Interspecific and sexual differences in morphometric characters in five thrush species of the genus Turdus (TURDIDAE, AVES)

Abstract

The data presented in this article is the first complex ecomorphological study of five close species of thrushes of the genus Turdus (T. pilaris, T. merula, T. iliacus, T. philomelos, and T. viscivorus). For the first time, on the basis of representative materials and using me­thods of univariate and multivariate statistics, the main forms of group variability and adaptive divergence were studied in the five species of Turdus. Interspecific and sexual differences in morphometric characters were also analyzed. In total, 124 museum specimens were processed, which were collected in the territory of the Ukrainian Polissia: fieldfare – 28 individuals (17 ♂, 11 ♀), song thrush – 27 individuals (14 ♂, 13 ♀), mistle thrush – 25 individuals (12 ♂, 13 ♀), blackbird – 25 individuals (12 ♂, 13 ♀), and redwing – 19 individuals (13 ♂, 6 ♀). It has been revealed that, according to the total body size, the five thrush species studied differentiate into groups of small (redwing and song thrush), medium (blackbird), and large (fieldfare and mistle thrush) species. The blackbird has the most unique body proportions, with a relatively large head, long beak, but shorter wing length. It is shown that sexual differences on the background of interspecific differences are practically not expressed in the five studied species. At the same time, it is important to emphasize that interspecific differences in linear body size are much larger than sexual differences. The mistle thrush and redwing differ the most in linear body size (DE = 51.0–60.4). The smallest differences are observed between the redwing and song thrush (DE = 10.1–15.1), as well as between the mistle thrush and fieldfare (DE = 8.1–16.4). Compared to the other four species, the blackbird has relatively longer head and, especially, beak, but shorter wing. In our opinion, these features in the body proportions of the blackbird are related to its life-style, and mainly to feeding specifics. According to the results of factor analysis, the first two principal components (PC1, PC2) quite fully (90.16 % of the total variance) describe the variation of the 14 morphometric characters in females and males of the five thrush species. The relatively high values of factor loadings of all characters on PC1 (-0.82…-0.98) indicate the consistency of their variability.