| Titre : | Selection of foraging sites in mixed Willow and Crested Tit flocks: rank-dependent survival strategies |
| Auteurs : | I. A. Krams, Auteur ; T. Krams, Auteur ; J. Cernihovics, Auteur |
| Type de document : | Article |
| Dans : | Ornis Fennica (78(1) 2001) |
| Article en page(s) : | 1-11 |
| Langues: | Anglais |
| Résumé : | The selection of foraging sites by Willow Parus montanus and Crested Tit P. cristatus flock members was studied in relation to the abundance of their arthropod prey in the plantations of young Scots pine Pinus sylvestris and in relation to hunting behaviour of Sparrowhawks Accipiter nisus. Arthropods were most abundant in the upper parts of the canopy and on the surface of ground vegetation. Sparrowhawks were seen attacking parids only in the upper parts of the canopy. The lowest parts of the pines were safer and this was confirmed by the anti-predatory vigilance of the birds. Crested Tits, top-ranking individuals in the mixed flocks, tended to be frequent ground feeders under snow-free conditions, which was not the case under snowy conditions suggesting the importance of snow cover. Although the lowest parts of trees was the poorest site in terms of arthropod abundance, dominant individuals of the Crested Tit remained there under snowy conditions. Foraging height of alpha individuals of the Willow Tit did not differ from one climate condition to the other. Subordinate Willow and Crested Tits, by contrast, significantly increased their foraging heights. Although subordinate Willow Tits foraged in the highest canopy parts, however, their survival rates did not differ from those of higher-ranked Willow Tits. The results suggest that foraging in the most vulnerable tree parts may not be always linked to the decreased survival. The observed shift of subordinate Willow Tits supposedly made their anti-predatory vigilance more effective, suggesting a possible trade-off between concealment and visibility. |
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