For years I have struggled to answer a reader’s query about whether some species of cuckoo return to collect their young after they have been raised by surrogate parents.
The query has been partly answered by the discovery this spring that one of the cuckoo species visiting Tasmania during the breeding season, the pallid cuckoo, does indeed return to take over the parenting of their fledglings after they have been raised by other birds.
I’m indebted to BirdLife Tasmania researcher Mike Newman for his observations of pallid cuckoo behaviour.
I joined Mike and other BirdLife Tasmania volunteers for two surveys of pallid cuckoos on the South Arm near Hobart recently, the last outing turning up 20 individuals.
I’d been studying as much literature as I could about cockoos since the intriguing question of the whether they actually took part in rearing their young was first raised.
I had learned of anecdotal evidence of a mainland cuckoo species, the koel or rainbird, returning to collect outsourced young but never considered this behaviour might apply to the four cuckoo species visiting Tasmania, the fan-tailed and shining and Horsfield’s bronze-cuckoos and the biggest of our visitors, the pallid.
Although I have witnessed outsized pallid cuckoo chicks being fed by a common host species, the much smaller black-headed honeyeater, I had never seen pallid cuckoos feeding their own young.
Mike Newman tells me that it does occur, but the frequency of the behaviour has not been established. It is easy to accept that pallid cuckoos might be attracted to their young calling for food, but the intent of the cuckoo action reclaiming young appears remarkable.
It is believed the cuckoos might be motived by a desire to see their young move on to a more appropriate nutritious diet.
The host species largely feed small insects to young and, although these are rich in protein, the much larger cuckoos need a diet more in line with adult pallid cuckoo food in spring – caterpillars.
Not only are these feed to the chicks but it appears the pallid cuckoos also teach their young to hunt this insect food in the dry woodlands where the cuckoos make their home in summer.
Much research worldwide has still to be conducted into the natural history of cuckoos.
The survey on the South Arm was designed to kick-start a more thorough and wider study of this one cuckoo species, a study which might not only reveal numbers but its distribution in Tasmania.
Already the survey has established the South Arm as a pallid cuckoo “hotspot” which bucks a trend on the south-eastern mainland, where the pallid cuckoo tends to be found further inland.
Research continues and for my own studies Mike Newman has recommended a landmark work on the cuckoo family, Cuckoo, by acclaimed British ornithologist Nick Davies. The book is on its way.