Cleidoic, Amniotic Egg Amazing Life Support System

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Cleidoic, Amniotic Egg Amazing Life Support
System I think that if required on pain of
death to name instantly the most perfect thing in
the universe, I should risk my fate on a birds
egg Higginson 1863 Handling all
metabolic requirements and byproducts independent
of parent except temperature regulation
Egg Size, Shape and Color shaped by Morphology
grebes versus owls Life History cavity
versus cup vs ground Chick development
precocial vs altricial
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Energy Yolk Protein yolk and
albumen Calcium/phosphorous shell Water
Albumen Oxygen Air Cell in part Waste uric
acid (allantois) CO2
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Outside
Chorion or Chorioallantois
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Shell porosity adaptations
Length of incubation
Shearwater incubation 2.5X longer than
chicken 2 x fewer pores
Burrow-nesting seabirds More pores
Nest microclimate
Black tern- wet nests Fewer pores
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Fertilization, Egg production, Early Development
All Birds Internal Fertilization and Oviparous -

• Sex Organs Male Homogametic ZZ
• Testis and Penis/Cloacal Protuberance CP
• Female Heterogametic WZ
• Ovary (ovaries)
• Copulation
• 3) Internal Fertilization
• Ova (Ovum) released via LH
• Yolk 1/3 Lipid, ¼ Protein, Water
• Associated compounds (androgens,
  carotenoids)
• Maternal Effects

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Fertilization
Magnum 3hrs
Isthmus 1 hr
Uterus 19-20hrs
Cloaca minutes
Usually 1 egg/24 hrs. Laid in AM - Why?
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Incubation of eggs provide heat (below 26 devpt
stops) and
shade (gt40 fatal) Brood patches Prolactin,
estrogen and progesterone in either or both
sexes
Incubation periods
Time on nest
Time off nest

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• Given that 1 egg laid/day, brooding of multiple
  egg clutches can
• Begin immediately after first egg asynchronous
  hatching of young
• Falconiformes, Strigiformes, Ciconiiformes,
  Pelecaniformes, Psittaciformes
• Delay incubation until clutch is laid
  synchronous hatching

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Megapodes and Incubation via external heat
sources - geothermal/biotic decay
Australian mallee fowl
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Hatching -
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Developmental Mode
Altricial
Precocial (ancestral)
Ugly!
Cute
Table 18-6
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Contrasts of precocial vs altricial
development Precocial advantageous because once
hatched, chicks can immediately fledge
(nidifigous) feed on own and escape nestling
predators. Disadvantage eggs take longer to
develop, longer exposure to egg
predators Altricial allows greater growth (esp
of brain) before maturation, so larger brain
size Due to trade off between organ growth and
differentiation (maturation) Disadvantage
although egg stage shorter, nestling phase
longer, greater nestling predation risk,
increased demands of parental feeding of
nestlings
Fig 16-4 maturation of quail leg muscles reduces
energy for growth early on, then costs of
locomotion and feeding do so slower to reach
adult size
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Extremes of parental care
None
Helpers Parents plus Previous broods
Abiotic incubation Brood Parasitism
Both
Single parent
Interspecific brood parasitism Cowbirds,
cuckoos, honeyguides
Intraspecific brood parasitism Egg
dumping Ducks, colonial swallows
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Evolution of brood parasites Increasing
adaptations Increasing host species
Faster devpt, In utero incubation, earlier
hatching, Egg ejection and host killing behaviors
Figure 19-5
Common Cuckoo egg mimicry (on W chromosome)
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Helpers at the Nest - why forego reproduction
and help?
Offspring perspective Direct
benefits Indirect benefits Ecological
Constraints
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Clutch Size Determinate vs. Indeterminate Layers
- will a bird replace eggs?
Clutch size variation Correlated variables
Lower latitude, lower altitude, body size,
age Evolution Lack (1947) maximum parents
can feed and nourish Alternatives Trade-off
hypothesis long-term repro output reduce
clutch to inc adult survival Predation
reduce time exposed , attractiveness and cost
of loss where predation high (tropics) Seasonali
ty greater the pulse in resources over
baseline, the greater the clutch
(latitude)