Habitat use of two sibling species, the Short-toed Calandrella brachydactyla and the Lesser Short-toed C. rufescens Larks in mainland Spain
Published: Volume 49(2), December 2002. Pages 259-272.
This paper makes a comparative analysis of (1) the physical factors and habitat types that determine the spring abundance of the Short-toed Lark and the spring and winter abundances of the Lesser Short-toed Lark at a wide, peninsular scale and (2) the microhabitat use of both species with respect to vegetation structure. In the first analysis we considered 82 localities, while the second was based on presence-absence data for the species along 100 m transect lines (1036 transects in 34 localities). Short-toed larks were present in 82% of the census localities. Its abundance was primarily linked to habitat type, longitude and bioclimatology. General linear models including these variables explained approximately 40% of the variation in the abundance of this species. Lesser Short-toed larks displayed a more restricted breeding distribution (33% of localities) and its abundance was basically linked to the type of habitat (29% of variance explained by the model). In winter, the localities where this lark was contacted were the same as in spring. Annual rainfall was the only predictor variable for abundance in winter (26% of variance). The transect lines where Short-toed Larks were contacted differed in practically every structural parameter of vegetation from those where it was absent. This pattern was similar for Lesser Short-toed Larks in spring, while in winter there were differences in the cover of short shrubs (<40 cm tall) and the mean vegetation height only. The comparison of vegetation structure in localities where one species or the other was present revealed differences in the vegetation parameters in transect lines with either recorded presence or absence. In the sympatric localities, the observed frequencies for transect lines with either one or the other species were lower than expected. In these localities, a discriminant analysis based on vegetation structure traits classified correctly 100% of observations of one lark or the other. Although the mechanisms involved in the segregation of these two larks in the sympatric zones are not clear, the results indicate a spatial segregation on two scales: i) geographic, determined by physical factors as well as habitat type, and ii) local, set by certain parameters of the vegetation structure. Differential microhabitat use by the two species, together with a clumped distribution of Lesser Short-toed Larks, may be the cause of this segregation, although interspecific territoriality should not be ruled out. The range of the vegetation structure parameters selected by the two sibling larks may prove to be highly useful in designing conservation programmes for these two species, classified as vulnerable in Europe.