Pukeko-the indomitable swamphen
Popularly regarded as brainless kamikazes lacking all road sense, pukeko are confounding scientists with their complex, flexible social lives. And, while other native birds struggle to survive environmental changes, pukeko seem to take everything in their strutting stride.
In just about every culture, certain plants and animals are held in high esteem for religious or mythological reasons. Cattle are revered by Masai and Hindu, bears by the Ainu of northern Japan, eagles by American Indians. The cat was revered in ancient Egypt, while the Mayan culture worshipped sacred mushrooms.
To the Maori, all living things were the children of Tane, the creator of life, and each species had its own special relationship with humans. Some, such as the huia bird and the totara tree, were associated with nobility, and were revered. Others were harbingers of good luck—for example, if a kereru or native pigeon was heard cooing during the birth of a boy, it was said that the child would be destined for greatness.
Such status was not the lot of the cheeky pukeko. As Margaret Orbell notes in her book The Natural World of the Maori, gardeners spent much time and energy chasing pukeko away from kumara and taro plots, firing insults at the birds as they went:
“Hie, hie! Haere ki to huhi, haere ki to repo,
Haere ki a Hine-wairua-kokako! Hie, hie!”
“Away, away! Go off to the swamp, go off to the bog,
Go off to Hine-wairua-kokako [the spiritual ancestor of wading birds]! Away, away!” Pukeko are still considered pests by market gardeners and farmers, especially those whose properties adjoin wetland areas. Tony O’Carroll, who farms cattle on land next to the Whangamarino wetland at Mere-mere, says pukeko are a constant nuisance. “In winter, I’ve seen the paddocks black with `pukakas.’
They fly in from the swamp, then march across the farm pulling out the grass and pooping in the water troughs,” he says.
Pukeko are also disliked by hunters, who claim they prey heavily on duck eggs and young (although these are probably rare events). They are shot in relatively high numbers in some districts during the hunting season, which runs from the beginning of May until the end of July.
Regarded by most as inferior game, pukeko nevertheless have a few champions. Peter Lapwood, a Waikato Fish and Game Council ranger, believes they are underrated, and swears that pukeko makes a delicious soup. And if Tui’s Commonsense Cookery is anything to go by, stewed “pukaki” regularly made its appearance on the post-war rural dinner table, along with partridge and rabbit.
Pukeko are not indigenous to New Zealand, but occur across many South Pacific islands and in Australia, southern Asia, Africa, parts of Europe (Spain and Portugal, for instance), Central America and Florida. Outside of New Zealand, the birds are usually referred to as purple swamphens. They are classified as a single species, Porphyrio porphyrio, with six subspecies. The swamphens which colonised New Zealand probably flew across from Australia a thousand years ago or less, and share the subspecies name melanotus along with swamphens in the Kermadecs, Tasmania, eastern and northern Australia and the South Pacific. Despite their belonging to the same subspecies, New Zealand swamphens are slightly larger than their Australian neighbours.
Plumage characteristics vary slightly from region to region, but swamphens generally have a purple-blue body, black wings and red legs, bill and frontal shield. The colour of the back varies from blue in the Mediterranean subspecies, blue-black with a tinge of green in African and Asian subspecies to black in the Australian and New Zealand races.
The swamphen’s prominent frontal shield characterises it as a gallinule—part of the rail family. Rails are long-legged, stout-bodied birds which include crakes, weka and takahe—the latter being a par ticularly close relative of the pukeko (see box, page 66).
Like most rails, pukeko are generally found in or near wetland habitats. Their long legs and feet are well adapted for wading through shallow waters with muddy bottoms. They feed mainly on roots, seeds, and shoots of grasses, which they typically hold with one foot, parrot-fashion, while stripping off the outer layers with their beak to get at the tender tissues within. A small proportion of their diet, especially when feeding chicks, is made up of earthworms, grubs, grasshoppers and other small insects. Adults have been known to feed their chicks small fish, frogs, mammals and birds, as well as carrion, but pukeko are for the most part vegetarians.
Pukeko are capable fliers, as indicated by their presence on many offshore islands around New Zealand. However, their flying does appear awkward and laboured at times, especially when taking off and landing, and, given a choice, they seem to prefer to walk or run than fly. They are also good swimmers, and will readily paddle their way across ditches or ponds.
For all their lowly status in this country, swamphens have been held in high regard by other cultures. According to the French biologist Buffon, the Greeks and Romans imported swamphens from Africa and let them walk freely in palaces and temples as guests worthy of such places because of their gracious nature and the beauty of their plumage.
These attributes were noted by the early natural historians in New Zealand. In 1888, Walter Buller wrote: “The swamp-hen may fairly be considered one of the best of our native birds. The brightness of its plumage and the extreme elegance of its movements at once arrest and please the eye, while, on the other hand, it is in very good repute as a game bird. It is interesting to watch it as it strides about, balancing its body with ease on its long slender legs, jerking its head gracefully, and flirting its tail with every movement.”
Perhaps today we take pukeko for granted. They are not endangered, like many of our native bird species, and can be abundant in some areas. Although they prefer to breed and nest in marshy areas, they spend considerable time foraging for grubs and grasses in adjacent pasture land. In fact, the pukeko is one of the few native species to have expanded its range and increased in numbers with the clearance of native forests for farmland, although this trend has been reversed in areas where swamps have been drained.
Commo though they may be, pukeko have a low public profile compared to many other native birds. I am always impressed by how much the average person knows about the habits and natural history of kakapo, kokako, and takahe, despite theirnever having seen one in the wild. Yet the same people are almost shocked to discover that the pukeko they see feeding in drainage ditches along the roadside can actually fly.
That being the case, I suppose these people would be flabbergasted to find out that pukeko often live in communal groups, mate with several partners (many of which are close relatives) and sometimes exhibit homosexual-like behaviour. Yet this is precisely what research on pukeko over the past 20 years has revealed. There is a lot more to this ungainly bird than the image conjured up in the minds of many New Zealanders of a dumb bird that frequently gets hit by cars. As it turns out, the pukeko may have one of the most interesting and complex social systems of any bird species in the world.
John Craig of the University of Auckland was the first to investigate the social dynamics of pukeko. In the early 1970s he discovered that the pukeko social system varied according to where the birds were living. At one study site near Linton in the Manawatu, Craig found low pukeko densities and birds breeding as pairs. Territories were small, and each male had a relatively short boundary to defend against one other neighbouring male. At this site, once a pair’s offspring became independent, they were ejected from the parents’ territory, and either moved away from the area or joined large non-territorial flocks.
In contrast, pukeko at a second Manawatu site near Pukepuke bred and lived in groups consisting of 2-3 adult males, 2 adult females (who bred promiscuously with each of the males), and 1-2 nonbreeders who were offspring from previous broods. All of the group members, including the nonbreeding “helpers,” assisted in the raising of chicks. The two females laid their eggs in a single nest and shared in the incubation duties along with the breeding males.
For two female birds to share the same nest is extremely rare and is known to occur only in a few other species such as ostriches, Tasmanian native hens, the anis of South America, and acorn woodpeckers in California.
Unaware of the existence of these communal tendencies in pukeko, early naturalists were surprised by their exceptionally high clutch sizes. One published report noted that a female pukeko had managed to lay 19 eggs in one breeding attempt. We now know that these large clutches are cases of communal nesting. They can be verified because each female lays eggs with a distinct colour and spot pattern; on careful investigation two sets of eggs can be identified in the shared nest.
The average clutch size for females nesting by themselves is five eggs. Interestingly, for communal nests the average clutch size per female is seven eggs, and there can be as many as 25 eggs in total. It might be that joint nesting females are showing a subtle form of competition, with each female trying to outlay the other.
But why would females want to share a nest in the first place? Craig did not come up with a satisfactory answer to this question, but he did make two important observations that allowed him to speculate why males sometimes share territories and mates. First, he noted that territory boundaries are much shorter, and resident males have fewer neighbouring males to defend against at the Linton site than at Pukepuke. Second, he estimated that males breeding as pairs in Linton produce more chicks per capita than do males breeding in groups in Pukepuke. In the few cases where a pair tried to breed in Pukepuke, they were invariably unsuccessful in raising their young, and ended up spending most of their time defending against neighbouring groups with two or more males.
Craig concluded that although individual male pukeko are reproductively worse off breeding in groups, in some areas where competition for breeding space is high, a male may have to allow another to join him to help defend a nesting territory at the expense of giving up exclusive breeding access to his mate.
In such a situation, one would expect there to be competition between the resident males for the females. In 1983, I set out to test this idea at Shakespear Park, a 460-hectare park at the tip of Whangaparaoa Peninsula, near Auckland.
Here, pukeko groups were even larger than those in the other study areas, containing 3-7 adult males, 2 adult females and 1-5 non-breeding helpers. Within each group there was a defined pecking order or dominance hierarchy among both males and females.
This pecking order is routinely asserted in disputes over food, territory, incubation duties and even preening. The positions of head and beak are the key elements in interactions between birds. A dominant bird holds its head high and fluffs up its plumage; a submissive bird bows, holding its head close to the ground and exposing its vulnerable tail. (The tuft of white tail feathers is an apt symbol of submission.) By using such postures, birds keep potentially damaging beak-and-claw aggression to a minimum.
Given the rigid dominance hierarchy which exists in pukeko groups—and which remains largely unchanged from year to year—the question I needed to answer was this: was the dominant male fathering all or most of the offspring?
A simple count of the number of times various males copulate does not give an accurate answer to this question. To become a father, a male pukeko must mate at the right time. Fertilisation has to occur within 15 minutes of ovulation, or the hardening shell membranes of the egg become too tough for sperm to penetrate.
Also, the laying down of the shell layers takes about 24 hours as the egg moves down the oviduct prior to laying, and only after that presumably fairly effective contraceptive is out of the way can sperm swim up the oviduct to fertilise the next egg. So successful matings have to take place within a few hours of egg laying.
Could it be that, within a communal group, dominant (alpha) males were timing their copulations to coincide with the peak fertile period of the female? And, at the same time, “conning” subordinate males into thinking that they were fathering offspring, when in fact their copulations were mere background noise to the alpha’s Rhapsody in Blue.
Predictably, male courtship of females proved most intense in the morning (after egg laying), but, contrary to expectations, alpha males made few attempts to prevent lesser males mating. Occasionally, an alpha male pecked a female who was crouched in mid-copulation, causing her to straighten up and the subordinate male to fall off, or he distracted other eager males by crouching in a copulating position himself. A crouching pukeko is evidently an irresistible target, for one of the males would then mount him and attempt to mate.
Normal matings are a raucous 20-second culmination of a vigorous “courtship,” in which males chase a female around the territory, raking her back with their feet in an attempt to force her into a copulatory position. When she finally gives in and crouches, the nearest male mounts her, while the others look on. Alternatively, all may attempt to mount, but this invariably causes the female to collapse under the weight of her suitors, producing a chaos of feet and feathers from which the female escapes, and the merry-go-round recommences. Typically, two or three males each succeed in copulating several times with a female in the few hours following egg laying. Such rapid mating undoubtedly produces a mixing of sperm in the hen and even greater uncertainty of paternity.
As for the females, a maximum of two breed and lay eggs at any one time. The alpha female generally lays first and contributes more eggs to the communal clutch than does the beta bird, but, as with males, there is little or no overt aggression shown between them, and alpha females make little attempt to prevent betas from mating or from using the shared nest. Nor are eggs belonging to other females destroyed or thrown out of the nest (as is the case with ostriches and acorn woodpeckers, for example).
There are usually two or three additional hens of breeding age, but lower status, living in the group, plus several low-ranking males, but none of these birds is sexually active. Somehow the older, dominant birds inhibit younger birds of both sexes from becoming sexually mature until about three years of age, although in other populations pukeko can breed at 12 months.
Behavioural biologists believe that there are strong evolutionary reasons why animals and birds act as they do. According to their paradigm, the only type of success is breeding success—leaving one’s genes in as many offspring as possible. When all the individuals in a group or population try to achieve this goal, it naturally leads to competition for mates—common behaviour in most higher animals.
Pukeko behaviour at Shakespear Park, however, is a little difficult to reconcile, because breeding between seniors in a communal group seems relatively amicable and largely devoid of expected competition. But suppose all the animals in such a group were closely related. In that case, competition among breeding adults to spread essentially the same genes would be wasteful, and even the co-operation of the non-breeding helpers could be explained.
Bird families usually have mechanisms that ensure the young move out of the natal area, to reduce inbreeding and the genetic defects this can lead to, but at Shakespear the pukeko population was large and hemmed in by sea on three sides and encroaching suburbs on the other. All available pukeko territory in the park was packed tight. Perhaps under these conditions the safest strategy for a youngster was to stay in the family territory until a breeding opportunity arose, even if it was only with relatives, and even if the mate had to be shared. Better a shared bird in the hand than two in the neighbour’s bush!
From the parents’ point of view, allowing the youngsters to “stay at home” makes sense, too. To push their offspring out into a world of stringent competition for space could put their reproductive fate (and the parents’ genetic “investment”) in jeopardy. Letting them stay assures the parents of free home help in exchange for breeding opportunities when they are older.
Banding studies of chicks over several years showed, in fact, that 70 per cent of pukeko at Shakespear ended up breeding with close relatives (fathers, sisters, cousins, etc.) in their natal territory. Close relatedness seemed to offer a good explanation for mate sharing and cooperation in raising young.
However, two doubts remained. First, I lacked hard evidence to prove or disprove that paternity was spread evenly among the adult males. Mate competition could still be happening, but at a level so subtle that our observations were not picking it up. Second, would such an egalitarian breeding system occur in a pukeko group where the members were not closely related?
When I moved to Dunedin in 1990 to take up a lectureship at Otago University, I had the opportunity to address both these questions with a large pukeko population at Otokia. Banding and video observation revealed that group composition and dynamics differed markedly from the North Island study sites. Breeding group composition proved highly variable and ranged from male/female pairs, through trios (with two of either sex) to larger groups embracing two or three males and two females. Moreover, all juveniles dispersed from their parents’ territories during their first year, and there were no non-breeding helpers in breeding groups.
My co-workers and I were able to use the new technique of DNA analysis of blood samples (so-called DNA fingerprinting) to determine unequivocal parentage of all birds at Otokia. We found that, unlike the situation at Shakespear, group members were not closely related.
Furthermore, we discovered that there was no relationship between dominance rank and the proportion of offspring fathered, nor between number of offspring fathered and parental work effort. All males contributed evenly to egg incubation and feeding of young birds.
So much for our hypothesis that low competition for mates was a consequence of close relatedness.
Perhaps, we wondered, it is the smaller, less aggressive males that form coalitions in order to gain breeding territory in desirable pukeko “suburbs.” Several males are better able to defend a prime territory than one on his own, but in return they must all be assured of having a good chance of fathering some of the partnership’s offspring. Otherwise, a male that was continually usurped by his coalition partner would depart to join another group and leave the resident male to defend alone.
Once eggs are laid, presumably neither males (nor nest-sharing females) can tell which eggs belong to whom, so all co-operate equally in sharing duties, trusting that they have some genetic stake in what is raised. For male pukeko, breeding begins to look like a lottery: each male buys as many tickets as he can afford, but never finds out exactly how much money he has won.
Of course, birds don’t make conscious decisions about their reproductive strategies. We assume that certain behavioural “rules of thumb” have evolved over many generations, and that the most stable rules with the highest average reproductive payoffs come to predominate in the population as a whole.
We can’t test this evolutionary scenario directly, but we can do so indirectly by temporarily removing one of two males from a communal group and holding it in an aviary for a few days during the fertilisation period. Once the female has laid her eggs, which presumably have been fertilised by the remaining resident male, the removed male is returned to his territory and his behaviour observed. If he does not incubate the eggs and/or leaves the territory, then this would support our initial hypothesis: males that are prevented from mating, and hence with little or no certainty of paternity, should not contribute any parental care to the offspring.
However, how would one know that holding the bird in captivity didn’t have some unrelated effect on its behaviour?
We can determine whether there is such an effect by doing a similar experiment on another group of males, except this time the male would be temporarily removed after the eggs had been fertilised. In this case, when the male was returned we would predict that he should incubate the eggs. These are precisely the experiments we plan to carry out with our birds over the next two years.
Clearly, there is much more to the pukeko’s world as they stride to get to the other side of the swamp than simply trying to avoid those fast moving, four-wheeled carnivores. The pukeko’s sex life is a complex one full of conflicts, compromises and trade-offs. Yet, it is only through the recent advances in molecular genetics, combined with the tried and true methods of colour-banding birds and spending long hours observing them, that this intricate world has come to light.
Perhaps these discoveries don’t warrant the worshipping of the pukeko and its being allowed to wander freely through our temples or market gardens. But the pukeko does deserve more recognition than it has had in the past. More than any of our more famous endangered native birds, the pukeko has adapted amazingly well to a changing world. And quite possibly the main reason for its success is its highly unusual egalitarian and co-operative social system.