Nicht-territoriale Systeme bei Corviden: das Beispiel des Tannenhähers (Nucifraga caryocatactes) in den Alpen

Abstract

The Nutcracker is considered a territorial species even though some studies have shown that conflicts are rare. Previous research suggested that Nutcrackers from two Alpine sites did not use territories during autumn and winter. The aim of the present study was to describe the Nutcracker’s spacing system during the reproductive period to provide a general interpretation of its spacing ecology. The study was carried out from March to May in the Aleve forest (north-western Italian Alps) with radio-tracking and bird census techniques. Vocal activity was recorded throughout the year to make possible a better interpretation of the census results; recorded calls were also used for experimental play-back tests in the field. Home ranges were very small (median value of 22 ha, minimum convex polygon 95 %) and overlapped to a great extent (72 %, on average). No territorial confrontation was detected. Strangers were usually tolerated near the nest and a few experimental playback tests elicited no significant interaction initiatives. Present data indicate that the Nutcracker cannot be considered territorial, at least in our study area. We believe the spacing pattern of this species can be explained, at least partially, by its storing habit. In typical territorial systems, food resources are threatened by neighbours or strangers. In the Nutcracker’s spring spacing system, food stores are not threatened because their location is known only to the owner. Thus, border trespassing is tolerated because strangers or neighbours are not food competitors. Estimates of Nutcracker density varied significantly among months, habitats and years. Arolla pine forests were preferred over the other habitats, probably because of autumn seed availability there. Vocal activity, which was weather-dependent, significantly changed among periods. Seasonal variations in vocal activity suggest caution when densities are compared among different periods.