Morphological variation in the Sabota Lark Calendulauda sabota in southern Africa
Separation of the eight southern African subspecies of Sabota Lark Calendulauda sabota into thick-billed and slender-billed groups has been proposed. This study used biometric data obtained from museum skins in South Africa to evaluate morphological variation in the subspecies as a basis for the delineation of Sabota Lark into the thick-billed, slender-billed and intermediate groups. Six mensural characters were measured by a single researcher. Box plots were used to identify outliers, the 75% rule for diagnostics was applied to determine whether subspecies were distinct, and discriminant function analysis was used to evaluate the validity of the thick- and slender-billed groups, and the existence of a putative intermediate group. The results of this study support the separation of Sabota Lark into slender-billed (C.s. sabota, C.s. sabotoides, C.s. suffusca and C.s. waibeli) and thick-billed (C.s. bradfieldi, C.s. herero and C.s. naevi) groups based on culmen-nare length and bill width. The results failed to provide evidence for an intermediate group. Some C.s. ansorgei specimens had thick-billed characteristics, whereas others had slender-billed characteristics, implying sympatry of the thick- and slender-billed groups in southern Angola and north-western Namibia.
Keywords: 75% rule for diagnostics, Alaudidae, biometric data, delineating subspecies, discriminant function analysis, geographic variation