brood parasitism - Brood Parasitism(laying your eggs in...

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Brood Parasitism (laying your eggs in another bird’s nest) Reproduction in birds is: Costly A big gamble (high predation) Two types: 1.Interspecific (species A parasitizes species B; obligate parasites) 2.Intraspecific (species A parasitizes species A) Brown-headed cowbird
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Interspecific Example #1: Cuckoos Largest group of brood parasites 50% of 130 species are brood parasites Egg laying is fast ( 5 seconds!) well – timed (this is critical) Parasitize small hosts Parasitize many species (but are not generalists)
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Cuckoos Usually 1 egg laid per nest Eggs mimic those of host Females keep an eye on nests and may move eggs When cuckoo egg hatches, the young evicts the host’s young and eggs This creates one “monstrous” young . .. why do parents feed it?
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Widow Birds Africa Highly specialized One species of widow bird parasitizes one species of host (estrilid finches, usually) Host young not evicted Female widow bird often removes one host egg Cost to host not severe Mimicry of eggs and young
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Honeyguides Africa and Asia Young kill host’s young in nest
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Cowbirds North and South America Young are not hostile, but host young often starve 6 species. Some parasitic. Some not. (A good group for seeing evolutionary progression to obligate parasitism) Bay-winged: not a brood parasite, but does use nests of other species. Screaming: only parasitizes bay-winged cowbird Giant: parasitizes 7 species, all icterids Shiny, Bronze, and Brown-headed: all parasitize many species.
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Ducks Black-headed duck (the only species that is an obligate brood parasite). Has many different host species (swans, gulls, coots, ibis, caracara) Host used essentially for incubation only Facultative brood parasitism is common in ducks (Manitoba study: 1 in 5 nests contained redhead eggs)
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Intra specific Brood Parasitism Conventional wisdom was : It’s rare Conventional wisdom now : It’s common and makes a lot of sense as a reproductive strategy. Example: Snow Geese 6% of chicks not related to parents Parasitic females have their own nest and lay eggs in nest of a neighboring pair. How to get egg into a guarded nest ….
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Another example of intraspecific parasitism Cliff Swallows Parasitic females always have their own nest. Nest in colonies, and parasitize neighbors
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brood parasitism - Brood Parasitism(laying your eggs in...

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