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Winged Predators and an Ill wind threaten newly fledged Tahiti Monarchs

By Caroline Blanvillan, 29 Feb 2016

Half way through, 2015/2016 breeding season has been a record year for the critically endangered Tahiti Monarch.  The good news is that the 53 adults so far this year have, initially, fledged 14 young – with at least one more expected. 

But this year was different in not a good way.  Maybe because of El Niño, there was an ill wind blowing through the valleys.  There was the sudden disappearance of five young after fledging.  BirdLife partner SOP Manu and their illustrious community helpers we left with only nine survivors among the 14 that flew in 2015.

So what has happened? Because no one was able to watch these birds continuously, SOP Manu staff can only speculate on the culprit/s.  They need the services of a real detective.  Something that would challenge Hercule Poirot! 

In 2015 the obvious nest predators - black rat, and Indian myna can be eliminated from the list of suspects. Why? Because there are no more, thanks to rat control by SOP Manu and the trapping of myna over four years by the volunteer network. There are no longer any mynas in monarch territories and that is a major reason for the baby boom amongst monarchs over those last few years. Black rats are controlled but still some of small nests are still the scene of a bloody home invasion.  Other flying species like robins are also killed as are even many bulbuls - and they fly and are not normally effected by rats!

Number one suspect is the swamp harrier.  Originally from New Zealand and falsely called hawk in French Polynesia, it was introduced to Tahiti in 1885 by the German consul, with the intention of limiting the number of rats.  From Tahiti, they flew onto other islands severely impacting on the endemic species of those islands without making any difference at all to the populations of rodents that are able to increase the size of their litters to compensate for losses due to predators.   They launch themselves, slalom between trees at full speed, and fall on their prey. The endemic land birds, which have evolved over millions of years in environments free from such aggressive predators, are easy prey.  

The second suspect is the Bulbul.  A species native to Asia, it was introduced in 1970 in Tahiti, according to radio coconut, having escaped from an aviary destroyed by a cyclone. But this abominable bird, ranked among the 100 most invasive species on the planet, like the Indian myna, is so aggressive that the Indians use it as a replacement for cockfighting in countries that is prohibited.  They aggressively attack the young monarchs in their nests.  In 2015, the number of bulbuls grew in monarch territories despite the efforts to control them.

The third suspect is El Niño itself! : It brings different climatic conditions and some extreme events - floods, spectacular storms, even localized, disrupt the normal course of seasonal weather.  These may weaken the young monarch and make them more vulnerable to predators.  At least one of them probably has been an extreme weather casualty.  Just at time he was starting fly, his disappearance coincided with the observation of many fallen branches on the ground. 

So who is the culprit!  Even the great detectives cannot be sure but the case shows how hard it is to bring a species back from the brink where every bird is a treasure.  That is why there is such an imperative to get the numbers up and to find a home for a second population so that, even if there is a home invasion in one place, there is still a safe population.

And Cyclone Winston reminds us how precarious is their future.