I find it interesting to ponder these two species and what influences their presence in Abel Tasman National Park.
These two honeyeaters belong to the family Meliphagidae which has more than 180 species, all in the South West Pacific and with more than 40 species native to Australia. We have just the two species, which are endemic to New Zealand. The stitchbird used to belong to the Meliphagidae but has now been awarded a family of its own. Within New Zealand there are four subspecies of bellbird and two subspecies of tūī. With a little practice you can distinguish the sexes: the female tūī being quite a bit smaller and obviously so when the two are together. The female bellbird is less green, lacks the purple sheen on its head and has a pale stripe across its cheek.
Regardless of where you are in the forest of this national park, it is likely that either bellbird or tūī will be one of the most obvious native birds. The Atlas of Bird Distribution and eBird tend to confirm this with most of the records submitted containing both species, although bellbird is recorded more frequently than tūī. I guess none of this is too surprising, both species feed on fruit, nectar and invertebrates and both are very adaptable to different habitats and food sources. Both species are able to travel long distances to seasonally abundant foods—flowering gums would be a good example.
Could the park support greater numbers of these honeyeaters and what would it take, better habitat or fewer predators? This question is not easy to answer but a couple of observations may throw some light on it. Last spring I found that both bellbirds and tūī were more abundant in forest along the Coastal Track than they were along Evans Ridge. It seems that despite more predators in the coastal forest this was more than compensated for by a richer foraging habitat.
Within this coastal environment Adele Island has always had a lot of bellbirds and I had thought that despite the presence of stoats the island had never had rats. Now, as many of you may have noticed, stoats have been eradicated from the island and bellbirds are super abundant. An interesting twist to this is that tūī are virtually absent from Adele. Is the habitat not suitable or do the multitude of bellbirds just give any colonising tūī such a hard time? A further anomaly is that while Adele is full of bellbirds neither bellbirds nor tūī are very evident on Tonga Island, which has no predators! Is the abundance of beech honeydew on Adele really that important?
How can we expect tūī and bellbird to respond to the intended Project Janszoon pest control? Possum control will have a very prompt effect on the rātā forests and the seasonal flush of nectar will certainly provide additional food. A similar effect can be expected from fuchsia and a range of understory fruiting shrubs. And with predator control the Adele Island phenomenon will surely spread to the mainland.
In the meantime, your observations on the current situation will be so valuable to help describe these changes. Species lists from a location or observations on a single species can all be entered on eBird (see we need your observations).