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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	[Parental investment of Jackdaws Corvus monedula in a colony in Sachsen-Anhalt, eastern Germany.]
Auteurs :	Christoph Unger, Auteur ; Hans-Ulrich Peter, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (123(2) 2002)
Article en page(s) :	55-64
Résumé :	A Jackdaw colony in an old monastery was studied in 1996 and 1997 with particular emphasis on parental investment and provisioning of broods. Two nests were surveyed by video (ca. 150 hours per nest). Adults were individually colour-marked to study sex roles. Jackdaws bred in nest-boxes on the building since 1988, the colony contained 10-12 breeding pairs. Males provided 78-81% of the nestling diet; brooding of nestlings was performed only by females, who spent more time in the nest-boxes than males. The female's share in provisioning rose only slightly during the nestling period. Provisioning rates were highest when nestlings were 16-20 days old. No relationship between provisioning rates and ambient temperature was detectable. During their stay within the nests, females spent 10-12% of the time with care for nestlings, 4-7% with comfort behaviour; vigilance increased from initially 20% to about 43% over the course of the nestling period. Brooding intensity was independent of ambient temperature (70% of total time) up to a nestling age of 8-9 days, when chicks become thermoregulatory. After this stage, brooding intensity was clearly related to ambient temperature, varying between 11% on warm days (chick age 10-16 days) and 31% on cool days (chick age 17-20 days). Females provided intensive care (30-45% of total time in the nest) to nestlings during the time of feather growth. Overall, both sexes invested about equal amounts of time in caring for the brood, with males doing most of the provisioning and females most of the activities in the nest. The highest rate of chick mass gain was 8.4 g per day at an age of 3-12 days. Most mortality occurred up to an age of 14 days. Nestling mortality was high (62%), breeding success was low (1.6 fledged young per breeding attempt). This was most likely due to the low availability of insect food (normally 60-70% of nestling diet), which in turn was related to the habitat around the colony. Jackdaws need large tracts of grassland for foraging at close distance (600-800 m) from the colony. At the study site, however, grassland covered less than 10% of the area around the colony. The birds, therefore, fed a large propotion of human discards to their young.

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