Utilisation de l’espace par deux espèces jumelles Certhia brachydactyla et familiaris en zone de sympatrie

Abstract

The use of space by two sibling species of passerines, the Treee creeper, Certhia familiaris and the Short-toed Tree creeper C. brachydactyla was studied in the Alpes-Maritimes, Southern France. The two species were found differ mainly by their altitudinal distribution, the Short-toed Tree Creeper living at low altitudes, and the Tree creeper occuring at higher elevations. This replacement took place gradually, and an important area of sympatry was found between 1200 and 1800 m above sea level. In this altitudinal belt each species had a definite preference for a few tree species (the Tree creeper for Spruce Picea excelsa and Fir Abies alba, and the Short-toed Tree creeper for Scots pine Pinus silvestris), as well as for a different kind of forest (the Tree creeper prefering dense stands, and the Short-toed Tree creeper more open ones). In Larch Larix decidua forests at middle altitudes, however, the two Tree creepers were found to occur at similar densities and were syntopic. In such Larch woods, a large overlap of foraging sites (substrate, foraging height, and foraging posture) was observed throughout the year. No interspecific territoriality was noticed during the breeding season, and the two species displayed few interspecific reactions to song playback. Interspecific agonistic behaviour was observed at four occasions only. Therefore, these two morphologically very similar species did not show any evidence of competition during their reproductive season in Larch woods. Some spatial segregation did, however, occur in winter, when the Tree creepers joined flocks of tits, in which the two species were seldom seen together.