Chapter 5: Seabirds
Classification of Sea Birds
| Kingdom | Animalia |
| Phylum | Chordata |
| Class | Aves |
Orders Families |
Sphenisciformes |
Characteristics of Seabirds
All birds are Endothermic (warm blooded), covered with feathers, have
wings (of some size), beaks, and claws. Seabirds make their
living on the open ocean. Some seabirds like the Laysan Albatross (pictured on top) are extraoridary flyers.
When juvenile albatross take
flight for the first time they may not set foot again on land until the
reach reproductive maturity (as many as 10 years later). Other
seabirds like penguins and flightless cormorants have competely lost the ability to fly in order to become better swimmers.
Most seabirds only come to land to breed. Prime breeding locations are often
remote islands and cliff sides that were historically free of predators. They form dense breeding colonies, with hundreds or thousands of birds packed together in a small area. Almost all
species of seabird lay one or two eggs with both parents assisting in feeding the chick. Many seabirds, like the Waved Albatross or the Christmas Frigatebird have elaborate courtship rituals.
Seabirds are long-lived (e.g., Albatross >80 yrs) and are late to
reach reproductive maturity. Seabirds are distinctively different
from shorebirds like the Phalarope that feed and nest on the shoreline. Most sea birds are some
combination of white, black, and grey colors. Brighter colors may
apear on males during the breeding season, but the drab colors make
seabirds less visable to their prey underwater. (image is a Yellow Legged Gull, from Wikipida Commons)
- Click to see an impressive slideshow of sea birds, narrated by sea bird expert Theodore Cross.
Seabird Feathers
Feathers are one of the defining characteristics for all birds. There are several types of feathers. Contour feathers are large feathers used in flight. They can be highly modified in diving birds like penguins or auks. Downy feathers are short soft and fluffy. They serve to insulate a bird against the cold. Downy feathers have a fantastic ability to trap air. It is for this reason, that we like to make winter coats from downy feathers. Powder feathers are used to repel water. They are often coated in a thin layer of oil that helps to keep the other feathers dry. In order to maintain this oil layer, sea birds must regularly preen their feathers. This behavior also cleans the feathers and helps to maintain their insulative value. Most sea birds are shades of white and black. They may appear drab, but the colors help them hide from both predators and their prey. However, most will develop seasonal breeding colors that can be bright reds, oranges, and yellows.
- Click to see a bird Preening its feathers. (Image is from wikipedia commons)
Seabird Systems
Seabirds have a high metabolic rate. Birds don't have the advantage of size, like many marine mammals. In combination with downy feathers, it is their high metabolism that helps keeps them warm. Birds must maintain warmth in order to fly. Much like an athlete trying to perform before they have properly warmed up, cold birds often struggle to fly. Se birds also have, a one direction flow four chambered heart, much more like mammals than their closest relatives the reptiles. Four chambered hearts are very efficient at delivering oxygen.
The bones of seabirds are hollow. This makes them both very strong and lighter in weight than mammal bones. The image to the left is a scanning electron microscope (SEM) image of bird bone.
Seabirds primarly drink salt water. This would quickly kill you and I, but seabirds have special glands to help them remove excess salt. The excretions from these glands at the nasal cavities, looks like a white "snot" but is almost pure salt.
Most seabirds will take huge migrations. In fact the migration of the Arctic Tern, is the longest migration of any species on Earth. As such seabirds have excellent eye sight but they are also aided by a special "sixth sense" that allows them to sense magnetic fields. They use this sense like a compass. This combination of eye sight and magnetic field detection helps them to navigate over long distances and return to the same breeding colonies where they were born. (image credit: Steve Gschmeissner/ Science Photo Library)
Feeding
Surface Feeders collect items of food floating or swimming at the surface. Click to see a Sooty Shearwater demonstrate surface feeding.
Plunge divers will fall from impressive heights and dive into the water to obtain food swmming below the surface. Click to see a group of Gannets plunge into the water to capture prey.
The term pursuit divers is given to birds like Puffins or penguins that use their wings and feet to fly or swim underwater.
Scavengers are birds like Skuas, Gulls and Frigatebirds that feed largely on the wing, stealing the food or chicks of other birds.
Issues in seabird conservation
Almost all seabirds lay their eggs on islands or in cliff sides. Historically, these were locations safe from nest predators. However, the introduction of non-native species (many of which are nest predators) has become the leading cause of sea bird decline. Introduced cats, rats, and (in Alaska) foxes have devastated many sea bird breeding colonies. Click on the links below to read or watch more.
- Introduced foxes transform Alaskan islands from lush grassland to tundra
- Video of introduced mice eating an albatross chick
Unintended by-catch of sea birds by fishing vessels has become a big problem for lots of sea bird species. Sea birds often follow long lining boats trying to pull bait off of hooks, inevitably many birds catch themselves on the hooks are dragged down into the depths and drown. Efforts have been made by the Alaskan longlining fleet to reduce bycatch. Simple technical changes called streamer lines that scare birds away from hooks have been very successful. Click on the link to read more.
Plastics are increasingly a big problem for sea turtles and birds. Surface feeders, in particular, frequently ingest plastics causing gut and bowel obstructions. Many species may also get plastics caught
around their necks leading to suffocation. It has been estimated by researchers that there are 6 lbs of floating plastic garbage for each pound of surface zooplankton
in the North Pacific central Gyre. (Slide show of floating plastic debris in the Pacific)
"I often struggle to
find words that will communicate the vastness of the Pacific Ocean to
people who have never been to sea. Day after day, Alguita was the only
vehicle on a highway without landmarks, stretching from horizon to
horizon. Yet as I gazed from the deck at the surface of what ought to
have been a pristine ocean, I was confronted, as far as the eye could
see, with the sight of plastic."... Charles Moore in "Natural History" 2003 (full text of article online, image is from the article)
Questions to Research
- Bird feathers are a wonder. Make a sketch of a contour feather (showing its leading and trailing edge) and a downy feather. While downy feathers make great insulation, most sea bird's legs are bare. How do they keep bare legs from freezing? Click on the link and describe how they do it.
- Watch some of the video clips in the feeding section. Write a brief description for each style of sea bird feeding.
- Using the flashcards section of The Seabirds of Cook Inlet, briefly describe one member of each of the four major orders of seabirds that resides in Cook Inlet.
- The wanderings of tagged pacific seabirds, this website provides information from researchers who have been tagging sea birds to see where they go. Once there, click on the article about black footed albatross. Explain what you have learned about the tagging of these birds and the migrations that they make.
- Go back to the map showing the tagged birds. Observe the map as it goes through one year. Can you tell what month these birds nest? Where do they go to feed when they are not nesting?
- Explain the differences in bone density and wing shape between a bird that uses a diving or plunging feeding style verses a bird that feeds at the surface.
- Read the preface to the book "Living on the Wind: Across the Hemisphere with Migratory Birds" by the great ornithologist Scott Weidensaul. In it he says, "Bird migration is the one truly unifying natural phenomenon in the world, stitching the continents together in a way that even the great weather systems, which roar out of the poles but fizzle at the equator, fail to do." From the preface, provide three examples of these epic migratory journeys that stitch together our continents.
- Click on the article about introduced species. Read the article.
- Explain how seabirds disappeared on many of the Aleutian Islands
- Explain what impact seabird extinction had on those islands.
- Finally, explain in your own words what this quote by Don Croll (about halfway through the article) means. "The terrestrial ecosystem was being subsidized by marine-derived nutrients, and the foxes basically cut off the subsidies by interrupting the flow of nutrients coming from offshore, It transformed the plant community from one that does well in nutrient-rich conditions to one that does well in nutrient-depleted conditions."
- Longline fishing is generally considered to have a low bicatch rate. However, in the 1980's it was discovered that longlining was killing thousands of seabirds each year. Birds follow boats, and attempt to grab bait off of hooks when they are thrown overboard. Many catch themselves on the hooks and they drown. Click on the article about sea bird death through longline fishing. Identify particular types of seabirds that are most at risk from longlining, and explain ways in which longlining could be made less dangerous for seabirds.
- Suggest a one sentence caption for the picture in the "plastics" section above. Then read the article and describe how death by plastic can occur in seabirds.