The song of the rifleman
Zip, pip, chuck, goes the call of Aotearoa’s smallest bird. It may turn out to be one of the earliest forms of language.
On the flanks of Harbour Cone, on the Otago Peninsula, riflemen nest in the hollows of kānuka—on my neighbour’s land, but not mine. The birds haven’t made a home at my place yet, even though the habitat is the same. It’s covered in regenerating native bush, mostly kānuka, with various broadleaf species elbowing their way into the sun. Here, the bird life is tremendous, but riflemen aren’t among them, and I’m determined to find out why. I guess you could say I have rifleman envy.
Watch a pair. His plumage is khaki, hence his English name—riflemen in an early New Zealand regiment wore green coats. She is bigger, and her feathers are buff and brown. But bigger is relative—they’re both tiny, like ping-pong balls with a beak and wings. He weighs a little more than a sheet of paper, while she’s about as heavy as two teaspoons of sugar.
Riflemen cling on in many parts of New Zealand where other native bird species are fast disappearing. That’s partly because they’re adaptable, nesting under hedges, in chinks in rock walls, even in the side of a rolled-up garage door. They can also tolerate the cold: if it’s too chilly, they enter torpor, a kind of mini-hibernation that conserves their resources.
“They have a habit of defying theories,” says Sarah Withers, one of the first people to look closely at North Island riflemen for a PhD comparing different populations of the birds.
It’s beanie-and-gloves weather, and there’s a southerly in my face. Among the kānuka the shadows are monochrome black, striped with streaks of sunlight. Through the branches, the bright-green hills edging the harbour remind me how this place might have looked 50 years ago.
I’m wandering along a one-kilometre transect at my neighbours’ place, counting birds: watching, listening, recording. Similar counts are made on more than 20 properties on the Otago Peninsula each spring, and have been every year for the past decade. These counts measure changes in the numbers of birds, tracking what has happened in response to intensive possum control. The trends are positive.
The birds don’t mind the cold. It’s early spring, the breeding season, and they’re in full voice. I tick them off on the sheet: tūī, blackbird, silvereye, bellbird, grey warbler. There is only one absentee—I haven’t heard any riflemen.
I’m new to bird counts, so I’ve been listening to bird calls online. Most native species have loud, distinct calls, but not riflemen. Though I played several versions of the call, I could barely make them out. Across the room, my wife, Jeannie Hayden, heard them clearly.
Rifleman calls are very high-pitched, with a frequency of about 20,000 Hertz, which is at the upper limit of human hearing. Most people can detect frequencies between 20 and 20,000 Hertz, but some of us—mostly males over 40—lose their high-frequency hearing. I’ve just discovered I’m one of them.
Jeannie has joined me this morning as an acoustic consultant. She hears two calls, and she points up to the right. I see a tiny bird beelining to a small hole in an old kānuka. He has feathers in his beak—he’s putting the finishing touches on one of his nests. The male is the primary nest builder, and may have built several before this one. The female decides which nest is best. She’s nearby, feeding on a gnarly old kānuka. As she spirals up the trunk, she flicks her wings, twisting side to side to tweeze insects and spiders from the bark.
A rifleman nest is the definition of cosy: a small dome of interlacing blades of grass and other lightweight materials, lined with feathers and down. The birds enter the dome by squeezing through a slit at the side.
This pair is chattering to each other, and I realise I can hear them. I may be missing a part of the conversation, but to me it sounds like a high pitched ‘pssssst’, a whisper to someone to get their attention.
In Hawke’s Bay, researchers from the University of Auckland are analysing the full range of rifleman conversation. Bioacoustic recording systems are paired with video cameras at nests to determine which calls are used when. Then, outside of the breeding season, the team is recording and analysing individual birds’ calls in order to detect any variations in calls between birds—differences from year to year, for instance, or between individuals and their parents. All this is to figure out whether riflemen are capable of vocal learning: whether they learn their calls as youngsters by imitating others.
“We think we’ve got a handle on bird sensory systems, but most information is based on very few species,” says study leader Kristal Cain. “New Zealand wrens are important for researchers the world over.”
If riflemen are capable of vocal learning, this is potentially a big deal. While most animals can make sounds, only a few are capable of learning specific calls and using them to communicate specific information. Whales, dolphins, bats, elephants, many songbirds and humans have this ability.
We have become very good vocal learners, but we’re also newbies at it on an evolutionary timescale. If we’re to understand how vocal learning evolved, we need to interrogate birds: they picked it up before we did.
But why pick the tiny rifleman for such a big assignment? There are plenty of great songsters and vocal learners in Aotearoa—tūī, kōkako and bellbirds.
Riflemen belong to a unique group of birds, the New Zealand wrens, which occupy an ancient branch on the tree of life. The lineage of these birds goes back further than any other songbird in the world, forming a previously missing link between parrots and songbirds. Wrens have been in Aotearoa longer than moa and kiwi—they are Gondwanan originals, like tuatara—but this heritage has only recently been identified.
“They are critical to understanding not only the evolutionary history of songbirds and parrots, but the evolution of vocal learning and human language more broadly,” says Cain.
Only two members of the wren family survive: the rock wren, which lives in the alpine zone, and the rifleman, which is scattered unevenly around the country, with fewer in the upper North Island. Sarah Withers reckons this is because the majority of populations of North Island riflemen live at higher altitude—many on mountains—which suits their tolerance for cold and their superpower of torpor. It’s also likely that there are fewer predators at higher altitude.
This doesn’t really help me create a rifleman-friendly property in the South Island, though. Until I learn that the genetic makeup of different populations of rifleman, even those quite close to each other, can be radically different. The genetic differences are so great that rifleman are more similar to flightless birds or invertebrates, which don’t move far at all. That makes sense: riflemen aren’t very good at flying. Maybe that’s why they haven’t come over the fence—they don’t move far or fast. Perhaps I need to be patient.
Jeannie leads me to another pair nearby. They are using a nest box, and it looks like they have begun laying eggs. Females lay up to five eggs, and the eggs’ combined weight is heavier than her eight grams. To accomplish this, she takes her time: after laying an egg, she spends 48 hours furiously feeding, which kickstarts oogenesis—development of the next one. Only after she’s finished laying will she begin incubating the eggs, which takes about three weeks.
The first pair I spotted have chicks in their kānuka tree-hole nest. Jeannie can hear them, which means that predators can hear them too. The trunk of a tree is a highway for stoats, weasels, possums, and ship rats, which also make nests in trees and live close by the birds they predate.
This is the main reason why rifleman populations are declining around the country. A major part of my neighbours’ success in keeping riflemen has been their decade-long effort trapping rats, possums and stoats. By contrast, I’m only just getting started.
On my next visit over the fence, the chicks are out of the nest: four bundles of feathers huddled together on a branch.
Riflemen are unusual in that random single birds often turn up to help feed the chicks: often they’re chicks from a previous clutch returning to give mum and dad a hand with their younger siblings. It’s called cooperative feeding.
Chicks, parents and helpers are all chattering away. From all this rifleman racket, Cain’s team is isolating and analysing calls using software that can detect minuscule differences between them. In particular, Cain wants to know how long the ‘baby talk’ stage lasts among chicks, as this could be key to determining whether riflemen are vocal learners.
“This is a cool part,” says Cain of the chicks’ chattering. “We know from songbirds that the babbling period is quite protracted in learners and can take up to nine months to produce full adult song.”
This period is much shorter in non-vocal learners—chicks transition more quickly to making adult calls.
I’ve had an idea: perhaps there’s a difference between my kānuka forest and my neighbour’s. On my next visit, I’m looking more at the forest than the birds. The trees over the fence seem bigger, older, more mature. My neighbour confirms this: growth rings and early photos of his hillside puts the ages of the trees between 50 and 80 years. Mine, also based on old photos, are barely 30 years old. His trees have developed crevices and holes suitable for rifleman nests. When I investigate this, I discover that research by Landcare Research–Manaaki Whenua scientist John Innes supports this idea, too. It seems as though riflemen like a more mature environment—and if that’s the case, I don’t have the patience to wait.
The first thing I need to do is predator control, and the second is to install nest boxes. If my trees don’t provide a nesting environment, these will. I’m organising for 50 new ones to be made—why stop at my place, after all? I want riflemen back on Otago Peninsula, big time.
Nest boxes have one crucial feature: a metal washer for a door. Previous nest boxes had the entrance holes chewed out by rats, but these reinforce the doorway, with a hole just big enough for a rifleman and too small for a rat.
Turns out there are some advantages to being tiny.