Seabird Characteristic Page 2

Breeding - Colonies - Mate for Life- Site Fidelity
Food Gathering
Plumage
Water Intake

Gannet colony at Cape Kidnappers in New Zealand. Gannet colonies can be seen in Newfoundland and the Gaspe Peninsula. See Breeding Colonies for information on how to visit.

Breeding
Breed in Colonies
Ninety five percent of seabird species breed in colonies (Löfgren 4).

A seabird colony can be defined as a group of birds nesting in close proximity and finding their food outside the breeding area. The colony may consist of 10 pairs along a cliff ledge or thousands of pairs of birds. The picture above shows a large colony of
Gannets at Cape Kidnappers on the north island of New Zealand.

Despite the close proximity, Gannets defend a territory around the nest. You can see in this picture that the nest sites are evenly spaced.

Shearwater and Storm-petrels build their nests in underground burrows. The only evidence of a Short-tailed Shearwater colony in the day time are the burrow openings. An observer can tell it is an active shearwater colony and not just rabbit burrows by the smell.

Increased vulnerability to predators
Large colonies are vulnerable to attacks of predators. Leopard Seals patrol the shore near Penguin colonies and are assured that if the first bird gets away, they will have plenty of other chances. Tiger Sharks show up in the lagoon at Midway Atoll every year just when the baby Laysan Albatross are learning to fly. A fox will visit a colony regularly to obtain prey. Historically it was man that posed the greatest threats to seabirds in colonies stealing eggs, meat and even boiling seabirds to render the fat into useable oil. Most seabird colonies today are protected from men if not from their domestic animals.

Most seabird colonies are near the sea
While it seems only logical that seabirds would breed near the sea, the Snow Petrel may breed 200 miles inland and the Marbled Murrelet nests only in old growth forests. Jaegers and Skuas breed on the tundra usually near colonies of kittiwakes, penguins, or puffins on which they prey.

Mate and Site Fidelity
Seabirds in general return to the site where they were raised to breed and raise their young. Once they start breeding at a site they return year after year to the same place and often breed within feet of where they bred the year before. When a colony becomes too large, individuals may prospect a new colony site.

Site fidelity supports monogamy and pairs tend to remain together as long as both live. Mate fidelity requires elaborate bonding rituals such as the dances performed by the Albatrosses. Since the birds depart the breeding grounds and roam the seas as singles, returning to the same site is necessary to re-establish pair bonds.

Pomarine Jaegers feed exclusively on lemmings during the breeding season and are an exception to the rule that seabirds show site fidelity and mate for life. Lemming populations fluctuate from year to year, but there are always places with large populations. A male Pomarine Jaeger will find a territory with sufficient lemmings and wait for a mate of opportunity much like the more familiar land birds.

Why colonies?
The main advantage of colonial breeding for seabirds seems to be that it provides an opportunity for finding a suitable mate and for meeting up at the start of the breeding seasons for established pairs. This is important to birds that spend up to 95% of their life roaming the sea.

Young unmated birds return to their natal colony after several years to find and bond with their life partner. The colony can be compared to a singles bar or a college campus.

After spending up to four years roaming the sea, young adult Albatrosses like these Laysan Albatross return to the natal colony. Here they work to find a mate.

Pair bonding is accomplished by performing elaborate dances. The Albatross on the left is performing the under the wing preen while the one on the right is standing at attention.

This was photographed on Midway Atoll by Emmalee Tarry. The dance of the Albatross is one sight all birdwatchers should see in person.

After forming a pair bond, the mates return to the sea. They return the following years at the start of the breeding season to meet up and renew their bond. Albatross spend only a few minutes together before copulating. Then both return to the sea separately. The female returns to lay a single egg. The male returns shortly after and takes the first incubation shift while the female returns to sea to feed and rebuild her body after laying the egg. Thereafter they take turns incubating, brooding, and guarding the chick until the chick is several weeks old. The chick is then left on its own while both parents go to sea to feed. Mated pairs spend very little time together during their entire life time.

Disruption of a breeding site has serious consequences. Mated pairs return annually to their nesting site to meet up. What happens if a bird returns to the site to find it has been turned into a new hotel?

Food Gathering
Depend on the Sea For Food
It seems only logical that seabirds would find their food in the ocean even during the breeding period and most do.

Many seabirds are scavengers feeding on dead whales, squid and fish. This leads many seabirds to follow ships and fishing boats. One of the main reasons that seabird populations are declining so rapidly is that scavenging seabirds are accidentally caught by fishing hooks and nets. This is called the bycatch.

Dependent on the sea for food they are not helped by the depletion of fish stocks. Albatrosses are especially sensitive to the increased fishing for squid. Humans can live without squid. Boycott!

Pomarine Jaegers breed on the arctic tundra and depend on lemmings for their primary food source while breeding. Other Skuas and Jaegers also hunt lemmings, but can use other prey in years when the lemming population crashes. All skuas and jaegers except the Pomarine Jaeger exhibit mate and site fidelity. There are always sufficient populations of lemming in the arctic, but not always in the same place. The Pomarine Jaeger male must first locate a territory with sufficient lemmings and then attract a mate. In this the Pomarine Jaeger is more like land birds.

Most seabirds rest on the water, but not all are able to dive under the water to pursue food or to escape predation. Notable examples of birds that do not usually dive are Storm-petrels, Skuas, Jaegers, and Gulls. Frigate birds do not even rest on the water.

Seabirds that dive include: Alcids, Ducks, Gannets, Terns, Shearwaters. Albatrosses can dive down as a far as 1 meter. If all the fishing boats called Long-Liners which fish by trailing long lines with hooks behind the boat would use a simple device that keeps the line in a tube until it is at least 2 meters under the water, the accidental bycatch of Albatrosses could be eliminated. The fishermen would profit by not losing bait to unwanted prey.

Feeding Habits

Plunge Diving
Some birds, most notably the Northern Gannet make spectacular dives into the water from the air. Terns are also known for plunge diving.

Surface Diving
The bird dives while sitting on the water. Typical of Shearwaters, ducks, grebes, and Alcids. Shearwaters are know for putting their head under water to look for food before diving.

Pursuit Dives
Alcids, loons, grebes and ducks pursue fish underwater. Alcids use their wings to fly through the water while the others paddle with their legs. These birds make extended dives and may resurface some distance from where they went down.

Surface Picking
The bird picks food from the surface of the water. Some birds like Storm-petrels do this while flying or on the wing. Others birds (Phalaropes) only pick up food only while sitting on the surface. Wilson's Storm-petrel is known for pattering on the water while picking up food.


Kleptoparisitism
Some seabirds are pirates stealing food from other seabirds. Gulls, terns, skuas, jaegers, and frigatebirds are good at pirating food from other birds. The pirate usually harasses the bird with food until it drops the food whereupon the pirate will capture the food in the air or from the surface of the water.

On Midway Atoll, the author witnessed an amazing example of Kleptoparisitism by Great Frigatebirds. A large fish drove a school of smaller fish toward the shore and they were washed onto the beach by a wave. As the fish flopped around on the sand trying to get back in the water about 6 Great Frigate-birds began swooping down to the beach to capture the fish in their beaks. They were very inefficient and on most passes missed the fish. When one bird got a fish, the other Great Frigatebirds immediately began to harass the lucky winner. As a group of enchanted birders watched all the commotion, most of the fish were dropped back into the sea.

Take Food Back To the Young
Feeding the young birds back at the nest is a big problem for seabirds. Many seabirds must fly long distances to find enough food and then carry the food back to the nestlings.

Black-footed Albatross regurgitates food to chick on Midway Atoll.

Regurgitate
The most efficient way to carry food long distances is to swallow it into the intestine and then regurgitate into the chick's mouth.

The chick of a Black-footed Albatross pecks on the parents bill to induce regurgitation. Photographed on Midway Atoll by Emmalee Tarry

A Puffin bringing 5-6 small fish back to its burrow is an endearing sight, but not typical of seabirds. This behavior makes the Puffin easy prey for the kleptoparisitism of jaegers and skuas.

Plumage

Black, White and Brown
Seabirds are not very colorful. Most plumages are combinations of black, white and brown. Most seabirds do not exhibit a difference in plumage between males and females. Seaducks, phlaropes and frigatebirds are exceptions to the later.

White below dark above
Most seabirds and marine animals have light underparts. When viewed from below by a predator like a shark, the body is back lighted and blends in with the light. The same is true of most animals that live in the sea including whales, seals, and sharks.

To avoid predators, marine animals are usually dark on top. When the animal is viewed from above, the dark color blends in with the dark background.

There are some notable exceptions including all dark shearwaters, Sooty, Light-mantled Sooty and Black-footed Albatross.

Razorbill photographed on Machias Seal Island by Emmalee Tarry

The Razorbill exhibits typical seabird plumage; white below, black above.

Color Accents for Breeding Plumage

Atlantic Puffin has colorful bill in breeding plumage

Some seabirds exhibit colorful feathers or body parts during breeding.

The Atlantic Puffin has a colorful bill in breeding plumage. The colored part sloughs off after breeding leaving a smaller dull bill. Rhinoceros Auklet also has a colorful bill which shows that it is more closely related to Puffins than to Auklets.

Some penguins and auklets have colorful feathers on their heads.

Adult Gannets have golden heads as do the Stellar's and Galapagos Albatrosses.

Water Intake
Salt Glands
One of the big problems man has at sea is his inability to drink seawater because of the high salt content. Seabirds do not drink seawater, but rather get water from their food and ingest water with their food accidentally. They must have a mechanism to remove the excess salt.

Many seabirds have special salt excreting glands on the top of their heads .

The birds known as Tubenoses have these glands drain through separate tubes on top of the bill. In the photograph of the Northern Fulmar by Jim Besada the tube is clearly seen on the top of the bill.

In other seabirds the glands drain through the nostrils. There is no apparent advantage to having the separate tubes.

Birds That Require Fresh Water
Gulls do not have salt excreting glands and must drink fresh water. While standing on the cliffs at Rathlin Island in Northern Ireland, I watched an impressive stream of Kiitwakes flying through a wash to drink from a small lake.

Small fresh water ponds on Skommer Island built to provide water for cattle attract gulls which then prey on the Manx Shearwaters nesting on the island.

What Is A Seabird

Page author: Emmalee Tarry