cowbird

Urban birds that nest in wooded areas don’t do as well (reproductively-speaking) as their non-urban counterparts. Conventional wisdom suggested that this was because of the presence of more egg-eating predators (eating bird eggs, obviously) in urban settings. New research suggests, however, that it might have more to do with fitter (larger, older) birds preferring (and getting) larger, non-disturbed wooded areas:

Urban areas attracted lower-quality birds which, compared to those in rural areas, arrived later in the spring, left earlier in the fall, made fewer nesting attempts and were much less likely to return to nesting spots from year to year.

Acadian flycatchers (Empidonax virescens) were the bird species studied, and it would seem that the urban flycatchers managed to raise one young versus two in the case of the non-urban flycatchers. Knowing just what makes these urban spaces unappealing to these birds is unknown. The brown headed cowbird (Molothrus ater) is a nest parasite–meaning that it lays eggs in another species’ nest and lets those birds raise the cowbird’s young–and is suggested as perhaps playing a role here. Urban nests were two times more likely to be parasitized than rural ones.

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