The Rhabdothamnus plant relies on bellbirds and stitchbirds for pollination. Dave Kelly of the University of Canterbury explains that, where these birds are absent, the plants are not surviving well. Research on offshore island reserves, with conditions similar to those on the mainland before bird numbers declined, has confirmed the link between low bird numbers and problems with bird-pollinated plants.
DR DAVE KELLY
Rhabdothamnus is an endemic plant found only in New Zealand, and it’s an understorey shrub. So we’re in a forest here and it grows underneath trees, and it has these very attractive bird-pollinated flowers – one of the nicer New Zealand flowers. And these are visited only by birds, insects seem to ignore them, so the pollination depends on birds.
Rhabdothamnus grows on islands around Auckland that have bird reserves, and we were able to go and work there where you’ve got the pre-human set-up, you’ve still got the stitchbirds, you’ve got lots of bellbirds – both of those birds used to be on the mainland around Auckland and they’re not there anymore. So 20 kilometres offshore, you’ve got this island where stuff works because there’s no rats, no stoats, no possums – you’ve got lots of birds, so it’s a window into the pre-European system. And then 20 kilometres away the same year, you do all the same things on the mainland and you can see what the birds are managing to do there. And what we discovered was, on Little Barrier, on Tiritiri Matangi, there’s so many birds, they do as good a job as we can do with a paintbrush, so that proves that actually if you’ve got enough birds, the pollination works well, and then on the mainland, it’s failing because there aren’t enough birds.
And so you’ve got all those links through. It really nails the fact that it’s the absence of birds. There are still tūī and silvereyes on the mainland, but they’re not pollinating the plant well. The tūī don’t come down to it, they’re doing kōwhai and whatever up in the canopy, and the silvereyes go to it but they don’t pollinate it effectively. So it really establishes every link in that whole chain – that it’s the absence of birds that’s causing the problem.