1. Hatching asynchrony decreases the magnitude of parental care in domesticated zebra finches: empirical support for the peak load reduction hypothesis. Ethology 120:
Mainwaring Lucy Hartley

2. Hatching Asynchrony
Offspring from a single reproductive event hatch/born over extended period of time

3. Hatching Asynchrony
Offspring from a single reproductive event hatch/born over extended period of time
Hypotheses concerning the functional significance of hatching asynchrony fall into
four broad types. Hatching asynchrony might:
arise because of selection on the timing of events during the breeding cycle;
facilitate the adaptive reduction in brood size;
increase the energetic efficiency of raising the brood, or
be non-adaptive and result from environmental or phylogenetic constraints .
From Magrath 1990

4. Peak load reduction hypothesis

5. Hatching Asynchrony
Title –Include the species name!
First criticism
one species
one species
not mentioned
one species

6. Hatching Asynchrony
-seems maladaptive – reduced survival of later born offspring
Incubation behaviour ⇒ level of asynchrony
∴ hatching patterns should be an optimal strategy for parents
AND
Benefits offspring – reduces sibling competition & begging intensity ?

7. Hatching Asynchrony
Support for hypotheses - mixed
Mock & Schwagmeyer (1990)
-Energy savings for parent - minimal
-need large clutch size and extreme asynchorny
Empirical support – depends on the species worked on

8. What does this have to do with load reduction hypothesis?
Hatching Asynchrony
Final point in introduction -
-may have a role in sexual conflict
-if parents provision differently
∴ have parent-offspring conflict & male-female conflict at the same time
What does this have to do with load reduction hypothesis?

9. Species used and Hypotheses
Domesticated Zebra finch – Taeniopygia guttata
Replicating study done with wild finches
-lay egg/day for 5 days
-incubate from outset
-early hatchlings get more food ⇒ grow larger
Hypotheses
1) Parental feeding effort will be greater in synchronous broods
2) Male and female will differ in provisioning

10. ♂ ♀ Materials and methods Nest box Used males and breeding females
What does “breeding” female mean?

11. Materials and methods
-took eggs each day & replaced with artificial egg
- Put in a bowl to mimic nest conditions
“turned daily to prevent the yolk from settling” ??
-no effect of manipulations on hatching success

12. Materials and methods
Quantifying parental behaviour
-videotaped for 3h – start between 9 and 10
-recorded when chicks were between 8 and 13 days old
-chicks marked with white correction fluid
Recorded
1) which nestling got food
2) Duration of regurgitation feeding
3) Maximum begging intensity score for each nestling

13. Materials and methods
Quantifying parental behaviour
Recorded
1) which nestling got food
2) Duration of regurgitation feeding
3) Maximum begging intensity score for each nestling
Said this was a measure of feed load size
4 point scale

14. Materials and methods
Statistics
Tested covariance of a number of factors
What they did is poorly explained

15. Materials and methods
Statistics

16. Where is synchronous vs asynchronous?
Results
Where is synchronous vs asynchronous?
No mention of females

17. Justification??
Equations??
r2 ??
p values??

18. Discussion
1. Main finding – parental feeding effort lower for asynchronous broods
???
Hatching asynchrony decreases the magnitude of parental care in domesticated zebra finches: empirical support for the peak load reduction hypothesis.

19. Discussion
1. Main finding – parental feeding effort lower for asynchronous broods
2. No benefits to nestlings from reduce parental workload
3. No difference in begging intensity between the hatching patterns
-rejection of sibling rivalry reduction hypothesis

20. Discussion
1. Main finding – parental feeding effort lower for asynchronous broods
2. No benefits to nestlings from reduce parental workload
3. No difference in begging intensity between the hatching patterns
-rejection of sibling rivalry reduction hypothesis
4. No support for the parentally-based favouritism hypothesis
Not clear from their results if this is valid or not
- Especially given the way they measured food delivery

21. Discussion
Final point in discussion
-dealing with domesticated birds
-asynchrony good for parents but no advantage for offspring
How does this related to theories of parent-offspring conflict?

22. Discussion
Final point in discussion
-dealing with domesticated birds
-asynchrony good for parents but no advantage for offspring
Compared their study to Gilby et al (2011)
- similar result except for reduced begging in wild birds
Domesticated
Wild
-ad lib food
-search for food
-frequent feedings
-less frequent feedings
-predator free
-predator present
-chicks beg more
-chicks beg less

23. Discussion
Are we then functionally dealing with the same species?

24. Discussion
Is this evolution or just phenotypic plasticity?
Are we then functionally dealing with the same species?

25. Questions??