by Darryl Jones
These were the formidable challenges facing Ralph Powlesland and Brian Lloyd as they began to plan one of the most unusual supplementary feeding experiments ever taken. How this was carried out is described in various scientific articles.46I had read these carefully many times but knew that there was much more to this remarkable story than would have been suitable for academic journals. To fill in the details, I was privileged to spend a few days with Ralph in his remote home in the extraordinarily beautiful Marlborough Sounds at the ragged top of the South Island (and within sight of Maud Island, once home to a bunch of lonely bachelor Kākāpō). Over many a coffee and dry Marlborough sauvignon blanc we discussed science, birds, and rugby, as well as supplementary feeding experiments.
The first problem was deciding where to place the feeders in the extremely dense forest landscape of Little Barrier Island when your target bird is effectively invisible. To find out where Kākāpō were likely to occur, Ralph, Brian, and their small team made hundreds of kebabs (or skewers) consisting of pieces of carrot, apple, and sweet potato (kumara) impaled on wire stakes and placed these at regular intervals along the network of tracks that had been formed to allow easier movements around the rugged terrain.47 In places where the baits showed signs of having been “chewed,” new stakes were moved progressively closer over several nights into a relatively flat site where the more substantial feeding station could be installed. Initially, the food items were simply placed in a dish on the ground, but the effects of weather and persistent raids by kiore forced progressive changes to the design of the feeder.
First, a circular tray was attached to a metal rod and positioned 350 millimeters (14 inches) above the ground, with a plastic cover above to protect the food from rain. Although the feeding apparatus became increasingly complex in design, the Kākāpō continued to visit and feed. But the device was about to get even more complicated. Rats were strongly attracted to this new foraging resource and, with squirrel-like tenacity, were soon finding ways to climb or jump up to the feeding tray. Even more serious was the effect of the weather. The combination of persistent wind and rain and, in the higher sites, heavy mists, was spoiling the food often within a single night. To make matters even worse, replacing the food regularly—sometimes daily—was proving extremely difficult; simply keeping the supplies available in this demanding landscape was taking up almost all the scientists’ time. What was needed was a feeder that could protect the food from weather and rats and in sufficient quantity to last several nights yet still allow the Kākāpō to get at the food.
These were the sorts of fundamental engineering challenges that Ralph had grown up with on the family pig farm where he had seen his father’s natural ingenuity at work, designing and constructing rat- and bird-proof food hoppers. Ralph’s father was successful in thwarting all sorts of pests attempting to steal the pigs’ food. Ralph and Brian’s challenge was almost the opposite: allowing the birds in while keeping the damp and vermin out. The simplest solution was obvious but risky: a tight-fitting lid that covered the food but with a hinged flap that could be raised by a visiting Kākāpō. Although the birds had become familiar with the feeder and knew it provided food, the task of lifting the flap represented a major behavioral challenge. Plenty of species would simply be unable to make the connection between lifting the flap and accessing the food. But Kākāpō are not your average birds. After leaving the flap propped slightly open to allow the birds to get used to the construction, the flap was then lowered, requiring the bird to lift it with its head to access the food. Despite these challenges, almost all were feeding freely from the complicated feeding apparatus within a few days. The final innovation was a hopper made from plastic drainpipe with a liftable flat at the base that could be stocked with several days’ supplies.48 These hopper feeders were used for the more remote locations to minimize the amount of time spent visiting to add food.
Having solved the problem of feeder design, it was time to test what food types the Kākāpō would eat. The scientists started with a blank slate: just about anything vegetable that could be obtained was on the menu. In all, 45 different foods of an extraordinary variety were offered. The feeding stations were visited each day and the remnants examined closely to assess the culinary preferences of the pampered clientele.49 Only two items—dried figs and parsley leaves—were rejected entirely, while a further 20 were nibbled but not consumed, including banana, bread, and peanut butter. However, about half the smorgasbord of offerings was eaten regularly and these tended to be root vegetables, seeds, and nuts. Intriguingly, Kākāpō loved frozen but not raw corn on the cob. They also rejected raw potato yet devoured it if it was boiled or baked. These initial taste tests led to a short list of six foods that were both preferred by the birds and could be easily procured and stored for long periods of time: apples, sweet potatoes, almonds, brazil nuts, walnuts, and sunflower seeds. On the other hand, the birds may have loved the special porridge (oatmeal) the scientists ate for breakfast each morning but hospitality can only stretch so far.
It did take a while for a Kākāpō to establish a routine, but within a few months of the construction of feeding stations, almost all the birds were visiting their local canteen each night. And the birds were certainly consuming plenty of the supplementary food now available: the feeders needed continuous renewal and the birds’ weight (recorded on an electronic scale hidden under the platform a Kākāpō stood on while feeding) began to increase almost immediately. Over the first 2 years of the initial trial, the average weight of the males went up by 42% and females by 36%.50 But was there any effect on breeding activities, the main goal of all this work?
Although male Kākāpō on Little Barrier Island had engaged in their booming courtship displays most years since their arrival, in the first summer following the start of supplementary feeding Ralph and his colleagues noted booming every night and eventually determined that they persisted for much longer than any previous summer. In the second year, these boomers were at it nightly for 6 full months (October to April). It seemed that the additional food was stimulating the males, but what of the females? The first positive evidence that something may have been happening was the discovery of the telltale “feather clusters,” places where contour and down feathers had been trampled into the leaf litter—clear evidence of vigorous Kākāpō copulation—only 4 months after the start of the experiment. Even more exciting was finding the first nests a few months later, located by following the now stationary radio tag to the carefully hidden incubation bird within dense undergrowth, in a hollow log or among the roots of a tree. Of the five radio-tagged females being studied, all of whom were utilizing the feeders, two produced eggs during the first year and four did so by the second year. The fifth female, labeled opaquely simply as “D” in the scientific articles but known as “Bella-Rose” to the scientists (“All of the Kākāpō had names,” declared Ralph. “Every single one.”), failed to show any interest in breeding though she did exhibit perhaps too much interest in her feeder. Bella-Rose features frequently in the supplementary feeding literature as a cautionary example: those individuals for whom the benefits of additional food can become a serious liability. Within the relatively short period of about 20 months she came to weigh in at 2.1 kilograms (4.6 pounds), 60 % heavier than the average of the other females and the heaviest female Kākāpō ever recorded.51 That is quite an achievement for a largely “veggies and nuts” diet but given the intentional high protein composition of the food, not entirely surprising. Nonetheless, when a prominent outcome of an intervention aimed at improving reproduction actually results in obesity and a complete lack of breeding activity instead, concern is certainly justified.
Unfortunately, fat females were only part of the story. After the joy of finding nesting birds so quickly after the start of the feeding experiment, when it appeared that the addition of food was clearly having the hoped-for effect on breeding, both females abandoned their eggs for unknown reasons. The following year, with four birds nesting, on
ly a single fledgling was successfully raised; a remote camera captured the juvenile feeding from a feeding station with its mother about 4 months after leaving the nest. Supplementary feeding seemed to be increasing breeding activities— booming and mating and even egg laying—but this was not necessarily resulting in regular and successful reproduction. The conclusion drawn by Ralph and Brian from this first experiment was that while the additional foods were obviously important and influential for breeding in Kākāpō, there was still a lot to be learned.52
Nonetheless, this exploratory study was an important first step in the long and laborious journey toward securing the future of this remarkable bird. Despite the many unknowns associated with the diet provided, there was no question that providing additional food was essential to the ongoing management of Kākāpō on islands such as Little Barrier. The feeding continued—using Ralph’s special feeder designs—but understanding in more detail the physiological and nutritional requirements of the birds became a major goal for the next phase of the research. For example, years of careful attention to the bird’s foraging activities, before and after the advent of supplementary feeding, indicated that the periodic masting events remained central to the control of breeding activity among Kākāpō.
Even on Little Barrier Island, where only one mass seeding tree, the Kauri, was present, the birds appeared more likely to at least begin breeding activities during years when lots of seed was produced. Indeed, although the birds utilized their personal feeders extensively, the feeders provided only part of their overall diet. Apart from the unfortunate example of Bella-Rose, who appeared to forsake the chore of foraging on natural foods, most fed Kākāpō continued to browse extensively on the naturally occurring stuff. The scientists were pleased with this observation; they were initially concerned that making it so easy to find food may lead to a reliance on the feeding stations, but such fears proved unfounded. The Kākāpō still spent much of their night searching for the natural foods they subsisted upon.
Kākāpō remained terrifyingly close to the abyss of extinction so any assistance, including supplying additional food, was considered an important part of their conservation management. As the supplementary feeding continued, so too did efforts to understand the influence of food on reproduction. Over the long term, the key benefit of the supplementary foods seemed to be enhancing the physical condition of females so that they were better prepared for egg production in years when breeding might occur. Providing additional food supplies, however, did not influence the likelihood of breeding; that trigger seemed to be associated with natural cues, including masting. Nonetheless, food supplements seem to have resulted in more eggs being produced and increasing the survival of chicks when natural food supplies began to wane later during the breeding season.53
Supplementary feeding Kākāpō also had an important effect that no one saw coming. When the sex ratio of the offspring of fed birds was compared with those who had not received additional food, it was found that feeding was leading to far more male than female young.54 And not just a slight increase: feeding seemed to result in two-thirds of chicks being male, while unfed females produced one-third. Both of the proportions are bizarre: in almost all species the typical sex ratio is remarkably close to 50:50. However, even among adult wild Kākāpō, the ratio was 62:38 in favor of males. The most obvious explanation is that females, engaged in prolonged ground nesting, are more likely to be vulnerable to predation (though booming all night from the same spot would surely be risky for males). Another possibility is that the production of more males is normal in Kākāpō, a view supported by remarkably detailed examination of ancient Kākāpō bones, which found twice as many males as females.55 This idea actually accords well with a theory that moth-ers of some species may be able to manipulate the sex of their young.56 The ability to influence the gender of offspring appears to be important in species where there are large differences in the reproductive success among adult males, which is certainly the case in Kākāpō. While all the adult males compete for the available females, few are chosen, but the chance of raising a stud is definitely worth the attempt when food is readily available, from an evolutionary perspective. Because young male Kākāpō are larger and grow more rapidly than females, they are more costly to produce because additional effort is required to rear them: producing males is simply more “expensive” than females. During regular years, females are “cheaper” but in good years, when females are in better physiological condition, producing males is not so costly. Providing additional food to females seems to have made any year a good year, with more males being the result.
This remarkable and unexpected finding has been used in even further fine-tuning of the supplementary feeding regime being used for Kākāpō.57 While the objective of supplying additional food would appear to be all about the production of more Kākāpō in general, in the case of this weird species, more males is not going to help. The challenge is to feed adult females in such a way as to ensure that the nutritional threshold required for breeding is met (though apparently triggered by other factors), yet somehow manage to keep their condition low enough to avoid male-biased clutches. But wait: “A surer way of obtaining female progeny,” explain the researchers, “would be to delay provisioning until after the eggs are laid, but this might [result in] lower egg production and poorer hatching success of eggs due to ‘unfed’ females spending more time foraging [and risking their eggs getting chilled].”58 With both clarity and understatement, they conclude that this degree of micromanaging the supplementary diet: “clearly presents a considerable challenge for the Kākāpō conservation program.”
Getting the Timing Right
I have spent a lot of time on these strange birds from a distant land—so vividly unlike the typical birds visiting our feeders—because these conservation stories center on the use of food as a key management tool. Working with species on the very edge of extinction, the extraordinary people involved in these programs have been forced to try all sorts of new approaches and solutions, whatever might work, to ensure that these species remain with us. With every egg and offspring vital, the level of scrutiny directed at individual birds in these species is extremely unusual, but the insights have often been invaluable and, in some cases, entirely unexpected. These findings lead to better understanding of the relationship between the birds’ diet and reproduction—among other things—and on to ever more fine-tuning of the foods being supplied. For example, detailed analysis of the natural diet of the Kākāpō has led to the development of pelletized food made of nineteen different ingredients, resulting in larger clutches, a major win.59 More recent iterations have involved targeting the best time of the year to provide the food.
Although the degree of intervention occurring in the New Zealand examples is somewhat extreme, it is by no means unusual in the hands-on end of active conservation biology. There are numerous examples of situations worldwide where the survival of extremely threatened species is based directly on supplementary foods. Spanish Imperial Eagles in Spain, Seychelles Magpie-Robins, and Red-crowned Cranes in Japan, to pick some far-flung examples, all currently benefit from carefully managed supplementary feeding programs. On the island of Mauritius in the Indian Ocean no fewer than four endemic species (Mauritius Kestrel, Mauritius Parakeet, Mauritius Fody, and Pink Pigeon) are effectively being preserved through supplementary feeding. In the case of the Pink Pigeon, whose entire wild population in 1990 was 10, the provision of additional food (just plain wheat) has raised the free-flying population to about 350 birds in 2006.60 Interestingly, while almost all (99%) wild Pink Pigeons utilized the feeding stations at least once every few days, visits grew less frequent with age. Indeed, even in this precarious situation, over three quarters of the bird’s feeding time was spent foraging on natural food plants. The importance of the supplementary supplies was in meeting the shortfall following cyclones and other periods when natural food may be difficult to find.
One (of the many) patterns emergi
ng from such studies as these is that access to supplementary foods can be of critical importance at specific times in a species’ annual schedule. These times may include the period leading up to the breeding season or when eggs are being formed or during the females’ recovery time immediately after laying their eggs. Being able to feed on high-quality foods during these times has been shown very clearly to improve the adults’ condition, providing a sound foundation for vital activities such as fighting for a decent territory, developing large, healthy embryos, and recovering quickly enough from the efforts of egg production to be able to assist in incubation and the raising of the young. The importance of food supply in these phases has been demonstrated in numerous supplementary feeding studies (as discussed in Chapter 5).
There is another phase of the breeding cycle in birds that is probably even more important to successful reproduction: the nestling stage. This period between hatching and independence, when the juveniles fly off into the sunset, is fraught with dangers and risks. Newly hatched baby birds— defenseless, vulnerable, noisy, smelly, unaware—are obvious targets for predators and highly susceptible to cold, wet, and wind. It is no surprise at all that this is the period when the greatest mortality occurs in birds.61 Nestlings are also extremely prone to starvation if a sufficient and suitable supply of baby food is not available. Baby birds grow extremely rapidly, often doubling their body weight in a matter of days, a process entirely dependent on the ability of the parents to find enough food. In the vast majority of species, this means insects—typically larvae such as caterpillars and grubs—which the adult birds must find and bring back to the ravenous brood in an endless and exhausting process.62 If the supply of bugs is insufficient, the effects back in the nest may be catastrophic. Competition among the clamoring chicks can become extreme, and the adults may even begin to deliberately favor certain individual young over others. The inevitable result is that some of or, all too often, the entire brood can simply die of starvation.