Feeding

1
Feeding

• Surface feeding while flying (sometimes with
  pursuit plunging)
• 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.

2
Feeding

• Surface feeding while swimming (sometimes with
  pursuit-diving)
• Feed by sitting on the surface or forcing
  themselves slightly below
• Albatrosses and Shearwaters
• 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.

3
Feeding

• Plunge diving- could be truly deep divers, or
  merely surface
• Deep plunge divers Gannets and Boobies
• Heavy birds, they may begin dive with either wing
  beats, or just falling. 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
• Pouch opens rapidly to surround the fish, while
  the upper mandible closes rapidly
• Pouches hold 10liters of water (3 gallons)

4
Feeding

• Diving from the surface and underwater pursuit
• Difficult to fly well in air and in the
  waterPuffins, Auks, Guillemots,
• 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
• 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

5
Feeding

• 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.

6
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.

7
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.

8
Notes on Migration

• 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.

9
Navigation

• Visual Landmarks
• Used first and foremost
• Follow watercourses, coastlines and mountain
  ranges
• Causes birds to be funneled by bays, channels
  and straits
• Solar Compass
• Use the position of the sun as a mark by which to
  set their path. When its 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.
• Dont know if nocturnal birds compensate for the
  movement of stars over time.

10
Navigation

• Olfaction
• Olfactory clues supplement other navigation
  systems
• 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 birds orientation relative to these fields.
• Internal Maps
• A compass isnt 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.