Sooty Shearwater- We Still Have No Idea

 

2020 Sooty shearwater chick a couple of days before fledging, doing wing exercises. Burrow is at bottom right.

Readers will know that the main sooty shearwater colony is very up-and-down in its productivity. In 2019 for example, we think only one chick fledged despite the usual active start to nesting. 2020 was much better, with 18 occupied burrows in January and 14 in March. We lost the last two months of burrowscope monitoring after that because we stayed away during the various levels of Covid lockdown, but we haven’t previously had big losses after February and presume all or most of the 14 burrows active in March  fledged chicks this year.

In an earlier poor season we had asked Graeme Taylor what he thought was going on, and he reckoned that productivity had been average around the rest of the country, and that we should look to problems on site. This season we asked Henrik Moller to think about what we were doing and to see if we could influence anything. Henrik suggested firstly that we look more widely for evidence of colony expansion than just the monitored burrows, as obviously this would be the desired outcome rather than just monitoring burrows for monitoring’s sake. We were aware of that but his comments helped overcome the ever-present activation barrier to searching the less-than-level terrain. Over the entire accessible forest floor we found one new burrow, which we decided not to include in the monitored group given the likelihood of taking a decent slide downhill while getting to it. To be certain, I tested this likelihood and confirm that gravity does indeed work on site. We also decided there was little to be gained by actively monitoring the northern outlying burrows discovered by Jo Sim and Rua. In particular, the larger of the two known areas is quite unstable and we are likely to collapse burrows if we go there often.

Henrik Moller also said that sites he has been involved with can have a proportion of false negatives, when the burrow appears empty but the chick merely moves deeper away from the probing burrowscope and can’t be seen in time. We don’t think this is a massive problem with our colony, as the burrows are not highly convoluted and interlinked like some well-established sites. However, the video at the top is from a false negative burrow. It was obvious a chick was present (swept entrance, excreta, smell: so we put the camera on it) but it did come up empty in the burrowscope inspection. Now that I in particular am more aware of false negatives, I’ll be making special effort to avoid unconscious bias in effort and attention when looking at a burrow that measured empty the previous month.

Given the disrupted monitoring season, we don’t know if falcon or weka got any chicks this year, but the trail camera showed half a dozen single-weka visits to the burrow in the video above. These were by way of a passing inspection, and the weka did not attempt to enter the burrow as far as we know. We seem to have weka at very low levels now, and indeed we heard only a single bird over the entire island this June with the previous two visits turning up nothing.

This is also a good opportunity to back away somewhat from a claim I made in 2013, that the speaker system by the colony was responsible for the birds coming back after a long absence. The basis for this was that the colony looked seriously deserted in May 2012, yet for the 2012-3 season after the speakers went in there was plenty of activity and obvious cleared areas throughout, which were not there on our initial visit. If 2011-12 had been a no-fledge season though, then the colony might just have looked sufficiently forlorn in May 2012 for us to pronounce it extinct at that time. We still think the speakers did work, but must allow for the possibility that we were fooled. We’ll never know.

So, what’s going on then? Our best guess remains that the colony is just like Titi Island  nearby, which has been static or shown only very slow growth over the last 20-30 years. The Cook Strait area is not rich in sooties and may be a bit far from the southern feeding grounds, so inexperienced breeders (like we allege ours to be) may not be invested enough to carry on with chick feeding if the krill moves further south in a given season. Henrik Moller also points out, ominously, that the southern colonies of sooties have been declining an average of 2% per year. For a bird that lays a single egg in a season and not every year, that is a path to extinction and mirrors the numbers that prodded the Key government into a small amount of action on that photo-opp CMF, kiwi (CMF? It’s a TLA; answers by email please). Maybe our role is just to hold the line on a small outpost colony until population-wide declines can be fixed (if we as a country care enough), rather than look to the sooties by themselves to turn Puangiangi into the seabird island it once would have been. We need to accept that the island is more likely to really get pumping seabird-wise if we can attract some fluttering shearwater or one of the other petrels (not forgetting little penguin and gannet as nutrient-bringers-in either) that are more common locally. This winter we put in some wooden boxes with plastic entrance tunnels at our flutterer speaker site, so that prospecting birds may be more likely to stay if they have somewhere weka-proof to shelter. It’s no coincidence the boxes are the same design as those on Mana and Matiu. Some of their flutterers might recognise the comforts of home when passing by and give them a go.

Lastly a bit of product endorsement which might be of interest to the seabird folk. We have had a long-term loan of the current state-of-the-art NZ-made burrowscope, but needed to give it back last year. Thanks Nicky Nelson, the loan much appreciated. They work very well, but run at $5000 and are quite bulky to carry around, albeit much less so than earlier iterations by other makers.

We had earlier tried out a little colour inspection camera sold to tradies, brand not remembered, which was pretty useless. For this season though, inspired by the videos on their site, I bought a specific inspection camera, the Tradesman Record from UK firm eazyview.com. This has proved to be at least the equal of its larger cousin. The screen is colour and has more than adequate resolution. It can also record photos and video clips, in my case usually accidentally as the record button falls rather too readily to hand. I suspect the daylight LEDs will lead to more false negatives than the infrared ones in big cousin, but it’s quick to deploy, get a handle on what the camera is showing and finish the burrow, so I think it will prove only as invasive as the big one, which Graeme Taylor has described as being about as disturbing to the chick as an adult returning to the burrow. The colour display is better at showing up downy chicks against dirt than the big monochrome instrument. It is easy to deploy and direct, with the flexible camera wand being of just the right stiffness to be controllable in the average to shorter burrows we have. The big one could not get any further than the new one down the longer burrows before we lost control of it. It’s more than possible to do a burrow by yourself, but we still prefer to have one person getting the wand into the burrow and the other watching the screen, as for the big burrowscope. Battery life is excellent, and we can do two months of checking 30 burrows, without recording, on a single charge of the 3 Eneloop Pro AAs (bought separately). Alkalines can also be used and there is a setting to select battery type so it doesn’t shut down early on the rechargeables. The supplied cheapie carry case protects the camera nicely and stuffs into a day pack easily. The afterthought pockets in the case are useless for spare batteries and the screwdriver you will need to change them, unless you like throwing small items down a hill in a dark forest when you unzip the case, but I suggest you get a little accessories bag and chuck that in the case instead. I haven’t managed to break it yet, or scratch the camera lens. It is also good for peering into kakariki nests (yes, there will be an article on kakariki some time soon).  Highly recommended, and landed in New Zealand for about $200. You will not notice the affiliate links at the bottom of this article, because there aren’t any. If I get excited about my new role as an influencer (hah!), then beware boot manufacturers (Lowa, I’m looking at you and your disintegrating rands).