Lect 16

Question 1

Avian phylogeny

Answer 1

Most diverse group of Sauropsida
• Taxonomy, phylogeny change frequently

Disagreement comes from
• Rapid diversification in time around end-Cretaceous extinction
• High rates of hybridization and gene flow during that diversification
• Extensive convergent evolution in non-related clades

Question 2

Paleognathae vs. Neognathae

Answer 2

• “Old jaws” and “new jaws”

• Birds do not have secondary palates (diff from closest relatives crocs and distant relatives endotherm mammals)

• Paleognathae: pterygoid bone fused to other palate bones

• Neognathae: pterygoid bone forms joint to other palate bones
- Allows greater flexibility and a wider range of beak shapes

Old - emus, rheas, ostriches

New - joints instead of fusing - more flexibility

Question 3

Feathers

Answer 3

Penguins are the only birds that grow feathers across entire surface of skin
• Most grow feathers on certain areas of their bodies

Feathers made of beta-keratin
• Calamus grows out of integument
• In pennaceous feathers, the rachis supports a vane on each side, and the vanes are composed of barbs, branching barbules, and hooklets hold the barbules together

Question 4

Types of feathers

Answer 4

• Down feathers provide insulation

• Contour feathers provide shape (doesn’t have to be whole feather, depends of location on bird)

• Semiplume feathers lack hooklets so do not form vane; provide insulation and shape (streamlining, don’t help with flight)

• Bristle feathers surround eyes or beak; keep debris out (also some sensory info about what’s going on around face)

• Filoplume feathers relay sensory information about position of other feathers
Adaptations for communication (some)
- peacocks
-birds of paradise

Question 5

Feather colouration

Answer 5

Pigments
• Melanins = black, gray, dark brown to tan
• Carotenoids = red, orange, yellow
• Porphyrins = fluorescent red under ultraviolet light

Structural colouration
• Barbs contain air-filled structures that intensify or reduce certain wavelengths of light (interacts between barbs and air filled structures reflect result in diff colours)
• Structural and pigment colouration can combine

Question 6

Flight muscles

Answer 6

Pectoralis major (larger one, increased depth of sternum allows it to be bigger)
• Powers downstroke
• Attaches to keel of sternum and ventral side of humerus

Supracoracoideus (shoulder muscle, is deeper to pectorlis, derived modification —> goes through the bone)
• Powers upstroke
• Attaches to keel of sternum, passes through opening in coracoid, attaches to dorsal side of humerus

Having both muscles on ventral surface keeps centre of gravity low (chest side)

Question 7

Aerodynamics

Airfoils

Answer 7

Flight requires generating thrust to counteract drag and lift to counteract gravity

Wings are airfoils
• Wing is cambered – curved dorsally
• Packets of air move more quickly over curved dorsal surface
• Reduces pressure, causing partial vacuum, drawing wing up
• Most lift generated by proximal part of wing
• Most thrust generated by distal part of wing

Question 8

Aerodynamics

Alula

Answer 8

Tilting wing more steeply into airflow increases turbulence (and therefore drag) across wing

Alula
• Anterior digit, separate from rest
of fused hand and wrist
• Supports separate feathers
• Provides extra airfoil, which further increases camber of wing and velocity of air over wing
• Air slot reduces turbulence

Question 9

Aerodynamics

Wing aspect ratio

Answer 9

Wing aspect ratio = wing length divided by wing width

High aspect ratio wings:
• Long and narrow; efficient for long flying or soaring
• Proximal limb bones longer (ones closer to body)

Low aspect ratio wings:
• “Elliptical”; adept at precise maneuvering
• Distal limb bones longer

Question 10

Terrestrial locomotion

Answer 10

• On the ground, birds can hop with both feet, or walk or run

Toe positions
• Ansiodactyly: three toes forward,
one toe backward
• Zygodactyly: two toes forward, two toes backward
• Tri/didactyly: reduction of toes

• Birds that swim have webbing between or around their toes

Question 11

Beaks and diets

Answer 11

• Generalists: Simple, tapered beaks

• Seed eaters: Robust beaks to break through tough coverings (b/c of extra covering)

• Filter feeders: Beaks with specializations to strain small organisms out of water

• Probers: Long, narrow beaks to find and extract invertebrates from substrate

• Gleaners: Narrow, tweezer-like beaks to pick insects off surfaces

• Fish eaters: Long beaks, often with serrations to grip wriggling fish (increased grip)

• Eating small vertebrates: Heavy, pointed beaks (stabbing prey)

• Falcons: Special notches in their upper and lower beaks, used to snap the necks of their prey

• Eating larger vertebrates: Heavy, curved beaks (for tearing)

• Eating insects in wood: Woodpeckers have strong beaks and specialized skeletons and muscles to distribute the force
- Long tongues with barbed ends to pull insects out of holes (starts at hyoid and wraps around head)

• Eating nectar: Hummingbirds have long, narrow beaks
- Long tongues with hair-like ends that adhere nectar via capillary action (this requires less energy)

Question 12

Digestive system

Answer 12

• Esophagus: Swallowing

• Crop: Storage for extra food

• Proventriculus: Glandular portion of stomach (includes glands - stomach acids. Larger or smaller —> diff compounds to break down. Meat don’t need much)

• Gizzard: Muscular stomach for mechanical breakdown of food (may eat stones or sand for help)

• Intestines: Absorbing nutrients

• Ceca: House symbiotic microorganisms, especially for herbivorous diets

• These structures can have different proportions based on diet

Question 13

Vision

Answer 13

• Birds strongly rely on vision

• Eyes are large (in comparison to overall size)
- Eye muscles are small, so birds turn neck to look around
(Extra bone in eye and may not be able to move eye well as a result so the neck vertebrae extra flexible)

• Birds have a fourth photosensitive pigment in their cone cells

• Can see in ultraviolet spectrum

Question 14

Hearing

Answer 14

• Middle ear bone: stapes

• Inner ear not as elaborated as in mammals, but sound receptors are more densely packed
- Sensitive to changes in sound frequency and timing

• Owls have asymmetrical skulls, which allows them to pinpoint the location of sounds

Question 15

Smell

Answer 15

• More important to birds than previously understood
• Olfactory bulb enlarged in species that rely heavily on scents
• Scent used by some scavengers to find dead carcasses
• Scent also used to detect threats

Question 16

Touch

Answer 16

• Bill-tip organs: mechanoreceptors in the beaks of some birds
• Found most in birds that use beaks for probing
• Bristles around beaks of birds that hunt on the wing

Question 17

Magnetic fields

Answer 17

• Used in migration, particularly the first migration a bird performs in its life
• Inherent and not taught

Question 18

Communication

Answer 18

• Vocal calls for simple communication (‘hello, food here, threat. Adults and juveniles use it)

• Vocal songs for establishing territory, mating (only males)

• Visual communication via wing waving, flashy feathers, complex mating dances

Question 19

Fertilization and egg formation

Answer 19

• All birds are oviparous

• Genetic sex determination: ZZ (males) vs ZW (females)

• In most species, males do not have a penis or other intromittent organ
- Both individuals evert their cloacae during mating

• Females release one ovum a day during mating season

• Carbohydrates and water are added to albumen

• Egg passes to shell gland where minerals are deposited (minerals are deposited into females bones to be used for egg shells)

Question 20

Parental care

Answer 20

• Extensive
• Nest building • Incubating
• Feeding
• Brood parasite species take advantage of this by laying their eggs in other birds’ nests
• Foster parent birds care for the brood parasite at the expense of their own offspring

Question 21

Conservation

Answer 21

Population loss
• Even species that have not gone extinct are facing significant reductions in population
• Grasslands species are currently faring the worst
• Large areas converted from natural ecosystems to agriculture
• Climate change
• Loss of insect prey

Question 22

Key Concepts

Answer 22

• Birds rely on their feathers and wings to provide thrust and lift for flight powered by two sets of muscles that stretch between the keeled sternum and the humerus.

• Bird beaks are specialized based on diet, and the organs of the digestive tract also differ in size based on diet.

• Birds rely on multiple sources of sensory input to find food, mates, and migrate successfully.

• Birds are oviparous and provide extensive parental care.