The special problems of bird digestion
• High metabolic rate!– Digestive system must be efficient but
lightweight• Hence, most can’t afford a lot of heavy anatomy.
Meta
bolic R
ate
Sb
Birds
Mammals
Ectotherms
• Gannets conserve energy while feedingVideo
Entering water about 2.9m/s (not much deceleration)
Diving between <1-10m (passive momentum to surface – sometimes aided by wing or foot movement)
Retention time (in hours) for fluid & particulate digesta markers in the gastrointestinal tracts of representative reptiles, birds, & mammals (Based on: Stevens and Hume 1998).
Species Body massFluid retention
time Particle retention
time
Iguana - <48 207
Broad-tailed Hummingbird1 3.3 gm 1.2 -
Rock Ptarmigan 460 gm 9.9 1.9
Sooty Albatross 2.5 kg 6.3 15
Rockhopper Penguin 2.5 kg 3.8 17
Emu 38 kg 3.9 4.7
rabbit 2.1kg 39 27
pig 176 kg 39 48
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
• Multiple functions…
http://www.naturalhistorymag.com/master.html?http://www.naturalhistorymag.com/0904/0904_biomechanics.html
Bristles• Function
– Protect eyes– Increase gape width in insectivores
• Usually coupled with wide bill Hooded warbler bristles
American redstart
Morphology CCA 1
-2 -1 0 1 2
Att
ack
CC
A 1
-1
0
1
2
3
n
nn
n nn
n
nnn
nnnn
n
n
o
oo
o
o
oo
Morphology Contrasts CCA 1
0 1 2 3
Att
ack
Co
ntr
asts
CC
A 1
0
1
2
3
nn n
n
n
n
nn
n nno
oo
o
o
a.
b.
Pounce
Sally
HG
R2 = 0.8*
R2Cont = 0.9*
Longer TarsusWider bill
SA (“o”) and NA (“n”) Flycatchers
Morphology CCA 1
-2 -1 0 1 2
Att
ack
CC
A 1
-1
0
1
2
3
n
nn
n nn
n
nnn
nnnn
n
n
o
oo
o
o
oo
Morphology Contrasts CCA 1
0 1 2 3
Att
ack
Co
ntr
asts
CC
A 1
0
1
2
3
nn n
n
n
n
nn
n nno
oo
o
o
a.
b.
Morphology CCA 1
-2 -1 0 1 2
Att
ack
CC
A 1
-1
0
1
2
3
n
nn
n nn
n
nnn
nnnn
n
n
o
oo
o
o
oo
Morphology Contrasts CCA 1
0 1 2 3
Att
ack
Co
ntr
asts
CC
A 1
0
1
2
3
nn n
n
n
n
nn
n nno
oo
o
o
a.
b.
Pounce
Sally
HG
R2 = 0.8*
R2Cont = 0.9*
Longer TarsusWider bill
SA (“o”) and NA (“n”) Flycatchers
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
Tongues
Am. Robin (generalized)
Bananaquit (tubular - nectarivore)
White-headed Woodpecker (spear/probe)
Trogon (muscular frugivore)
Shearwater (fish eater)
N. Shoveler (food-strainer)
Golden-fronted WP
Detailed view of the horny tip (below) of the Guadeloupe Woodpecker tongue in vivo position (Villard and Cuisin 2004).
Oral Cavity
• Taste buds
• May be modified anatomically based on diet
– Fringes of anseriformes • Inter-digitates with tounge frills
– Ridges of finches and blackbirds
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
vocal
BLNI
Crop
• Expanded portion of the esophagus• Stores, softens foods• Regulates food flow through digestive tract• May become greatly modified for fermentation
– Kakapo– Hoatzin
keelcrop
Stomach
1. 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
Stomach (cont.)
• Gizzard– Posterior– Muscular (analogous to mammalian molars)– Keratinized– Grinding– Reverse
Peristalsis
“re-treat” food
Red KnotsAerts Island, Canada
(Morrison et al. 2005 - Condor)
Time period after arrival at breeding grounds
Diet – molluscsBody mass decreasesDigestive organ mass increases
Intestine
• Chief organ of digestion and absorption
• Receives bile and pancreatic secretions
• Small and large intestine
• Length related to assimilation efficiency
EA = assimilation/ingestion X 100
omnivorecarnivore
herbivores
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
Cloaca• Receives
– Wastes from digestive– Materials from other systems:
• Reproductive• Urinary
• 3 main divisions1. Corprodaeum – waste from intestines2. Urodaeum – N waste (uric acid) and sperm/eggs3. Proctodaeum – ejection site – closed by anus
• Bursa of Fabricus– Dorsal wall of cloaca in young birds– Site of B-lymphocyte production– Atrophies with age
Accessory Organs
• Liver– Hormone and bile production– Filter toxins
• Pancreas– Exocrine: Produces digestive secretions– Endocrine: Insulin and glucogon (islets)
• Regulates blood sugar levels
Feeding Behavior and Energy Balance
• Influenced by:
– Anatomy (morphology)– Food availability– Decisions…
– Search/locating, attack (pursuit), handling, assimilating/digesting conversion
aspects of the behavior
Profit = Energy Gain – Energy Cost
Foraging Time
Searching behavior also an example of a form-function relationship…
• Search time can be predicted by morphology – WHY?
Body Size
0
0.5
1
1.5
2
2.5
1.1 1.2 1.3 1.4 1.5 1.6
PC2
0
0.5
1
1.5
2
2.5
-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4
PC4
0
0.5
1
1.5
2
2.5
-0.1 -0.05 0 0.05 0.1
Tarsus Length
0
0.5
1
1.5
2
2.5
-0.3 -0.2 -0.1 0 0.1
Morphology
Sea
rch
Tim
e (l
og10
sec)
Body Size
0
0.5
1
1.5
2
2.5
1.1 1.2 1.3 1.4 1.5 1.6
PC2
0
0.5
1
1.5
2
2.5
-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4
PC4
0
0.5
1
1.5
2
2.5
-0.1 -0.05 0 0.05 0.1
Tarsus Length
0
0.5
1
1.5
2
2.5
-0.3 -0.2 -0.1 0 0.1
Morphology
Sea
rch
Tim
e (l
og10
sec)
Bigger the bird the longer the search time
Longer legs = shorter search times
Corbin 2002
Searching position
• Related to familiar food– Why would a bird search in particular places
or for particular food items?
s.i. III
Prey abundance
# of
pre
y ta
ken
satiation
• When to give-up searching?
– Searching specialists– Searching opportunist
Searching position
Profit = Energy Gain – Energy Cost
Foraging Time
O.F.T. – centered on adjustments
Chickadees eating mealworms in the lab
Aerial hawkerreturning to perch
Poor habitatRich habitat
Chick provisioning questions
Habitat quality
Tim
e aw
ay
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 doesn’t attempt a capture within a certain timeframe, it will move to a different perch.
Corbin and Kirika 2002
Search time
White wagtailsPrey size reflects “optimal” decision making
Prey available
Prey taken
Prey handling efficiency
Handling Time