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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Function of stone carpets at the nest entrance of Blackstarts Cercomela melanura
Auteurs :	Reuven Yosef, Auteur ; Daniel Afik, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (120(3) 1999)
Article en page(s) :	155-161
Résumé :	Several hypotheses try to explain the role of paving the nest area with flat stones as it occurs in several desert bird species. Suggestions range from discouraging predators to protection from weather, camouflage, facilitation of self-incubation by its ameliorative influence on the nest's micro-climate or sexual display. We suggest that in the cavity-nesting Blackstart stones at the entrance, along the tunnel leading to the nest, and the pile on which the nest is built could moderate large temperature shifts and have a thermoregulatory function. Stones might help to absorb heat and radiation during the day and radiate it back when temperatures drop in the evening and during the night. We studied three Blackstart nesting cavities at En Gedi, Israel, and made temperature measurements at various positions inside and outside the cavities. In all three cases the nests were placed on a layer of stones half-way into the cavity. Temperature fluctuations at the nests were within a narrower range than outside the cavity. The depth of the cavity influenced the range of temperature fluctuations, but temperatures were not significantly different between the deepest point of the cavity and the nest location. The one active nest studied had a greater variance in temperatures than the two pre- or post-breeding cavities, probably due to the adult birds bringing in outside air when entering the cavity. Apparently Blackstarts choose the optimal nest location based on the cost:benefit ratio of energy required to crawl in the narrow corridor and the minimum length of tunnel required to minimize temperature fluctuations. Our study illustrates that the self-thermoregulatory/incubation hypothesis could, at least partly, explain the building stone ramparts around, or in front of, nests of desert species.

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