1. 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 bird’s 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

2. Energy – Yolk
Protein – yolk and albumen
Calcium/phosphorous – shell
Water – Albumen
Oxygen – Air Cell in part
Waste – uric acid (allantois)
CO2

3. Outside
Chorion or
Chorioallantois

4. 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

5. 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

6. Usually 1 egg/24 hrs. Laid in AM - Why?
Fertilization
Magnum – 3hrs
Isthmus 1 hr
Uterus 19-20hrs
Cloaca minutes
Usually 1 egg/24 hrs. Laid in AM - Why?

7. Incubation of eggs – provide heat (below 26 devpt stops)
and shade (>40 fatal)
Brood patches – Prolactin, estrogen and progesterone in either or both sexes
Incubation periods
Time on nest
Time off nest

8. 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

9. Megapodes and Incubation via external heat sources - geothermal/biotic decay
Australian mallee fowl

10. Hatching -

11. Developmental Mode
Precocial (ancestral)
Altricial
Ugly!
Cute
Table 18-6

12. 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 maturation of quail leg
muscles reduces energy for growth
early on, then costs of locomotion and
feeding do so slower to reach adult size

14. Extremes of parental care
None
Helpers
Parents plus
Previous broods
Abiotic incubation
Brood Parasitism
Single parent
Both
Intraspecific brood parasitism
“Egg dumping”
Ducks, colonial swallows
Interspecific brood parasitism
Cowbirds, cuckoos, honeyguides

15. 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)

16. Helper’s at the Nest - why forego reproduction and help?
Offspring perspective:
Direct benefits:
Indirect benefits:
Ecological Constraints

17. 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)
Seasonality – greater the pulse in resources over
baseline, the greater the clutch (latitude)