Juvenile Pacific Koel  Photo: Gary Howling

September marks a noticeable change in the seasons along the Great Eastern Ranges, and one of the key indications that summer is just around the corner, is the return of our iconic cuckoos — their calls adding to the symphony of Aussie springtime soundscapes.

While most people are more familiar with the great migration events long documented in North America, Europe and Africa, few appreciate that equivalent mass movements occur across Australia. Every year, tens of millions of birds, bats, butterflies and moths embark on epic journeys spanning vast distances, from as far afield as Tasmania and Cape York, many leaving the continent to access areas across the Northern Hemisphere. Australasian cuckoos are emblematic of this phenomenon, with every species showing pronounced shifts in distribution between summer and winter habitat.

Twelve species, one remarkable phenomenon

Australia is home to 12 species of cuckoo. Most breed here, while some — like the Oriental Cuckoo — pass through as non-breeding visitors from further north. Among those that do breed on our shores, movement strategies range from sedentary, through partial migrants that shuffle within the continent, to long-distance migrants that cross open ocean to and from Indonesia, New Guinea and neighbouring islands each year.

They range in size from the diminutive, iridescent Little Bronze-cuckoos – the smallest cuckoo species in the world – to the unmistakeable Channel-billed Cuckoo at the other end of the size spectrum as the largest, a genuine heavyweight of the skies at well over half a kilogram. The Shining Bronze-cuckoo, meanwhile, holds a different distinction: together with the Long-tailed Cuckoo, it is one of only two land bird species that regularly complete the open-ocean crossing between Australasia and New Zealand — remarkably, New Zealand’s only overseas land-bird migrants are both cuckoos.

Their calls are just as unique as their journeys. Channel-billed Cuckoos announce their arrival with raucous, prehistoric-sounding shrieks as they pass overhead or gather in fruiting figs. The Pacific Koel’s piercing “coo-ee” call — a favourite talking point among sleep-deprived city dwellers — can continue around the clock through the warmer months. Deep in the understorey of forests, woodlands and along creeklines, the Fan-tailed Cuckoo announces itself with a distinctive descending trill.

Tracing a flyway down the ranges

The annual cuckoo season traces the birds’ movement as they spread along the length of the Great Eastern Ranges, from Cape York towards the south-east of the mainland — some, like the Shining Bronze-cuckoo, continuing all the way to Tasmania. Their calls begin echoing across our northern Regional Alliance landscapes from August, rippling down to reach the far south by October.

These signature calls underscore the importance of the Great Eastern Ranges as a seasonal flyway — one of many movement corridors mapped through GER’s Flyways program, which works to identify and restore pinch-points and gaps threatening these continental-scale migration routes. It makes the coordinated, landscape-scale efforts of our Regional Alliances all the more critical — not only to provide habitat for our annual visitors, but to protect the nesting success of the many resident bird species that host cuckoos’ eggs.

Why cuckoos make an ideal conservation focus

The return of the cuckoos and their unmistakeable calls serves as a useful indicator of the health of woodland and forest bird populations and, in turn, the wider ecosystem. A combination of user-friendly acoustic sensors and expanding capacity to process long duration recordings now makes cuckoos an ideal focus for the kind of multi-region, multi-faceted connectivity conservation project for which GER is well known. Cuckoos are:

• highly vocal and instantly recognisable, making them well suited to citizen science and other low-cost monitoring;
• acoustically consistent across their range, an ideal subject for automated data capture and analysis;
• indicative of wider ecosystem health, reflecting the abundance of food (fruit, insects and the like) and the condition of the host bird species on whose nests they depend for breeding success;
• conspicuously migratory, easy to detect when present and calling in an area during the spring/summer breeding season;
• reliant on large-scale, linked conservation efforts, spanning source and destination areas, stop-over sites used in transit, and the habitats used by species with strong site fidelity;
• poorly understood in their overwintering range across New Guinea, Indonesia and the Pacific islands; and
• under-represented in conservation and public policy attention, relative to their ecological significance.

Building the GER network’s capacity to listen

GER is collaborating with Charles Sturt University and the Australian Acoustic Observatory (A2O) — Australia’s national network of permanently deployed acoustic sensors, among the largest bioacoustic monitoring arrays in the world — to build the capacity of the GER partnership network to track the ebb and flow of cuckoo distribution across eastern Australia, and to detect changes in arrival and departure timing that may signal the effects of a changing climate.

Summary of detections for three bird species from the Cumberland Plain Acoustic Observatory site, calls identified automatically by the Bush Bird Classifier.  Compare the trace for Magpies which occur at the site year round with the strongly seasonal pattern of the two cuckoos.  By combining a regional call classifier with long duration recordings, occurrence patterns of species across Australia can be tracked with unprecedented resolution.

As you step outside this spring, listen for the shriek of the Channel-billed Cuckoo overhead, the koel’s insistent “coo-ee”, or the trill of a Fan-tail deep in the bush. Each call is a small reminder of the extraordinary journeys unfolding across the continent — and of why the vast corridor we’re working to protect matters so much to the species that depend on it.

Cuckoos are just one of the many migratory species GER’s Flyways program works to protect. Learn more at ger.org.au/our-work/wildlife/flyways or Donate to Cuckoo conservation at https://www.donatetoger.org.au