People might get the impression our penguins are jet-propelled while watching them zoom around in the water. It's really amazing watching their powerful flippers and their torpedo-like bodies zip past the windows. Sometimes they build up incredible bursts of speed and begin popping out of the water like porpoises. The tiny trail of bubbles that trail off behind a gentoo or macaroni has prompted some interesting questions. If you look closely at the penguin as it "flys" by you, you'll see those bubbles are coming from underneath the feathers. On land penguins can raise their feathers just a bit to allow some relatively warm air in close to their bodies. The feathers close down enough before diving that some of that air is trapped close to their bodies to help insulate them. It's a good thing penguins don't have to rely on air to keep them warm though. As they move through the water, that trapped air is escaping in the stream of tiny bubbles you see. Fortunately for the penguins, they have a layer of blubber or fat layer to keep them warm in chilly waters. Heat loss in water is much greater than in the air. Think about your trip to the Tennessee Aquarium and you have seen bubble streams in one other place as well. If you remembered watching the North American River Otters at play in the Cove Forest... you're right. They have two layers of fur. Waterproof guard hairs on the outside, and a thick underfur that traps air and helps insulate them. When the otters dive into the water, a trail of bubbles is released from their fur. Otters and penguins also seem similar in their underwater agility. Both animals can maneuver extremely well as you have probably already seen. But the penguins would be the champions if there was a contest between the two species over exiting the water. The way gentoos rocket out of the water and land on the rocks is simply awesome. Coming in second to their feathered friends is nothing the other guys "otter" be ashamed of though.