Life and Stress at the Ice Edge

After hundreds of underwater encounters with leopard seals, I thought I knew a thing or two about their behavior. This was a huge mistake that could have cost me my life. On the third day of my assignment to photograph emperor penguins in the Ross Sea, I stood next to a series of open holes and ice leads to see where the penguins were entering the water when I spotted the unmistakable head of a leopard seal poking through a hole in the ice. I smiled with anticipation as I recalled the many wonderful dives I have had with these mysterious and intelligent animals. I felt like I was seeing an old friend, and I could not wait to join this much misunderstood animal in the water.

The next second and without warning, the seal exploded from the water’s surface before my assistant and I realized what was happening. Even though we were 15 feet from the ice edge, the seal flew toward me, putting his entire 600-pound mass at eye level. I had time only to raise my arm to protect my face as his body slammed into mine, throwing me onto the ice. I was shocked, panicked and scrambling to get away from the seal, which lay next to me on the slippery ice. The seal, equally surprised, was rushing to get back into the water. It could easily have bitten me, but I clearly saw in its eye the moment when in the knick of time it realized I was not a penguin. What I had not realized is that comparing the hunting behavior of leopard seals that gorge themselves on 8-pound penguin chicks in the Antarctic Peninsula with those laboring to catch 70-pound adult emperor penguins in the Ross Sea is like comparing golden retrievers to lions.

Leopard seal catches a penguin in its mouth and looks very happy
Leopard seals are the apex predators of the Antarctic.

Looking up from underneath the ice, I later realized why that seal had confused me with prey. Through the translucent glassiness of the ice, I could easily distinguish the dark shape of my assistant standing 30 feet away from the ice edge just like the penguins do. I could not only see his silhouette, which looked remarkably like that of an emperor penguin, I could also hear him moving around on the ice. It dawned on me that as leopard seals patrol the ice holes that emperor penguins use to enter the water, they look for shapes on the ice and listen for sound cues as they wait in ambush for the birds.

Weighing between 55 and 90 pounds and standing more than 3 feet tall, emperor penguins are the largest and most majestic of all penguins. Not only are they beautiful, their behavior is also fascinating. Most of what we know about them, however, revolves around their extreme parenting behavior: the harsh isolation of their nesting colonies and the arduous treks to and from the sea to get food as they take turns caring, first for their egg and then for their chick. What little we know about this resilient bird from movies such as March of the Penguins has left many of us yearning to find out what happens when the penguins reach the ice edge and enter the frigid Antarctic waters. The knowledge that the death of even one parent will cost the chick its life made me interested in observing the survival strategies that these “extreme parents” have developed to avoid predation. This was the essence of my assignment.

I sat on the ice for hours observing how the penguins hesitated before entering the water. When they first approach the ice edge after the arduous march from the colony across the frozen landscape, they stand for a little while about 30 feet from the water’s edge. Their heart rate accelerates to more than 200 beats per minute in anticipation of going into the water. They know a deadly predator awaits them underneath the ice.

Emperor penguin coming up for air through ice hole
Although they move awkwardly on land, emperor penguins are the picture of grace in the water.

Watching the penguins exit the icy waters in gravity-defying leaps was the most intriguing aspect of the assignment. Air is 800 times less dense than water, and I wanted to understand how these large birds achieve sufficient underwater speed to overcome the influence of gravity and leap clear out of the water and onto the ice.

Fully aware that I might have the opportunity to document a leopard seal attack, I had no choice but to get into my drysuit and slip into the icy water through a hole in the thinning sea ice. In this small hole, barely larger than an average hotel room, hundreds of penguins raced, executed sharp turns, splashed on the surface and morphed from the awkward lumbering mass we have come to recognize on the surface into one of elegance, grace, power and speed in the frigid, crystal-clear water of the Ross Sea. I quickly understood why it is almost impossible for a leopard seal to outrun or outmaneuver an emperor penguin in open water.

During my first immersion I swam toward a group of penguins that were busy bathing and preening themselves on the surface, and I immediately became completely disoriented by a world of confusion and bubbles. In a flash, and before I could comprehend what was happening, all the penguins, who had never seen a human in the water, had darted into the depths of the ocean and left me floating alone in the midst of a sea of bubbles — a “smoke screen” so effective I could barely see my own hands.

Being naturally curious and very intelligent, the penguins quickly realized that I posed no danger to them. To my delight, they soon relaxed and allowed me to remain in the ice hole with them while they went about their seemingly endless back-and-forth in the water.

Over the next few days I observed how penguins use bubbles not just as smoke screens but also as powerful means of propulsion. I was mesmerized by the beautiful bubble trails penguins created as they emerged from the depths of the ocean, where they can dive down to 1,700 feet for as long 15 minutes. I couldn’t tell at first if the bubbles came from their lungs or from their feathers. This physiological adaptation, known as “air lubrication,” was only recently described by Professor John Davenport of the University College Cork and his colleagues in a study published in the Marine Ecology Process Series.

Watching and analyzing the film Blue Planet, the researchers discovered that, when on the surface, penguins raise their feathers to fill their plumage with air before diving underwater. As they descend, the water pressure increases, compressing the air trapped in the feathers. At a depth of 80-100 feet the air volume has shrunk by as much as 75 percent. When they are ready to surface, the birds depress their feathers, locking them around the reduced volume of air. As they speed vertically toward the surface, the air trapped in the plumage expands and pours through the feathers.

Seal catches a penguin and it is bloody
Not every penguin makes it back onto the ice.

The structure of the feathers is highly complex, and the pores through which the air is pushed are so small that the bubbles are initially very tiny. They’re so tiny, in fact, that they form a coat on the outer surface of the feather. This coat of small air bubbles is the key to the penguin’s strategy for avoiding leopard seals. The bubbles act as a lubricant, drastically reducing drag and enabling the penguins to reach lift-off speeds.

Davenport and his colleagues described how if a seal is present, the penguins use their “bubble propulsion” strategy as they rocket to the surface, often clearing the ice edge by several feet before crashing onto the ice and giving out an “umph” and a squeak, having knocked the air out of themselves.

Over a period of three weeks I spent hours watching these amazing “flightless” birds soar as they exploded out of the water in an unforgettable show of power and grace. The seemingly simple adaption of using air bubbles to reduce the friction of water, increase speed and burst out of the water is a central element of emperor penguins’ predator-avoidance strategy. To witness first-hand the relationship between emperor penguins and their predators and observe the strategies they have developed to avoid predation was the opportunity of a lifetime and one that could only happen in a place as insulated from human impact as Antarctica. However, despite the cold continent’s remoteness, the future of the emperor penguin is intimately linked not to the leopard seal but to human dependence on fossil fuels.

As we continue to dump carbon dioxide into the atmosphere, the biggest threat to emperor penguins is the possible breakout of a large ice mass that blocks the way between the penguin colony and the ice edge.

© Alert Diver — Q1 Winter 2014