The feeding ecology of mountain chickadees (Parus gambeli): patterns of arthropod prey delivery to nestling birds

The diet of nestling mountain chickadees (Parus gambeli) (55 694 items in 34 730 feeding trips) is summarized. Larval Hymenoptera, Lepidoptera, and adult Coleoptera were the most common prey in the nestlings' diet. A single prey item was usually delivered per trip. Significant intersexual differences in delivery of specific prey types were rare; intersexual differences in overall diets declined with nestling age. Prey delivered by individual parents exhibited decreasing day to day variation as nestlings aged. Frequency of prey preparation declined with nestling age, with feeding frequency, and especially with increasing number of prey delivered per trip. Delivery of some prey, such as spiders, changed as a function of nestling age, whereas delivery of other prey was more directly related to calendar date and, by implication, to prey availability and environmental conditions. Take of most prey exhibited significant diurnal variation related to prey behaviour and to periodicities in nestling hunger state. Time spent waiting at the nest entrance often took up a greater portion of each foraging trip, and was more variable, than prey preparation time or travelling time between nest and foraging site and should be incorporated into foraging models.

Extensive Protein Similarity of the Hybridizing Chickadees Parus atricapillus and P. carolinensis

Starch gel electrophoresis of proteins was used to assess genetic differentiation and introgression across a contact zone between Parus atricapillus and P. carolinensis. Little or no differentiation was found at 35 presumed genetic loci, even between distantly allopatric population samples. Nei's (1978) genetic distance (D) was ≤0.001 for all comparisons. In contrast, Parus gambeli, another chickadee known to hybridize with atricapillus, was well differentiated at 3 loci (D ≈ 0.065). While the data suggest that atricapillus and carolinensis are closely related, they do not allow conclusions on the extent of introgression across the contact zone. The implications of these data are discussed in the light of the emerging pattern of isozyme variation in birds.