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Pests > Pest Management > Biological control > Bioagents – Birds > Mynas, coconuts, stick insects & Orytes, Fiji
October 2011. After an article in the Fiji Times was posted about increased numbers of Oryctes beetles and stick insects in coconut plantations in Fiji, a question was asked about myna birds as biocontrol agents. This sparked many responses, with some members missing the point. Myna birds are already in Fiji, and so the question is, how good is it at controlling stick insects? This question arises because people who are opposed to eradication elsewhere often say they keep pests under control.
Most of the responses discussed the wisdom of introducing myna birds, mistakingly thinking that this was the intention behind the post. This was not the intention. The following post from Hawaii sums up the feelings:
“Keep in mind that vertebrates are notoriously bad choices, in general, for biocontrol agents. There’s plenty of literature on why this is true. (“Use of vertebrates…as biocontrol agents has often been disastrous because most vertebrate predators have broad diets and do not restrict their dining to the target species” Kraus 2009 [tinyurl.com/fredsbook). Myna birds, for example, are generalists – which immediately eliminates them (or SHOULD eliminate them) from any consideration as being used as “biocontrol agents.”
If evidence of the non-target effects of mynas is needed, then the following references will be useful:
“Fiji has multiple examples of disastrous vertebrate introductions – the myna bird being one (introduced to control mosqitoes)”
It was pointed out by a member who had worked at ICRISAT, India, that myna birds (over their native range) do have benefits: they control insects:
“Increasing the actions of insectivorous birds by provision of perches, protecting nesting sites and discouraging hunting were pillars of management of armyworms on groundnut in Andhra Pradesh, India. When birds (mynas, drongos, cattle egrets, rosy pastors, etc.) were allowed to feed on the caterpillars, the armyworms were controlled, and where numerous insecticide application were made in the past (up to 15 times per crop season), the birds took over control of the pest almost completely and insecticide application was stopped almost completely. Since I was made aware of these actions of birds, I have seen cattle egrets and other birds controling pests in many environments accross the world. I also became convinced that generalist predators provide much more control than usually perceived, for the simple reason that you can quite easily rear parasitoids from pests to quantify their effect on pest populations but quantifying the effects of predators requires time consuming observations which sometimes have to be done at inconvenient times such as during the night, when some key predators are active only. “As was pointed out by Gillian Watson, mynas are present in Fiji. You just have to study whether they have any effect on the pests you hope they target and if so, improve their chances to survive and encourage them to feed on your pests. At ICRISAT this kind of research was done by the entomology group, especially by a lady from Birma who was completely devoting her time to study insectivorous birds in the agroecosystems. I hope John Wightman can fill in details here”. However, in the Pacific it is a different matter, and in some countries attempts have been made to eradicate them, e.g., Cook Islands (pacificinvasivesinitiative.org/pii/demo/mangaia.html). But do they have any pest control benefits? Is there any evidence? Yes, there is: in the Cook Islands, and a photo was provided, plus the story of the attenpt at eradication on the island of Atiu. The email is provided here in full: “I have attached an image to show that mynas do actually eat Coconut Stick-insects. Years ago myna parents sat outside my window before entering the nest to feed their young and everyday they took in at least six coconut stick-insects. And it is common to see a myna working along a frond and pushing its head down between the leaflets to look for prey – presumably coconut stickinsects.
“The question is, do they adequately reduce stick-insect numbers to be worth putting up with their other faults. When abundant, as they inevitably become, most people develop an extreme dislike for this bird because it attacks fruit ripening on plants, makes untidy nests in dwellings, sneaks into houses to get food, harasses the cat, is loud and aggressive, and they harasses other birds especially when nesting. Our work on Mangaia showed that about 25% of the endemic kingfishers nests failed because of myna harassment – usually that the digging stage.
“Since May 2009 we have been reducing and are now eradicating mynas on Atiu, at least initially to protect the 23 reintroduced Rimatara Lorikeets in April 2007. Mynas were seen harassing two lorikeet nests and a fledgling in August 2008.
“Various surveys indicated about 6,000 in May 2009. In that year about 3,000 birds were taken out with Starlicide, and about 1,000 by residents trapping and shooting ($1 bounty). Poisoning was useless during the breeding season (Sept – Feb) and the mynas got back to 3 or 4,000. Poisoning reduced them somewhat during the winter of 2010. In Aug-Sept locals trapped 514 birds (@ $4-a-right-foot), which was so far below my target of 1,200 that we were ready to quit if the community would not accept imported shooters using 12ga shotguns in pre-advertised sectors of the countryside.
“They agreed and between October and March our shooter killed 2,027 birds (80-90 per day) and local trappers and shooters took out 500, which means we are going into the current breeding season with about 1,000 birds. We now have a bigger pool of suitable shooters and they shoot one-week-in-four, which gives the community time to normalise between battles. Shooting during the breeding season is especially effective because the mynas are in their territories and hang around to be shot, especially if a juvenile is shot first. Our shooters can usually take out both parents and the typically four juveniles. Shooters are currently averaging 30-40 birds a day, about 50:50 adults:juveniles – but they work 12-hours-a-day!
At this stage, I ‘predict’ we will come out of the breeding season with 500 birds left and with a final push the shooters, trappers and poisoner will taken them out before the next breeding season.
“And then back to the point – we have not done quantitative surveys of the coconut stick-insect but the locals will sure let us know if the increased damage is significantly worse or not. The deal is: if the stick-insect damage is unacceptable to the community and we cannot find an adequate alternative control mechanism, then we bring the myna back. I certainly hope it does not come down to this.
“I tell this story so that anyone thinking of introducing the myna to an island will appreciate that changing your mind later is not an easy option. What we are doing on Atiu is possible because of the high level of community support and the fact that everyone lives in one area, which means the countryside is relatively free of people and pets. The main issue in the countryside is the guns scaring away free-range domestic pigs, but so far this pill is more acceptable than having the myna increase again”.