The Great Storm Petrel Hunt of 2004
It was 9.20pm on New Year's Day, and all hopes of going birding the next day had faded. We had our names on a waiting list to go on a search for the New Zealand Storm Petrel, a bird which was supposed to have gone extinct so long ago that even most birders had never heard of it. But in January 2003, a strange storm petrel had been sighted off Whitianga by Brent Stephenson, Sav Saville and others (see report of that sighting here).
It looked like a Black-bellied Storm Petrel (BBSP), but a few key features didn't match, and it was the wrong time of year for this species to be around. Almost as a joke, someone said it looked a bit like the extinct New Zealand Storm Petrel (NZSP). That seemed crazy: the three known specimens of that bird had been collected way back in the 1820s, and there had been no suggestion since then that they might still exist. It happened that Ian Southey was heading to Europe to check out museum bird collections, so while he was in Paris and London he had a look at the NZSP specimens. His verdict was that they looked like the same thing.
That's where things may have rested, but in November two British birders, Bob Flood and Bryan Thomas, saw and photographed 10 or 20 birds that were clearly of the same species (their report, with stunning photos, is here). These were on the outer side of Little Barrier Island. So the hunt was on to find more. A trip was planned by Karen Baird and Chris Gaskin of Kiwi Wildlife Tours for January 2, and this is where we came in. We sent off an email to get our names down for the trip, but it was already full. By the evening of January 1 we'd resigned ourselves to spending the next day around the house. Then Iris noticed the cat had knocked the receiver off the phone, and checked to see if we'd missed any calls. "Dad," she said, "I think you'd better listen to this!"
Sure enough, there was a message from Karen, saying they'd had some cancellations, and could we ring back and let her know if we could make the trip at such short notice. Hmm, 11 and a half hours to get some sleep, get packed, and drive two and a half hours. Yep, that's possible!
So at 6.15 the next morning we were on our way, through a bit of early morning fog, then, once we were north of Auckland, into a beautiful clear blue day, with hardly a breath of wind. We met up with Karen, found our boat, the Assassin (must be a fisherman thing), and headed out to sea bang on time at 9am.
The Assassin was small (about 10m) but speedy, and it only took an hour or so to get out to near Little Barrier. On the way we saw a few Blue Penguins, Fluttering, Flesh-footed and Buller's Shearwaters, and, as we got further out, some Cook's and Pycroft's Petrels. These were a bit tricky to tell apart - the Pycroft's are darker on the back, with a slightly more pronounced cap. It was good to see both together. Then we started seeing a few White-faced Storm Petrels, which are the common storm petrel around the North Island. We also passed close by a shark, which gave a couple of quick flicks of its tail to take it out of the way of the boat. David spotted a whale blowing in the distance.
A couple of miles beyond Little Barrier we started chumming - Brett the skipper hung a bag of minced fish off the back of the boat, and threw chopped pilchards and squid into the water. The resulting smell and slick brought several WFSPs and Flesh-foots close in around the boat, but with nothing more exciting in evidence we decided to carry on.
We hadn't gone far when Brett spotted a small, dark bird on the water with a couple of Cook's Petrels. As we approached, it flew, but didn't go far. It was clearly a storm petrel, dark on the back, head and breast, pale on the belly, and with a bright white rump. We circled round slowly, cut the engine, and resumed chumming. The bird flew close in by the boat and circled us, occasionally helping itself to fragments of chum. Everyone had excellent views under perfect conditions. There was no doubt it was the same bird that Brett Stephenson, Sav Saville, Bryan Thomas and Bob Flood had seen.
The main field character which distinguishes the New Zealand Storm Petrel from the BBSP is that the posterior margin of the breast has streaky black-brown extensions into the white of the belly, whereas the BBSP has a cleaner appearance, with a usually well-defined posterior margin to the breast, but a black stripe extending back along the belly (there some BBSP photos for comparison here). But it's not that simple. A few BBSPs lack the belly stripe, and they can have some speckling along the posterior margin of the breast, though not usually as pronounced as on the NZSP. The bird above seems to have black axillaries ("armpits") but this may be a trick of the light. Here's another photo which shows the streaking on the belly quite well.
There's also a bird called the White-bellied Storm Petrel (WBSP), which lacks the belly stripe, and can have a streaky or spotty margin to the breast. But they're generally paler on the upper surfaces, whereas our birds were quite dark.
WBSPs have short legs which don't usually extend beyond the tail, whereas our birds had very long legs and toes which extended well beyond the tail when flying.
This next shot also shows the long toes, as well as the streaking on the belly. There's a suggestion of a line running diagonally from the undertail coverts up to the axillaries, which Bob Flood also commented on.
So these are not WBSPs. They could conceivably be rather odd BBSPs on the basis of the characters discussed so far, but they would be a long way from home. BBSPs breed in the subantarctic; the closest populations are on the Auckland, Bounty and Antipodes Islands. In the spring and autumn they migrate along the east coast of NZ on the way to and from their feeding grounds in the tropics, but they don't hang around. These birds have been in this small area for at least six weeks.
Another thing that distinguishes these birds from BBSPs is size. BBSPs average 20cm long, about the same as a White-faced Storm Petrel, and have a 46cm wingspan, compared with 42cm for WFSP. The birds we saw were substantially smaller than WFSPs. Here's a photo of the two birds side by side (WFSP to upper right).
If the WFSP in this picture is an average individual (ie about 20cm long, with a 42cm wingspan), then the other bird appears to be about 19cm long, with a 39cm wingspan. Obviously this is only approximate, but it was clear from our observations that these birds were smaller than the WFSPs they were flying around with, whereas if they were BBSPs they should have been bigger. Here's another shot of one (upper left) with a WFSP and a Flesh-footed Shearwater (which is intermediate in size between a Red-billed and Black-backed Gull) which gives a good idea of how small they are.
Brent Stephenson and Bryan Flood have commented on the wing proportions of these birds - they're very long and slender compared with BBSPs (even though they're smaller overall), with very pointed wing tips. This shows well in the photo below.
They had a very direct style of flight, quite different from the butterfly-like fluttering of the WFSPs, and didn't go in for a lot of foot-pattering (which BBSPs are supposed to do a lot), preferring to touch down with their feet briefly then fly on. Here's a shot which shows the feeding behaviour, touching lightly with the feet, rather than splashing in breast first as BBSPs are supposed to do. This bird looks very dark under the wing (especially compared to the bird with the WFSP above) - the original bird was joined by at least two others - it was hard to keep track of them all. Maybe some of this is tricks of the light - at the time they all looked very similar.
This next photo shows the tail shape well. Rounded, like a BBSP, as opposed to forked, as is the case with some other storm petrels. According to WRB Oliver's 1955 classic "Birds of New Zealand" (one of the very few relatively accessible publications that even mentions the NZSP), the NZSP has a "doubly emarginate" tail, which probably means it has two indentations in its rear edge, ie, an open W-shape. It's hard to know what to make of this; no other storm petrel has a tail this shape. It's probably quite difficult to spread the tail of a specimen that's more than a century old, so this may not be accurate, although Godman's 1907 monograph on the petrels apparently also shows this feature for NZSP (he called it by a different name, but apparently he was referring to the NZSP specimens).
Virtually everything else in Oliver's description matches the birds we saw. One other minor discrepancy is that Oliver describes the chin as "white mottled with sooty black", while our birds (and the other birds seen in January and November) had black chins. From Ian's pictures, it looks like the chin feathers may be white with black tips - so that, when ruffled as in an old museum specimen, they appear mottled, even though in life only the black tips are visible. You get the same effect in Kerguelen Petrels, which look black in life even though the greater part of their feathers (everything except the tips) is white.
So we really couldn't have asked for more (except David and Iris were feeling queasy, despite the calm conditions!) - at least three of these birds, coming up to about 5 metres from the boat, in bright sunshine, with next to no wind, for about an hour. It'll be interesting to see the photos the others on the trip have taken. There was also some excellent video footage taken, which shows the flight patterns and general behaviour very clearly. Well satisfied, we carried on to the Mokohinaus, pausing only to socialise with a friendly group of bottle-nosed dolphins. It may have been a mating group, lots of belly-to-belly swimming, twisting around each other and leaping.
We had lunch among the islands at the Mokohinaus, giving David and Iris a chance to recover their gastric equilibrium - a truly magical spot.
David and some of the others on the trip had a swim, and had a good look at the local fish life with a face mask borrowed from Brett. Brett also took Annette and Iris and one other for a row through the arch in the cliff (to the left in the picture above) in the boat's rubber dinghy. Red-crowned Parakeets (almost extinct on the mainland) and a Kaka flew between the islands, above our heads.
Then we headed due south to the Maori Rocks, which has a large gannet colony, with many well-grown but still downy chicks. But the real highlight was a group of 11 Grey Ternlets on rock ledges on the shady side of a rock stack. Another new bird for all of us! They had been seen there a year or two ago, but hadn't been seen in recent visits, so they were a real bonus. No sign of breeding, though. These are a tropical species; there are thousands up in the Kermadecs, but around the North Island they're very thin on the ground.
After this we steamed out beyond the islands into open ocean, then stopped and did some more chumming. The wind died completely, and it was very hot. Most of the birds were just sitting on the water, and not many came up to take advantage of the free feast we were laying on. The keenest were the Flesh-footed Shearwaters, and we had a small group hanging out at the back of the boat. There were also a few Black Petrels, a much rarer bird (the only remaining breeding colonies are on Great Barrier Island, with a very few on Little Barrier), very similar to the Flesh-foots, but slightly larger, a deeper, glossier black, with paler bills and black rather than pink feet. Good to see them sitting on the water side by side to get a clear idea of the differences, which really are quite subtle. It was magical to be able to detect WFSPs coming in by hearing the sound of their feet dabbling in the water.
With little result from this activity, we decided to just cruise along the current lines - long patches of smooth water snaking through the slightly rippled general ocean surface. The WFSPs seemed to be feeding along these, dabbling for plankton. We hoped we might pick up more of the other species, but they weren't forthcoming. So we headed in past Fanal Island, seeing more of the same birds we'd been seeing all day - plus a single Grey-faced Petrel, most of which had already left on migration.
Time was marching on, so we headed for home. At about the point where we'd first encountered the strange storm petrels we spotted another one, but despite wheeling the boat around and retracing our path we couldn't relocate it. But one mustn't be greedy, we'd already had a day that far exceeded our expectations.
So what to make of the New Zealand Storm Petrel? Officially, they're a subspecies of Wilson's Storm Petrel, but they look completely different. Wilson's is completely dark underneath for one thing - if it exists, the NZSP is most likely a distinct species. So were the birds we saw New Zealand Storm Petrels? Well, they looked just like the museum specimens, and for all the reasons discussed above they don't seem to be Black-bellied Storm Petrels, the species which is superficially the most similar. So our money is on the NZSP, back from the dead. Whether the Ornithological Society's Rare Birds Committee will be convinced remains to be seen. In some respects (colour pattern and distribution) they seem intermediate between BBSP and WBSP, in others (wing shape, size, behaviour) they're out on their own. It may require someone to get one of these birds in the hand, get some accurate measurements and even DNA samples before this issue is resolved once and for all.
The other big question is, where are they breeding? The most likely place is on one of the islands that have been cleared of rats in the last 18 years. Progressively larger islands have been cleared of rats since 20ha Korapuki Island in the Mercuries was done in 1986. The Mokohinaus were cleared in about 1990. If there had been a relict population of NZSPs on the Mokes hanging on in the face of ongoing predation by kiore, they would now have had about 14 years for their numbers to recover to the point where people are starting to see them. There has been very little work done on Mokohinau seabird populations (David spent a week there in 1979, most of it spent looking at marine stuff - no one on that trip looked specifically at seabirds), this could be a good place to start looking for a breeding colony. It would be a difficult job - storm petrel burrows are often widely dispersed among other seabirds, and large areas of the Mokes are covered in dense stands of flax, which are a pig to move around in. Something else that's a bit tantalising in Oliver - a bird identified as a BBSP flew into the lighthouse at Mokohinau "some years" after 1868. Could this have actually been a NZSP?
Another possible breeding site is Korapuki, or one of the other Mercuries, given that the first sighting was off Whitianga. There may even be more than one colony. One thing's for sure, this story has a long way to run, and will be fascinating to follow.