Birds Flashcards
Birds are the descendants of what ?
Of theropod dinosaurs who evolved feathers
Why would feathers evolved ?
- early feathered theropods not capable of powered flight
- feather used for other purposes at first
- structural exaptations
- courtships display
- thermoregulation
What other characteristic does the Theropods shares with birds ?
- shared structural feature.
- lunate wrist bones ( permits swiveling)
what is the name of the class for birds
Aves
What have to be selected for the power of flight ?
- birds must meet stringent structural adaptations that conform to aerodynamic specifications
- selection for more power and less weight
- but must balance this with other needs (feeding, escaping,predators, reproduction, etc.)
Feathers
- homologous to scales of nonavian reptiles outgrowth of epidermis rolled into a cylinder & strengthened by deposition of keratin.
- most are contour feathers – cover &streamline body
- hollow quill ( calamus ) emerging from epidermal follicle
- continues as shaft (rachis) that bears numerous barbs on the vane
- branch into smaller barbules held together by tiny hooks
Do they shed their feathers ?
Yes , most shed (molt) feathers at least once a year in a highly ordered fashion.
also feathers are dead structures when fully grown (like hair)
Is cleaning their feathers important ?
- Yes , preening (cleaning) important to smooth feather
- barbs & remove dirt so they will lock together
- also apply oil from gland to stop sticking
Skeleton
- need a light but sturdy scaffolding
- loss of features to reduce weight.
- have an extremely light-weight skull with large orbits and keratinized beak.
- bones reduced & those that remain are pneumatized
- honeycomb structure with air cavities
Muscular system
- need substantial musculature to power
flight
-pectoralis is largest (pushes wings down during flight)
-need large attachment site (keeled sternum) -tendons extend from leg muscles into toes
-arranged in toe-locking mechanism
Why are birds feet resistant to freezing ?
cause its mostly scales & tendons
Digestive system
-need a lot of food (high metabolism)
- must have efficient digestive system
must overcome lack of teeth.
crop
pouch in esophagus acting as a food reservoir
gizzard
powerful grinding organ ( swallow pebbles, grave )
large intestine
paired ceca (fermentation if herbivore)
Circulatory system
- have a 4 chambered heart with complete ventricular separation
- evolved independently from that in mammals
Why this convergent evolution ?
- both have very high energy demands
- high metabolic rate – high oxygen needs
- both groups very active
- both groups are endotherms (heat from metabolism)
Excretory system
-large, paired kidneys
-excrete uric acid (like nonavian reptiles)
-less efficient than mammals at removing salts
excess moved via salt glands (very common if marine)
why fly ?
- escape from terrestrial predators
- travel to & exploit new habitats
- benefits of migrating with the seasons
alula
mid-wing group of feathers
wing-tip
slotting between primary feathers
wing tip vortex
- turbulence at high speeds reduced in wings that sweep back & taper to a tip.
Nervous system
- reflects complexities of coordinating flight & being a highly visible object
- well-developed cerebral hemispheres, cerebellum & optic lobes
Sensory
- excellent hearing and sight
- avian eye relatively larger & almost immobile
Pectern
highly vascularized organ attached to retina (provides nutrients & oxygen)
fovae ( how many )
2 fovae
- allow very keen focus
Greatest power of flight occur when ?
- during downstroke
- primary feathers bend & twist into steep angle to slice into air to pull entire wing & body forward
what happens during upstroke ?
primary feathers bend in opposite direction during upstroke & provide lift
Upstroke essential for ..
powered upstroke essential for hovering
& steep, fast takeoffs
what are the name of the 4 type of wings ?
1) Elliptical
2) High-aspect ratio
3) Dynamic soaring
4) High-lift
Elliptical
- low-aspect ratio (length to width)
- both alula & wing-tip slotting
- high manoeuvrability
High-aspect ratio
- wings sweep back & taper to slender tip
- no wing-tip slotting
- efficient for high speed
Dynamic soaring
- also high-aspect ratio
- long & narrow
- lack wing slot all together
- good for soaring over seas with strong, reliable winds.
High-lift
- have prominent camber
- noticeable wing-tip slotting & anulas
- promote high lift at low speed
- good for soaring over land with heavy loads
what triggers birds to start migrating ?
-development of gonads & accumulation
of fat triggered by increased day lengths
- stimulation of anterior lobe of pituitary gland to release hormone
-starts northward migration behaviour (opposite occurs in late summer)
How do they find their way ?
- navigation chiefly through sight
- recognize topographical landmarks
- follow familiar migratory routes
- aided if flock migration with older birds
- accurate sense of time (i.e. how long to fly in a direction)
- likely also use earth’s magnetic field
- ability disturbed by magnetic on head
- magnetite (Fe3O4) deposits in beak
What else do they use to find their way ?
use celestial cues (sun &stars)
-can maintain compass direction by referring to sun regardless of time of day (sun-compass navigation)
Why do birds flock together ?
-decreased predator success with increased prey group size
-also decreased individual odds of being eaten
- faster detection of predator
-often more efficient feeding (even though there is increased competition for food)
cooperative feeding behaviour
more time spent on feeding if less on being vigilant (scanning for predators)
-greater ease in finding mates
- less time looking & more time wooing
Birds testees and penis
- testees greatly reduced most of year - enlarge during breeding season
most species lack penis – mate by aligning
cloacal openings
Female reproductive system
- most females only have functional left of reproductive system (ovary & oviduct) – right side is vestigial
- fertilization in upper oviduct – albumin & shell membranes added during passage through oviduct to cloaca
monogamy
-each individual has only 1 mate
- can be permanent situation or for season
- fairly rare in most animals but common in
birds (over 90%)…or is it?
polygamy
-either (or both) have more than 1 mate during the breeding period
but usually polygyny.
polygyny
male mates with more than 1 female
Nesting & parental care
almost all eggs must be incubated
- usually female, sometimes both, rarely only male
- most build a nest for rearing young
- extremely varied materials & structure
Nest parasite
-species lay their eggs in nests of other bird species.
altricial
more immature at birth , require lots of care
precocial
more developed at birth, greater independence.
What are the 2 types of parental care needs
altricial and precocial
Human effect on birds
-extinction of many species (>140 since 1681)
-overhunting as one cause
contaminants : bioaccumulation in predatory species.
- lead poisoning still occurring.
Paleognathae
large , flightless
neognathae
powerful flight muscles
living birds belong to the lineage ..
Neornithes
Neornithes divided into 2 groups..
1) Paleognathae
2) Neognathae
Paleognaths (traits)
- flightlessness usually evolved on islands with few predators
- those on continents adapted to run fast enough to escape predators (70 km/h for ostriches!)
- also evolved independently in some neognaths
Neognathae (members)
most living birds belong to this lineage
Order Passeriformes
key traits: most with highly developed voix box. - feet adapted for perching on stems & twigs -altricial young members: perching songbirds - largest order (60% of all birds)
Order Falconiformes
key traits: strong fliers
- keen vision
- sharp, curved talons
members: many birds of prey
Order Anseriformes
key traits: broad bills with filtering edges
- webbed front toes
- low keel
members: many aquatic birds
Order Sphenisciformes
key traits: short wings - flightless - very aquatic with webbed feet solid bones members: penguins
