Caring for the environment  |  1 Mar 2019

A proposal to protect monarch butterflies from marauding rats will be considered by a Christchurch City Council committee.

A report being presented to the Social, Community Development and Housing Committee on 6 March proposes that trees at Abberley Park and Burnside Park should be banded with pest-proof steel bands before the butterflies start their overwintering behaviour.

Monarch butterflies roosting in trees.

A Council committee will soon consider whether to band trees in local parks to protect monarch butterflies from predation by rats.

This is when they roost in large numbers on tree branches.

The report, by Council Ecologist Antony Shadbolt and Vicky Steele of Project Wingz, says the banding is likely to prevent significant monarch mortality at the parks. It is also a relatively cost effective measure.

If nothing is done, the butterfly colonies could be exposed to “possible decimation by rats”, the authors say.

If the banding does go ahead, butterfly mortality at the proposed sites should be monitored and compared with other non-banded sites to assess its effectiveness.

Council staff were alerted by members of the community to high monarch butterfly mortality at some parks in winter 2016 and 2018.

In 2018 the population at Abberley Park dropped from 700 in late April to 15 in mid-July with most of the deaths due to predation.

Investigation showed they were likely to have been killed by black rats which are good climbers, although there is no scientific evidence to prove this conclusively.

Monarchs are not considered to be a threatened or at-risk species in New Zealand but the report authors say their overwintering sites are a novelty in urban parks and their presence supports Christchurch’s Garden City image and identity.

They are also one of the first wildlife species that young children recognise and are captivated by.

The report also recommends that winter flowering plant species could be planted to help improve the butterflies’ robustness at this time of year.