Feral Cats & Kakapo Birds

In today's lecture about feral cats and wild birds, we discussed briefly the differences in predation levels with cats on islands, and I believe someone also asked about the issue of flightless birds. As Professor Tantillo demonstrated, a lot of the research that paints cats as huge threats to birds lacks strong data and support, and often contain lots of potential biases/uncontrolled variables. I agree with him on many of these points, however (not to be anti-feline or anything, but..) I do know a rather unique example that involves both flightless birds and an isolated island situation, in which feral cats have been heavily implicated in their near extinction (after other initial causes of population decimation).

Professor Tantillo talked about how Fitzgerald & Turner drew the conclusions that cats on islands tend to prey more frequently on birds than do cats on continents (see page 166 of Dennis Turner's book, Domestic Cat: The Biology of it's Behavior). This example I'm about to discuss is in keeping with their conclusions, as it is about feral cats on very isolated islands, but I just wanted to share it because I think the flightlessness aspect adds a great facet to the feral cats vs. birds debate. (And it should also be taken into account because regardless of the extremely unusual qualities of this parrot, a bird is a bird is a bird.)

Conservation officer Daryl Eason feeding a Kakapo.

The Kakapo bird (Strigops habroptilus), also known as the owl parrot, is a large flightless parrot that is  nocturnal, like cats. They can climb trees and 'parachute' down using wings for balance and breaking, but primarily stay on the ground. They are suspected to be the oldest bird species, evolutionarily speaking, that is in existence today. They are almost entirely defenseless against predators such as cats because they evolved on New Zealand, which actually contained no mammals (except two species of bats) for millions of years. Their only predator was the giant eagle, which also went extinct, giving them no reason to evolve any defenses against predatory mammals.. The Kakapo once numbered in the hundreds of thousands. but after the arrival of humans (of course, who else?), much of their habitat was destroyed, they were hunted for food and feathers, and various predatory mammals were introduced. Humans eventually slowed down on habitat destruction & hunting about 150 years ago, leaving Kakapo populations significantly smaller, but still at a maintainable number with the removal of human pressures. Predation from introduced mammals still continued from stoats and feral cats, leading to a nearly complete extinction of the Kakapo.

In 1970 they were declared entirely extinct, but in 1974 two males were discovered in Fiordland. In the next four years, 16 more males were discovered, which still qualified the kakapo as extinct as there were no females. Finally, in 1977 around 200 birds were found on Stewart Island (a relatively uninhabited island in Southern NZ that was free of stoats but filled with cats), with the first females seen in nearly 100 years. Extensive research was performed in the next 4 years, where it was determined feral cats had become the main predatory threat. Admittedly, there are numerous variables/biases that come into play on this issue as discussed in class, since cats are certainly not the only factor affecting Kakapo population numbers. They have very low fertility and reproductive rates as they take 9-11 years to reach breeding age, and are also entirely herbivorous and will postpone breeding until good seed production years where they are certain to be able to raise chicks. There are also still pressures from other predators such as polynesian rats. However, when the Stewart Island population was fitted with radio-transmitters and monitored by researchers, it was found over 50% of the adults were killed within 12 months by feral cats, suggesting them as the primary threat.

Alarmed by the high death rates, in 1982 the NZ Wildlife Service was brought in to eradicate the feral cat population on Stewart Island. Initially it worked well, dropping predation rates from ~56% to nearly ~0%. This ultimately failed as cats quickly reoccupied the area and death rates went back up, so they finally relocated the remaining 61 Kakapo to three smaller cat-free islands. The NZ government stepped in and over the next few decades began implementing a Kakapo recovery program which has been fairly successful. The IUCN red list of threatened species's most current population size from 2009 states the total number of post-breeding season Kakapos left is 124, and of those, ~55 are mature adults.

So.. what do you think of this particular example of cats versus birds? Do you agree with the steps they took in re-establishing the Kakapo population? How sustainable is this path if the Kakapo still can't deal with predatory mammals? Is eradicating feral cats from the area justifiable to preserve this species of birds? Or are these birds just evolutionarily slow and haven't successfully adapted/deserve to go extinct?



Note - If you want more information, all my information was taken from sources that were hyperlinked to throughout this post, as well as you can take a look at this extensive list of kakapo related scientific publications.