This Bird of the Month is presented by Dr. William Feeney, a research fellow at the University of Queensland. The interactions between cuckoos and their hosts form part of Will's current research.
The Fan-tailed Cuckoo (Cacomantis flabelliformis) is one of Australia’s ten brood parasitic cuckoos (eleven if you include the Oriental Cuckoo [Cuculus optatus]; though, this species does not breed in Australia) and is common throughout Queensland’s woodlands. It visually resembles the closely-related Brush (C. variolosus) and Chestnut-breasted (C. castaneiventris) Cuckoos, and can be distinguished from the Brush Cuckoo through the presence of its conspicuous yellow eye ring, and from the Chestnut-breasted Cuckoo through its noticeably duller breast colouration. The Chestnut-breasted Cuckoo is also restricted in its distribution to northern Queensland. While over 70 songbird species have been recorded to be parasitised by the Fan-tailed Cuckoo, 17 species are recognised as biological hosts but the majority of parasitism records are from the White-browed Scrubwren (Sericornis frontalis) as well as the Brown (Acanthiza pusilla) and Inland (A. apicalis) Thornbills
Like most of Australia’s cuckoos, the Fan-tailed Cuckoo is remarkably understudied (e.g. outside of its inclusion in species lists, there are no articles on this species in The Sunbird); However, it has been the focus of some of my research over the past few years into cuckoo-host interactions at Lake Samsonvale, near Brisbane. At this site, my team and I have found that they primarily parasitise White-browed Scrubwrens (approximately 30% of nests per year between 2015-2018) and occasionally the Brown Thornbill. While fairy-wrens are recorded as occasional hosts, we are yet to record any evidence of parasitism of fairy-wrens by Fan-tailed Cuckoos.
Interestingly, while most cuckoos are famous for being discrete near host nests, we regularly observed them near active scrubwren nests, with scrubwrens (and other species) actively attacking them. Whether this has any consequences for host defences (as it presumably increases the host’s perceived risk of being parasitised) is not known.
The eggs of the Fan-tailed Cuckoo appear to resemble those of the White-browed Scrubwren, but, I have not seen any evidence of egg rejection – perhaps there is egg rejection but we just have not seen it yet. Also, while I’ve only seen evidence of this on a few occasions, I suspect that White-browed Scrubwrens are able to reject cuckoo chicks, which is a very rare behaviour (currently only known in other Australian hosts, such as Superb Fairy- wrens [Malurus cyaneus] as well as several gerygone hosts of the Little Bronze-cuckoo [Chalcites minutillus]). However, unlike these other instances, it seems as though newly-hatched Fan- tailed Cuckoos take approximately 48 h to gain the strength required to reject the White-browed Scrubwren eggs and chicks from within the nest. While rare, it seems as though the parents do not feed the newly hatched cuckoo when it hatches before the other scrubwren eggs. This leads to the cuckoo chick becoming weak, and then once deceased, the parents remove it from the nest and save their unhatched eggs in the process. This would be fascinating if confirmed, but very difficult to test. Despite being common, there’s a lot left to learn about this interesting species.
For further information on this topic, visit Will's web site at http://www.williamefeeney.com
Header image: adult fan-tailed cuckoo with caterpillar (photo by William Feeney)
Below: A newly-fledged fan-tailed cuckoo (left) being fed by a male white-browed scrubwren (right). Photo by Ms Danielle Ferrara.