Digestion and Food Habits

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Digestion and Food Habits
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The special problems of bird digestion

• High metabolic rate!
• Digestive system must be efficient but
  lightweight
• Hence, most cant afford a lot of heavy anatomy.

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• Gannets conserve energy while feeding
• Video
• Entering water about 2.9m/s (not much
  deceleration)
• Diving between lt1-10m (passive momentum to
  surface sometimes aided by wing or foot
  movement)

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General Overview
Carnivore mammal
Herbivore mammal
No teeth Limited jaw musculature
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• A few muscles control a lot of jaw movement

Position of the depressor mandibulae
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Retention time (in hours) for fluid particulate
digesta markers in the gastrointestinal tracts 
of representative reptiles, birds, mammals
(Based on Stevens and Hume 1998).

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General Overview (cont.)

• Alimentary Canal
• Oral cavity
• Esophagus
• Crop
• Proventriculus
• Gizzard
• Small Intestine
• D, J, I
• Cecum
• Large Intestine
• Cloaca
• Accessory Organs
• Beak
• Salivary Glands
• Liver
• Pancreas

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• Bill Morphology
• Bony structure
• keratin

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//www.naturalhistorymag.com/0904/0904_biomechanics
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• Multiple functions

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Bristles

• Function
• Protect eyes
• Increase gape width in insectivores
• Usually coupled with wide bill

Hooded warbler bristles
American redstart
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Tongue

• Functions
• Aids in gathering and swallowing food
• Usually no tastebuds on dorsal surface
• Epithelium of mandibles
• Not muscular (xs) but reinforced by the hyoid
  apparatus
• Morphology of the avian tongue varies with food
  habits
• How much processing must be done?
• What kind of processing is done by the tongue?
• Fish-eating species
• typically have small, undifferentiated tongue
• fish are often swallowed whole
• Woodpeckers
• long, extensible
• Barbed at tip

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Tongues
Am. Robin (generalized)
Bananaquit (tubular - nectarivore)
Trogon (muscular frugivore)
White-headed Woodpecker (spear/probe)
Shearwater (fish eater)
N. Shoveler (food-strainer)
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Golden-fronted WP
Detailed view of the horny tip (below) of the
Guadeloupe Woodpecker tongue in vivo position
(Villard and Cuisin 2004).
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Nectarivores
Distal tip
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Oral Cavity

• Taste buds
• May be modified anatomically based on diet
• Fringes of anseriformes
• Inter-digitates with tounge frills
• Ridges of finches and blackbirds

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Esophagus

• Features
• Connects oral cavity and stomach
• Larger, Muscular (peristalsis), expandable
• Lined with mucous glands
• Nutritive food production
• Sloughed epithelial layers
• Inflatable
• Visual cues
• Sound production

BLNI
vocal
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Esophagus

• Mucous Glands

mammalian
avian
lumen
lumen
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Crop

• Expanded portion of the esophagus
• Stores, softens foods
• Regulates food flow through digestive tract
• May become greatly modified for fermentation
• Kakapo
• Hoatzin

crop
keel
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Stomach

• Proventriculus glandular stomach
• anterior
• receives food from the esophagus
• secretions
• Mucus
• HCl
• Pepsinogen HCl ? Pepsin (proteolytic enzyme)
• Can dissolve bone rapidly
• Petrels - Oil by-product storage
• Nutrition
• defense

Band-rumped storm petrel
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Stomach (cont.)

• Gizzard
• Posterior
• Muscular (analogous to mammalian molars)
• Keratinized
• Grinding
• Reverse
• Peristalsis
• re-treat food

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Red KnotsAerts Island, Canada(Morrison et al.
2005 - Condor)
Diet molluscs Body mass decreases Digestive
organ mass increases
Time period after arrival at breeding grounds
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Frugivore stomachs
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Intestine

• Chief organ of digestion and absorption
• Receives bile and pancreatic secretions
• Small and large intestine

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• Length related to assimilation efficiency
• EA assimilation/ingestion X 100

omnivore
carnivore
herbivores
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Large intestine

• Relatively short
• Absorb water
• Contains out-pocketings (caeca)
• Some species histologically similar to rest of
  intestine
• Symbiotic bacteria/fungi, lymphatic activity
• Others lymphoid caeca lymphatic only

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Cloaca

• Receives
• Wastes from digestive
• Materials from other systems
• Reproductive
• Urinary
• 3 main divisions
• Corprodaeum waste from intestines
• Urodaeum N waste (uric acid) and sperm/eggs
• Proctodaeum ejection site closed by anus
• Bursa of Fabricus
• Dorsal wall of cloaca in young birds
• Site of B-lymphocyte production
• Atrophies with age

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Accessory Organs

• Liver
• Hormone and bile production
• Filter toxins
• Pancreas
• Exocrine Produces digestive secretions
• Endocrine Insulin and glucogon (islets)
• Regulates blood sugar levels

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Feeding Behavior and Energy Balance

• Influenced by
• Anatomy (morphology)
• Food availability
• Decisions
• Search/locating, attack (pursuit), handling,
  assimilating/digesting conversion
• aspects of the behavior

Energy Gain Energy Cost
Profit
Foraging Time
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Searching behavior also an example of a
form-function relationship

• Search time can be predicted by morphology WHY?

Bigger the bird the longer the search time
Longer legs shorter search times
Corbin 2002
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Searching position

• Related to familiar food
• Why would a bird search in particular places or
  for particular food items?

s.i. III
satiation
of prey taken
Prey abundance
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• R. MacArthur 1959

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Searching position

• When to give-up searching?
• Searching specialists
• Searching opportunist

O.F.T. centered on adjustments
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Search Time
Poor habitat
Rich habitat
Aerial hawker returning to perch
Chickadees eating mealworms in the lab
Chick provisioning questions
Time away
Habitat quality
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Search time

• Give-ups are always longer than attempts. Or, at
  any given perch the attempt time is shorter than
  the give-up time. Hence, this suggests a
  threshold whereby if a kingfisher doesnt attempt
  a capture within a certain timeframe, it will
  move to a different perch.

Corbin and Kirika 2002
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White wagtails Prey size reflects optimal
decision making
Handling Time
Prey available
Prey taken
Prey handling efficiency
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Attack and/or Foraging Time

• Related to foraging strategy

Attacking
Searching
Sit-and-wait
Active
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• Depends upon
• energetic payoff

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• Is also related to morphology (past lecture
  material)