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Biological sciences

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Egg laying in Dusky Flycatchers and White-crowned Sparrows

Article Abstract:

The physiological processes involved in egg formation determine the daily egg-laying schedule in passerine birds such as Dusky Flycatcher (Empidonax oberholseri) and Mountain White-crowned Sparrow (Zonotrichia leucophrys oriantha). The hour of laying changes every day over a range of almost 10 hours in the Dusky Flycatcher, whereas the Mountain White-crowned Sparrow lays in the early morning across a range of three hours. Factors such as food intake and energetic costs probably influence the time of egg development in the oviduct. Oviposition intervals in some species may thus depend on processes controlling egg production.

Muscicapidae, Flycatchers, Bird eggs, Bird nests

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Effects of sex and birth date on premigration biology, migration schedules, return rates and natal dispersal in the mountain white-crowned sparrow

Article Abstract:

Natal dispersion of Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) occurs right after fledging. Migration starts on or near September 25, and this species exhibits increased mortality with later birth dates. Natal dispersal distances are greater and philopatry lower in females because females are more vagile as juveniles. Homing ability and philopatry in males is directly proportional to the juvenile time spent on the study area. Familiarity with the breeding area in males enhances breeding success. Dispersal patterns in females may be due to intrasexual competition.

Animal migration, Sexual behavior in animals, Animal sexual behavior, Animal dispersal

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Nest predation in the Mountain White-crowned Sparrow

Article Abstract:

The nest predation rate in Mountain White-crowned Sparrows was studied. Nestling sites along the Sierra Nevada mountains were observed to determine the various known and potential predators of the sparrows' nests. The predation rates per day were then calculated according to Mayfield's technique. Results indicated that the nest predation rates in Mountain White-crowned Sparrows do not vary with parental age.

Predation (Biology)

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