They are also used at Whakatāne Airport, where birds are a safety hazard for aeroplanes.
In April this year, due to complaints from the public, the council decided to advocate on the community's behalf for bird-scaring alternatives and to start a process that could result in changes to its district plan regulations for the devices.
The council is at the evidence-gathering stage of this process and will be recording sound levels at a variety of sites around the Rangitaiki plains over the coming weeks.
Council senior policy planner Deborah Ganley said the first stage of the evidence gathering had been a desktop study.
An independent acoustic engineer based in Tauranga creates an acoustic model by merging aerial photos of the area with topographical data, taking into account what the terrain is like, how built up it is, the types of vegetation, wind direction and ambient noise.
"Then it models a set decibel rating and what that might, in theory, sound like. So you get a radius, from a central point of how far the sound would go," Ganley said.
They field-tested this by taking a cannon onto an orchard and driving around the immediate vicinity with an acoustic measuring device measuring the sound levels in different positions.
The second part of the study, on-site field monitoring, is taking place now.
Ganley has identified two different routes, one in the eastern Rangitaiki Plains and another in the western part, which she travels on alternating days.
"We've identified sites that are based at the legal road boundaries adjoining, kiwifruit orchards because that is currently where bird scaring devices are being used. However, we recognise that other horticultural activities may equally use bird scaring devices. We do know that in summer some of the berry orchards use them."
Some of the sites being tested were identified due to complaints received in previous years while others were chosen because of the large numbers of kiwifruit orchards around them.
As there was no requirement to get a permit to use them it was not known how many audible bird scaring devices were being used in the district.
"Therefore, we needed to spread our net wide to start with to see where they were being used.
"As we've been going out, we've been finding that, in some areas, no bird scaring devices are being used, the boomers anyway.
"We have then fine-tuned where we're going to, otherwise you spend a lot of time monitoring areas where there's nothing being used.
"Also, because of the letters that have gone out to let everyone know that we were going to be coming around to monitor, some people have called in to say 'there are some in this area'."
She said they spend a minimum of 10 minutes at each site recording a range of measurements, including ambient sounds such as road or industry noise.
"They're not pristine, you-could-hear-a-pin-drop environments, they're still the rural-industrial zone, in a way, but obviously when a bird scaring device goes off, depending on how close you are, it can be quite a spike in the sound."
The sound is recorded digitally and sent back to the council before moving on to the next site.
She said they aimed for morning and early evening recordings, but because there were a lot of sites the time of visiting could be quite random.
"A lot of this process is around public awareness of what the impact is of various activities and what effect that might be having on other people around them," Ganley said.
"Not all activities are annoying. Some people aren't bothered by bird scaring devices at all and others might be more sensitive to it, and that could be because they're a lot closer to where they are or there being more of them being used in a particular area compared to other areas.
"That's why we've been quite upfront and obvious about what we do and where we're going and why we're doing it just to make people think about whether there are any alternatives that can be used. And there are other methods that can be used and some are using a range of methods.
"It's also recognising that it is for a very short time each year, albeit that it is, for some people, a very annoying time of the year."
