Living on shaky ground

The moderate earthquake that hit Fiordland last week is reminder that tawaki have chosen a particularly precarious stretch of coast to breed. The species’ entire breeding distribution follows one of New Zealand major geological boundaries, the Alpine Fault.

Here the Pacific Plate meets the Indo-Australian Plate, two of the earth’s major tectonic plates. Or more specifically, the Pacific Plate moves over its counterpart, pushing it downwards while lifting itself up – forming the Southern Alps in the process. It’s a pretty lively zone where earthquakes are a common occurrence. So tawaki live in a pretty shaky region.

That wouldn’t be half so bad, if they would breed in earthquake proof burrows. But a lot of them don’t. Many tawaki establish their nests under rocks or boulders, sometimes along the course of old landslips which in itself is a reminder of the violent forces of earthquakes. As researcher, it is a pain to find your way through this jumble of rocks because not every stone you step on is as stable as it seems. Even larger boulders may give way and start to roll when you try to climb over them. Obviously, that is the last thing you want as there might be tawaki breeding under that very same rock.

What does this mean for tawaki when there is an earthquake?

Well, first of all, as stated before earthquakes are a common occurrence along the Alpine Fault. So we can probably assume that a lot of the rocks the penguins have decided to breed under have been shaken into place already and are unlikely to be moved by another wee quake.

However… there is a very big earthquake waiting to happen. The Alpine Fault has ruptured four times in the past 9 centuries, which is about one big earthquake every 225 years. And the last rupture dates back to 1717 – almost 300 years ago. So the next big one is overdue. In fact, geologist estimate the next rupture of the Alpine Fault to occur in the next 50 years. And it will create a massive earthquake of magnitude 8 or more, at least as violent as the 2015 Nepal earthquake. If not more so. To put that into perspective, the devastating earthquake that hit Christchurch in February 2011 was of magnitude 6.3.

The predicted epicenter is about half way between Jackson Head and Harrison Cove. Actually the isoseismals (blue lines in the graph above) forecasting the spatial distribution of seismic activity, neatly cover the core breeding areas of West Coast and Fiordland tawaki. So penguins occupying this stretch of coast will be in for a wild ride indeed. And it is safe to assume that the rocks under which tawaki are breeding will move once more when that happens.

If the quake hits during the breeding season tawaki might indeed be in trouble. In this case, a lot of penguins attending their nests may be crushed by shifting rocks or buried under the rubble of landslides. With such a big earthquake, tsunamis are probably to be expected as well so that birds not breeding under rocks may get washed away. So it could be quite bad. But tawaki would have to very unlucky for that to happen.

How likely is it that tawaki will be at home during quake?

Tawaki spend most of their lives at sea. So the timing of the quake would have to be spot on and coincide with the penguins’ breeding season (August to November) or moulting (February), the only periods of the year the birds spend substantial time on land. This means that the penguins are only in the region for four months every year. That’s only a 1:3 chance of tawaki witnessing the quake first-hand. It’s more likely that they come back from their migration to find their breeding site layout altered substantially.

If it happens during the breeding season, will it be enough to wipe them out completely?

Highly unlikely, as there will be a lot of non-breeders and juveniles as well as foraging parents at sea and therefore likely spared from quake-related misfortune. And at sea, those birds can handle all kinds of turmoil…