70 10.4 Marine Birds
The ocean is also home to a variety of birds. These birds are referred to as seabirds because they spend a considerable amount of time around the sea. Many seabirds spend their entire lives in the ocean, only coming to land to reproduce. Some seabirds dive and swim below the surface, such as penguins, whose wings are modified into flippers, or cormorants, whose webbed feet act as paddles. Others stay at the surface, only hunting in the uppermost meter of the water (Keddy).
Birds evolved from reptilian ancestors
Birds split from the main reptile branch about 150 million years ago with an intermediate form known as Archaeopteryx, which was about the size of a crow. They have reptilian characteristics, such as their feet and lower legs are covered with scales and terminate in claws, their reproductive physiology is basically reptilian (laying eggs out of water), their feathers are believed to have been derived from scales, and have many other developmental and structural similarities with reptiles. Yet, unlike reptiles, birds are warm-blooded (endothermic) and maintain a constant internal body temperature.
Marine birds
Marine birds tend to be larger and stronger than their land counterparts. They have a lightweight, low-density body structure with hollow bones. Their wings are long, pointed and cupped underneath to support a large and muscular organism aloft for long periods of time.
They do not drink freshwater. Instead, they have salt glands over their eyes that remove the salt, thus permitting them to drink seawater, freeing them from dependence on freshwater from the land. The salty fluid is expelled through their bills.
The albatross
- This is one of the largest of the oceanic birds, with a wingspan of up to 12 feet
- They are the best gliders in the world – may remain aloft for months at a time, taking advantage of the west wind drift (winds that blow completely around Antarctica)
Pelicans
- This prehistoric-looking bird feeds by diving on its prey and entrapping it in its large gular pouch
- It has air sacs in its shoulders that absorb the impact with the water
Arctic Terns
- This bird feeds on small fish swimming near the surface that it catches by diving. It may even swim below the surface after them
- It lives at high latitudes and breeds on all far north rocky coasts
- However, it dislikes cold weather, so makes the longest migration of any animal, 15,000 miles each way
Penguins
- Penguins are found only in the southern hemisphere
- They are flightless birds that “fly” through the water after fish, squid and krill
- They slow their heart rate
- Have subcutaneous fat layers for insulation
- Have heavy plumage for insulation
- Their bodies are streamlined
- They have heavy feet for paddling and kicking against the water
- Their blood is shunted to the heart and brain and the extremities are deprived of blood, in order to slow heat loss
- These apply to most diving birds
Emperor Penguin: These are the largest diving birds in the world, up to 4 ft in height
- They’re the best bird divers in the world, can routinely dive for 5-10 minutes (most bird dives last 30 seconds to a minute) and at best can stay down for 15-18 minutes, diving to over 1000 feet
- They eat small fish and krill – penguin populations have increased as a result of the killing off of the great whales – more krill is available as food for penguins
Penguin Adaptations
- They fluff their feathers to create trapped air in a dead space
- They have long feathers
- They rock back and forth on their heels on the ice to limit the area in contact with the ice and slow heat loss
- They can reduce blood flow to and heat loss from their wings and feet
- They exhibit “huddle” behavior – gathering in large groups and constantly changing position so that each gets a turn in the center, where it’s warmest
The first paragraph, by Keddy (University of California, Davis), is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts. Download this book for free at https://geo.libretexts.org/Courses/Diablo_Valley_College/OCEAN-101%3A_Fundamentals_of_Oceanography_(Keddy)
The rest was written by Dr. Cristina Cardona.