Professor Rolland Merch M. Arriza
Mindanao State University – General Santos City
such as insects,
seeds, fruits, and
digestive system is
energy from small
amounts of food at
a rapid rate.
Figure 1: Internal Organs of a Typical Chicken
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The beak, bill, or rostrum is an external anatomical structure of birds which is used for
eating and for grooming, manipulating objects, killing prey, fighting, probing for
food, courtship and feeding young
Beak - Swiss Army Knife
Figure 17: Pied Crow (Corvus albus) Figure 18: Common Raven (Corvus corax)
Beak - Summary
Seed eaters like sparrows
and cardinals have short,
thick conical bills for cracking
Birds of prey like hawks and
owls have sharp, curved bills
for tearing meat.
Woodpeckers have bills that
are long and chisel-like for
boring into wood to eat
Beak - Summary
Hummingbird bills are long
and slender for probing
flowers for nectar.
Some ducks have long, flat
bills that strain small plants
and animals from the water.
Birds like herons and
kingfishers have spear-like
bills adapted for fishing.
Beak - Summary
Insect eaters like warblers
have thin, pointed bills.
Crows have a multi-purpose
bill that allows them to eat
fruit, seeds, insects, fish, and
Most birds have tongues, though unlike ours. A bird's tongue has 5 bones in it that support
and strengthen it, together they are called the 'Hyoid apparatus'. A bird's tongue is
generally harder and less flexible than ours.
Figure 19: Great Blue Heron (Ardea herodias) Figure 20: Blue and Gold Macaw (Ara ararauna)
The esophagus is large in diameter, particularly in birds that swallow large meals.
Swallowing is accomplished by esophageal peristalsis, and in most birds appears to be
aided by extension of the neck.
The esophagus conducts
food from the mouth to
the stomach in all
animals. In this case with
birds it goes to the
gizzard first before the
proventriculus (a birds
Figure 23: Jugular part of a bird
Figure 28: Non-lactating crop (A) versus lactating crop (B and C)
Nearly all birds have a stomach made up of two parts. The first part of the stomach, called
the proventriculus, secretes strong digestive juices. The second part of the stomach, called
the gizzard, has strong muscular walls that act like teeth to grind and pulverize foods.
Figure 29: Avian stomach Figure 30: Proventriculus and gizzard
Figure 31: Cross section of the proventriculus Figure 32: Proventriculus cross section
Figure 33: Proventriculus and Gizzard Figure 34: Gizzard
Figure 35: Mucosal layer of ventriculus Figure 36: Closer look of the mucosal layer
Figure 37: Secretory region of ventriculus Figure 38: Pellicle material being pushed out into the
Figure 39: Particle size of material in the gizzard vs. proventriculus.
Some birds practice geophagy or the practice of eating earthy or soil-like substances such
as clay. This provide grit for digestion. Because birds lack teeth, many ingest pebbles or
coarse soil with which to grind food in their gut. It also helps neutralize toxins from their
Figure 40: Gastrointestinal tracts of a carnivorous hawk, an omnivorous chicken, and 4 herbivorous birds.
Unlike other birds, owls have no crop. A crop is a loose sac in the throat that serves as
storage for food for later consumption. Since an owl lacks this, food passes directly from
the mouth to the gizzard.
Unlike mammals, birds don't urinate. Their kidneys extract nitrogenous wastes from the
bloodstream, but instead of excreting it as urea dissolved in urine as we do, they excrete it
in the form of uric acid. Uric acid has a very low solubility in water, so it emerges as a white
paste. This material, as well as the output of the intestines, emerges from the bird's
Figure 54: Avian cloaca
Figure 54: Bird poop Figure 55: Bird poop
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