LECTURE 22 - Aves

Question 1

What are reptilian features found in avian skulls?

Answer 1

• Sclerotic ring that support the eye
• Single occipital condyle
• Lower jaw articulate on quadrate

Question 2

What is the Archaeopteryx?

Answer 2

• Earliest bird, Late Jurassic (145 Ma)
• Mosaic of BIRD and REPTILE characteristics
  
  • bird: feathers, 3 digits forward and 1 back
  • reptile: small teeth, unfused digits, no keel on sternum, long tail

Question 3

Could Archaeopteryx fly?

Answer 3

CHARACTERISTICS OF FLIGHT IN MODERN BIRDS SHARED BY ARCHAEOPTERYX
1. Asymmetrical flight feathers on its wings and tail
2. Wing feather arrangement shared with modern birds
3. Flight muscles strong enough for ground-upward takeoff
4. Absence of keeled sternum, but robust furcula for anchoring of the pectoral muscles
5. Encephalisation, with dominance of the sense of vision
6. Proportion of the inner ear: expanded auditory and spatial perception

Question 4

What is the cursorial hypothesis on the origin of flight?

Answer 4

• Feathers originated early in the Theropod radiation (hypothesized to be for insulation), while flight is a later innovation during the Mesozoic
• Protoavians thought to have hunted by running quickly and leaping after large flying insects
• This may have evolved into flight, but it would have been highly energetically costly (speeds > ~10 m/s to take off)

Question 5

What is the arboreal hypothesis on the origin of flight?

Answer 5

• Made use of gravity and expanded body surface area to slow descent during falls and leaps
• But, transition from gliding to flapping would be difficult (feathers increase drag more than adding lift)

Question 6

What is the K/T mass extinction?

Answer 6

• 65 million years ago
• ~70% of species disappeared
• Thought to have created ecological opportunity for many new species
• Followed by the radiation of modern birds

Question 7

What is a bird?

Answer 7

• Size constraints
• Adapted for flying
• One-way breathing
• Efficient digestive system
• Excellent vision and hearing
• Oviparous (egg laying)

Question 8

Explain how body size can affect a bird

Answer 8

• Body weight in birds spans about a 1:6,000 ratio, much less than in other animal taxa (e.g., mammals = 1:1,000,000)
• Small birds have problems obtaining enough food due to high surface to volume ratios causing rapid heat loss
• Large birds have problems flying due to high weight to wing ratios causing excessive wing loading

Question 9

How are birds adapted for flight?

Answer 9

• Light and agile
• Weight reduction: hollow bones, large eye sockets take up much of the forepart of the skull, reduced jaw without teeth, reduced tail, spindly legs
• Weight concentrated at centre of gravity: large sternum provides a point of attachment for massive flight muscles, legs retracted during flight to reduce drag

Question 10

What is aspect ratio in birds?

Answer 10

• Measure of wing shape
• AR = wing span^2 / wing surface area
• High AR indicates narrow wings, low AR indicates broad wings

Question 11

What is wing loading in birds?

Answer 11

• Measure of the relative size of the wing
• WL = body weight / wing area
• Larger birds have disproportionately larger wings and wing area

Question 12

What are the different types of flight?

Answer 12

• Elliptical wing
  
  • Low speed
  • Highly maneuverable
  • AR low
  • e.g., Woodland birds
• High-speed wing
  
  • High speed
  • AR high
  • e.g., birds that feed during flight, migratory birds
• Gliding wing
  
  • Dynamic soaring
  • Less maneuverable
  • AR very high
  • e.g., seabirds
• High-lift wing
  
  • Static soaring
  • High maneuverable
  • AR intermediate
  • e.g., hawks and eagles

Question 13

What are the important skeletal elements for wing shape in birds?

Answer 13

• Humerus
• Ulna
• Radius
• Metacarpus
• Basal phalanx
• Terminal phalanx

Question 14

Describe the hindlimbs in birds.

Answer 14

• Optimized centre of gravity for flight, which makes balance difficult during other forms of locomotion using hindlimbs (e.g., walking) since the pelvic girdle is well behind the centre of gravity
• Birds have overcome this problem by having the femur project forward along the side of the body, bound to the body by muscles
• Lower end of this bone (or knee) acts as the new “hip” joint, to which the lower left is attached and well positioned with respect to the centre of gravity

Question 15

What are some weight reduction adaptations in birds?

Answer 15

• Large, heavy jaws and teeth of reptilian ancestors have been lost and replaced with the gizzard, a muscular portion of their stomach
• Reduce the amount of water carried in waste products by obtaining most of their water from their food using the hind gut
• Reproductive systems keep weight low by greatly reducing size of sexual organs of most for most of the year except breeding season

Question 16

Describe feathers in birds

Answer 16

• The most characteristic feature of birds
• A bird can have between 2000-25,00 feathers (can weigh 2-3x the bird’s body)
• Made from keratin (same proteinaceous substance used to make mammal fingernails and hair), homologous to reptile scales
• Evolved for insulation, but serve a number of functions

Question 17

How did feathers become coloured?

Answer 17

• Feather colours produced in one of two ways (or a combination of both):
  
  • Pigmentation from a biochrome deposited in the feather:
    
    • Melanin: brown, grey, black
    • Carotenoids: orange, yellow, red, certain blues
    • Porphyrins: bright brown, green, magenta
  • Structural colour caused by special physical properties of the feather that reflect only part of the visible wavelength - can cause metallic and iridescent colours

Question 18

What is the advantage of one-way breathing?

Answer 18

• Bird lungs are supplemented by a number of air sacs throughout the body
• Air flow through the lungs is uni-directional: air passes first into posterior air sacs, then the lungs, and then out of the anterior air sacs
• This allows constant inflow of fresh air with high oxygen content
• Almost the entire volume of the lung to be replaced with each breath, asa opposed to the “ebb-and-flow” system in mammals

Question 19

What does beak shape tell us in birds?

Answer 19

• Beaks are a common feature of birds
• They often show adaptations that are well-suited to the ways in which different species acquire resources
• Some show incredible co-evolution with their food sources (e.g., nectar feeding birds)

Question 20

Describe the supreme field of vision in birds.

Answer 20

• Vision is the most important sense for birds, followed by hearing (same as humans)
• Can typically keep good focus over about 20 degrees of their field of view (vs. ~2 degrees in humans)
• Some birds possess multiple fovea (the spot in the retina with the highest resolution) that allow their eyes to act like a zoom and macro lens simultaenously
• Eyes are relatively immobile, but birds often have very mobile necks that allow them to turn their heads easily
• Birds with eyes on the sides of their heads can sometimes see a whole 360 degrees, and those with eyes high on the head (e.g., woodcocks) can sometimes also see over the top of their heads as well
• Birds with more forward facing eyes (e.g., owls) have (relatively) narrow field of vision but very good binocular vision

Question 21

Describe night and ultraviolet vision in birds.

Answer 21

• Many birds have exceptional night vision due to very large and sensitive corneas
• Nocturnal predators like owls often combine this with other adaptations such as specialized wing feathers that reduce turbulence and aerodynamic noise to create silent flight
• Many birds can also see ultraviolet light, which is important for sexual displays and also for hunting (e.g., tracking urine trails of prey, which contain high levels of phosphorous)

Question 22

Describe the hearing in birds

Answer 22

• Hearing is employed in communication between birds, and is especially valuable in wooded areas where visual contact is difficult
• Birds can distinguish sounds that are very close together
• Hearing also useful to detecting prey in predatory birds
• Owls have disc-shaped feathers to help funnel sound to ears, and asymmetrical ears which helps pinpoint the precise location of prey based on minute time differences (30 millionth of a second) in which sounds reach each ear

Question 23

What is the reproductive behaviour in birds?

Answer 23

• Bird eggs take a considerable time to develop (12-60 days from laying to hatching)
• During this time, both the incubating parent and eggs are vulnerable to predation
• Some birds protect the eggs by breeding in colonies, others hide the nest, or lay eggs with camouflaged markings

Question 24

NEST DIVERSITY (CHECK LAB)

Question 25

Describe migration in birds

Answer 25

- Thought to have evolved in tropical birds that dispersed northward, where seasonal abundance of insect food and greater day length allowed them to raise more young - Triggered by environmental and genetic factors - Navigate via sun, stars, magnetic field, landmarks - Migration is risky - Mortality rates have been recorded as being at least 6x higher during migration vs. stationary periods, with half of all annual mortality occurring during migration

Question 26

(IN AVES - IN NEORNITHES) What are Palaeognathae?

Answer 26

- emus, ostriches, and relatives - mostly flightless (parallel evolution) - Flat breastbone - Simplified wings and strong legs - Males incubate eggs - Proportionally small brains

Question 27

(IN AVES - IN NEORNITHES) What are Neognathae?

Answer 27

- Flying birds that have a keeled sternum anchoring flight muscles - Virtually all extant bird species (~10,000 species) - Includes the order Passeriformes (perching birds), the largest clade of land vertebrates, containing 60% of living birds - Divided into two lineages, the "fowl" clade GALLOANSERAE and NEOAVES

Question 28

(IN AVES - IN NEORNITHES - IN NEOGNATHAE) What are Galloanserae?

Answer 28

- Fowls - Big clutches (5-10 or more eggs) - Many are polygamous, e.g., one rooster with a whole flock of females - Very frequent hybridization (even at the genus level) - Precocious young, e.g., many waterfowl are able to swim and dive a few hours after hatching - Galliformes ("landfowl"): - quail, pheasants, grouse - 290 species, worldwide distribution - Ground nesting herbivores, strong beak and heavy feet - Anseriformes ("waterfowl") - Ducks, geese, swans - 190 species, worldwide distribution - broad bill, webbed feet

Question 29

How many clades do Neoaves have?

Answer 29

5 major clades from successive sister groups - Strisores - Columbaves - Gruiformes - Aequorlitornithes - Inopinaves

Question 30

(IN NEOAVES) What are Strisores?

Answer 30

- Torpor and other metabolic pecularities are found frequently in the group - Spend most of their waking time in flight - Nighthawks - Medium-sized - Long wings, short legs - Nocturnal - Worldwide - Swifts - Among the fasts animals on the planet (169 km/hr) - Insectivorous - Worldwide - Pootos - Very large eyes with slits in eyelids - Nocturnal - Camouflaged to match tree stumps - New world distribution - Hummingbirds - Smallest birds (5-13 cm) - wings beat 50 times/second - Can fly over 50 km/hr - Highest metabolism of any homeothermic animal (torpor drops rate to 1/15th of normal)

Question 31

(IN NEOAVES) What are Columbaves?

Answer 31

- with exception of Bustards, are generally small, compact birds - Primarily seed and plant eaters - Pigeons - Highly abundant, particularly in cities (many species domesticated) - Common prey item for raptors - Bustards - large and terrestrial - omnivores - nocturnal - old world - Mesites - endemic to Madagascar - near flightless - all species threatened - Cuckoos - primarily arboreal - primarily tropical - some species are brood parasites - Sandgrouses - Africa and Asia - Seed eaters - Cryptic pluamge - Turacos - unique pigments giving bright green feathers - Africa - Strong climbers - flexible 4th toe

Question 32

(IN NEOAVES) What are Gruiformes?

Answer 32

- Wading and terrestrial "crane-like" birds - Cranes - Long-legged and lon-necked - Fly with necks outstretched (as opposed to herons) - Construct platform nests in shallow water - Monogamous - Many species threatened - Crakes - Marsh habitat - Hide in dense vegetation - Short, conical beaks - Swimmers and waders - Omnivores - Rails - Many flightless species (parallel evolution on islands) - Mostly sexually monomorphic - Omnivores - Many threatened (vulnerable to introduced predators)

Question 33

(IN NEOAVES) What are Aequorlitornithes?

Answer 33

- "waterbirds" - Shorebirds - wetlands and coastal habitats - waders that forage for insects and crustaceans along shorelines and mudflats - Many are strongly migratory - Flamingoes - usually stand on one leg with the other tucked beneath the body (not understood why) - Pink/red plumage due to carotenoids obtained from diet - Filter feeder on brine shrimp and algae - Very social with large colonies - Grebes - Freshwater diving birds (some are marine during migration) - Narrow wings - Excellent swimmers, poor flyers - Diverse bills depending on prey type - Dense, waterproof plumage

Question 34

(IN NEOAVES) What are Inopinaves?

Answer 34

- Extremely diverse clade of "landbirds" - Vultures - Scavengers - on every continent except Australia and Antarctica - Bald heads (cleanliness or thermoregulation?) - Corrosive stomach acid to deal with putrid carcasses - Parrots - tropical distribution - strong, curved beaks - typically nest in tree hollows - many are vividly coloured - feed on seeds and plant material - highly intelligent, some can imitate human speech - Owls - mostly nocturnal - mostly solitary - binocular vision - binaural hearing - sharp talons - feathers adapted for silent flight - wide distribution except Antarctica - Passerines - >110 families, and <1/2 of all bird species - "perching birds" with 3 toes pointing forwards and 1pointing back - most are small in size - highly diverse songs