The explosion of Wellington’s kākā population has come with an unintended consequence – the birds are eating the Botanic Gardens’ rare trees to the point of extinction.
The kākā population has increased a whopping 250 per cent between 2011 and 2020, and now the native birds can be seen across the city.
David Sole, the manager of the Botanic Gardens told NZME the birds have “really taken to” the garden’s Northern Hemisphere conifers and redwoods, due to their soft bark and sugary sap.
“I have to say a lot of people are quite disappointed at the damage, but we take a lot more positive view,” he said.
“Kākā were here before people, and ultimately the problem was people, so people have to solve it and the way we’ve had to do that is diversifying our species – we know what species they’re attacking so we just won’t replant those.”
He said the best example is the redwoods – the trees have soft bark, and the birds peel it off to access the sap.
“Over a period of time with sustained attacks, they re-bark the tree – stopping all the nutrient flow, the tree declines and dies... It looks like someone has been around the branches with a sewing machine.”
This means the Botanic Gardens must re-think its planting strategy, as the population of birds will continue to boom.
“We know which natives they coexist with, and we can’t replant [the redwoods] because they will just continue to kill them.
“New Zealand has a lot of native conifers so we are committing to maintaining a conifer network so we’ll probably move to New Zealand conifers.”
He added that if people want to help, they should avoid feeding the kākā - something Zealandia chief executive Dr Danielle Shanahan has also reiterated.
“Feeding them could be a real issue,” she told NZME.
“We could end up with artificially increased numbers in a place where we don’t want increased numbers, we want them living in sustained populations so they could be here in the long run.”
Shanahan said if the birds are being fed lots of energy-dense food like seeds and nuts that they would usually expend energy foraging for, the birds could put the excess energy into reproducing – ending up with artificially enlarged populations in places that they shouldn’t naturally be in.
As for the tree damage, she said it’s a “learning curve”.
“We’re one of the only cities in the world where native bird biodiversity is on the rise – along with that comes a learning journey. We’re re-learning how to live with nature, these species have been gone from our landscape for at least 100 years, which means we’re rediscovering how people in a modern urban context can live and deal with this.”