|Kakapo are unique among the ~ 400 parrot species (Psittaciformes) for being flightless, nocturnal and extremely long-lived (up to 100 years!). Additionally, they are herbivorous (seeds, fruits, polen, plants), males can weigh up to 2-4 kg (40% heavier than females), and females lay their eggs on the ground or cavities – i.e., 3 eggs in a single clutch annually, although 2 clutches might occur if the nest fails at the beginning of the reproductive season or if the eggs are taken for artificial incubation.Native to New Zealand, kakapo once inhabited the subalpine fringes of forest and scrub. Polynesians (1000 years ago) and Europeans (mostly in the XIX Century) arrived in the archipelago accompanied by dogs, cats, rats and mustelids that cornered kakapo populations in the Fiordland region (south-west of the South Island) where it was declared extinct in 1989. In 1977, a population of some 200 individuals was found on Stewart Island – this population was already in decline to the claws and jaws of feral cats. By the 1980s, the failure of captive breeding programs prompted the transfer of 60 individuals from Steward to carnivore-free islands. The global (known) population ‘rocketed’ from 50 individuals in 1999 to 126 in the 2012 censuses and, consequently, the kakapo’s IUCN status changed in 2000 from ‘Extinct in the Wild’ to ‘Critically Endangered’. Under the management of the Kakapo Recovery Programme, kakapo are now present on the islands of Codfish, Anchor and Little Barrier.|
Inbreeding, system shocks caused by fire or cyclones (for example), or demographic stochasticity (by which two or more outcomes are possible) such as how many males and females will be born in a single year, are all factors that threaten the persistence of small and fragmented populations. They can, however, be reverted by conservation actions.
If you have ever taken dancing classes, you will be familiar with the scarcity of male partners and how this can jeopardize group learning. When reproduction, rather than salsa pirouettes, is at stake, a biased sex ratio can compromise the persistence of species. For instance, when females are unable to find males (or vice versa), fertility rates can collapse as a result – a well-known cause of an Allee effect (1). Curiously, natural selection can promote such bias by favouring a species’ investment in litters dominated by one of the two genders. The evolutionary formulation of such scenario is that females can adjust the sex ratio of their offspring depending on the amount of available resources (2) – see contrasting cross-taxa studies on this subject (3-5). Thus, when resources abound (e.g., food), mothers can afford the offspring’s gender requiring more resources to reach adulthood or once adulthood is reached, is less likely to reproduce successfully (6). This predisposition to one gender or another can be key to the conservation of endangered species (7).
The kakapo case
At the end of the 1990s, the New Zealand Department of Conservation placed dispensers of supplementary food in the territories of some kakapo (a rather enormous, flightless parrot Strigops habroptilus) to encourage their reproduction. Back then, only 60 individuals were left of the entire species . Unfortunately, those females with access to the supplemental food conceived 67% of male chicks (so exacerbating the fact that kakapo populations are naturally male-biased), while those females without extra feeding had 71% of female chicks (8). Something wasn’t working. Read the rest of this entry »