To Feed Or Not To Feed?

The Kakapo is a critically endangered, long living bird that is endemic to New Zealand. In 1996 it was classified as extinct in the wild but due to intense conservation efforts, it has now become critically endangered. Kakapo can live up to 90 years and there are only 123 individual birds left in the world (Fig.1). The kakapo is a ground dwelling, nocturnal parrot that is flightless due to having wings which are not strong enough to lift its large body weight. The arrival of humans to New Zealand caused the initial decrease in their population as the traditional Māori people hunted the kakapo for decorations, clothing, pets and their meat. The main cause of their population decline is from invasive species. The kakapo had no natural mammalian predators before cats, dogs, rats were introduced but was well adapted to avoid any birds of prey. However, these adaptations are useless against mammals and so since these mammals have been introduced there has been a dramatic decrease in their population. In addition to this, the kakapo originally filled the ecological niche that is normally held by mammals and so the introduction of the mammals has removed the niche the kakapo fills. Ecological restoration has begun in order to remove invasive mammals from the natural habitat of the kakapo but is this enough to save the species?

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Fig.1. Kakapo with Eggs from kakaporecovery.org.nz

Reproduction

The kakapo is one of the only birds to mate in a polygynous lek during the lek season and the males exhibit no paternal care. The kakapos themselves are sexually dimorphic which helps when they are attracting a mate. They only breed once every two to five years and this is dependent on food abundance as well as the weight of the females. The females will not mate unless they weigh over 1.5kg and so they must receive enough food in order mating to occur. They lay between 1 and 4 eggs and chicks take up to 11yrs to become sexually mature.

Current Conservation Efforts

At present, the kakapo is only found on three islands of the coast of New Zealand; Codfish, Anchor and Little Barrier. They are predator free and inhabited by a team of dedicated rangers who provide the birds with a diet of leaves, stems, fruit, and seeds, depending on the season which are ground up using the kakapos beak. In addition to this, each of the 123 individual birds has its own name (Fig.2.) as well as being radio tagged and monitored permanently using infra-red cameras. The eggs are also covered with a heat blanket when the female goes foraging to ensure that they do not drop below the optimum temperature for incubation. At present, the chicks are not hand reared but the rangers are working out the best way to make this possible. However, by giving them names and caring for the birds in this way, we are removing their ability to fend for themselves, thereby decreasing their chances of ever being released back into the wild. Therefore, are these scientists saving the species or aiding its extinction?

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Fig. 2. Sirocco the Official Spokesbird for Conservation Celebrating His 14th Birthday (blog.doc.govt.nz/author/docnz/)

Sex Ratios & Sex Allocation

Sex ratios are the ratio of males to females in a population. This ratio is normally 1:1 but can change according to various factors, including sex allocation theory. Sex allocation is the allocation of resources to male versus female production in sexual species. This is seen in Seychelles Warblers; when there is plenty of food, the female will produce more females as these do not leave the nest and so help to raise any future chicks as well as helping with nest maintenance. In contrast, when there is little food she will produce males as they are not as costly and leave the nest meaning that they do not require feeding once they have left. In Kakapos, we see the opposite.

Female kakapos produce more males when they have more resources available. This is due to males growing larger and faster and so requiring more resources from the mother. The mother wants to produce the largest male offspring that she can as these are more likely to win fights and reproduce. In contrast, female offspring require less resources as they are smaller and so take less from the mother. This means that in a poor environment, the mother is more likely to produce female offspring. In addition, females are likely to mate regardless of their size and so it’s more beneficial to the mother to produce smaller females than males.

To Feed or Not To Feed?

Supplementary feeding (Fig.3.) has been shown to increase successful breeding in the kakapo. However, research has also shown to skew sex ratios in many species which affects sex allocation theory. If there is a male bias, then this is bad for conservation as females are rare and as a result, less offspring will be produced. In addition, the males are more likely to get injured as they fight for a female mate. If its female biased, then this is not as bad as one male can mate with multiple females producing many offspring. However, this will create an inbreeding depression and the genetic diversity of the population will decrease as the population is more vulnerable to disease and climate change as they cannot adapt quickly. We need to be aware of this in conservation because if there is a bias then they may not want to feed all of the kakapo population.

Screen Shot 2016-12-13 at 20.02.33.pngFig.3. Kakapo eating from a feed dispenser. Photo Credit: Andrew Digby – New Zealand Department of Conservation

If the rangers were to vary the levels of feed given to each kakapo so that half have an excess of food and the other half have enough, but not too much to cross the threshold for the females to breed, then they would be able to reduce any skewing in the sex ratios. It has already been shown that by feeding a diet with low macronutrient to calcium ratios there will be an increase in reproduction. This would hopefully lead to a more genetically diverse population as well as increasing the rates of reproduction.

References

  1. Clout, M.N., Elliott, G.P. and Robertson, B.C., 2002. Effects of supplementary feeding on the offspring sex ratio of kakapo: a dilemma for the conservation of a polygynous parrot. Biological Conservation107(1), pp.13-18.
  2. Powlesland, R.G. and Lloyd, B.D., 1994. Use of supplementary feeding to induce breeding in free-living kakapo Strigops habroptilus in New Zealand. Biological Conservation69(1), pp.97-106.
  3. Robertson, B.C., Elliott, G.P., Eason, D.K., Clout, M.N. and Gemmell, N.J., 2006. Sex allocation theory aids species conservation. Biology Letters2(2), pp.229-231.
  4. Sutherland, W. J. (2002). Conservation biology: Science, sex and the kakapo. Nature 419:265-266.
  5. Tella, J. T. (2001). Sex-ratio theory in conservation biology. Trends in Ecology & Evolution 16(2):76-77.
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