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19 Cards in this Set
- Front
- Back
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Cooperative Breeding
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any situation where >2 individuals care for a clutch/litter of young
'helping behavior' |
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2 types
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*Pair helped by greater than or equal to 1 non-reproductive helper
* more than 3 adults in a group all mate and all rear a clutch/litter of young |
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Benefits
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* with mate sharing- some chance that helpers are caring for their own young (shared matings hypothesis)
* Helpers may be gaining experience at caring for young (experience hypothesis) * helpers may be 'paying' for the right to remain in thier natal territory (payment to stay hypothesis) * Helpers may be indirectly passing copies of their genes to future generations by helping close relatives (kin selection hypothesis) * Helpers may be trying to impress possible future mates (mate attraction hypothesis) |
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CB in Australia
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More common than in N hemisphere
-why? * Unpredictable climate makes it difficult for young birds to breed * have high survival rates, so vacancies are rare on territories sutible for breeding |
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Grey-crowned babblers –early work on cooperative breeding in Australia: experimental approach to determine whether helpers really do help
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• Occur as pairs with
helpers (older offspring), up to 12 birds/group • Insectivorous, feed mostly on ground • Live in open eucalypt woodlands Control- left alone Experimental- Removed all but one breeding pair, and one helper Control- reared average amt (2.4) of fledgleings Experimental- (.8) Helpers did help- KIN selection hypothesis |
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Dusky moorhens (Gallinulatenebrosa) – cooperative breeding involving mate-sharing
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• 1-4 adults of each sex in
each group • All males usually mate with all females –mating system called polygynandry • Females from a group lay eggs in a joint clutch • All adults incubate eggs and care for young • All group members jointly defend their territory |
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Dusky moorhens are unusual
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* Genetic polygynandry
Chicks raised in a single clutch can have multiple genetic mothers and fathers * The adults within a group are not close relitives |
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Why they are polygynandrous
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* Have very specific requirements for breeding
* Likely that only a fraction of the pln can get space for breeding territories * Possible that larger groups are better able to defend breeding territories--> maybe Y unrelated indiv band 2gether |
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Why do they do it?
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'Shared mating hypothesis'- all group members help b/c they might be mother or father of some of the offspring
NOT KIN selection hypothesis Helping by juvenile dusky moorhens- only happens when a group has two successful clutches in the same season |
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Cooperative breeding in white-winged choughs (Corcoraxmelanorhamphos)
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• Are obligate cooperative breeders – pairs without helpers can’t breed successfully
• Young birds of both sexes usually stay in their natal group, so group members are CLOSELY RELATED • Are not reproductively mature until at least 4 years old |
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Why is reproductive maturity so late in choughs?
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* It takes young several years to learn to feed themselves and nestlings efficiently
* This suggests that they wouldn't be able to breed succ before 4 |
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Why does learning to feed take so long
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* Young are fed for 4-8mo
* feed by searching soil and leaf litter for inverebrates- takes a while to learn * Dig to 15cm deep * In breeding season- choughs spend all say foraging * unpredictable climate * when not nesting, home ranges of groups can be 25km2 |
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Helpers, do they help?
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YES!
have higher repro sucess More helpers= greater # of young that survive Pairs of 2 or 3 never successful, can never pair up and breed |
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Why do helpers help (in choughs)
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-Experience hypothesis: staying at natal groups and helping to raise young- learn about foraging and gain experience
-Kin Selection hypothesis: most helpers are closely related to the young theyre raising -Payment to stay hypothesis: have to help if they want to stay in their group |
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Kidnapping
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In territorial battles fledglings switch and live with other group
Helpers from the larger group attract fledglings |
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Why kidnapping?
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- kidnapped young do well in new group
- at 15-20 birds they split into smaller groups. get to large size quicker - provide helpers for new breeders in new smaller units - stop inbreeding |
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Noisy miners (Manorinamelanocephala)
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the extreme of cooperative breeding
• In the honeyeater family • Eat primarily nectar and insects • Highly social species • Unlike most other cooperative breeders, are not territorial • Each female has one mate, who is most likely to have fathered her young, but young are also cared for by male helpers • Nestlings are fed by up to 22 males; on average ~4 • Males help at multiple females’ nests |
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Why do male noisy miners help at so many nests?
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• Known that males in such a
community of noisy miners tend to be close relatives, so some degree of KIN SELECTION is involved in helping behaviour (kin selection hypothesis) • if a female’s mate dies, she is likely to take the best helper at her nest as her new mate (mate attraction hypothesis) |
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Why do some species have helpers?
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• If breeding vacancies in good territories are rare, young birds may have to delay their own breeding
• In this case, it is often safest for them to stay in their natal territory • It may then be beneficial to them to help –either to gain kin selection benefits, gain experience at rearing young, or impress possible future mates • In other cases, birds who can’t breed on their own share mates |
