La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

Titre :	How does the size of beech crop influence population density and breeding biology of the Nuthatch Sitta europaea in the Harz Mountains?
Auteurs :	Herwig Zang, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (124(4) 2003)
Article en page(s) :	193-200
Résumé :	Annual beech Fagus sylvatica crop varies greatly between four levels (0 = low to 3 = high). In a study area in the Harz mountains, beech crops were intermediate (levels 1, 2) from 1981 to 1991 with low fluctuations, but between 1992 and 2002 full beech crops (3) or complete failure (0) happened in quick succession. Effects of this variation on the population and breeding biology of Nuthatch were studied from 1982 to 2003 based on a total of 409 broods (all of them in nest-boxes). The size of beech crop in the proceeding year positively influenced population density and breeding success, advanced average hatching date, but was associated with lower average clutch size and reproductive output per successful pair. These correlations were statistically significant from 1993 to 2003 only, but not between 1982 and 1992. The influence of forest damage through "acid rain" (Waldschaden) on beech crops and consequently on the Nuthatch population is discussed. It appears that the quick succession of full and zero beech crops between 1993,and 2003 had a negative effect on the development of Nuthatch population.

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