There is no surprise about the attractions of a shady waterway when the temperature drifts into the 40s. The end of a blisteringly hot day in western Sydney found me walking along a creekbank in Scheyville National Park. I was making slow progress, expecting at any moment to disturb a snake in the dense grass and leaf litter.
Birds were calling but were difficult to spot in the tangle of vegetation along the creek. I finally stumbled upon a muddy-brown bird sitting on a branch near the ground. It seemed confident in its camouflage, turning a watchful eye my way but staying put. I recognised the distinctive yellow eye-ring of the Fan Tailed Cuckoo. It was obviously a young bird, the mottled brown not yet replaced by the striking slate-grey back and rufous belly of the adult.
A Willy Wagtail was bouncing around nearby, sparking the thought that it was the young cuckoo’s host parent. A diminutive adult feeding a comparatively huge baby cuckoo is one of those classic wildlife images, so I found a convenient stump and settled in the hope of witnessing a feed. The Willy Wagtail departed so I decided to get a little closer. The young Fan Tailed Cuckoo took offence and flew off up the creekline. I figured that if it was expecting a parental feed it wouldn’t go far, and sure enough spotted a brown form only twenty metres away. This started a cycle where I’d almost get close enough for a clear shot through the foliage before the cuckoo flew away. Each time it moved I congratulated myself on finding it again, right up to the point that not one but three cuckoos flitted off ahead. As realisation that there was more than one cuckoo sunk in I looked around and realised that there were at least six of the juvenile birds perched in plain sight.
I was genuinely surprised. Fan Tailed Cuckoos insert a single egg into the nest of a thornbill, wagtail or flycatcher and leave the host to raise their offspring. The host is always much smaller than the cuckoo, and raising just one oversized chick is a big job. So why was I surrounded by a whole bunch of juvenile cuckoos?
I stopped disturbing the birds, sat and watched. The juveniles were competently snatching insects from bark and ground. My guess that the Willy Wagtail was off to find food to feed its adoptee was obviously well off the mark. That left the question of why such a concentration of juvenile cuckoos? One possibility was that the combination of creek, woodland and dense understory provided particularly wonderful habitat for young Fan Tailed Cuckoos, acting as a magnet for birds from a broader catchment. The creekline may well have been wonderful habitat, but after a few moments observation I could see that the birds were moving as a loose flock, slowly leapfrogging their way along the creek. There were at least ten and perhaps as many as fifteen individuals moving in tandem.
I had no idea that this species forms flocks. Adult Fan tailed Cuckoos are decidedly territorial, loudly proclaiming their ownership of a patch of bush. Juveniles sometimes have different social structures then adults. I’d always wondered how cuckoos break the parental conditioning (‘I’m just another thornbill’) and start to recognise other cuckoos as their own species. Perhaps the juveniles join these loose flocks as part of establishing their identity as cuckoos before finding their own territory.
Whatever the reason for the flocking behaviour, it was a great reminder about making assumptions about wildlife behaviour. I had been so sure that the first cuckoo was a dependant juvenile, quietly sitting while it waited to be fed by its host. Based on that assumption was reason to think there would be any other cuckoos nearby, and in fact I was looking for anything other than a cuckoo as the potential companion. I was sure I was skilfully tracking a single bird rather than wandering through the middle of a dispersed flock. Not so much yet another victim of the cuckoo’s deceit, more a case of misplaced confidence!
Odds and sods