42 AUSTRALIAN FIELD ORNITHOLOGY 2006, 23, 42–45 Shining Bronze-Cuckoo Associating with and Imitating Alarm Call of Chestnut-rumped Heathwren DANNY I. ROGERS1,2, KEN G. ROGERS2 and JOAN SANDBRINK3 1Johnstone Centre, Charles Sturt University, P.O. Box 789, Albury, New South Wales 2640 ([email protected]) 2340 Nink’s Road, St Andrews, Victoria 3761 3Deceased Summary We describe an observation of a juvenile Shining Bronze-Cuckoo Chrysococcyx lucidus being attended by a pair of Chestnut-rumped Heathwrens Hylacola pyrrhopygia, apparently the first record of this cuckoo–host association. An alarm call given by the young Cuckoo appeared identical to that of the female Heathwren, and we suggest that this was a case of vocal mimicry. Introduction Host specificity of brood parasites varies considerably, from generalists such as cowbirds Molothrus, which will parasitise most small passerines potentially available, to others that are specialised to parasitise one particular host species (e.g. some of the whydahs of the genus Vidua: Campbell & Lack 1985). Australian representatives of the bronze-cuckoo genus Chrysococcyx appear to be selective in their choice of hosts. Although each species has been found parasitising a number of passerine species, it has been possible to identify preferred biological hosts for all (Brooker & Brooker 1989). Similarities between egg and nestling patterning of cuckoos and their hosts have long been thought to play a role in the success of parasitism attempts (Gill 1983; Brooker & Brooker 1989), and it has also been suggested that juvenile Chrysococcyx species may imitate the nestling calls of their hosts (Courtney 1967; McLean & Waas 1987). The finding that Superb Fairy- wrens Malurus cyaneus are more likely to reject the nestlings of an occasional parasite, the Shining Bronze-Cuckoo Chrysococcyx lucidus, than those of a regular parasite, Horsfield’s Bronze-Cuckoo C. basalis (Langmore et al. 2003), suggests that there may be selection for mimicry of host-nestling attributes in Chrysococcyx. However, distinguishing genuine mimicry of egg and nestling attributes from similarities resulting from other causes is difficult (Grim 2005). It is therefore worthwhile documenting infrequently seen host–parasite associations, which is what we do in this short note. Study area and methods This note describes opportunistic observations made on 16 January 2005 while banding passerines in Rushworth State Forest (36°39′S, 144°58′E), a box–ironbark forest in North-central Victoria. Rushworth State Forest is one of the largest box–ironbark remnants in Victoria (Tzaros 2005) and has been the base for a mist-netting study since 1994, with fieldwork being undertaken at five sites within the forest where box–ironbark abuts patches of mallee or Yellow Gum Eucalyptus leucoxylon. The subsite at which observations were made was a large clearing of regrowth Blue Mallee E. polybractea about a metre tall, surrounded by a narrow strip of taller and older mallee (including Green Mallee E. viridis and Bull Mallee E. behriana), in turn abutting box–ironbark forest. VOL. 23 (1) Shining Bronze-Cuckoo Associates with MARCH 2006Chestnut-rumped Fieldwren 43 The Chestnut-rumped Heathwrens Hylacola pyrrhopygia observed were sexed on plumage characters (Higgins & Peter 2002), the female having a less bold supercilium, and a considerably stronger buff tinge to the sides of the breast and flanks than the male. Wing-length (maximum chord), tail length, total head length, moult, and condition of brood-patch and cloaca were recorded using the methods described by Rogers et al. (1986). Results In the course of a mist-net round made at about 1000 h on 16 January 2005, DIR heard an unfamiliar begging call and, on trying to find the source, found a female Chestnut-rumped Heathwren feeding a juvenile Shining Bronze-Cuckoo at the edge of a mallee clearing. A male Heathwren was also present, seen briefly on a low branch next to the female and the Cuckoo before it flew to the ground a few metres farther away. It was not possible to confirm whether the call that was initially heard was actually given by one of these birds, as viewing was restricted by thick vegetation. The birds were about 20 m from one of the mist-nets, so the opportunity was taken to flush them in. The male Heathwren bounced out of the net and refused to fly back in, though it remained nearby as the female Heathwren and the young Cuckoo were extracted, at times approaching to within 2 m of DIR while giving scolding calls. The female Heathwren was vocal in the hand, singing inside the bird-bag with much mimicry while being taken back to the banding station. Its measurements (wing 54 mm, tail 61 mm, total head length 34.9 mm) were typical of the species. It had yet to start primary moult, though it had traces of early moult of body plumage. It had a large, vascular brood-patch; the onset of refeathering at the sides of the brood-patch, and the wrinkled oedematous texture, indicated that the bird had completed incubation in recent days or weeks. The young Cuckoo was fully grown (wing 102 mm, tail 65 mm, total head length 36.0 mm, weight 19.9 g). It was still in complete juvenile plumage, showing the species’ diagnostic features including iridescent green upperparts without distinct buff tips to the feathers, narrow brown barring on the flanks, a plain grey- brown to white face and throat without distinct barring or eye-stripe, and an absence of rufous markings in the tail-feathers. Although it was fully grown, the puffy yellow gape and orange-yellow base to the lower mandible of this individual indicated that it had only recently fledged (Higgins 1999). After the birds were processed, DIR and KGR took them back to the capture site for release. On the way we had been discussing whether young cuckoos learned any calls from their foster-parents, so were listening specifically for flight calls as the birds were released. The Heathwren was released first and flew strongly and directly for about 30 m, landing in the middle of the regrowth mallee. While in flight it gave a strident single-note call tzeet; DIR had heard this call before and considered it a typical alarm call for the species. The young Cuckoo was then released. It flew in the opposite direction to the Heathwren, flying 25 m to land about 2 m above the ground, in an old mallee tree. In flight it too gave a strident single-note call tzeet. DIR and KGR were both confident that the call was given by the Cuckoo, and considered the call identical to that of the female Heathwren. Discussion Several aspects of our observations suggest that the Cuckoo we observed had been raised by the Heathwren pair. These included: (1) feeding of the young AUSTRALIAN 44ROGERS, ROGERS & SANDBRINK FIELD ORNITHOLOGY Cuckoo, (2) the apparent anxiety of the adult male Heathwren while the juvenile Cuckoo was in the mist-net, (3) the apparent imitation of a Heathwren alarm call by the young Cuckoo (discussed below), and (4) the refeathering condition of the brood-patch of the adult female Heathwren. However, none of these lines of evidence proves that the juvenile Cuckoo that we observed was actually raised by the hosts with which we observed it. It could have already fledged with other foster-parents and then elicited a response from the Heathwrens by its begging calls. Either way, this observation appears to be the first record of an association between the Shining Bronze-Cuckoo and a species of Hylacola (L. Brooker pers. comm.). Brooker & Brooker (1989) carried out an extensive review of cuckoo hosts in Australia, and identified two species of fairy-wren (genus Malurus) and eight species of thornbill (Acanthiza) as biological hosts of the Shining Bronze- Cuckoo. There are several records of eggs of Horsfield’s Bronze-Cuckoo and the Fan-tailed Cuckoo Cacomantis flabelliformis in the nests of Chestnut-rumped Heathwrens, and the related Shy Heathwren Hylacola cauta is known to be parasitised by these two species and by the Black-eared Cuckoo Chrysococcyx osculans (Higgins 1999; Higgins & Peter 2002). The alarm call given by the young Cuckoo on release was of interest. To our ears it sounded identical to the typical alarm call of the Chestnut-rumped Heathwren. Alarm calls can be difficult to interpret as they tend to be convergent across bird species, possibly owing to selection for acoustic characteristics that are difficult for a predator to locate (Marler 1955). Nevertheless, the call that we heard does not correspond with any of the known vocalisations of the Shining Bronze-Cuckoo listed by Higgins (1999). There is evidence strongly suggesting that young Chrysococcyx cuckoos mimic the begging calls of their biological hosts (Courtney 1967; McLean & Waas 1987; Langmore et al. 2003). Such mimicry is usually assumed to be innate, selected for by natural selection, as nestling cuckoos that eject other young from the nest presumably have little or no opportunity to learn their begging calls. (In some species, however, they might be imitating begging calls given by the female parent when being fed at the nest by the male: J. Courtney pers. comm.). We have not been able to find any previous records of young cuckoos imitating the alarm calls of their hosts, and we do not know if this is because it does not happen, or because it is not reported. It would be of interest to know if alarm calls are a normal part of the repertoire of young cuckoos, not least as it may give some insights into how their calls develop. For example, if the young Cuckoo that we observed was giving a Heathwren alarm call, this would be far more likely to have resulted from imitation than through innate mimicry, given that association between the Shining Bronze-Cuckoo and the Chestnut-rumped Heathwren appears to be rare.