VOL. 11 (4) DECEMBER 1985 103 AUSTRALIAN BIRD WATCHER 1985, 11, 103-113 Parental Care and Investment in the Tooth-billed Bowerbird Scenopoeetes dentirostris (Ptilonorhynchidae) By C.B. FRITH and D.W. FRITH, 'Prionodura', Paluma via Townsville, Qld 4816 Summary The known southern distributional limit of the Tooth-billed Bowerbird Scenopoeetes dentirostris is extended from Paluma (19°00'S, 146°l3'E) to Mt Elliot(l9°30'S, 146°57'E) near Townsville, Queensland. Records of the rarely found nest of Scenopoeetes, clutch size, egg weight, egg-laying and nestling periods are summarised. Systematic observations over 45 hours at three nests strongly suggest, but do not conclusively prove, uniparentalism presumably by females. Data for a single-nestling brood at one nest are compared with similar data for the uniparental Golden Bowerbird Prionodura newtoniana and monogamous biparental Spotted Catbird Ailuroedus melanotis, which provide further evidence in support of uniparentalism in Scenopoeetes. Meagre nestling diet information is summarised. Parental care and behavioural records are reviewed and previous erroneous and confusing reports discussed. • Introduction The Tooth-billed Bowerbird* Scenopoeetes dentirostris is one of the least known of the 18 bowerbird species and is certainly less known than the other eight species in Australia. It occurs in upland rainforests between c. 600 and 1400 m above sea level from Mt Amos (15°42'S, 145°18'£) southward to Saddle Mountain on Mt Elliot (l9°30'S, 146°57'£) just south of Townsville, Queensland, where Dr George Heinsohn (pers. comm.) was attracted to an active court by typical male vocalisations on 13 November 1980. This is an extension of the previously known southern limit of this bird's range of 55 km due south or 90 km to the south-east from the previously recorded location of Paluma or Mt Spec (Storr 1973, Griffin 1974). The Tooth-bill is an atypical bowerbird in being a very cryptically plumaged, sexually monomorphic rainforest dweller long thought to breed monogamously (North 1904, Jackson 1909, Marshalll954, 1964, Chaffer 1984) but which is now considered a species in which males are promiscuous and females uniparental (Gilliard 1969, Schodde 1976, Donaghey et al. 1985). Both sexes have conspicuous serrations on the mandible edges, which are used in eating foliage (Lavery & Grimes 1974, Frith & Frith 1979), hence the common name. Males do not construct bowers, as do males of other polygamous bowerbird species, but clear a court area of rainforest-floor leaf litter and place selected leaves paler side uppermost on to the clearing as decorations. At their courts males are spectacularly vocal, but are very wary and quickly retire to higher forest foliage if approached without great care. *Tooth-billed CatbirdAiluroedus dentirostris in the Interim List of Australian Songbirds, 1975. AUSTRALIAN 104 FRITH & FRITH BIRD WATCHER Fema"te Tooth-billed Bowerbird biology is unknowl} save some anecdotal, misleading and confusing accounts in early oologicalliterature (see below). It is assumed that females are attracted to courts where they assess the quality of male vocalisations, displays, courts and decorations and perhaps male attendance levels (time investments) before soliciting a selected male. Females apparently incubate eggs and rear young unaided (i.e. without male assistance). The nesting season, clutch size and brood size George Sharpe (Anon 1909) collected a nest and two eggs on 7 November 1908. Jackson (1909) found nests with eggs between 8 and 27 December: three clutches of two, and one of a single egg incubated for about 5 days which suggested a completed clutch. He also found two fertilised eggs in each of two females that he shot at male courts. Moreover, he found four additional nests containing one nestling between 5 (not 10 as cited by Marshall 1954 and repeated by Cooper & Forshaw 1976) and 26 December. The estimated age of one of these nestlings was 3 to 4 days on 5 December and another was 'rather well feathered' on 19 December. We add to this our nests: two with a clutch of two, and one nest with a single nestling (see below). The clutch of eggs collected by Sharpe on 7 November and one we found on 21 November appear to be the earliest recorded egg-laying dates for Scenopoeetes. Warham's (1962) very recently fledged nestling provides an approximate latest known fledging date of 22 January. Beruldsen (1980), however, gave the 'nesting season' as October to December and Schodde (1976) stated that 'nesting' occurs from September to January which is unlikely as males do not commence court clearing in any significant way . until September (pers. obs., in prep). Parental care - the historical background Male Tooth-bills often appear the most conspicuous and numerous birds in their highland rainforest range during the summer, and yet remarkably very few nests have been recorded. A nest found by Mr G. Sharpe on 7 November 1908 (Jackson 1909, p. 265) appears to be the first record. Sharpe met S.W. Jackson in the Evelyn Scrubs and gave the latter hints on locating Scenopoeetes nests. Jackson was on a major three-month search for nests and eggs of highland rainforest birds but particularly for those of the Tooth-billed Bowerbird. He eventually located nine nests, by methodically sending aboriginal climbers up vine-covered forest trees, or by observing the movements of birds. None of these nests were visible from the ground, being small, sparse cup structures of fine tendrils placed in high, dense vine tangles. Jackson (1909) has published excellent photographs of nests and eggs, and of a nest containing a nestling. A note by W.S. Day (in North 1904, p. 70) states 'At the end of June they [Tooth-bills] begin to mate, and go about in pairs only' but this is contrary to our experience and that of others (Lavery & Grimes 1974) and is without foundation. Often, Jackson referred to 'Tooth-bills' or a 'pair' of birds being observed in order to locate a nest, or becoming excited when a nest was approached; or VOL. 11 (4) DECEMBER 1985 Tooth-billed Bowerbird: Parental Care & Investment 105 First published photograph of an incubating, presumed female Tooth-billed Bowerbird Scenopoeetes dentirostris, Paloma (north Queensland), December 1984 Plate 28 Photo: C. & D. Frith even to watching a fledged young being fed 'by the parents'. Moreover, he stated (1909, p. 276) that the 'pair' at a nest containing two eggs on 8 December involved a female that had maintained a court prior to nesting and a male that maintained his court until at least 13 December. His reference to male Tooth-bills taking any part in nesting can, we feel, be discounted as he was misled by the contemporary assumption that the Tooth-bill was a monogamously breeding bird (North 1904, p. 70) and therefore misinterpreted what he saw, or thought he saw. Our observations and those of others clearly suggest uniparentalism in Scenopoeetes whilst other statements by Jackson clearly indicate his confusion on this point. On several occasions Jackson noted only the one Tooth-bill at a nest He also specifically noted that Tooth­ bills 'sit close' on eggs, permitting a man to approach within a few metres. Such behaviour is also typical of sitting uniparental female Golden Bowerbirds Prionodura newtoniana and Satin Bowerbirds Ptilonorhynchus violaceus (pers. obs.), but is far less so of sitting monogamous female Spotted Catbirds Ailuroedus melanotis which quit the nest whilst an approaching human is further away relative to the close approach that the above uniparental females will permit (pers. obs.). Jackson's (1909, p. 256) first personal observation of the species involved 'a pair' of birds 'evidently conducting a primitive courtship ... rubbing their bills together'. We have seen similar activity on several occasions, involving two, three or four birds, but these instances appeared more likely to be aggressive encounters at a feeding tree. This initial observation of Jackson's may, however, have given him a lasting wrong impression. AUSTRALIAN 106 FRITH & FRITH BIRD WATCHER Also indicative of Jackson's predisposition to the nption that both sexes of Scenopoeetes share nesting duties is his reference t<{'long-watched pairs of rifle birds' (Victoria's Riflebird Ptiloris victoriae) a(lnests. His error in this respect was not unique, as (promiscuous) bowerbirds and birds of paradise were widely thought to nest in pairs and were therefore 'seen' to do so by the biased observer. Foster (in Campbell 1901, p. 68) recorded both female and male Paradise Riflebirds Ptiloris paradiseus nest building. Hislop (in North 1904, p. 28) reported a 'pair' of the latter species driving a Blaclc Butcherbird Cracticus quoyi 'from the neighbourhood oftheirnest'. Significantly, however, all three references to riflebirds actually seen sitting on nests in Campbell (1901) involve female-plumaged birds only, and clearly the aforementioned records of apparent 'pairs' obviously involved a nest-building or nest­ defending female whose scolds had temporarily attracted the attention of a male. Our experience is that the scolding distress calls of a nesting female uniparental bowerbird (Prionodura, Ptilonorhynchus, Scenopoeetes) often quickly attract conspecifics which may join in the scolding. Whilst direct evidence ofuniparentalism in Ptiloris spp. is lacking (LeCroy 1981), members of this genus are invariably considered to be promiscuous in males and uniparental in females (Gilliard 1969, Cooper & Forshaw 1977, LeCroy 1981, Beehler 1983, Beehler & Pruett-lones 1983). Most regrettably Chaffer (1984) has, without any justification, repeated the assumption that male Tooth-bills assist not only in the· raising of young, but also in nest building. The recorded Tooth-bill clutch of only one or two eggs (Jackson 1909, Anon 1909; pers. obs.) and the apparently not uncommon brood of a single nestling (Jackson 1909; pers. obs.) indicate a small clutch size (x = 1.50, N = 14). The mean clutch size of monogamous catbirds is 2.12 for the Green Catbird Ailuroedus crassirostris (N = 17: Donaghey 1981) and 2.03 for the Spotted Catbird (N = 66: pers.