Die Ansiedlung junger Kleiber(Sitta europaea) im Spätsommer und Herbst

Zusammenfassung

In einer Laubwaldfläche von 8 ha wurden Kleiber farbberingt. Gefangene Kleiber riefen beim Freilassen im Revier, wenn sie seßhaft und gepaart waren; sie riefen nicht außerhalb ihres Reviers. Nach diesem Kriterium war die Untersuchungsfläche vollkommen in nicht-überlappende Reviere aufgeteilt. Zwischen August und Dezember 1982 verschwanden 5 ♀, aber nur ein ♂. Sie alle wurden durch neue Vögel ersetzt. Ein Revier wurde durch ein überlebendes ♂ und ♀ von zwei nebeneinanderliegenden Revieren besetzt, die sich verpaarten. Dispersion von juv. fand im August, weniger im September statt. Beim Ansiedeln halten sich junge Kleiber einzeln an der Grenze zwischen Adultrevieren, wobei sich je nur ein Individuum jedes Geschlechts am gleichen Ort aufhält. Falls diese Grenzgebiete durch das adulte Paar nur wenig verteidigt werden, kann dort ein neues Revier entstehen. Häufiger jedoch ersetzten diese juv. einzeln einen verschwundenen Revierinhaber, wobei sowohl das weniger günstige Revier als auch der eventuelle Partner in diesen Zwischenrevieren verlassen wurden.

Summary

In a small deciduous woodland plot of 8 ha, in which nuthatches have been trapped occasionally since 1981 we made a detailed study of the Nuthatch population between August and December 1982. We found that Nuthatches, released after capture, will call if territorial and released inside their territory but will not call if released outside their territory. We used this criterium to delimit the part of the home-range that formed the territory and found no overlap between territories. At the beginning of August 7 territories were occupied by adults. Six of the males and 3 of the females had been trapped, in the same territory in the previous winter. Between August and December 5 females and only one male disappeared. All birds disappearing until October were replaced within two weeks. The two other birds, which disappeared later, a male and a female from neighbouring territories, were not replaced. Their surviving partners formed a new pair claiming both territories.

Our data show that juvenile dispersal is most intense in August, although the movements recorded were over short distances only. Of the 15 juvenile or unpaired nuthatches trapped, 6 remained for a maximum of 8 days. The remaining birds (4 ♂, 5 ♀) settled in the study area for varying periods of time. One juvenile pair settled, at the beginning of August, in part of an adult territory. The other juveniles settled individually either as replacements for disappeared adults, or at the border between territories. These birds in small transit territories gradually replaced paired territorial birds which had disappeared, or they disappeared themselves. In December only one unpaired male remained in such a transit territory. We conclude that young Nuthatches settle individually at the borders between adult territories whereby only one bird of each sex occupies the same site. If these border areas are poorly defended by the adult pair a new territory may be formed. More often, however, the juveniles will individually replace territory holders, which have disappeared, whereby they abandon both the (poorer) territory and an eventual partner. We suggest two reasons why Nuthatches do not follow the “Underworld Strategy” of Costa Rican Sparrows: (1) young Nuthatches are produced only once a year, so that, if they survive sufficiently long, they will eventually find a vacant territorial position; (2) Nuthatches cannot hide while feeding, since feed mainly on trunks and thick branches.