Ka tangi te wharauroa, ko ngā karere a mahuru
If the shining cuckoo cries, it is the messenger of spring
“Ka tangi te wharauroa, ko ngā karere a mahuru - If the shining cuckoo cries, it is the messenger of spring”
At around this time each year many people listen out for the call of the pīpīwharauroa /shining cuckoo, a welcome sign that spring has arrived. It is that distinctive loud whistling call: multiple slurred ascending whistles usually ending with – at last! – 2-3 descending ones. Have you heard any yet? If you do, you can contribute to a study of their migration patterns by recording your information here.
They are often heard in Wellington in September. However, they are not so often seen since their calls, although loud and easily recognisable, can be very difficult to track and the birds tend to remain concealed. But it is worth waiting and watching as they are strikingly beautiful, especially when seen in sunlight.
Pīpīwharauroa are one of our two forest bird species that migrate outside New Zealand. They spend the winter 4,600km further north, mainly in the Solomon Islands. As well as their major annual migrations, the other distinctive feature is that they are brood parasites – they lay their eggs in the nests of riroriro/grey warbler and let those birds raise their young!
Pīpīwharauroa lay one egg in several nests after the warblers have started laying their own eggs. There is no egg rejection and the female warbler goes back to incubate, even if she has observed or attacked a cuckoo while it is at her nest – though this visit of course might just seem to them like a successfully foiled predation attempt since the same number of eggs are still present.
Because the nest is enclosed with a tiny warbler-sized entrance hole, it seems a puzzle how the pīpīwharauroa gets her egg inside the nest. Indeed, it was sometimes thought that she laid it outside and then carried it in her beak – a belief possibly reinforced by observing pīpīwharauroa carrying eggs this way near riroriro nests. However, camera footage has shown that the female cuckoo does manage to squeeze into the nest head first – leaving tail and wingtips outside – and then carries off one of the original eggs in her beak as she leaves after laying her own.
The incubation period of the cuckoo egg is a few days shorter than that of the warbler’s, so the cuckoo chick has a ‘head start’: at about 4 days old it pushes the warbler eggs or chicks out of the nest so it has no competition. Since it needs to grow to almost 4 times the weight of a single warbler chick it needs the dedicated care of both riroriro adults. And dedicated they certainly are! These busy little 5.5g adults spend 3 weeks feeding the voracious chick, which grows to a whopping 23g and begs at a frequency and volume of a whole brood of riroriro chicks. Even after it has fledged it follows them around and begs incessantly for another 3-4 weeks. This is when they are often seen, as the pīpīwharauroa fledgling makes so much noise it is hard to miss, and the riroriro look as though they may be eaten alive.
Of course, it is only fitting that we also (figuratively) sing the praises of the host species, the riroriro. Weighing just 6g, the riroriro rivals the titipounamu for the title of New Zealand’s smallest bird although, by virtue of its shorter tail, the titipounamu usually wins.
The riroriro is the most widely distributed of our forest birds, and one of the few not considered to be under any threat. It seems to have actually benefitted from human modification of the landscape in a way few of our other birds have done, and is now found throughout the country in rural and suburban habitats as well as forests. Thus it is the endemic bird people are most likely to have in their gardens, although being a diminutive greyish bird busily searching for insects high in the trees, it is certainly not as often seen as tūī or korimako/bellbird. Its long melodious warble is surprisingly loud however, and frequently heard.
Only males sing this full song, but females sing the first two phrases, often repeated several times. They pair for life, and pairs stay together all year round, usually foraging within a few metres of each other. In the breeding season the male may often be seen alone as only the female builds the nest and incubates the eggs. They are one of the earliest birds to start nesting. This is important as it means they can get their first clutch under way before their brood parasite, the pīpīwharauroa, arrives in September. The first eggs are usually laid in August, but the female may start building in July as the nest is an elaborate structure taking her up to 4 weeks to complete. On thin outer twigs she suspends a large, intricately woven, pear-shaped dome thickly lined with feathers or tree-fern scales and fully enclosed except for a small entrance hole. To appreciate the scale of this accomplishment, compare the delicate wispy hammock of the tauhou/silvereye, who is twice her weight, with the tiny riroriro’s cosy construction. A remarkable bird indeed!
Photo credit: Tom Lynch