Wildfowl (1973) 24:141-143 The systematic status of the Cape Barren Goose as judged by its photo-responses J. KEAR a n d R. K. MURTON The Cape Barren Goose Cereopsis novae­ (genera Cygnus and Coscoroba) is noted in hollandiae has a possibly relict distribution, the fact that the gander undertakes a prime breeding on scattered islands off the south­ share of nest-building, a task predominant­ ern coast of Australia from the Recherche ly left to the female in Anser, Branta and all Archipalago in the west to the Furneaux tadornines (Kear, 1970); and in an incuba­ Group in the east (Frith, 1967). In the past, tion period of 35 days, 5 days longer than it perhaps ranged further, but is now con­ any anserine goose, but similar to many fined between longitudes 122°-148°E and swans. The species has two other ‘primitive’ latitudes 32°-40°S. Ecologically the bird features: goslings are occasionally oiled by was probably always restricted to the coast, their parents (Scott, 1972), as are screamer as suggested by the immense development (Anhimidae) chicks, and copulation occurs of its salt-extracting glands, a feature it on land with no indication that this is a shares with its relative, the extinct and secondary feature. flightless Cnemiornis of New Z ealand. No taxonomic clues can be obtained from The species is considered by Delacour hybrids, simply because Cereopsis has never (1954) to be an aberrant member of the hybridized. To some extent this is not sur­ tribe Tadornini of the sub-family Anatinae prising as it breeds in the winter while most (ducks) and by Johnsgard (1965) to be of of its supposed relatives are in reproductive the Anserini (swans and geese). Indeed, condition only in spring or summer. But when first described it was labelled Cygnus one goose, the Nene Branta sandvicensis, cendré (Delacour, 1954). No true geese also breeds on short days and copulates {Anser and Branta) occur in the southern (secondarily) on land. In 1968, a young hemisphere nor have any been certainly hand-reared Cereopsis female mated with a identified as fossils, so it is unlikely that Nene gander at the Wildfowl Trust, Slim­ Cereopsis is at all closely related to these bridge, England. The pair were encouraged genera. However, it has a typically goose­ with a spacious pen of their own where they like triumph-ceremony which is performed copulated, apparently successfully, and by the mated pair after an enemy has been nested during the following 3 years. The repulsed (Johnsgard, 1965); and in the eggs were always infertile. This might sug­ reticulated tarsus, absence of a syrinx and gest a degree of genetic incompatibility in the structure of bones and muscles (in­ between the two genera, although further cluding the number of cervical vertebrae), investigation is clearly needed. Cereopsis resembles the Anserini rather Recently we have examined the photo­ than the Tadornini (Verheyen, 1953; Wool- responses of various wildfowl species by fenden, 1961). relating the median date of first egg-laying In anserine geese, tadornine sheldgeese, in the Slimbridge collection (and the day and Cereopsis the young are grazers of length on that date) to the mid-latitude of grass and other low vegetation, so in body their natural breeding range (Kear, 1966; proportions, the goslings are rather similar. Murtón & Kear, 1973a,b). The plots of However, young shelducks and sheldgeese egg-laying date against latitude can be (except the Kelp Goose Chloëphaga hy­ described by regression lines for groups of brida) are strongly patterned in black-and- closely related species and these are white, while anserine goslings and cygnets summarized in Figure 1. It can be seen that tend to be unicoloured, white, grey, yellow swans emanating from any particular lati­ or brown. On this basis, the pied Cereopsis tude lay earlier in the year, that is, respond gosling closely resembles the tadornines. In to shorter daylengths, than do goose species tw o other features, Cereopsis shows sim ilar­ from the same latitude. But this is only ities to the sheldgeese rather than to the true above latitude 50°N. Further south, true geese: opponents are attacked with the true geese must breed later, because at low ‘wrists’ of the wings, which have bony latitudes they need a longer photoperiod carpal knobs; and erect, chest-puffing dis­ than swans, and it is significant that only plays are given as a greeting to the mate Branta sandvicensis occurs further south (Veselovsky, 1970). than latitude 40°N as a breeding species. Resemblance of Cereopsis to the swans We have argued that closely related species 141 142 J. Kear and R. K. Murtón / 2 120 80 40 ® -J________I________I________I________i_ 20 40 60 Latitude Figure 1. Regression lines relating date o f egg- (3) Shelducks (6 species) laying (represented as number of days from 7 = -12-3+ 2-8x; rt = 0-941, P < 0-01 1 January = 1) of various wildfowl species at (4) Sheldgeese (5 species) Slimbridge to the mid-latitude of their natural y = 81-6 + 0-4x ;rs = 0-786, not significant. breeding range. The isolated point with co-ordinates y = 1 ; (1) Anser and Branta geese (25 species) x = 36 represents Cereopsis and its relationship .y = 6-9 + l-6x; r.a = 0-871, P < 0-001 to the regression lines depicted is examined (2) Swans (8 species) statistically in the text. -3 5 -4 + 2-47x;re = 0-882, P < 0.01 share common regression lines because the equation which describes the swan data we physiological mechanisms controlling their predict that: photo-responses and breeding behaviour have not evolved significant divergences Pm = <*i + M o = -35-44 + 2-47(36) from the ancestral pattern (Murtón & = 53-48 Kear, 1973a). On this basis, we can enquire whether the breeding of the Cape Barren and the divergence from expectation is Goose at Slimbridge shows any resem­ given by blance to the response patterns of the groups featured in Figure 1. 4 = y * — >>oi = 1 -53-48 = - 52-48 The median date for first eggs of Cer­ The standard deviation of the predicted eopsis at Slimbridge over 23 years has value yol is: been 1 January, designated day 1, and the mid-latitude of its natural breeding range is 36° S. The regression lines in Figure 1 relate to eight swan, Cygnus and Coscoroba, species, twenty-five Anser and Branta species, six shelducks Tadorna species and five sheldgeese Neochen and Chloëphaga. = 12-68 0 - 3 1 2 = 14-524 Regression equations, correlation coef­ ficients together with their significance We calculate t, = d js \ = -52-48/14-524 = levels are given in the caption to the figure. 3-613 with n¡ —2 = 6 degrees of freedom. Statistically we wish to determine to which The two-tailed probability that this differs of the regression lines in Figure 1 the from zero is between P = 0-02 — 0-01. isolated point y0x 0 is closest and w hether it Similarly, if y„ can be defined by the regres­ might be regarded as belonging to one of sion line for true geese we obtain a t.¿ value the four groups whose taxonomic relation­ = d.,/s'2 = -63-5/13-145 = 4-831 w ith 23 ships are reasonably certain. degrees of freedom (d.f.). This is very If y 0 can be defined by the regression significantly different from a value of zero Systematic status, Cape Barren Goose 143 {P < 0.001). Considering the shelduck Slimbridge, England, is plotted against the mid­ regression in the same way we obtain t3 = latitude of their natural breeding range. The 39-954 which with 4 d.f. gives P < 0.001. result for the Cape Barren Goose Cereopsis Perusal of Figure 1 shows that the regres­ novaehollandiae is closer to the pattern for the sion line (correlation coefficient not signi­ swans than to that of the true geese or the sheld­ ficantly different from zero) describing the geese. An evolutionary tree placing Cereopsis photoresponse of the South American closer to the swans than to any living goose or sheldgoose species and perhaps closer to the sheldgeese cannot be nearer to the Cereopsis ancestral Anatidae stock is proposed. point than the regression line for the shel­ ducks just considered. Thus the statistical analysis confirms the References visual impression from Figure 1 that the photo-response of Cereopsis is totally un­ Delacour, J. 1954. The Waterfowl o f the World. related to the pattern shown by the true Vol. 1. London: Country Life. geese or sheldgeese, rather different from Frith, H. J. 1967. Waterfowl in Australia. Sydney: the shelducks and that it is closer to the Angus and Robertson. swan group than to any of the above. This Johnsgard, P. 1965. Handbook o f Waterfowl Behavior. Ithaca: Cornell U. Press. suggests that Cereopsis might be close to the Kear, J. 1966. The food of geese. Int. Zoo Yb. ancestral stock which led on the one hand 6:98-103. to the shelducks and on the other to a line Kear, J. 1970. The adaptive radiation of parental that has terminated with Cereopsis. We care in waterfowl. In: Social Behaviour in propose an evolutionary tree in which the birds and Mammals, ed. J. H. Crook. London: swans and Cereopsis are closer to each other Academic Press. than to any living goose or sheldgoose Murton, R. K. & Kear, J. 1973a. The nature species and perhaps closer to the ancestral and evolution of the Photoperiodic control of stock from which the Anatidae arose. These reproduction in certain wildfowl (Anatidae). relationships might be illustrated as fol­ J. Reprod. Fert. Suppl. lows: Murton, R. K.