This part discusses its behaviour in the Cook Islands and in New Zealand and the long time it took to prove it was migrated long distances over the ocean. Part 2 next week discusses its Polynesian names, the likelihood that its migration helped ancient Polynesians discover Aotearoa, and alternative bird omens of New Zealand.
The Long-tailed Cuckoo is dark brown with pale brown spots topside and white with brown streaks below; its conspicuous long tail is dark brown with pale brown bars.
In the tropics the cuckoo is solitary, secretive and inconspicuous except for the occasional loud screeching "wrrrrisssSST" call from high in trees. They are sometimes seen in fast direct flight between trees or slinking along tree branches in search of insects and lizards.
On Ātiu, twice in March and once in November, I have seen gregarious behaviour of small groups with much chasing associated with a rattling "chi-chi-chi-chi-chi-chi" call. The significance of this behaviour is unknown.
Nesting birds in the Cook Islands, such as the Rarotonga Flycatcher (Kākerōri) and the Rimatara Lorikeet (Kura), react very strongly to the presence of a cuckoo and chase it away. In New Zealand the cuckoo is a well-known predator on the eggs and nestlings of other birds and presumably they do the same here when the opportunity arises.
New Zealand behaviour
Each year the Long-tailed Cuckoo is first noticed in New Zealand in October and November. Although generally inconspicuous, they make their presence known with an occasional "wwrrrrissST" call while perched high in a tree or when flying. Around mid-November the males start to gather in small choral groups, singing "wwwrrrissST" and "chi-chi-chi-chi-chi" to attract females which are receptive from mid-November to mid-December. After mating the females go their own way, in search of food and a suitable nest into which they can lay an egg.
In the North Island the cuckoo lays exclusively in the cup-nest of the common Whitehead (Pōpokatea/ Pōpokotea), while in the South Island they lay mainly in the cup-nest of the common Brown Creeper (Pipipi) and sometimes in the tree-hole nest of the endangered Yellowhead (Mōhua). These closely-related bush birds are tiny compared to the cuckoo - a mere 15cm in length and 20g in weight versus 40cm and 130g of the cuckoo.
The cuckoo approaches the nest of prospective adoptive parents with stealth, for if they detect her they are alarmed and chase her away - only to have her sneak back again and again. The host nest usually has two-four eggs; the cuckoo lays directly into the nest and its own egg is usually not noticed because it is similar in colour, even if significantly larger (23x17mm compared to 20x15mm). It is not known if the Long-tailed Cuckoo sometimes uses its beak to remove one of the host's eggs before laying its own, as is known for some other species of cuckoo.
The cuckoo egg hatches in 16 days; the nestling is an aggressive beggar for food and grows rapidly. As soon as possible it pushes the host's eggs or hatchlings out of the nest. The adoptive parents struggle to keep up with its demand for food. They must be relieved when after three weeks the lone nestling leaves the nest, only to discover that it will sit on a nearby branch demanding to be fed for another month. At this stage it is four times the size of its foster parents and it is ready to fly away to find its own food. In total, the small birds worked for nine weeks to get rid of their super-sized foster child; as a result it is too late in the season to have a family of their own.
The mystery bird
Māori and early naturalists in New Zealand were very aware that the two cuckoos - the Shining Cuckoo (Pīpīwharauroa) and Long-tailed Cuckoo - appeared in spring and disappeared for the winter.
The cuckoos were well known to Māori as the joyful harbinger of spring, but where they went for winter was a mystery. There was a widespread belief that the cuckoos buried themselves for the winter - in riverbed mud, in holes in Puriri trees, or in rock crevices. Some believed that when buried they transformed into lizards, and reversed the process in spring. There was no suggestion that the cuckoos arrived and departed over the ocean.
By the 1850s, New Zealand ornithologists increasingly believed that the cuckoos were tropical migrants, undertaking non-stop flights of more than a thousand miles over the ocean - to land in the sea was certain death for a land bird. In contrast, overseas biologists were less convinced. In 1876 the great Alfred Wallace, co-founder of the theory of evolution with Darwin, wrote that New Zealand ornithologists had “insufficient evidence” to prove that the cuckoos migrated non-stop over more than a thousand miles of open ocean, which he thought was “extremely improbable”.
Undaunted, two years later in 1878 Walter Buller declared in his Royal Society paper that the Long-tailed Cuckoo “migrates every winter to the Society Islands”. In the 1888 classic “The History of the Birds of New Zealand”, Buller mentioned cuckoos in Fiji, Samoa, Tonga, Societies and Marquesas and declared that they migrated to New Zealand.
Hutton in 1901 and Fulton in 1903 both presented a wide range of scientific evidence before the Royal Society and established beyond reasonable doubt that the Long-tailed Cuckoo migrates between New Zealand and the islands of the tropical Pacific.
Meanwhile, on islands in the tropical Pacific, some of the collectors of cuckoo specimens, including immatures, were claiming the bird bred in the tropics. As late as 1917, the renowned American ornithologist Alfred Wetmore accepted these claims that the cuckoo bred in the tropics. With further support based on a difference of plumage colour he proposed two subspecies: Urodynamis taitensis taitensis breeding in the tropical Pacific islands, and Urodynamis taitensis pheletes breeding in New Zealand.
Migration pattern established
In 1937 the American biologist Cardine Bogert published an extensive study of specimens and proved that the Long-tailed Cuckoo that breeds in New Zealand migrates to tropical islands in the Pacific.
After breeding in New Zealand the adult cuckoos leave during January and February to migrate to the tropical islands of the Pacific, mainly to the islands of Fiji, Samoa, Tonga, Cook Islands, the Australs and Societies which are 3000 to 4000km from North Island.
The cuckoo has been recorded in New Zealand flying 80km/hr, if we assume it can sustain a modest 50km/hr during migration, it would take two-and-a-half days to fly the 3000km to Rarotonga. With the initial support of the common westerlies it probably transits in less than two days.
Some cuckoos migrate much further afield, to Micronesia in the northwest and the Marquesas and Pitcairn in the east, 5000 to 6000km from New Zealand. Future satellite tracking will show if they island-hop or fly direct.
The young cuckoos leave New Zealand in March and April and migrate by themselves northward to the tropical islands using inherited knowledge. Recent evidence shows that young cuckoos do not just fly north and stop at the first island. Their knowledge enables them to migrate to the full adult wintering range from Micronesia to French Polynesia – an amazing feat.
The juvenile birds have conspicuous cream spots above and a pale brown underside; by September most have changed into adult plumage. It is not known how many first year birds accompany the breeding adults south in October and November, but it is thought that the adults in the tropics during the summer are first-year birds, and they will migrate to breed in their second year.
The migration story took a surprising twist in 2012 when ornithologists Gill and Hauber published a new study of specimens and observations. They concluded that many cuckoos in tropical Eastern Polynesia, such as the Cook Islands, do not migrate directly southwest to New Zealand. Beginning in June they use the persistent Southeast Trades to move westward to Samoa, Tonga and Fiji; it is from there that they migrate to New Zealand in October and November, thereby avoiding the unfavourable westerlies below 30°S.