Tuesday, April 3, 2012

Ulva Island "Bioblog"

March 5th
No trip to Stewart Island is complete without a visit to Ulva Island, especially for nature-loving biologists. So what follows is mainly a biology blog and is especially for my favorite birdwatchers, my dad and Elizabeth, and Professor Katie in Wisconsin. I hope you all enjoy it though!

While most biologists know Ulva as a genus of green algae, this island was named after another Ulva Island in the Inner Hebrides of Scotland. Ulva Island is just over 1 square mile in area, but is irregularly shaped with a beautiful rocky coastline interspersed with sandy coves.  No one lives on the island, and there are no shops – just two pit toilets, two shelters, and lots of benches to rest on.  Peter, our boat captain, said we could walk all the tracks in just 1½  hours, but that the slower we went the more we would see. It took us six hours, and we enjoyed every bit of it, though we both got neck cramps from holding binoculars up to peer into the trees for well-camouflaged birds!

Captain Peter (Photo by Vera)

The DOC pamphlet description follows: “Ulva Island's relative isolation, but easy access from Stewart Island has allowed it to become an important natural resource area. It is a sanctuary for both birds and plants, holding species that on the mainland of New Zealand are rare or have died out. In 1997, the island was declared rat-free, following an eradication program, and extirpated birds have been reintroduced to the island. The birds include the South Island saddleback (tieke), yellowhead (mohua) and Stewart Island robin (toutouwai). Other birds on the island that are rare on the mainland include the Stewart Island Brown Kiwi (tokoeka), Rifleman (Tititipounamu), Yellow-crowned and Red-fronted Parakeet, and South Island Kaka or forest parrot, as well as several other species. The endangered Yellow-eyed penguin uses the island for breeding sites.”
We spent all day looking for birds and were rewarded with a flock of Yellowheads moving through the forest and also a Saddleback that was being chased away by a much smaller Stewart Island Robin. Twenty robins were released here in 2000, and there were 200 by 2007. They are all banded and are being studied for the effects of inbreeding on brood size and success. They are aggressively territorial judging by the display we were lucky enough to see.

A banded Stewart Island Robin
The robins are common on the paths as they look for insects you are scratching up as you walk. Another common bird that looks a little like the robin but is smaller and has a nice yellowy-orange bib is the South Island tomtit.

The South Island form of the Tomtit (Photo by Vera)
The wood pigeon was also common, yet remains majestic. And you could clearly identify it as it flew through the woods.  It had a much different sound than the more raucous kaka, a large parrot.

Kerera, Wood Pigeon (Photo by Vera)
Besides birds, we went a little crazy over the ferns. New Zealand has around 200 species of fern, and 40% of them are endemic.  One of the joys of island life is the high rate of endemism. Not to mention the sheer bounty we found here. Ulva Island had almost Jurassic-size tree ferns!

I'm being hidden by a giant tree fern (Photo by Vera)

Another fern gets its fronds curled by the native rolling caterpillar. It lays its eggs on the fronds and when the larvae hatch and start eating the fern, they coil it around themselves for protection.

Rolling caterpillar effects on a fern
One of the neatest adaptations we saw is the Hen and Chick fern. Instead of solely relying on spores to reproduce it has another strategy. Some of the spores develop into tiny ferns while still on the “mother” plant. When they get large enough they drop off and grow into an adult plant. Pretty sweet!

Hen and Chick fern with the "babies" growing out of the spores
Our DOC pamphlet also had an explanation for the black trees that Scott and I had seen at Mt. Thomas. Parts of the beech forest there were covered by a sickeningly-sweet black crust and there were wasps flying all over it. The story begins with a scale insect that sticks its snout into the phloem of the tree and taps the sap that then comes through a tube in the insect as honeydew. A black mold lives off this sticky liquid and builds up on the tree bark. The bellbirds, tui and native insects also lap up the honeydew before it drops to the ground.  Unfortunately, introduced wasps have interrupted this cycle. They lick up honeydew faster than the birds and insects, leaving nothing for them. They also form gangs to attack native insects, so the forest environment loses that critical link. Thankfully, Ulva and Stewart Islands do not have breeding wasp populations. They also don’t have beech trees, but the scale insect uses the manuka (tea) trees instead there. And we did see a bellbird feeding on the black trees!

The bellbird (just under white branch on black mold) is lapping up the honeydew from the scale insect
Another plant we saw was the ancient Tmesipteris, a dark green waxy plant about 10 cm high that is related to the first leaved plants and has looked the same for 400 million years. There are none in the Northern Hemisphere. I took a picture of it, but must have deleted it for not looking very interesting. Classic – it survives 400 my and I can’t even save its digital photo for a few weeks!

I showcased the Lancewood tree in a previous blog, but we finally saw juvenile, young adult and older adult all together on Ulva Island, which helped us understand how the tree changes the shapes of its leaves as it matures. The juvenile is in front with the upright, spiky leaves. Then the young adult with leaves that are becoming shorter and rounder, with the mature adult behind that with almost round leaves. Crazy, eh?

Three stages in the life of a lancewood - look carefully!
When we got back to the dock to wait for Peter’s water taxi to Stewart Island, we looked down into the ocean and saw these CRAZY pinkish things on stalks. I thought they were some kind of crinoid, a sea lily… but – if you want the explanation for this mystery, stay tuned…

And an extra thanks to Vera for our great day on Ulva Island and for contributing her photos to this blog.

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