Some Lincoln residents have reported seeing 40 to 200 butterflies in the domain each autumn and winter for at least the last five years.
But they are difficult to spot. The butterflies generally rest with their wings closed, making them harder to see.
They can move between trees before ultimately settling for the winter.
Bowie said he had been to the area where he had heard about the colony in previous years and set out to look again just recently.
This time he was successful, his attention having been drawn to the site as one or two butterflies fluttered their wings when another landed on the tree.
He said the colony this year comprised about 200 butterflies, high up in large eucalyptus trees, which can be viewed from a walkway bridge over Liffey Stream off Leinster Tce.
He said the large number could be due to a range of factors, in particular, the possibility that more people were planting swan plants.
“The only reason they are in New Zealand is because people are planting swan plants, which are not a native of New Zealand,” Bowie said.
Bowie said while it was good to see people encouraging monarchs with swan plants, he urged gardeners to also give consideration to planting for other native or endemic butterflies, such as copper butterflies, red admirals and yellow admirals.
“The admirals feed on stinging nettle species, while coppers feed on ground covers, including Muehlenbeckia complexa (pohuehue),” he said.
