KEYWORDS: Chatham Island Taiko, Pterodroma magentae, study skin, bones, intestines.
 
 

    On 6 March 1997 the bird was skinned by Noel Hyde, the Museum’s bird taxidermist in the presence of MJI, AJDT and GAT. The skin was removed, washed and dried. Before preserving as a study skin (reg. no. 25209), the left wing was removed and preserved in the fully-open position. The humerus, radius, ulna and carpometacarpus were removed from that wing; the entire left leg and all bones removed from the body were skeletonized for the osteological collection. The cranium (but not the maxilla or mandible) was removed from the head. A cranium of a White-headed Petrel (Pterodroma lessonii) from Antipodes Island was used as a replacement to preserve the shape of the head in the study skin.
Phthirapteran lice were collected from the corpse. These were preserved in the Museum’s entomological collection by R.L. Palma. Lice had also been collected from this bird when alive. A separate paper is being prepared on all Phthiraptera collected from Taiko (Palma & Imber unpubl.).
A photograph (Fig. 2) was taken of the digestive tract and abdominal contents. Small tissue samples of heart, liver, kidney, lungs, intestine and fat have been kept frozen. The rest of the viscera, muscle, fat and other soft tissues were preserved in ethyl alcohol.
 
 

Moult
Most plumage was fresh or only slightly worn, but some upper wing coverts were worn and there was active moult of the back feathers. All primaries, secondaries and rectrices were new

Internal organs (Fig. 2) and food items
The bird was a male; its testes were round, black and each measured 4-5 mm in diameter.
The upper intestines were helicoidally twisted (cf. Imber 1985), with 60 lefthanded twists.
The proventriculus was empty but for some paste apparently derived from fish. The gizzard contained some residual food items and the only identifiable item of food: a cephalopod beak of a juvenile Nototodarus sp. As there is nothing published on the food of Taiko, we include this collation of data on all other food items collected to the present.

Cephalopoda: 1 Brachioteuthis sp. (beaks) regurgitated by a non-breeder , November 1993;
1 Gonatus antarcticus (lower beak) at the entrance of North 1 burrow, November  1996;
1 Teuthowenia pellucida (beaks, some flesh) regurgitated at South 10 burrow , February 1995.
Fish: 1 Sio nordenskjoldii (otoliths, some flesh) regurgitated at South 10 burrow, February 1997.

Measurements
The following measurements (mm) were taken on 3 July 1998. Dimensions in brackets are those taken when the bird was alive on 2 October 1990 (Taylor 1991). The culmen was measured from the tip to the anteriormost feathers above the nostrils, and bill depth at the same posterior point of the culmen measurement. The wing measurement was taken with the outer wing flattened.

Culmen  32.1 (32.6)     Bill depth 16.3 (16.9)
Tarsus  41.5 (42.2)     Mid-toe and claw 58.5 (57.1)
Wing 300 (300)     Tail 129 (128)
Mass (g) c.460 - in frozen state, December 1996 (435)

The maximum length of the specimen’s bones, and of some bones of the 1982 remains, are compared with those of sub-fossil bones from the Chatham Islands attributed to Taiko by Bourne (1967) (in brackets). Total head length was measured before the cranium and maxilla were separated and includes the unguinal plate’s thickness, whereas Bourne’s measurements would have excluded this plate.

Total head length 84.4 (84-91)
Cranium 47.2 (45-48)     Sternum 60.4, 59.2 (56-59)
Coracoid 35.6, 33.6 (29-34)     Humerus 103.7 (95-109)
Ulna 106.9, 106.7 (-)     Radius 105, 104.4 (-)
Carpometacarpus 50.3 (-)     Femur 37.1 (33-40)
Tibiotarsus 74.4 (73-80)     Tarsometatamus 41.1 (-)
 
 

    A fight with another male Taiko is thought the most likely cause of the injuries. In the Snow Petrel (Pagodroma nivea), Brown (1966) describes fighting between males in which they grappled bills, the bird locking onto his opponent’s lower mandible invariably winning. Identical fights have been observed in male Grey-faced Petrels (Pterodroma macroptera gouldi) (MJI, AJDT, GAT pers. obs.), with other males seen with damaged bills, especially lower mandibles. Subsequently victorious Snow Petrels were observed to chase and grasp the flanks of the loser, leading to further fighting which could be prolonged. Such fights have lead to death in Grey-faced Petrels and Cook’s Petrels (P cookii) (pers. obs.). The damage to the Taiko’s lower mandible (suggesting it was the loser) and injuries to the flank area are consistent with such a hypothesis. It may be noted that this male was relatively small (most male Taiko weigh nearer 500 g), with a small bill also, and could have been thus disadvantaged in a fight. The injury at the wing base may have prevented its departure to sea after eviction, where it could have cleaned its wounds and escaped blow-flies.
The persistent visits to its burrow during the month after its death may have been by this other male, but why visits ceased (none since early December 1996) is curious. As no egg was laid there in 1996. despite the male having been present at mating time in early October, and no chick reared the previous year (so no reason for the female not to return if alive), it seems that his mate, with whom he had apparently reared at least seven chicks, was already dead.

Subfossil and recent bones from Chatham Island
    Comparisons of bone measurements of this specimen with those of putative P magentae subfossils measured by Bourne (1967), indicate that most of the bones were correctly attributed to Taiko by Bourne. However, some of his coracoid and sternum measurements are smaller and may not all be Taiko. The remains of the suspected Taiko found in 1982 are now confirmed as that species using bone measurements. Further work is in progress on collections of subfossil bones from the Chatham Islands (AJDT pers. comm.).

Relationships of Taiko as shown by the intestines
    Helicoidally twisted upper intestines (Fig. 2) with 93 to 100% of twists lefthanded (Table 1) are characteristic of subgenus Pterodroma petrels as defined by Imber (1985), which includes all species in Table 1 and others. Thus, this Taiko’s intestinal structure is consistent with its currently accepted taxonomic placement (Turbott 1990). The number of helicoidal twists in this Taiko places it close, not only to P macroptera with which it is usually associated (Bourne 1964, Turbott 1990), but also to the Soft-plumaged Petrel (P moiis) and its close relatives, Madeira Petrel ~P madeira), Desertas Petrel (P deserta) and Cahow ~P cahow) , with which it shares other features (Imber 1985).
    As summer breeders on islands at or near the southern subtropical convergence, Taiko and Soft-plumaged Petrel occupy similar çcological niches. Given the abundance of the Soft-plumaged Petrel in the southern Atlantic and Indian Oceans its former absence from the southern Pacific Ocean is notable, but possibly due to Taiko occupying its ecological niche there. The present and ongoing expansion of
 

TABLE 1 — Number of helicoidal twists, and percentage of left-handed twists, in the upper intestines of Taiko and closely related species of Pterodroma. Data for all but Taiko, Desertas Petrel and one Grey-faced Petrel from Imber (1985).

Species	No. of specimens	No. of internal twists	% left-handed twists
Taiko ( P. magentae )	1	60	100
Soft-plumaged Petrel ( P. mollis )	2	60-61	93-100
Madeira Petrel ( P. madeira)	1	44+	c.100
Desertas ( P. deserta )	1	68	100
Cahow ( P. cahow )	1	64	95
Grey-faced Petrel ( P. macroptera gouldi)	4	61-80  mean = 70
White-headed Petrel ( P.lessonii )	1	88	94

the Soft-plumaged Petrel colonies on Antipodes Island (Imber unpubl.), first discovered in 1969 (Warham & Bell 1979), may be a consequence of the demise of the vast Chatham Island population of Taiko. Both Taiko, feeding southwards from Chatham Island (Imber et al. 1994b) and Soft-plumaged Petrels, ranging northwards from Antipodes Island (pers. obs.), feed in the same marine zone, mainly between 44oS and 50oS.