hull in press): bill length, bill depth, bill width, head length and flipper length, and mass. The mass was measured using a Pesola scale. The plumage, gait and vocalisation of the bird were also noted. A 2 ml sample of blood was taken from the brachial vein (following Samour & Jones 1983) and submitted for DNA analysis, using protein-coding genes from the mitochondrial DNA, to determine the maternal parentage of the bird. The paternal parentage was not determined.

Results

Plumage description and measurements The bird had a black face, head and cheeks (although paler in places on the cheeks), with a sharp demarcation across the throat, separating the black face AUSTRALIAN 96 HULL & WILTSHIRE BIRD WATCHER

The apparent hybrid Royal x Rockhopper Penguin, with a Rockhopper Penguin in the background Plate 24 Photo: Cindy Hull from the white breast and abdomen, as is found in both Rockhopper and Macaroni Penguins E. chrysolophus (Warham 1963, 1975; Marchant & Higgins 1990) (Plates 23-24). The crest was bright yellow, and most similar in colour to that of a Rockhopper Penguin, rather than the chrome-yellow crest of a Royal Penguin. However, in form, the crest resembled that of a Royal Penguin, as it was fibrous VOL.18 (3) SEPTEMBER 1999 Hybrid Royal x Rockhopper Penguin 97

An apparently mixed pair of Royal and Rockhopper Penguins near where the 'hybrid' was observed Plate 25 Photo: Cindy Hull

(see Simpson 1985), and arose from a central patch on the forehead. However, the forehead of the 'hybrid' was black, and lacked the yellow band which links the two sides of the crest of a Royal Penguin. The crest differed from that of a Rockhopper Penguin in that it lacked both a yellow superciliary stripe and a black occipital crest connecting the plumes of each side of the head. In addition, unlike the Rockhopper Penguin, the crest did not droop or project laterally behind the eyes (Warharn 1963, 1975; Marchant & Higgins 1990). The back, flippers and tail of the bird were blue-black, and the underflippers were white, with black patches in places. The bill was dull orange-brown, with the mandibles separated by pink skin. The eyes were red, and the feet and legs were pink, all features common to both species (Warham 1963, 1975; Marchant & Higgins 1990). The black chin and long crest ofthis bird suggested that it was at least two years of age (see Warharn 1963, 1975; Marchant & Higgins 1990). The bird was noticeably larger than a Rockhopper Penguin, but smaller than a Royal Penguin: measurements taken indicated that in all variables, except mass and bill width, the 'hybrid' was approximately intermediate in size between Royal AUSTRALIAN 98 HULL & WILTSIDRE BIRD WATCHER

Table 1

Measurements of the 'hybrid' penguin, compared with Royal and Rockhopper Penguins, from Hull (in press) and previous studies. Mean ± standard deviation; mass is given for birds in late October. M = male, F = female. Measurements Royal Penguin Rockhopper Penguin 'Hybrid' M (n = 67) F (n = 71) M (n = 60) F (n =57) Mass (kg) 3.25 6.0±0.3 5.7±0.3 3.6±0.3 3.8±0.5 Bill length (mm) 54.9 68.7±2.9 61.1±2.6 46.4±2.1 41.9±2.1 Bill depth (mm) 23.9 30.4±1.6 26.8±1.3 21.0±0.1 18.7±0.9 Bill width (mm) 10.9 14.1±1.2 13.3±1.2 10.8±0.8 10.0±0.9 Head length (mm) 131.0 143.5±4.7 133.8±4.3 115.6±3.0 109.6±3.6 Flipper length (mm) 188.0 217.0±4_51 215.7±8.11 165.0±4.92 161.0±4.42

1 From Falla (1937) 2 Birds from Campbell Island (Marchant & Higgins 1990) and Rockhopper Penguins measured during this and previous studies (Hull1997; see Table 1).

Other features The gait of the bird was similar to that of a Royal Penguin, as it walked in a lumbering manner, rather than with the hopping or jumping technique of a Rockhopper Penguin. It had a loud braying call like that of a Royal Penguin, and not the more raucous, higher-pitched call of a Rockhopper Penguin (Warham 1963, 1975). Analysis of its DNA determined that the bird's maternal parent was a Rockhopper Penguin.

Differences from other species The lack of superciliary stripe and the length of the crest discounted the possibility of the 'hybrid' being a Snares Penguin E. robustus, which is the species most similar in appearance to the Rockhopper Penguin (Marchant & Higgins 1990).

Discussion The DNA analysis conducted on this individual confirmed its Rockhopper Penguin parentage, and the appearance of the bird suggested that it was an unusual example of the species. The crest, size of the bird, gait and call all suggested that this bird was a hybrid Royal x Rockhopper Penguin. A few examples of hybrid Eudyptes penguins and mixed pairs have been described previously from several subantarctic islands. A museum specimen of a hybrid Royal x Rockhopper Penguin was collected from a colony at North Head on Macquarie Island (Simpson 1985), and a mixed pair of Royal and Rockhopper Penguins has been observed at Penguin Bay, on Campbell Island, during November 1996 (AW pers. obs.) . A hybrid Rockhopper x Macaroni Penguin has been observed on Heard Island, and two such hybrids have also been seen on Marion Island (Woehler & Gilbert 1990). In addition, a mixed pair of Macaroni and Rockhopper Penguins was found incubating eggs on Marion Island during the 1987-88 breeding VOL.18 (3) SEPTEMBER 1999 Hybrid Royal x Rockhopper Penguin 99

season, but no chicks were successfully raised (Woehler & Gilbert 1990). Mixed pairs of Erect-crested E. sclateri and Rockhopper Penguins have been recorded on the Falkland Islands (Napier 1968) and on Campbell Island, where they were incubating what appeared to be an 'A egg', which later disappeared (P. Moors pers. comm. ). To date, no successful breeding attempts have been observed in mixed-species pairs, although the existence of hybrids suggests that such matings have sometimes been successful. It is unknown whether the hybrids are capable of producing fertile offspring, as none has been observed to do so (Woehler & Gilbert 1990). Therefore, it appears that pairing of two species of Eudyptes penguins can occasionally occur. As the populations of Royal and Rockhopper Penguins on Macquarie Island are both large (estimated at 850 000 and 100 000-500 000 breeding pairs, respectively; Warham 1963, Rounsevell & Brothers 1984, Copson & Rounsevell1987, Scott 1994), interbreeding is clearly uncommon, being recorded only twice at this site. It is possible, however, that more hybrids may occur, as systematic surveys of all colonies have not been carried out. Given the few ( < 10) records of hybrids and mixed pairs of Eudyptes penguins, and given the size of populations of Eudyptes penguins in the subantarctic (total populations of Rockhopper Penguins are estimated at about 1.8 million pairs, and Macaroni Penguins at about 9 million pairs; Woehler 1993; Bingham 1996, 1998; R.J.M. Crawford unpubl. data), interbreeding is rare. Studies have shown that the rates of hybridisation between some other species of birds are low: 6% in nightingales Luscinia (Becker 1995); and up to 0.5% in pochard ducks Aythya, although mixed clutches have been observed regularly in this genus (Schuett 1994). Both studies found that hybrids exhibited low fertility, and in the case of nightingales, female hybrids were sterile (Becker 1995). Reduced fertility and assortative mating of individuals of different sizes minimised gene flow in both genera (Schuett 1994, Becker 1995). It has been speculated that hybridisation may occur more often in inexperienced birds, and is possibly inhibited by spatial division (Solberg & Ringsby 1996). Therefore, in mixed colonies of Eudyptes penguins there may be an increased probability of interbreeding. The role of assortative mating, age and experience in minimising interbreeding can only be explored further by gathering data on the age and sex of birds in mixed pairs.

Acknowledgements This work was conducted under permits MI/34/94 and MI/3/95. We thank Dr Allan Baker and Mr Mark Peck of the Royal Ontario Museum, Toronto, Ontario, Canada, for analysing the DNA, and Dr Phil Moors and Dr Eric Woehler for their helpful comments on a draft of the manuscript.

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