Behavior toward vocalizations of the sibling species, interspecific territoriality and habitat in the Goldcrest and Firecrest (Regulus regulus, R. ignicapillus)

Abstract

Playback experiments showed that Goldcrest (Wg) and Firecrest (Sg) not only posses species specific songs (fig. 2), but also calls which are distinguished from those of the sibling species (fig. 4). The territories of the two species normally overlap in areas where they occur syntopically (fig. 5). In Central Europe 2 of 35 Sg-♂ were interspecifically territorial, while no interspecific territoriality was found among 35 Wg-♂. The highest population densities of Wg and Sg in Central Europe are attained in spruce and fir forests. There is no evidence for the preference of decidous forests by Sg, nor for the displacement of Sg into such forests by Wg. Pine forests are avoided by both species. Playback experiments support the results of sonagraphic analysis which was able to show neither character displacement in sympatric areas nor a reduced contrast in the songs of allopatric areas. Interspecific territoriality occurs only exceptionally. In two areas of Spain near Soria and Luarca a higher number of interspecifically territorial ♂ (Soria: 6 of 17 Sg, fig. 9; Luarca: 2 of 4 Wg), as well as males singing both Wg and Sg songs (or mixed songs; fig. 8, 10), were found in the species occuring with the much lower population density. This can be explained through incorrect imprinting on the song of the sibling species and is not attributable to increased song similarity ("character convergence", Cody 1974), ecological factors or hybridization. Allopatrically occuring Wg-♂ do not reaot any more than sympatrically occuring Wg to the song of Sg (fig. 6 a), but 53 and 64% of Sg-♂ in two areas where only Sg occurs react to the song of the sibling species (fig. 7 f, g). Since reduced contrast in the song has been disproved as the reason for this, it may be that allopatrically occuring Sg possess a less selective releasing mechanism. This would mean that when in sympatry with Wg, Sg must learn not to react to the song of the sibling species. In Wg and Sg, reaction to the song of the sibling species, interspecific territoriality and mixed singing males seem to be the result of errors in the imprinting processes. © 1977 Verlag der Deutschen Ornithologen-Gesellschaft.