Diet and Foraging Behavior Flashcards
What is a seabird diet composed of?
- Fish
- Squid
- Invertebrates
What are foraging fish?
Pelagic schooling fish
Why are forage fish important to marine ecosystems?
They represent a link between primary and secondary producers as well as top predators
What are the three main habitats that seabirds forage in?
- Coastal
- Diving: exploit depths to gather food
- Pelagic: explore vast expanses of the ocean in search of prey at the surface
What are the four main feeding methods of seabirds?
- Aerial predators
- Pursuit divers
- Surface feeders
- Plunge divers
Describe aerial predators
Steel food from other birds (kleptoparasitism)
Describe surface feeders
Peck or grab prey items from at or below the surface (while sitting on the surface or on the wing)
Describe plunge divers
Dive from high altitude and utilize the momentum from the dive to move underwater
Describe pursuit divers
Pursue prey from substantial distance by swimming underwater (penguins)
Describe Phalarope spinning
- Spinning creates upwelling
- Prey items = drawn closer to the surface
- Only works in shallow water
When do seabirds feed?
- Daytime (most seabirds)
- Nighttime (Squid eaters ex: albatrosses, gadfly petals etc.)
- Dawn / Dusk (Common murres etc.)
Describe diel foraging patterns
- Refers to the vertical migration of prey
- Prey = down deeper in the day and closer to the surface at night
What is a possible cause of diel foraging patterns?
Prey species could be attempting to avoid visual predators at the surface during the day
Describe the foraging patterns of Red-legged Kittiwakes
- Forage at night on vertically migrating prey
- Surface feeders (feed on myctophids)
- Feed on prey when its closer to the surface
Why do species such as penguins not rely on diel patterns?
They are deep divers
What other factors drive the timing of foraging?
- Flood tides (more birds tend to forage during the ebb-tide)
- Breeding seasons (foraging trips = longer during brood-guard / chick rearing stages)
Why do many seabirds associate with sub-surface predators?
Sub-surface predators help drive prey to shallow depths
What seabird species are closely associated with sub-surface predators?
- Brown noddies
- Wedged-tailed shearwaters
How can we study what seabirds eat?
- Direct observation
- Studying what prey is brought back to the nest
- Examining stomach contents
- Tissue analysis (blood samples)
What are the pros and cons of direct observation of seabird diets?
Pros:
- Easily collected (bird must be in sight)
Cons:
- Only useful for surface feeders
- Expensive, labor intensive
- Small number of observations
What are the pros and cons of studying regurgitates?
Pros:
- Easily collected (when bird is present)
Cons:
- Biased (different prey types have different digestibility)
- Only recent diet is reflected in the sample
What are the pros and cons of studying prey that is dropped near the nest?
Pros:
- Provides information on recent diet
Cons:
- Biased towards larger spiny deeper bodied prey
- Contain high proportions of refused prey items
What are the pros and cons of studying prey that is carried in the bill?
Pros:
- You can estimate the size and mass of the prey item
Cons:
- Useful for identifying prey items fed to chick but not adults
- Relies on remote observation
What are the pros and cons of studying seabird stomach contents?
Pros:
- Can give detailed understanding of seabird diet
Cons:
- Biased towards prey with “hard parts”
- Only most recent prey items can be assessed
