Reproductive success of the northern cardinal, a large host of brown-headed crowbirds

Article Abstract:

The impact of brood parasitism by brown-headed cowbirds on the reproductive success of northern cardinal is examined. Observations during the breeding seasons from 1993 to 1995 indicate that nest survival was greater in parasitized than unparasitized nests in all phases of the nesting cycle. It was found that parasitized cardinals did not experience losses related to lower hatching success or nestling competition. Also, there was no difference in the growth rates of cardinals in parasitized and unparasitized nests, and in the growth rates of cardinals and cowbirds in a single nest.

Parasitism, Animal reproduction

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Nest defense by willow flycatchers to brood-parasitic intruders

Article Abstract:

An investigative study deals with the adaptive value and specificity of the willow flycatcher's responses to brown-headed cowbird intrusions. The flycatchers were hypothesized to be less prone to the parasitic intrusions of cowbirds because of their relative quietness when near their nests. The flycatchers' responses to the simulated and live intrusions were found to vary with the context of the intrusion. Results show that the willow flycatcher sample differentially recognized female cowbirds and differentially responded to them according to their distance from the nest.

Muscicapidae, Flycatchers, Bird eggs, Bird nests

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Vicinity of sparrowhawk nest affects willow tit nest defense

Article Abstract:

Female willow tits reduce their defense intensity directly in proportion to the closeness of their nests to the nearest sparrowhawk nest. It is clear in terms of spatial arrangement that tits breeding close to sparrowhawk nests face hawks more regularly than tits breeding further away. The distinct nature of the responses to the sparrowhawk nest distance was corroborated by the control experiment. There is no dependency on hawk-nest distance in responses towards stoats.

Hawks, Nest building

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