By Peter Balwin (text) and Dr Ruedi Abbühl (photos)
Rockhopper penguins know their way around steep terrain. New studies show that the little guys have a lot going for them in other ways, too.
The waves of the South Atlantic crash against the rocky coast with unbridled force. Spray splashes, and the stormy wind of late winter blows whitecaps far up the wild cliffs. When the next wave gathers its force and the water recedes a bit for a moment, the furrowed rocky landscape seems to lift up like a ship in a hurricane. And in the middle of this archaic scenery are penguins. This is their landing site! It is a daring feat to try to jump onto the rocks in this roaring ocean and reach the breeding colony. Again and again the water pulls the birds back — or knocks them crisscross to the rock with the next wave, drags them over the rock terrace and lets them sink in the roar.
But rockhoppers would not live up to their name if they failed now. They try again — and again, until they escape the waves and hop away, excited and carried away.
While these small, compact seabirds were just moving like torpedoes in the water, they now have to climb up the steep rocky face. Powerful leaps from one rock niche to the next bring the penguins quickly forward. Rockhopper penguin is the name given in English to this bird, which is about 55 to 60 centimeters tall, rockhopper…
The rockhopper penguin occurs circumpolar in subantarctic and temperate zones. It is divided by experts into two species: the southern rockhopper penguin (with subspecies Eudyptes chrysocome chrysocome and Eudyptes chrysocome filholi) and the northern rockhopper penguin (Eudyptes moseleyi). This division into two different types has only existed since 2006.
According to this, the southern rockhopper penguin lives at the southern tip of South America as well as on the Falkland Islands (subspecies chrysocome) and on numerous subantarctic islets such as Prince Edward, Crozet, Kerguelen, Campbell, Macquarie and others.
The northern rockhopper penguin, on the other hand, inhabits tiny islands in the South Atlantic (Tristan da Cunha and Gough) and in the southern Indian Ocean (Amsterdam and St Paul Islands).
As soon as the penguins — after a successful landing — have climbed the cliff, the colony is reached and the breeding business can start. Amazingly, rockhopper penguins do lay two eggs – but usually only the chick from the last egg laid survives. The first egg laid is usually up to 40% smaller (about 78 grams) than the second egg (about 110 grams). When the young breaks the shell with its egg tooth after an incubation period of a little over a month, it is about February and the peak of the southern summer has arrived.
Now the penguin parents begin their mission; their most important task is to provide food for their offspring and defend them against predatory seabirds, such as skuas, or intrusive neighbors. Especially the fathers are challenged, because male rockhopper penguins guard the chicks during the first three to four weeks after hatching — without eating. During this paternal fasting period, the females have the task of bringing food to the nest for the young birds. In the process, the females swim between 30 and 60 kilometers out to sea every day.
This type of infant care is found only in crested penguins (Eudyptes), to which our rockhopper penguins belong to. In most other penguin species, the partners take turns: one guards the nest, the other fetches food outside in the sea; then they swap.
On food tour
The routes of such “shopping trips” are different, depending on the location of the breeding colony. Southern Rockhopper penguins, which breed on the Argentine Staten Island at the southern tip of Tierra del Fuego, forage in the open ocean southeast of the breeding colony. Their congeners from the Falkland Islands are quite different: they choose a marine area above the shelf and the continental slope, which lies northeast of the Falkland archipelago.
A group of ornithologists in the Falkland Islands wanted to know how much food a rockhopper penguin returns from the sea to its nest with. To find out about such things, the researchers unceremoniously installed a small weighbridge. Rockhopper penguins inevitably had to pass this scale – on their way to forage in the sea and on their way back. This way, the researchers were able to measure the difference in weight.
Lo and behold, returning penguins were between about 240 and 290 grams heavier.
But not only the weight was measured — at the same time, the scientists noted the wind direction and speed at sea. It was found that these two values had a significant effect on the weight gain of rockhopper penguins after foraging. Weight gain was lowest in gale force winds.
In the last five or six weeks before fledging, all the young birds in a colony come together in what is called a crèche, a true nursery. There, each young animal is catered for by its own parents, with fathers and mothers now sharing this task.
While the young are in the crèche phase, the adults grab their chance and go on several days of foraging trips to make up for their large weight losses during the breeding season.
Once the breeding season is over and the young have fledged (in the case of penguins: swum away), not a single penguin stays on land any longer. Off to the sea is now the plan for the approaching winter.
In winter, rockhopper penguins prefer marine areas where temperatures in the upper layers range from 5° to 8°C, depending on the winter month. Moreover, according to a study of penguins on the Argentine Staten Island southeast of Tierra del Fuego, winter hunting grounds were preferably found in hihgly nutrient-rich shelf seas less than 200 meters deep.
Thanks to modern technology, it is now possible to look over the penguins’ beaks even when they are diving. Southern rockhopper penguins, for example, have been observed diving from Little Noir Island on the west side of Tierra del Fuego in the Pacific Ocean. A foraging trip lasted on average about 42 hours. Diving was busy: each dive went down to an average depth of 21 meters and lasted 64 seconds. The birds dived almost 40 times per hour.
Such values vary naturally and depend strongly on the biological richness of the marine area visited as well as the timing within the breeding season.
A similar study by a South African-French team looked at the diving behavior of southern rockhopper penguins on Marion Island, a tiny volcanic island in the southern Indian Ocean, about 2,200 kilometers south-east of Cape Town. Here, 65,000 breeding pairs of rockhopper penguins make their home. Thirteen birds from this mass received a small data logger glued on.
To build up a fat reserve for the energy-sapping molt, these birds swam about 750 kilometers south (at an average speed of 3.5 kilometers per hour) to search for food for a little over a month in Antarctic waters where the temperature avaged 3.5°C. They mainly dived to depths of 30 to 60 meters (best performance: 122.3 meters, a new record for the rockhopper penguin!) and, thanks to their zigzag course, covered a total of about 1,800 kilometers in the open sea. Less productive marine areas they traversed more quickly than those with an abundant food supply.
The approximately 350 individual dives per day meant that each feeding bird spent a good eight to nine hours a day underwater combined.
And what seafood is on a rockhopper penguin’s menu? Those from the Falkland Islands prefer crustaceans such as krill in the first place. But also cephalopods (squid) and fish are consumed.
These winter forays into the southern seas have long attracted the interest of scientists. What are the penguins doing out there in the ocean? How far away are they moving? Where do most of them swim to? Today, modern, small data loggers make it possible for us to virtually accompany this bird on its migratory movements through the Southern Ocean.
For example, quite a few southern rockhopper penguins on the States Island were fitted with satellite transmitters – and were amazed at the remarkable distances covered. On average, penguins were 440 kilometers from their summer breeding colony at their farthest point in winter. However, because they are constantly swimming back and forth in search of food in the open sea, the distance actually covered is considerably greater. The average distance traveled was around 2000 kilometers. They move forward at around 3 kilometers per hour. Certain speeders reached a cruising speed of 7 to 9 km/h, with some reaching 17.3 km / h, though in these outling cases the ocean current probably also helped a bit.
While rockhopper penguins from States Island foraged in a vast marine area between the Falkland Islands, Drake Passage, and Antarctic South Shetland Islands in the southern late fall (March to May), the staging area shrank to marine areas around the southern tip of South America in the southern winter (June, July).
Their relatives from the Falkland Islands were different: their preferred winter resort was a marine area of about 12,000 square kilometers about 50 kilometers off the coast of Puerto Deseado in the Argentine province of Santa Cruz. A good 171,000 Falkalnd Island rockhopper penguins reside there. Unfortunately, just in those waters there are also many human activities, such as commercial fishing, and shipping routes with the risk of oil pollution.
Nowadays, living at sea involves risks. Even those who travel far away in the Southern Ocean get their quantum of pollutants. The rockhopper penguin is no different…
French environmental scientists conducted a detailed study of 170 birds of several penguin species in the southern Indian Ocean a few years ago. The goal was to measure the highly toxic mercury content in the bird’s body. The easiest way to do this is to analyze the feathers. At the same time, they went to museums and examined 62 stuffed penguins that had lived on the same islands in the 1950s and the 1970s.
The spread of mercury in food chains is a global problem. Penguins in particular are well suited bioindicators (pointer species) to detect polluted food chains.
The study’s conclusion up front: all penguin species, including rockhopper penguins, breeding in the French Southern and Antarctic Territories (TAAF; includes, for example, Adelieland in Antarctica, the Kerguelen Archipelago and several other islets in the southern Indian Ocean) had mercury in their bodies. Birds from Antarctica were less affected than those further north. In addition, main fish eaters had accumulated more mercury than those that hunt mainly crustaceans such as krill. And as expected, penguins that had lived in the 1970s were less contaminated than individuals today.
Rockhopper penguins from the southern tip of South America had just over 5 micrograms of mercury per gram of feathers. Their conspecifics on the Kerguelen Islands or the Crozet Islands were less poisoned, with around 1.8 to 2.5 micrograms.
But even without thinking about the cocktail of toxins in the body, the decline in populations gives pause for thought. The Falkland Islands currently have over 80% (!) fewer rockhopper penguins than in the 1930s. The numbers are alarming elsewhere, too, such as Marion Island: a loss of just over 50% from 1987 to 2013, from 138,000 breeding pairs originally to just 65,000 breeding pairs today. Or Campbell Island. From there, a loss of 1.5 million pairs (94% of the former occurrence) is reported between 1942 and 1986. Climate change is at the forefront as a cause. And on Staten Island, the population declined by a quarter between the years 1998 and 2010.
Although at present it is not entirely clear why there are fewer and fewer rockhopper penguins, the list of threats is quite long. In the past, egg collection was a reason for population decline in some colonies (until the 1950s). Or crabbers used penguin meat as bait in their catch baskets. In modern times, rockhopper penguins perish as victims of oil tanker accidents or from the exploitation of oil or natural gas. Commercial fishing over the Patagonian Shelf and around the Falkland Islands also leads to conflicts from which rockhopper penguins emerge as losers.
In addition, exploitative fishing and global warming are changing the food web in the ocean — to the penguins’ detriment. Climate changes favor the increased occurrence of storms at breeding colonies. Rising air temperatures have already caused rockhopper penguins in the Falkland Islands to start breeding later and to lay lighter eggs — two factors that in turn influence breeding success, unfortunately also in a negative way here. When the temperature of the seawater changes, the food web can get messed up. The penguins eventually find less or nothing to eat.
It has also been found that the penguins find more and better food under the current prevailing wind regime (southerly and westerly winds dominate) than when the winds blow from other directions. But this is exactly the prediction: in the future, the majority of the wind over the South Atlantic could blow from the north or east.
Not only at sea dangers lurk, also on land the rockhopper penguins have it hard in many places. Habitat destruction is the key word here. For example, in the Falkland Islands, where farmers’ livestock destroyed tussock grass. These dense, large tufts of grass, which can cover entire landscapes, provide excellent shelter, especially for young penguins, during heavy rains. Without tussock, however, the mortality rate among young penguins increases. On the lonely South Atlantic island of Tristan da Cunha, farmers used to burn the tussock to reclaim fields and farmland — much to the detriment of the rockhopper penguins there.
On Macquarie Island, grazing wild rabbits caused landslides. Penguins were killed and nest sites destroyed in the process.
The sad result of all these dangers: the International Union for the Conservation of Nature (IUCN) lists the southern rockhopper penguin as endangered and the northern rockhopper penguin as critically endangered.
Currently, 6.4%, or 22.8 million square kilometers, of the oceans have been designated as marine protected areas. While this is a good start, it is far from enough: by 2030, 30% of the global ocean surface should be protected. It will probably be difficult to even come close to achieving this goal…
By Peter Balwin (Text)
Dr Ruedi Abbühl (Photos)