Lecture Topic: Leks, Brood Parasitism,
Cooperative Breeding
Leks:
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males have display (type D) territories.
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all parental care by females in area away from male territories.
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traditional lek: many males display together in arena
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dispersed or exploded lek: males separated
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examples in: Galliformes, Charadriiformes; several families of Passeriformes
(e.g.manakins, cotingas, bowerbirds, birds of paradise)
Hypotheses for the evolution of multi-male arenas (traditional leks):
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female preference: females preferentially mate with males in a clump (more
choice of males possible).
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"hotspot": leks form in areas where females are likely to occur for other
reasons.
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"hotshot": leks form when less successful males cluster around a high quality
(hotshot) male.
Brood Parasitism: laying eggs in another bird's nest
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intraspecific "egg-dumping" vs. interspecific parasitism
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occurs in: Anseriformes (e.g. some redheads), Cuculiformes (some old-world
cuckoos), Piciformes (indicator-birds), Passeriformes (e.g. cowbirds, indigobirds)
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some parasites are specialists on one species (ex: indigobirds); others
are generalists, parasitizing many species (ex: brown-headed cowbirds.)
Benefits of parasite
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freedom from parental care
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decrease predation risk
Some parasite adaptations to decrease competition with other nestlings
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short incubation period, rapid nestling growth
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behaviors, structures of some young parasites -- killing other young, or
pushing eggs out of nest
Cost of parasitism to host
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generally higher cost to altricial than precocial species
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among altricial species, extremely variable: ingigobirds parasitizing firefinches,
little impact on firefinch survival; brown-headed cowbirds here often result
in death of all other nestlings
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expanding range of brown-headed cowbirds implicated in decline of songbirds;
range expansion has occurred because of habitat modification (more edge
habitat created by human activities.)
Adaptations of potential hosts to parasites: egg rejection, nest abandonment
Counteradaptations of parasites: egg matching (ex: European cuckoo
gentes)
Cooperative breeding: individuals other than the parents of young
help raise the young.
Phylogenetic and geographic trends:
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found in many species of: coots, gallinules (Ralidae), kingfishers (Alcedinidae)
and other Coraciiformes, woodpeckers (Picidae), jays & crows (Corvidae)
their & Australasian relatives, shrikes (Laniidae), wrens (Troglodytidae);
also found in few/ species in many other groups (e.g. the pygmy nuthatch).
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more common in milder climates (e.g. tropics)
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ex: local shrikes, wrens are not cooperative breeders but many tropical
shrikes, wrens are.
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particularly common in Australian groups
Why be a helper instead of breeding?
Helpers are often relatives (usually offspring from previous nest of
helped parents)
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helping relatives may evolve because helping relatives, who share one's
genes, gets those genes passed from generation to generation
Kinship is not the only factor involved; in many non-cooperative breeders
offspring leave the area instead of staying to help.
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little, no, or low quality breeding habitat available; high cost to leaving
parental territory
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Florida scrub jay: extreme habitat specialist; high competition for suitable
habitat
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acorn woodpecker: success depends on a "granary" -- a tree where acorns
are cached; there are a limitted number of territories with granaries.
Helpers may get direct benefits:
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get experience in raising young
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helpers may actually breed