Silence reigned in the intense darkness of the bush. The last glimmers of day had ebbed from the sky long ago. Suddenly, I felt a light eddy of wind on my face. My quarry, a morepork, was heading soundlessly to its nest inside a hole in a tree which I knew lay just ahead. I adjusted my camera equipment in preparation for another night attempting to photograph and so identify food items brought by adult moreporks to feed their chicks.
To disrupt the birds’ normal behaviour as little as possible, I had erected my hide slowly over several days. Now the birds had accepted it as part of their natural surroundings, enabling me to get an inkling of their night-to-night lives.
During the day, moreporks are inactive—asleep in their roosts in deep shade, their dark brown plumage making them difficult to see. The only disturbance to their slumbers is the occasional attack by other birds. Small birds such as bellbirds, fantails, blackbirds and silvereyes recognise moreporks as predators, and, if they discover one, will form a mob and shoo it away with irate cries and daring little thrusting flights. After suffering harassment for a while, the morepork usually withdraws to a more secluded spot.
But once the sun sets and dusk creeps over the land, the morepork awakens, ready for a night of hunting. Its prey includes small birds, mice and the occasional gecko, but insects are the main staple. Occasionally, larger birds such as blackbirds are captured.
David Mudge, who has photographed and observed moreporks in the lower North Island since the early 1980s, says he has never seen them take a flying bird cleanly. “They deliver a body blow with their talons, and then swerve around to pick up the shaken and confused victim from the ground. Birds already on the ground or perching are attacked by the morepork diving through the undergrowth with wings folded back like a falcon.” Prey—even insects—is always seized in the talons, a stratagem that keeps possible danger away from vulnerable eyes. The wings of large insects are quickly torn off, and the body devoured bite by bite if it is a larger animal.
Like other birds of prey, moreporks regurgitate pellets of indigestible material such as bones, fur and the exoskeletons of insects, and their diet can be accurately determined by examination of the pellets. Department of Conservation ornithologist Ray Pierce recently used this method to study the diet of moreporks on one of the Hen and Chickens Islands off Whangarei in conjunction with a kiore (Pacific rat) eradication project.
“About 95 per cent of morepork pellets contained traces of kiore before we did the poisoning, so they were obviously an important food item,” says Pierce. There is no concern about the welfare of the birds now that the rats have gone, because moreporks readily adjust their diets to whatever prey is most abundant. “The removal of kiore is already leading to great increases in the number of seeds germinating,” says Pierce, “and insects will become much more plentiful.”
While kiore had been favoured prey for Hen and Chickens moreporks, on the reptile-rich, rat-free Three Kings Islands lizards are the main fare. One morepork nest found there recently contained an egg, a day-old white chick and seven or eight dead geckos. It is likely that local dietary variations occur throughout the country.
Pellet analysis also helps ecologists glean new information about the occurrence of small, hard-to-find nocturnal animals. Owls are much more effective in the dark than any human searchers, and prey is often swallowed whole, so regurgitated bones may be intact. Such analysis is even helping palaeontologists reconstruct the biology of extinct creatures
Although primarily inhabitants of native bush, moreporks are also found in pine forests, in open country where there are scattered trees for shelter and nesting, and even in suburban parks. Little is known about their feeding behaviour. One of the few studies that have been made—in the forested Orongorongo Valley in the southern Rimutaka Range east of Wellington—showed that a breeding pair typically hunted over an area of three to five hectares. Investigation of one eight-hectare patch of rata/rimu forest revealed a total of 46 pairs of birds (33 pairs of which were native), including two pairs of moreporks. Native pigeons, kingfishers and cuckoos were less abundant, being represented by only a single pair of each species, while silvereyes, grey warblers, and fantails were the commonest, each represented by four to six pairs. From this study, moreporks could be considered one of our commoner birds.
Very limited evidence suggests that moreporks remain in their territories for a long time. Two of the Orongorongo birds stayed in place for at least five years.
Scientists argue that it makes good sense for a nocturnal hunter to get to know a single territory very well. Ornithologist Richard Holdaway says that familiarity creates a mental map of the topography of an area, which owls use to navigate by.
“Owls rely on memory in the same way that people get to know their way to the bathroom at night with the light off,” he says. “The price for a mistake in walking around your house in the dark is perhaps a stubbed toe or a sore nose. For the owl it is not only the possibility of flying at full speed into a solid object, but also of starving to death because of a broken wing.”
Experiments in Britain showed that owls knew their flight paths so well that when a perch was removed, the bird would try and settle where it remembered it to be, and fall. If a new branch was inserted into a familiar route, the owl collided with it.
David Mudge has been impressed by our own owls’ knowledge of their territories. “Moreporks know the whereabouts of the nests of other birds, and check them out systematically. I watched one pair visit the nests of three hapless starlings who had made the mistake of nesting in the same tree as the owls. The moreporks would go from one starling’s nest to the next, hovering outside and reaching in with their talons, feeling for young birds to grab. I have seen a pair of moreporks ferry seven chicks back to their nest in 15 minutes.”
Moreporks take their name from their haunting call, which the birds use to keep in contact with each other and to proclaim sovereignty over their territories.
According to the 19th century explorer Charlie Douglas, that mournful more pork must have sounded “unpleasantly suggestive” to new immigrants brought up on tales of cannibal feasts where “long pig” was the main course!
The call, which to some ears sounds like cor quo, is usually repeated every four to five seconds.
One night, when David Mudge played a recording of it, he was rewarded with an outraged morepork swooping down and mounting an impressive threat display on a post not two metres away.
The bird stretched itself forward and up, puffed out its feathers and held its wings out like a cloak, causing its body to appear much larger than it really was. The white spots under the wings merged with those on the chest, making it resemble a great shield.
Female owls sitting on the nest use a similar display to discourage predators.
Maori Regarded the morepork—which they call ruru—with some ambivalence. The birds were messengers to be heeded, and sometimes feared.
Margaret Orbell, author of The Natural World of the Maori and The Illustrated Encyclopedia of Maori Myths and Legends, notes that many family groups believed they had a special relationship with an ancestral spirit, which often took the form of a morepork. This owl guardian or kaitiaki was not recognised in just any morepork, but in one that exhibited unusual behaviour, such as sitting in a prominent place, fluttering against a wall or entering a house. Seeing such a bird might signify impending death, or merely announce the arrival of important visitors.
If you were discussing plans and heard the cry of the morepork, it was a bad sign, as was a cry heard at crossroads. But if a morepork was seen flying ahead or walking along a path, it was there as a protector.
The bird and its characteristics were used symbolically. Orbell documents an instance when a young man, grieving over a separation from his beloved, recalled the morepork’s dolorous call and lamented:
“The morepork’s cry keeps coming to me,
It is hooting out there where the paths meet.”
A woman defending herself against gossip cited the bird’s solitary habits when she cried, “I am like a morepork hooting in a lonely place,” while the breadth of the bird’s intense gaze was referred to when a man warned his enemies that he was aware of their mouthings about him:
“My eyes are like a morepork’s, staring from side to side,
Like the eyes of a hawk that soars over the plain!”
Orbell attributes the origin of the large staring eyes in many Maori carvings to the eyes of the morepork, in particular to a tapu bird which was sacrificed under the wall of the first carved house when Rongo learned to build such houses from a pattern he saw in the sky.
Anyone who has looked at an owl’s eyes will realise how important acute eyesight is to these birds. Their eyes have several features which serve them exceptionally well for a predatory night life.
In daytime birds, as in most vertebrates (including humans), the light-detecting retina at the back of the eye is predominantly made up of cone cells—cells which enable accurate perception and colour rendition of objects in daylight. A mere scattering of rod cells gives these animals some ability to detect objects in poor light.
In the retinas of owls’ eyes, however, rod cells predominate, enabling owls to better pierce the gloom, while their colour perception and long-distance vision are thought to be in ferior to that of humans and many other birds.
The retinas of owls are 100 times more sensitive to light than are thoseof pigeons. By constricting their large irises, though, owls can also see quite well in daylight.
Owl eyes are large and cylindrical (rather than spherical), and cannot move in the eye sockets of the skull. They are as fixed as car headlights. To look around, an owl must rotate its head—which it can turn through an arc of at least 270°. (Because it can swivel its head very rapidly, some ob‑servers have been fooled into thinking that the owl can rotate it through a full circle, but this is physically impossible.)
Super-silent flight is another owl hallmark. Soft fringes on the edges of their flight feathers and a velvet-like covering on their wing surfaces are largely responsible. They may slightly reduce an owl’s speed in flight, but they enable it to swoop upon prey with a completely silent approach.
Compared with many other birds, the wing area of owls is also large with respect to body weight, which contributes to effortless, quiet flight.
But silent flight is of even greater significance for owls than just allowing them to surprise their prey. All birds have acute hearing, and in owls this sense is particularly well developed. In experiments in which owls were kept in pitch darkness (and hence where sight was impossible), the birds were still able to accurately locate their prey. Observers have also noted that owls are much more successful at capturing mice in dry conditions, when leaves rustle, than when the ground is damp. They evidently depend on sound to a high degree when hunting, and facial feathers and skull bones are arranged to ensure optimal funnelling of sound to the large ear openings.
We humans stop moving—even breathing—when we are listening intently to a faint sound, because the noise of our own movements masks what we are listening to. Cessation of movement is hardly an option for a bird in flight, and some ornithologists now think that the primary function of an owl’s soundless flight is to maximise their hearing until prey is secure in talon or beak.
David Mudge recalls attempting to get an uncooperative owl to turn around—so that he could take a better photograph of it—by making a click with his tongue. The owl turned and flew at the canvas hide, striking it exactly beside Mudge’s face.
The wide, flattened heads of owls allow both eyes and ears to be placed as far forward and far apart as possible. For the eyes, this produces overlapping visual fields that allow true binocular vision and fine depth perception—something of a rarity in birds. Some small owls bob and turn their heads to further improve their depth perception of prey.
A wide separation between the ears permits accurate pinpointing of the source of a sound. Sound waves travel relatively slowly, and widely spaced ears allow minute differences in the time a sound reaches each ear to be compared by the brain. Differences in the intensity of sound in each ear also provide directional information.
In some owls, the skull bones around the ears are asymmetrical, so that the two ear openings differ in size and position. These anatomical refinements allow the birds to locate the source of a sound in three-dimensional space.
The morepork’s senses of sight and sound have not been specifically analysed, but it is likely that it has some or all of these special endowments.
In the wild, moreporks usually start nesting in October, although zoo specimens have been recorded nesting in midwinter, possibly stimulated by an ample food supply.
They typically nest in dry cavities in trees, in clumps of perching Astelia lilies and in mats of pine needles in the forks of pine trees. No additional nesting material is used. Nests on the ground in rocky terrain have been recorded in Otago, and one nest has been seen in a clump of pampas.
Little is known about courtship in owls. What is clear is that bringing two normally aggressive individuals armed with lethal weapons together for mating is a potentially hazardous business. Bill snapping—a warning signal in most owls—seems to be present in many courtship rituals, indicating the delicately balanced nature of the proceedings.
Close-quarters posturing—wing flapping, head bending, bowing, swaying about—accompanied by a variety of sounds and often food presentation by the male (always judicious when the female is larger, as is commonly the case with owls) precedes mating. After mating, the pair seem to grow in mutual amiability, often roosting pressed against each other flank to flank, and indulging in mutual preening.
This close roosting has been observed in moreporks in the couple of weeks before the hen takes to the nest. “In the evenings during this time, the owls are very talkative, often calling softly to each other with purring and meowing sounds,” says David Mudge. “The eggs are developing inside the female during this period, and she often sits around and doesn’t hunt much, so the male brings food to her. Very considerate.”
After the female has spent a week on the nest, two, and occasionally three, almost spherical white eggs are laid on the bare litter.
Incubation, which takes 31 days, is performed solely by the female. During this time, the male brings food to her at the nest, calling her with a soft, musical rippling cwree cwree. Hearing the call, the female leaves the nest to be fed by, or take food from, the male.
As the second egg is laid up to 48 hours after the first, and incubation begins after laying of the first egg, there is a slight difference in the size of the chicks.
When hatched, chicks are covered in light grey down, and have their eyes closed. The eyes do not open until the eighth day after hatching. The chicks are brooded by the female for several days, while the male does nearly all the hunting.
Although examination of the pellets indicates the type of food eaten during nesting, it cannot show the times or frequency of feeds. Here, night photography and precise notes are necessary.
When photographing at night, I use a dim red light to illuminate the area around the nest. This light show-, the bird’s arrival at the nest, but is too dim to identify the food brought. Only after the photographs have been developed will this become apparent.
Mudge thinks that moreporks are able to see infra-red light. When he has used infra-red beams—set up so that an owl breaking a beam triggers the camera shutter—owls often seem to deliberately avoid the beams, which are invisible to our eyes. Lately, he has been taking time-lapse video shots of owl’s nests, and to provide illumination has the nest bathed in infra-red all night. On those nights the moreporks delay the onset of their normal nocturnal activities by half an hour or more.
Being able to detect infra-red could help owls locate warm-blooded prey, since infra-red light is given off by warm objects.
During Nesting, feeding is frequent during the two hours after dusk and again before dawn, but over the central part of the night it is only sporadic.
At every nest that I have studied, around dusk the male bird calls several times, bringing a large item of prey, usually a mouse or small bird, to the nest entrance. The female then flies from the nest, taking the food in her beak. She is usually absent for about 10 minutes, feeding herself, before returning with a portion of the prey, from which she tears small morsels to feed her two chicks.
Although the male does most of the hunting, he does not actually feed the chicks, leaving this chore to the female. Often prey, such as small dead birds are left in the nest during the day, presumably for the female to feed to the chicks.
When they are about two or three weeks old, the owlets perch at the nest entrance, waiting to be fed and vigorously flapping their wings.
As they approach fledging, they gradually learn to feed themselves from food left for them by both parents near the nest entrance.
I was at one nest on a full moonlit night when the owlets were about to fledge, at four weeks of age. Both parents were perched on a totara branch about 40 metres from the nest, when one chick flew deliberately, and made a good landing near the parent, who greeted it with cree cree calls.
Not to be outdone, the younger, less developed chick, launched into space, but gradually lost height and landed on the ground. Anticipating that it would not last long down there, I returned it to the nest. It successfully flew the following night.
After leaving the nest, chicks stay with the parents for several weeks. In the first couple of weeks the parents bring them food, then for the next two or three the chicks chase the parents to collect it.
Four or five weeks after they have left the nest, they catch their first prey. In the Manawatu, this is usually big cock chafer beetles, which the young birds chase about on the ground and catch with their feet. After another couple of weeks they are able to grab them on the wing.
After the young are about six weeks out of the nest, the adults seem to disappear, perhaps deliberately leaving the youngsters to fend for themselves, having drawn them to the best feeding areas in preceding weeks.
Towards autumn, the adults reappear, driving their offspring away to find new territories, and there is some mortality among young birds at this time of year. From his observations, Mudge thinks that some young birds starve after the moths stop flying in late summer.
Moreporks often use the same nest site in successive years. However, in two cases I have seen the nest hole occupied by a possum, and in one case the animal had broken the eggs.
Mudge says that moreporks are very aggressive towards possums which approach their nests: “They dive at them, raking out fur with their talons. Possums feeding in the canopy nearby receive close fly-bys, with moreporks loudly clicking their beaks—like boys imitating machine guns—in threat displays.”
Where possums numbers are high, moreporks are forced to resort to nesting in holes that are so small a possum can’t squeeze in, and there aren’t too many such holes. Mudge has long observed a pair of moreporks in one particular patch of Manawatu bush, and only in the years that he has undertaken possum control have they bred successfully.
Humble as our morepork may appear in the universe of owls, in the last decade it has been part of a mission to rescue a Norfolk Island species.
The New Zealand morepork is one of several subspecies of boobook owl, a bird which is found in Australia, New Guinea, Indonesia and Malaysia. In Australia, the boobook is also called morepork or mopoke.
The Norfolk Island form declined to near extinction in the 1980s, with only a single female remaining.
The New Zealand morepork, considered to be the closest relative, was selected as a stud, and two males were despatched in 1987.
Paul Stevenson, a wildlife officer on the island, says that one of these individuals was never seen again, but after a couple of years the remaining male (now named Tintola, or sweetheart) and the female (Miamiti, after Fletcher Christian’s Tahitian wife) produced two chicks, and then a couple more the next year.
The progeny have bred successfully, and by the end of this year it is hoped that there will be 18 owls on Norfolk. Under consideration is the possibility of moving some of the birds to Lord Howe Island, where the indigenous boobook became extinct.
Could it be that the New Zealand morepork’s call will echo not just through the dark forests of Aotearoa but across other realms as well?