midterm 1 Flashcards
1
Q
name 11 things all MODERn birds have in common
A
- feathers
- lack of teeth
- fusion and reduction of bones
- pneumatic bones
- bipedal
- digitigrade
- small size and mass
- forelimbs adapted for flight
- centralized body mass
- high metabolic rate
- highly developed central nervous system and vision
2
Q
what is a taxon?
A
recognized group in a classification
3
Q
how were birds classified historically?
A
according to morphological similarities no dissimilarities
4
Q
how are modern birds classified?
A
phylogenetic. ie groups defined by having a common ancestor determined by genetic and morphological comparisons
5
Q
what is the comparative method?
A
- studying evolution and adaptation by comparing morphology and behaviour of species with different lifestyles
- ex. red grouse of britain remains dark all year while similar willow ptarmigan of newfoundland turns white in winter, suggesting an adaptive explanation
6
Q
what is biogeography?
A
the study of distribution of plants and animals across the surface of the earth
7
Q
what are the six faunal regions of the planet?
A
- Nearctic: north america
- Neotropical: south america
- Palaearctic: Europe, Asia, Northern Africa
- Ethiopian: Africa
- Oriental: East Asia
- Australasian: Australia
- Oceanic: Islands surrounding Australia
8
Q
what are the types of bird distributions?
A
- cosmopolitan: distributed across all regions ex. osprey
- occur in a few regions ex. loon are found in Nearctic and Palearctic
- endemic to one region ex. australian emus
9
Q
what era is the age of birds and mammals?
A
cenozoic
10
Q
what is the origin of birds regarding links to reptiles?
A
hypothesis: birds and reptiles have a common ancestor, ie birds evolved from some group of ancient reptile
11
Q
7 similarities between birds and reptiles
A
- single occipital condyle
- single middle ear bone (stapes)
- 5-6 mandibular bones on each side of the jaw
- sclerotic (bony) ring supports the eye structure
- scales on legs of birds virtually identical to reptiles
- ankle sighted in the tarsal bones
- females are the heterogametic sex
12
Q
what evidence is required to prove birds evolved from ancestral reptiles?
A
- a series of fossil intermediates between reptiles and birds
- investigate jurassic time period (age of dinosaurs): before earliest true bird fossils
- look in areas of fine-grained jurassic limestone
13
Q
what was the first reptile-like bird discovered and described and what were its bird-like characteristics?
A
Archaeopteryx:
- feathered wings and tail
- asymmetrical flight feathers
- bird-like overall body plan
- bipedal anatomy
- likely capable of weak flapping flight
14
Q
What were the reptile-like characteristics of archaeopteryx?
A
- clawed digits on the forelimbs (unfused)
- toothed reptile-like jaws
- tiny cartilaginous sternum
- rib without uncinate processes
- unfused tail bones
15
Q
what is a pygostyle?
A
fused tailbone on birds where feathers of tail come from
16
Q
what was the biggest fossil discovery for birds 2000-2023?
A
- hundreds of new bird and bird-like fossils from triassic and jurassic found in Liaoning China
- new fossil group called avialae
- overlaps period from first dinosaurs with feather-like appendages and age of archeopteryx
17
Q
what is the fossil group avialae?
A
- all dinosaurs with feathered wings used for flapping flight and birds directly descended from these
- found in Liaoning China
- proof birds descended directly from theropod dinosaurs
18
Q
what are almost all reptilian feather discoveries from?
A
- Coelrosaurian theropods
- ex. sinosauropteryx: definitively non-avian dinosaur with protofeathers
19
Q
what are the 2 theories regarding which group of mesozoic reptiles birds came from?
A
- Thecodontian theory
- dinosaur theory (coelurosurs, small theropod dinosaurs)
20
Q
what is the thecodontian theory?
A
- birds had an ancient ancestry (triassic 240my bp) among the thecodont ancestors of modern crocodiles, pterosaurs, and dinosaurs
- evidence: 14 characters shared between birds and crocodilian thecodonts ex. some had elongated feather-like scales
- the problems: no fossils during the 90my period between early thecodonts and oldest bird-like reptiles of late jurassic
21
Q
what is the dinosaur theory?
A
- birds evolved more recently (early jurassic <190my bp) from a line of small theropod dinosaurs (Coelurosaurs)
- evidence: 23 specialized skeletal characters shared between theropod dinosaurs and Archaeopteryx, known fossils bird-like reptiles coexisted with dinosaurs
- problem: the fossil record is incomplete, there is no direct chain of intermediates linking birds and one group of ancient reptiles
- archaeopteryx is now understood to be a member of a group that went extinct with the dinosaurs and thus not a direct ancestor of modern birds
22
Q
describe the later stages of the evolution of birds
A
- once a feather flying bird had evolved a rapid adaptive radiation proceeded
- a rapid radiation of the ‘new’ class Aves proceeded
- all modern orders of birds were living early in the Tertiary period (60my bp)
- giant birds lived during the Tertiary
- dino replacement theory: birds evolved to fill the niches left by extinction of dinosaurs
23
Q
what are some examples of large Tertiary terror birds?
A
- Diatryma
- Phorusracos
- Teratorn
24
Q
describe the evolution of feathers and flight
A
- modified reptilian scales?
- no intermediates are known from the fossil record
- feathers evolved in response to selection for what function?
25
describe insulation theory for evolution of feathers
- feathers initially evolved for insulation
- proto-birds were highly active warm-blooded creatures and needed an insulating coat to maintain body temperature in cool conditions
- then feathers secondarily evolved for aerodynamic function
- problems: limited evidence of proto-bird endothermy, fails to explain specialized structure of feathers
26
describe direct evolution of feathers for flight theory
- arising from selection on any fringe on forelimbs used for gliding
- arboreal theory: flight evolved in an arboreal reptile that first glided between tree limbs
- cursorial theory: flight evolved in a ground-dwelling reptile that pursued prey actively
27
what is the ilj theory for feather evolution?
- evolved for optical display function
- ie ornamental feathers for social signalling, sexual displays
- explains fringe-like feather and long showy tails of flight-less protobirds showing up in recent fossil discoveries
- another theory: evolved for sensory function
28
which order radiated explosively during the Miocene?
Passeriformes (songbirds)
29
when did birds reach their maximum diversity?
Pliocene - all modern genera present
30
when did half of all bird species go extinct and why?
- Pleistocene
- related to climate change and glaciation
31
how does speciation occur?
- genetic divergence of isolated populations
- colonization of oceanic islands
- isolation within continental landmasses by warming and cooling climates (or getting wetter or drier)
32
why do we use the species concept?
- classification of biodiversity
- facilitate communication among biologists
- need to be able to define and identify in order to understand evolution of behaviour, ecology, and morphology
33
what is the difference between bird speciation in the 1800s vs 1900s
- 1800s: ornithologists were 'splitters' and classified birds into 20k species, some of which were just age and sexually distinct forms of the same populations
- 1900s: 'lumping' began to prevail and the list of species declined to about 8600
- in 90s-2000s a new wave of splitting started and now we're back to 10000
34
early species concept
Linnaeus, Systema Naturae, 1758 - first classification of birds based on superficial morphological similarity rather than by specific criteria or an overarching concept
35
Ernst Mayer's definition of species
species are groups of interbreeding natural populations that are reproductively isolated from other such groups
36
biological species concept
species are based on reproductive compatibility or reproductive isolation
37
problems with the biological species concept
- practical application of 'reproductive isolation' rule is often difficult:
- very similar species separated by distance, some species are cosmopolitan
- hybridization of forms one would normally consider to be different species
- problems with extinct forms
38
phylogenetic species concept
species and higher taxa are defined by their evolutionary relationships
in some ways more realistic than biological but leads to splitting
portrays the evolutionary relationships of various lineages
data: taxonomic characters, measures of genetic similarity
39
how is the phylogenetic species concept applied?
- identify taxonomic characters and use these to reconstruct ancestry
- requires the analysis of characters shared because of common ancestry: natural genetic variation or morphological characters
40
what are conservative characters?
ones that do not change easily (ex. due to ecological adaptations) are the best type of character
41
requirements for taxonomic characters
- must be homologous structures shared by at least 2 organisms that can be traced phylogenetically to the same feature in the immediate common ancestor
- ex. presence of webbed feet is not good, patterns of small holes or anatomy of the palate are
42
derived vs primitive character states
- derived = novel, primitive = ancestral
- ex. toe number in woodpeckers, 4 is primitive 3 is derived
- best analyses use conservative homologous characters that occur in both their derived and primitive states
- reconstructing phylogenies is based on the cladistic analysis of species with shared derived characters
43
problem - how to identify good taxonomic characters?
- posed particularly by convergent evolution
- ex. meadowlarks and longclaws are very morphologically similar but genetically not closely related at all = convergent evolution
44
molecular genetic techniques
- solution to taxonomic character problem
- electrophoresis of allozymes
- DNA-DNA hybridization and melting point analysis
- mt DNA restriction site analysis and sequencing
45
what are feathers made of?
- made of keratin protein: a composite material like fibreglass, very strong and very light
- microscopic insoluble filaments in a protein matrix
46
what are the 3 primary functions of feathers?
1. aerodynamic lifting surface
2. smooth aerodynamic coating to body
3. insulation
47
what are the 3 secondary functions of feathers?
1. camouflage
2. communication
3. sensory
48
what are the 2 parts of feathers?
1. hard pennaceous (firm-vaned)
2. soft afterfeather which is plumulaceous
49
other characteristics of feathers
- highly resistant to bacteria or fungi
- resistant to uv radiation
- self repairing due to 'velcro' structure
- high maintenance
- subject to parasites
- replaced on regular basis by molt
- specialized feather types perform different functions
50
what are the main feather structures?
- calamus or shaft
- rachis
- barb
- vane (composed of barbs, including ramus, barbicel, barbule
51
main 6 feather types
1. contour feathers and flight feathers
2. down feathers: no firm vein, interlocking fibres that trap air
3. filoplumes: neither insulating or aerodynamic in function - sensory
4. semiplumes: space filling
5. bristles: mostly protective function, in raptors, flycatchers
6. ornamental feathers: contrasting plumes, highly modified adornments
52
what is preening?
- rearrangement and maintenance of feathers using foot and bill
- reorientation of the barbicel-barbule system
- cleaning off dirt, drying feathers if they're wet
- removal of parasites including bird lice
- sick birds: unable to preen, poor plumage condition
53
what is the uropygial gland?
- preen gland
- secretes an oily wax and fatty acid that maintains feather flexibility and probably waterproofing (seabirds)
54
parasites that affect feathers
1. feather mites: feed on feather and skin debris
2. itch mites: feed on feather follicles and skin
3. bird lice: feed on feathers and skin, some living within feather shaft
55
how do feathers grow?
- by molt
- growth of new feather occurs within follicles
- growing and differentiating cells (pulp) form rachis, barbs, and barbules
- transformation of living epidermal tissue into hard keratinized feather
- remaining living material withdraws from the finished feather through the inferior umbilicus
56
what are the names of the two molts?
1. prebasic: after breeding season
2. prealternate: grows specialized adornments before breeding season
57
what factors determine plumage colouration?
1. biochrome pigments
2. feather surface ultra structure
58
what are the 3 types of biochrome pigments?
1. melanins (common - grey, black, and brown)
2. carotenoids (common - bright yellow, orange, and red)
3. porphyrins (rare - unusual colours such as magenta)
59
what are melanins?
- manufactured in specialized cells melanoblasts
- granules deposited in growing feather
- functions: colouration, uv resistance 'sunscreen', protection from wear, heat absorption
60
what are carotenoids?
- derived from diet
- lipid soluble
- left in feather when lipids leave at last stage of feather growth
61
what are psittacofulvins?
produce red colour in parrots
62
what are spheniscins?
yellow colour in penguins
63
what are structural colours?
- blue, green, iridescence
- colour produced by diffraction off regular structures (plates or tubules) on feather surface
- short wavelengths (blue and green) reflected off gratings while longer wavelengths are absorbed
64
aerodynamics of wings
- airfoil: reduced air pressure on upper wing surface creates lift proportional to surface area of the airfoil
- gliding flight: wing acts like an airplane's wing
65
solutions for combatting drag
- flapping flight: increases airspeed flow over lifting surfaces
- dynamic soaring (seabirds)
- thermalling (raptors - slotted wings, alula)
66
what is wing loading?
the number of grams of body mass per square centimetre of wing surface area
67
what is aspect ratio?
- ratio of wingspan2/wing area
- how long and narrow the wings are
- determines gliding efficiency
- fast gliders have long thin wings
68
what is dihedral?
- the angle at which the wings are held relative to the body
- adaptation for low flight speed (characteristic of several soaring raptors)
69
what is curvature?
- non-flat wings in woodland species and gallinaceous birds
70
how are different wings adapted?
- soaring raptor: long wide wings with finger-like slotted primaries
-falcon: high aspect ratio but angled for maneuverability
- accipiter: short broad curved wings for rapid flight through thick cover
- Gallinaceous: short stiff curved wings for rapid acceleration (fast getaways)
- hummingbird: small stiff wings like pen-knife blades (beat 65 times/s)
71
what is the basic function of a tail?
- provide lift
- lift provided by a tail is only created by that part of the tail within its maximum span
- help birds make turns
- flightless birds often have short or no tails
- alternative function: ornamental display
72
four basic types of tail
1. normal
2. forked
3. graduated
4. streamer
73
what is a normal tail?
- most common
- compact (not vulnerable to damage)
- efficient with some limitations
- robin, dark-eyed junco,
74
what is a forked tail?
- most efficient
- found in raptors, aerial insectivores, terns
- limitation: susceptible to damage
- tern, swallow, storm-petrel
75
what is a graduated tail?
- not efficient for flight
- functions: balance, as a prop (woodpeckers), as an ornament (pheasant)
- very damage resistant
76
what is a streamer tail?
- long streamer produces only drag
- ornamental function?
- northern pintail, long-tailed duck, tropicbirds
77
what are the two extreme examples of birds with hardly any tail
1. swifts: rapid flight, built like missiles
2. wrens: mainly terrestrial - lack of flight importance has led to tail reduction
78
what is bird's body temperature?
- endothermic (warm-blooded)
- much higher body temp than mammals (38-44C)
79
benefits of high body temperature
- extremely high metabolic rate (power output is high - physiological processes increase with temperature)
- transmission of nerve impulses much faster
- endurance: high metabolic rate powers costly activities for longer duration
80
costs of high body temperature
- energetically more expensive
- more oxygen required
- more metabolic wastes produced
- 40C nearly lethal temperature: essential cooling requirement
- solution: higher capacity and complex circulatory and respiratory systems, efficient excretory system
81
describe the avian respiratory system
- no diaphragm: inhalation and exhalation aided by compression of air sacs and ribs and sternum
- small lungs compared to mammals
- loops through which air passes, spaghetti-like passages
- 6-12 air sacs connected to lungs
- complete exchange of air through the lungs with each breath cycle
82
what nine air sacs do most birds have?
- pair of cervical
- pair of anterior thoracic
- pair of posterior thoracic
- large pair of abdominal
- one interclavicular surrounding the vocal apparatus
83
how do birds breathe?
- high breathing rate: 7-150 times per minute
- high blood pH
- breathe through nostrils
- air sacs are crucial
- air sacs forcibly pump air through lung and aid in exhalation
84
what is the two stage cyclic process for avian respiration?
1. air enters air sacs first
2. anterior air sacs compressed, acting like bellows to pump air through lung passages
- chest compression squeezes air sacs to produce air pressure pushing air through lungs
85
how many chambers in a bird heart?
4, more mammal-like than reptile-like (3)
86
compare bird circulatory system to mammals
- heart rate much lower
- high efficiency maintained by more blood being pumped with each heartbeat
- larger heart relative to body size
- high blood pressure
87
what adaptations do diving birds have in their circulatory system?
- tolerance of asphyxia (atlantic puffin):
- blood flow is directed to essential areas only during dives
- bradycardia (slowing of heart) start six seconds into dive
88
how do birds control their body temperature?
- insulation: feathers insulate, adjustable by erection or depression of feathers
- by pigmentation: different coloured plumage conducts/absorbs heat differently
- by behaviour: seeking shade, shelter (cover), panting, shivering, bathing, sunning
- adjustment of metabolic rate
89
what is the thermoneutral zone?
- temperature zone of level oxygen consumption
- above or below the zone extra energy must be used to keep warm or cool
- species-specific
- metabolic rate increases outside the zone
- by body size: larger in colder climates
90
what are birds' cold stress adjustments?
- circulation reduction in legs (by valves)
- energy saving when too costly for normal body temperature:
- normal hypothermia: body temperature drops 2-3C at night
- torpor: profound hypothermia temp drops 5-6C (hummingbirds, swifts, nightjars)
91
how do birds adapt to cold stress
- extra insulation on body, feet, head
- reduction of extremities
92
how do birds respond to heat stress?
- panting (gular flutttering)
- raising feathers
- wetting feathers, bathing
- exposing blood engorged legs to breezes
93
avian drinking and excretion
- water loss replaced by drinking and/or metabolic water from food
- a few species use metabolic water only
- excretion: via kidneys using uric acid to dispose of nitrogenous waste, uses less water than urea
- seabirds: use salt glands to purge the blood of excess salt (can only drink seawater)
94
describe the avian digestive system
- no teeth, designed to swallow unchewed food
- food stored and softened in crop and ground up in muscular gizzard
- acidic stomachs to dissolve bones
- indigestible items formed into bolus and regurgitated (hawks, owls, gulls, fish-eating birds)
- some birds (ex. waterfowl) eat grass: rapid processing of low energy food through the gut
- scavenging birds routinely ingest and regurgitate indigestible items
- procellariiform birds concentrate food as stomach oil retained for long periods for chicks and to spit at predators
95
what are the parts of the avian brain?
forebrain, midbrain, and hindbrain
96
what is the forebrain for?
- centre for olfaction
- centre for learning and problem-solving
- 'intelligence'
97
what is the midbrain for?
- centre for vision
- coordination and balance
- physiological controls
- hormones
98
what is the hindbrain for?
- centre for linkage of the peripheral nervous system to the brain
99
what happened to the brain as birds evolved from reptiles?
- vast increase in midbrain and forebrain
- development of thee corpus striatum (striped body) especially the hyperstriatum and Wulst regions
- cerebral cortex is tiny and has minimal function
- same functions are carried out in different tissue types between birds and mammals
100
characteristics of the avian brain
- functional lateralization: right and left brains with different functions
- asymmetry in function vs morphology
- compartmentalized: functions have specific places in the brain where they ask place
101
what is the hippocampus?
the anatomical structure which stores memory information
102
what experiment proved hippocampus is used in memory?
- lesions to hippocampus destroyed ability to remember locations
- control lesions to nearby parts had no effect on spatial memor
- comparing anatomy: only food cachers have greatly enlarged hippocampus
103
what is a bird song?
- complex vocalizations produced by syrinx
- in some species acquired by hearing songs of conspecifics and learning
- in others song is innate
104
anatomy in brain for bird calls
- bird song controlled by left hemisphere
- new synapses grown during song learning
- species with complex songs have larger song nuclei
- males song nuclei larger
105
how does eye focusing work in birds?
both the cornea and lens change shape
106
bird retina
- relatively large number of cones
- no embedded blood vessels
107
what are fovea?
- deformations of retina
- higher cone density
- site of greatest sharpness of vision
- some birds have multiple
108
what is pectin?
- complex pleated or fan-like structure within eyeball
- function not well known
- probably serves to supply oxygen to the eye structure
109
how does ultra-violet sensitivity work in birds?
- cornea and lens are transparent to ultra-violet
- retina sensitive to these wavelengths
- birds can see a broader range of wavelengths than mammals
110
describe the hearing ability of birds
- not particularly amazing, most birds more dependent on vision
- no ultra-sonic hearing (<10Hz not audible)
- infra-sonic hearing (<20Hz sounds) better than mammal (for navigation)
111
what are some special uses of hearing?
- echolocation: oilbirds, swiftlets cave-dwelling, use audible clicks for navigation
- prey location: nocturnally-hunting owls
112
describe facial asymmetry in owls
- evolved several separate times in most nocturnal of owls
- permits prey location by sound alone in vertical and horizontal planes while owl keeps head level
113
describe bird smell ability
- most have a poor sense of smell
- olfactory bulb of bird's brains is usually tiny
- evidence of smelling ability has been found in most birds but far less important than vision
114
what are some birds with acute olfactory abilities?
- petrels: extremely good for foraging at sea, get trace odours and navigate colonies at night
- kiwis: nostrils at bill tip for foraging for earthworms
- honeyguides: locate bee nests by smell and guide mammalian predators there
- vultures: can detect even faint odours of rotting flesh
- crested auklets: can detect and orient to their species' distinctive tangerine-like odour
115
what is the magnetic sense?
- birds can navigate without any other aid than orientation to the earth's magnetic field
- magnetite crystals found in the forehead of pigeons
- rhodopsin: a pigment found in bird eyes, capable of producing nerve impulses in the presence of magnetic field
116
what is the difference between pure tone and harmonic vocalizations?
- pure tone: on a single frequency at a time
- harmonic: at multiple, related frequencies
117
physical properties of sounds
- high frequencies propagate poorly compared to low
- pure tones propagate better in cluttered environments
- short duration, frequency-modulated sounds are more locatable
- sounds with harmonics have greater complexity
- bird sounds adapted to acoustical environment of the performers
118
examples of non-vocal bird sounds
- ruffed grouse: wing drumming
- common snipe: tail feathers
- american woodcock: wing feathers
- short-eared owl: wing slapping
- common nighthawk: wing slapping
- woodpecker: bill drumming
119
what is the syrinx?
- avian vocal organ
- located near junction of bronchi (at base of trachea, inside chest)
120
where does air supply for vocalizations come from?
air sacs
121
what are the 3 components of the avian vocal apparatus?
- intraclavicular air sac
- tympaniform membrane
- syringeal muscles
122
how are sounds produced and modulation controlled?
- by tension on tympaniform membranes
- by air pressure
- by shape of air passage
123
what does bilateral symmetry of syrinx allow?
possibility of different sides producing different sounds ('two-voices') ex. song of wood and hermit thrushes
124
what is the difference between call and songs?
- calls: short simple vocalization, usually given by both sexes
- songs: lengthy, complex, repeated vocal displays often performed by males during the breeding season, for the purpose of territorial defense and mate attraction
125
what are avian vocabularies or vocal repertoire?
- repertoire of structurally and functionally different types of vocalization
- includes song (a single element of repertoire) and variety of calls (usually 5-15 elements, more in passerines)
126
list typical constituents of vocal repertoire
- alarm calls
- aggressive calls
- contact calls
- warning calls
- courtship calls
- song
127
how are songs and calls related to species recognition?
- songs are cnospicuously different among different species even if similar in appearance
- ex. willow and alder flycatchers originally identified as separate by song, later confirmed by genetics
- pre-mating isolating mechanism: only mate with individuals with sounds of their own species
- facilitated huge radiation of passerine species due to rapid evolution of distinctive songs
128
explain individual recognition by sound
- acoustic signals: individuals recognize each other in situations where vision is not an option ex. at night, in dense cover, in dense colonies with similar looking individuals
- between parents and young, mates, and rival territory holders
- individual distinctiveness of sounds evolves when it is needed, as does ability to recognize (brain space limitations)
129
explain the recognition case of ancient murrelet
- nocturnal seabird, nests in burrows on forested islands
- mates never see each other in the colony
- parents never see their offspring in burrow
- parents take their 2 day old chicks to sea and care for another 6 weeks
- burrow is hundreds of metres from ocean
- solution: adults and chicks have individually distinctive calls, each parent recognizes calls of its 2 chicks (converged)
- each chick recognizes calls of its parents (not converged)
130
examples of number of songs sung by birds
- single song: white-throated sparrow
- several songs: western meadowlark
- many songs: mockingbird, winter wren, marsh wren
131
how are songs learned?
- acquired by inheritance (ie genetic innate songs), by learning, or by invention (improvisation) or a combination of these
132
examples of different ways repertoire is acquired
- non-passerine birds: typically inherited songs
- inter-specific brood parasites: innate songs
- passeriformes: calls often innate while ones are learned
133
how does song learning work in passeriformes
- most diverse avian order
- extreme development of song learning
- unique brains related to learning ability
- vocal imitative learning = culture
- mostly in the first year of life
- individuals reared in isolation and exposed to conspecific songs after a year never acquire species typical songs
134
what are the 4 phases of song learning?
1. critical learning period
2. silent period
3. subsong period (babbling)
4. song crystallization
135
hypotheses to explain evolution of song repertoires
- why have more than one song?
- anti-habituation hypothesis (Hartshorne): one song is boring and listeners quickly lose interest
- different songs - different functions hypothesis: different songs have different meanings or messages
- Beau Geste hypothesis (John Krebs): repertoire function to confuse neighbours about how many individuals occupy an area
- badge of status hypothesis: large repertoire indicates experienced high quality male that would be a formidable adversary
- location confusion hypothesis (Eugene Morton): a way males prevent their neighbours from knowing their location
- sexual selection hypothesis (John Krebs): more elaborate repertoire more attractive
- functionless epi-phenomenon hypothesis: song repertoires have no function and are simply an unselected consequence of birds having big brains, song learning ability, and spare time
136
hypotheses on origins of bird song dialects
- unselected consequence of learning (null hypothesis)
- social signalling hypothesis (Payne): imitation of successful neighbours
- ecological hypothesis: dialects function to signal genetic adapted-ness to local environment
137
two functions of gonads
1. gamete production
2. sex hormone secretion
138
describe avian male gonads
- paired internal testis
- seasonal changes in size related to serum testosterone concentration cued by changing day length
- testosterone: determines behaviour and development of ornamental feathers and wattles
- comparative: testis size relates to body size and mating system (high frequency copulation = bigger testis)
- after production sperm go to seminal vesicles
- avian semen chemically different from mammals
139
sperm physiology
- acrosome, midpiece, tail
- morphology varies among different groups of birds
- ex. tail helical in passeriformes, twists or spins rather than tail beating
140
explain sex determination in birds
- by inheritance of sex chromosomes at fertilization
- ZZ male and ZW female
- female birds can adjust the sex ratio of their eggs to produce offspring of the desired sex depending on mate quality and/or environmental conditions
141
describe avian female gonads
- usually a single ovary on left side
- seasonal changes in size
- morphology like cluster of grapes - ova with small amounts of yolk
- at onset of breeding season ova mature one by one inside follicles
- mature ovum breaks free of follicle and enters infundibulum (ovulation)
- shell added let before egg is laid
142
how does bird sex work?
- straightforward internal fertilization (oviparous)
- dorsal mounting is universal
- cloacal kissing
- never multiple participants
- variable frequency
- diurnal
- some male birds have intromittant organ
143
what is an intromittant organ and what birds have one?
- external appendage on male cloaca
- grooved (unducted)
- variable in size and morphology
- multiple independent evolutionary events in Aves
- facilitates transfer of sperm
- found in species with high copulation rates
- ex. ducks to facilitate transfer of sperm underwear
- ex. white-billed buffalo weaver has biggest due to high copulation rates
144
where does fertilization take place?
- in the infundibulum
- sperm reach infundibulum within 30 minutes of copulation
- fertilization usually takes places within a few days of copulation
- some sperm remain viable for weeks-months
- sperm storage glands/tubules: store and protect sperm for later fertilization
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what is sperm competition?
- narrow definition: competition between/among sperm of 2 or more males to fertilize egg(s) within reproductive tract of a single female
- broad definition: involves all male and female behaviour, anatomy and physiology associated with competition for fertilization's, wherever females copulate with more than one male
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historic vs modern view on bird polygamy
- historic view: birds are monogamous creatures
- modern view: birds are socially monogamous but in many species individuals mate with others other than their primary partner (extra-pair copulations)
- evidence from DNA fingerprinting
- widespread extra-pair paternity
- longer sperm found in species wth more frequent EPCs
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examples of birds with extra-pair copulations
- northern fulmar
- smith's long spur
- red-winged blackbird
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why copulate with more than one partner?
- males: to increase number of offspring sired
- females: to ensure fertilization, to increase genetic diversity of offspring, to assess qualities of alternative male partners
- in most species forced EPCs impossible but frequent in others such as mallards
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behaviour associated with sperm competition
- mate guarding: by males to guard their paternity
- opportunistic sex by females
- frequent copulation: by pair male to increase chances of paternity
- differential investment: by males, according to chances of paternity
- cloacal pecking: in dunnocks
