SeabirdsLecture 10

Common Groupings of Marine Birds• Seabirds—e.g. penguins, pelicans, gulls, terns– Capable of feeding away from shore– Breed on islands or coastal zones

• Shorebirds—e.g. sandpipers– Feed on shorelines in sand/mud

• Wading birds—e.g. herons, egrets– Freshwater or marine– Marsh birds– Hunters

Seabird Diversity• 27 orders of birds—10,000 species– Four contain “true” seabirds

• Sphenisciformes—Penguins • Procellariformes—Albatrosses, Petrels• Pelecaniformes—Pelicans, Cormorants• Charadriiformes—Gulls, Terns

Representative Families

Family Sternidae: Terns—45 species• Slender, rapid wings• Smaller than gulls• Broad tail, often V-shaped• Feed on fish at surface• Many species highly migratory Royal Tern

Representative Families

Family Laridae: Gulls—56 species• Intelligent – Often adaptable to human

disturbance• Generalist carnivores– The least specialized of all seabirds

• More generalized morphology

Laughing Gull

Representative Families

Family Pelecanidae: Pelicans— 8 species

• Feed on fish at surface– Gular pouch on lower jaw

• One of the heaviest flying birds– Brown pelican is smallest species

Brown Pelican

Life History—Nesting • Generally occurs at inaccessible coastal areas– Isolated islands, cliff faces, coastal wetlands• Two reasons—

– Large nesting colonies– Adults return to natal area– Both parents involved with care

Life History—Offspring • Egg incubation 25-35 days• Fledging period 1-2 months• Juvenile seabirds often different plumage color– 4-5 years until maturity

Royal Tern Creche

Seabird Foraging—Gulls• Unhinging jaws—• Take live prey– Tool use• Baiting, breaking shells

– Plunge diving• Scavenging—• Kleptoparasitism—• Advantages of walking

ability?

Spring Summer Fall

% o

f die

t

Starfish

Mussels Crabs

Herring GullDutch Colony

Seabird Foraging—Terns & Pelicans• Plunge diving—pelicans

• Only two species dive• Impact on left side—• Impact may stun fish

– Pelicans may also feed from surface

– Air sacs beneath skin and in certain bones—

• Plunge diving—terns – Hovering

• Scavenging

Seabird Foraging—Terns

Seabird Foraging—other methodsNorthern Gannet

Dive from up to 100’Depth of up to 50’

Swim with wings/feet

Seabird Foraging—other methodsWilson’s Storm Petrel

Most abundant birdFeeds on inverts and small fish

Seabird Plumage Coloration• Generally drab coloration– White, black, gray, brown– Often countershaded

• Adaptive significance poorly studied—hypotheses?

• Wings shaped like airfoils— – Secondary feathers lift

• Primary feathers generate power—forward motion– Greater flexibility of motion• Connect to “hand” bones

– Large range of motion

Wing cross-section

Lift

Bird Wings—overview

Seabird Wings—high aspect ratio

Albatross

Grouse

Tern

Vulture

• Seabird wings not “slotted” to reduce drag• Extended secondary region increases lift• High apect ratio• Good for soaring (gliding)• Drawbacks?

Seabird Wings—high aspect ratio

Dynamic Soaring

Seabird Wings—High-speed wings

Albatross

Grouse

Tern

Vulture

• Streamlined• Greater proportion primary feathers• Good for sustained, high-speed flying• Hovering

• Energetically expensive

Seabird Osmoregulation• Nitrogenous waste Uric acid– Effective kidneys

• Salt Gland—• Many seabirds still require some freshwater• Pelagic seabirds months to years at sea

Seabird Conservation

• Loss of nesting habitat– Increased disturbance– Invasive species—nest predation– Oil spills

Seabird Conservation• Interactions with fishing gear– Long lines– Gill nets– Recreational entanglements

• Plastic pollution in ocean

Seabird Conservation—Success stories

Brown Pelican– Listed as endangered—1970• Delisted 2009

– DDT outlawed in 1972

Laughing Gulls• Nearly extirpated in U.S.• Late 1800s

• Plume hunters