Rats wiping out our butterflies
Christchurch’s monarch butterfly population is being devastated and rats are the number one culprit.
Butterfly specialist Vicky Steele wants the Christchurch City Council to do more to prevent the destruction of the butterflies after entire colonies have been all but wiped out this winter.
In May, Abberley Park, in St Albans, was home to about 700 butterflies. Now, 15 remain.
Burnside Park had 400 in autumn, and now has just 10. Ernle Clarke Reserve in Cashmere was home to 650, now there are about 250. Ruru Lawn Cemetery in Bromley had a colony of 900 and in July, 70 remained.
Butterfly numbers usually reduce throughout the winter, as they succumb to the weather or lack of food, but never to this level at so many parks across the city.
In 2015 the butterfly mortality rate at Abberley and Burnside Parks was just 4 per cent.
‘‘I have been doing it for so long, I know when something abnormal is going on,’’ Steele said. If the butterflies were wiped out at a park, there was a chance they would never return because they passed on information as to where to winter-over to their descendants. A small winter population would also affect the size of the summer population, Steele said.
Steele, who has studied butterflies for 20 years, knows how many have been killed because she regularly picked up their wings from the base of the trees. The wings were often all that were left.
Lincoln University ecology senior tutor Mike Bowie said rats were the most likely suspect as they have been seen in the trees and their prints were left on tracking panels.
Praying mantis were a known predator, but they generally only ate the head, he said.
The butterflies are killed at night and puncture wounds like claw marks had been found in the wings. Steele has also found rat droppings next to the butterfly wings.
However, the council seemed unconvinced there was any decline.
Council community parks manager Al Hardy said the council did not have any scientific evidence of a decline or that rats had been predating upon the butterflies, but staff were aware of the concerns that had been raised by Steele.
The council had taken several steps to minimise possible rat access to a butterfly colony in Abberley Park. Camera traps had been installed and a metal band – donated by residents – had been placed around a colonised tree, he said.
Steele said this was done on July 7, which was too late to make a difference.