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Accueil du site → Doctorat → États-Unis → 1965/1969 → PHYSIOLOGICAL AND ETHOLOGICAL ADAPTIONS OF THE RUFOUS-WINGED SPARROW (AIMOPHILA CARPALIS) TO A DESERT ENVIRONMENT

University of Arizona (1969)

PHYSIOLOGICAL AND ETHOLOGICAL ADAPTIONS OF THE RUFOUS-WINGED SPARROW (AIMOPHILA CARPALIS) TO A DESERT ENVIRONMENT

Ohmart, Robert D.

Titre : PHYSIOLOGICAL AND ETHOLOGICAL ADAPTIONS OF THE RUFOUS-WINGED SPARROW (AIMOPHILA CARPALIS) TO A DESERT ENVIRONMENT

Auteur : Ohmart, Robert D.

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 1969

Résumé
A 4-year study was conducted to determine the physiological and behavioral means whereby the Rufous-winged Sparrow, an endemic resident of the Sonoran Desert, successfully meets the demands of a hot, dry desert. Pair bonds and territories are maintained for life, but when reproductive rates were high (2.7 young fledged per pair), several additional birds associated with the territorial pair in winter. Territorial defense was year round in years of lower reproductive success. A daily summer foraging cycle was present, in which the birds foraged on unshaded ground surfaces at moderate temperatures early and late in the day, moved into shaded ground situations as temperatures rose and foraged in shrubs during the highest daily temperature. During the hottest portion of the day, foraging ceased and the birds sat in the shade inactive. Insect and possible plant materials were consumed during the shrub shade foraging. Foraging habits combined with an efficient kidney allows the species to exist without free water in a hot, xeric environment. Rufous-winged Sparrows normally nest only after the beginning of summer rains in July ; gonadal recrudescence occurs from early March into mid-June. The sparrows may nest In spring following unusually heavy winter and spring rains. Gonadal enlargement may be completed as rapidly as 3 weeks. Summer rainfall appears to be the stimulus initiating summer nesting, but an abundant food supply may stimulate spring breeding. Mean fledging success in summer ranged from 1.1 (6 pairs) to 2.7 (10 pairs) young per pair. Greatest success was associated with high insect densities resulting from heavy initial summer rains followed by frequent moderate showers. High insect densities serve as a buffer and reduce predation upon vulnerable Rufous-winged Sparrow nests. Low summer rainfall and low insect densities were associated with heavy nest destruction and low fledging success. Spring nesting occurred only twice and an average of 0.3 (4 pairs) and 1.1 (11 pairs) young per pair fledged. The data was highly suggestive that clutch size was regulated by food supply. Clutches following the summer rains all contained three eggs. Clutches laid in spring or subsequent clutches after the rains, contained from two to four eggs. I feel that the present age difference between New World deserts and the more ancient deserts of the Old World is less important for the evolution of highly specialized adaptations to a desert existence than is currently believed. Magnitude of the desert and selection pressure resulting from aperiodic rainfall appears to have been more important for avian specialization than time.

Mots clés : Adaptation (Biology) ; Birds — Arizona.

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