This Mother’s Day, spare a thought for mothers of the feathered variety who have been handed a rough deal as predators attack them, their eggs and their fledglings.
In the bird world, it’s often the mother that incubates the eggs – keeping them warm until they’re ready to hatch. Although egg-sitting isn’t a particularly arduous task, it does leave the female birds a sitting target, easily predated by rats, ferrets, stoats and weasels.
Adult black stilt on river bank nest. 📷: Liz Brown
Having evolved in a place where there were initially no land-based predators, New Zealand’s birds have not evolved defence mechanisms against these predatory mammals, making birds an easy target – usually the female as she sits on the nest.
Predation of mothers has led to an imbalance in the number of males and females, resulting in male-male pairs which don’t produce eggs. For a threatened bird population, this isn’t at all helpful.
Australasian bittern at nest containing eggs. 📷: M Soper
Fortunately, mother birds are being given a helping hand with the development of multiple pest control tools which are used selectively to combat predators. Used successfully, we’re able to reduce the number of mothers that are predated as we reduce predator numbers. Reducing the number of predators has a two-fold effect: firstly, bird populations flourish as they can breed successfully without being eaten. Secondly: without pests eating the seeds and leaves of forest plants, forest vegetation flourishes, leading to bountiful seeds for birds to eat and improved forest habitat.
Recent evidence of this came from a survey of North Island Kōkako in the Rotoehu Forest area, near Rotorua. A total of 157 pairs and 13 single birds were recorded during the survey. A 2013 survey indicated just 50 kōkako pairs, although the survey area was 600ha smaller.
Close up of a kōkako. 📷: David Cook
“The survey team reported that most of the kōkako pairs had fledglings with them indicating that we’re supporting a healthy and robust population” says Sarah Orton, Chairperson of the Rotoehu Ecological Trust (RET) who have actively managed pest control in the area since 2013.
“These results are fantastic and a testament to the time and effort RET dedicate to pest control. The primary cause for kōkako decline is predation at nest – the females incubate their eggs for 18 days and are effectively sitting targets for ship rats and possums” explains DOC Supervisor Carrie Abbott.
“Pest control can be a challenging line of work – rain or shine, traps need to be emptied regularly and baits replaced so they are attractive to predators. It’s arduous and time consuming. Undoubtedly, these survey results would be very different if it weren’t for the work of RET and the good use of a combination of pest control tools”.
Stoat trap set and ready for capturing. 📷: Don Merton
Rotoehu Ecological Trust are a volunteer organisation who are dedicated to protecting and managing the North Island kōkako population in the Rotoehu Forest area. The highly active group have received national sponsorship for their work including funding from Kokako Organic Coffee and the World Wildlife Fund (WWF). For further information about the trust, volunteer opportunities and how to donate, visit their website.
