Seabird Behavior

  • Feeding
  • Some adaptations revisited
  • Shorebirds- Beak type and length corresponds to food preference
  • Methods- Seabirds are adapted to the density and distribution of prey as well as the capture and handling of that prey
  • Surface feeding while flying (sometimes with pursuit plunging)
  • Used by small and aerially agile seabirds
  • Petrels, Storm Petrels, Frigatebirds, and Terns
  • Storm Petrels
  • Flit back and forth, lowering the feet and pattering the surface of the water, and dipping the head down to feed on zooplankton and small fish.
  • Frigatebirds
  • Skim the surface at full speeds and a downbent head, plucking food from the surface layer, a method facilitated by their long neck and long, sharply hooked bill.
  • Terns
  • Pick off fish or squid that are running away from larger predators, either by pattering, plunging or catching flying fish in the air.
  • Surface feeding while swimming (sometimes with pursuit-diving)
  • Feed by sitting on the surface or forcing themselves slightly below
  • Albatrosses and Shearwaters
  • Albatrosses
  • Feed mainly on fish, squid, cuttlefish, crustaceans and offal, but also eat jellyfish.
  • Usually feed at night by dipping their heads into the water, though they sometimes plunge dive. They feed at night because many fish and zooplankton surface at night.
  • Nomadism allows these birds to take advantage of rich, but widely separated food sources.
  • Shearwaters
  • Feed while swimming at the surface, but they all dive in order to catch prey.
  • Mostly feed in the dim light
  • Plunge diving- could be truly deep divers, or merely surface
  • Deep plunge divers = Tropicbirds, Gannets and Boobies
  • Gannets
  • Heavy birds, they may begin dive with either wing beats, or just falling
  • Wings held at an angle during the plunge
  • Go at most 10 meters deep and last for less than 10 seconds.
  • Air sacs cushion against the impact and occluded nostrils prevent water up the nose
  • Shallow plunge divers= Brown pelican
  • The plunge looks very awkward, but is expertly controlled, with neck bent back over the shoulders.
  • Pouch opens rapidly to surround the fish, while the upper mandible closes rapidly
  • Pouches hold 10liters of water (~3 gallons)
  • Diving from the surface and underwater pursuit
  • Difficult to fly well in air and in the water=Puffins, Auks, Guillemots, Penguins
  • Penguins
  • Feed mostly on fish, squid and crustaceans found at the surface
  • When traveling large distances, King Penguins ‘porpoise’ through the water, traveling 3-4 m in the air and 6-12 underwater
  • Emperor penguins can diver for up to 9 minutes to depths of 265m
  • Better divers than mammals because they carry more oxygen in their blood.
  • Good divers and flyers tend to be big and use feet as well as wings for propulsion= Cormorants and Shags
  • Cormorants
  • Water absorbent feathers reduce buoyancy and help with diving.
  • Forage singly or in loose groups, rarely diving deeper than 10m for 3 to 4 minutes
  • Eat mostly fish, but will also eat freshwater crustaceans, insects and tadpoles
  • Forage within 8 to 16 km of home
  • Scavenging and Piracy-Less important and usually only used as a supplement to regular foraging
  • Classic scavengers- gulls (Herring Gulls), Fulmars and Gannets
  • Feed on leftovers, either human or from other feeders
  • Usually strenuous competition amongst scavengers
  • Pirates- Skua, Frigatebirds, Terns
  • Attack other birds in order to steal their food. May also attack and feed on the young.
  • Frigatebirds and Skuas circle above their victims and then surprise them by dive-bombing.
  • Migration
  • A clear, seasonal shift in the center of a population from locality A to B and back again. It is different from dispersal and nomadism. Usually one location is a breeding area and the other is only a feeding area.
  • Dispersal- Movement is more random and preference for a particular location is weak.
  • Nomadism- Birds keep moving, perhaps randomly, as an adaptive response to covering vast areas.
  • True Migration vs. Continuous Migration
  • True Migration-
  • Breeding area empties and refills next breeding season.
  • Migration along fixed route, usually rapid and extensive
  • Continuous Migration-
  • Birds leave breeding area on a migration so extensive that most of the period between then and the return next breeding season is spent following the variably fixed migration route.
  • Seabirds migrate in order to utilize seasonally abundant food sources.
  • In a-seasonal environments (e.g. the Mediterranean) migration is not necessary
  • Migrants tend to always return to the same breeding and winter grounds year after year, though eruptions do occur.
  • Eruption- a mass emigration to areas not normally reached, depends on conditions at the time such as food shortages.
  • Migrants may, or may not, feed en route.
  • The greater the distance of migration, the greater the tendency for a quick migration, with few stops along the way.
  • Navigation
  • Visual Landmarks
  • Used first and foremost
  • Follow watercourses, coastlines and mountain ranges
  • Causes birds to be ‘funneled’ by bays, channels and straits
  • Example: Strait of Gibraltar, Cape May, NJ
  • Solar Compass
  • Use the position of the sun as a mark by which to set their path. When it’s cloudy birds tend to just wander randomly.
  • The position of the sun in the sky changes 15 degrees/hr, so the solar compass must be time compensated, i.e. they can keep track of the time.
  • Stellar Compass
  • Nocturnal birds use stars to navigate instead of the sun.
  • Don’t know if nocturnal birds compensate for the movement of stars over time.
  • Olfaction
  • Olfactory clues supplement other navigation systems
  • Not all birds use smell for navigation all of the time
  • Petrels and pigeons can smell their way back to their nests
  • Geomagnetism
  • The geomagnetic fields of the Earth provide a map of horizontal space, just as gravity and barometric pressure give information about vertical space. The intensity and dip angle- or inclination of the magnetic field-change with latitude in ways that provide reliable, omnipresent information about geographical position.
  • Special photoreceptors appear to be sensitive to a bird’s orientation relative to these fields.
  • Internal Maps
  • A compass isn’t enough to get you home. You need a map to which you can apply it.
  • A bird must know its own position relative to its goal.
  • It is not known how birds solve this problem.