Research results

Last September we deployed our new miniature penguin camera on a breeding female tawaki from Milford Sound/Piopiotahi. The results were incredible.

After the penguin spent the day foraging in the fjord, she returned the same night allowing us to recover the camera. The device recorded roughly 2.5 hours of footage and provides a fascinating insight into the foraging behaviour of tawaki.

While the camera was rolling the bird caught more than 50 individual fish larvae, simply by picking them up in a sort of drive-by fashion – blink and you miss it.

Particularly fascinating were the captures of three squid. When viewing the footage, it really seems like a bad idea for squid to squirt out ink when under threat. Commonly believed to be a strategy to confuse potential predators, for tawaki the ink seemed to indicate that there is prey to find. Squirting proved counterproductive for the cephalopods.
Also fascinating to observe were the pursuits of sprats directly underneath the surface. The agility of the sprat allowing them to do sudden U-turns seems to give the fish a fighting chance.

From a penguin perspective, it is extremely cool to see that all the prey captures occurred from below, where the prey item was clearly visible against the light backdrop of the water surface. So much for the countershading theory…
We plan to deploy more devices this coming season to get a better understanding of the prey composition and the varying foraging strategies of the penguins. So stay tuned!

Thomas caught up with Alison Ballance at the Birds NZ annual conference in Wellington last weekend. They had a chat about the study of the tawaki pre-moult and winter dispersal, the mind boggling results we got, and how we explain the penguins’ behaviour.

Alison published the interview as part of her “Our Changing World” podcast series for Radio New Zealand. You can listen to the episode here or go to the Podcast website over on RNZ.

Our ‘Marathon Penguins’ have made quite a splash! Quite more of a splash than we honestly expected. In the days after the paper was published on PLoS One, news stories started to pop up in media outlets across the world. All of a sudden our ‘tawaki at sea’ photo was featured in articles published in all kinds of languages reaching all kinds of audiences.

Probably we need to stop using the phrase ‘tawaki are one of the least known penguin species in the world’ now!

Below are a selection of news clippings we collected. (There are far too many to put them here!)

Today we celebrate the publication of our Marathon penguins paper in the Open Access journal PLoS One. For all of you that do not want to grind through a lengthy scientific text our friend Giselle Clarkson has summed in up perfectly:

Here we are, then. 2018, which will mark the fifth season of the Tawaki Project.

We have been quiet these past few weeks. The reason for that is that we were ‘out at sea’ with other projects. Of course, so were the penguins. Between mid-November and mid-December, the adult tawaki saw their chicks fledge and then headed off on their pre-moult journeys. Since then, the birds are absent from the mainland.

Well, until yesterday. We received word that the first tawaki have returned from their pre-moult journey.

The summer holidays are over. Whether we can call the post-breeding and pre-moult migration of tawaki a holiday is another question. Judging from the distances that the birds cover in the two to three months after their chicks have hatched, there is a fair amount of effort involved in their journey.

Back in mid-November we deployed satellite tags on 20 tawaki from Gorge River. Since then more than 3,000 locations were transmitted through the Argos system satellites. While some of the tags stopped submitting halfway through the birds’ journeys – most likely because the penguins managed to preen them off their backs – we still have a number of birds that are actively transmitting.

And one of them, a female tawaki, is close to home. Another 250km and she is back where she started 82 days ago. She travelled 3,830 km and distanced herself 1,370 km from her nest site in Gorge River. So the last few kilometres are peanuts. The amazing thing, however, is that this journey was just the prelude to the winter migration which the bird will go on after the moult in February. That, however, we will not be able to track as the tracker will fall off once the bird starts shedding its feathers. Good thing the Tawaki Project has another two years to go.

The pre-moult migration trip of a female tawaki from Gorge River

The analysis of the tawaki dive data we collected at Jackson Head and Milford Sound is largely in dry towels. And the results are pretty interesting.

The GPS data penguins brought home with them already highlighted tremendous differences in the foraging behaviour at both sites. The foraging ranges (that is, the distance the birds travelled during single foraging trips) differed by almost an order of a magnitude, with Jackson Head birds swimming up to 100 km away from their breeding colonies.

Foraging ranges of tawaki from Jackson Head and Milford Sound.

In comparison to other crested penguins this is not necessarily record breaking, but still was a lot further than any of the tawaki had travelled in the previous season. At the same time, the ranges of tawaki from Harrison Cove were unbelievably short. The average distance the birds put between themselves and their nest sites was a little above 3 km. Yes, not a typo – three kilometres. These are officially the shortest foraging ranges I have ever heard of in any penguin species!

So, how does that reflect in their diving behaviour and what does it mean?

One could for example assume that penguins that travel a lot show a lower average dive depth compared to birds that hop in the water and start feeding straight away. Why? Well, when trying to cover distances it makes sense to move primarily horizontally which means many shallow dives.

And that’s what we found in the far travelling tawaki from Jackson Head. Almost half of the ca. 13,000 dives recorded in eight penguins were not deeper than 15 metres. The other 6,500 dives went down to depths of up to 90 m, although the majority ranged between 20 and 60m. So that is probably where the penguin were on the lookout for food.

So without having to travel at all… did the Harrison Cove tawaki dive deeper? No, quite the contrary! We recorded about 9,500 dives performed by six birds. And on almost 80% of these the birds stayed in the upper 15 m of the water column. What gives?

Depths of all tawaki dives recorded in 2015 at Jackson Head (orange) and Harrison Cove (green).

Well, underwater visibility in a fiord is quite limited. The fiord is usually covered by a freshwater layer created by heavy rainfalls that also wash a lot of detritus from the surrounding land into the water. As a result you don’t have to go down deep if you want to experience a night dive in broad daylight. This is also why in Milford Sound you can observe deep water species just a few meter below the surface.

For penguins as visually hunters that means that the darker it gets the less likely they are to spot their prey. So it seems to make sense for tawaki to stay up there… until you start to wonder why their prey does not bugger off into the darkness?

Well, perhaps it can’t because the prey the penguins were after was itself looking for food in the sunlit ranges of the fiord. Or the penguin food is brought passively to the surface by water movements. That applies for example to krill – which we found in considerable quantities washed up on the shore and which is a staple food for the tawaki’s closest living relative, the Snares penguin.

Occasionally penguin prey may be found at greater, darker depths. That may be the reason why almost all of the penguins occasionally dove down to 50 m or more. The record for the greatest depth stands at 80.6 m. After we lowered a GoPro into Harrison Cove, we can be sure that at such depths there is not a lot to see anymore.

So what have we learnt?

We have learnt that the Harrison Cove penguins were a lot better off when compared to their Jackson Head counterparts. Not only did they not have to travel to some far away foraging grounds to find food. They also did not have to dive very deep to get to it. In short, foraging at Harrison Cove was pretty damn peachy.

Whereas at Jackson Head, life served the penguins lemons. And admire them for at least trying to make lemonade. The birds did everything they could to raise their chicks. And while it was unsuccessful for many of them, I am sure, next season will see the odds evened out between Jackson Head and Harrison Cove.