Pseudopodoces humilis, a misclassified terrestrial tit (Paridae) of the Tibetan Plateau: evolutionary consequences of shifting adaptive zones

Abstract

Pseudopodoces humilis (Hume's Ground‐Jay) is a small passerine bird that inhabits the high rocky steppes of the Tibetan (Qinghai–Xizang) Plateau. Although it was long classified as a small species of ground jay (Podoces), two previous anatomical studies cast doubt on its assignment to the Corvidae (crows and jays). We studied the evolutionary relationships of Pseudopodoces using three independent datasets drawn from comparative osteology, the nuclear c‐myc gene, and the mitochondrial cytochrome b gene. All three datasets agree on the placement of Pseudopodoces in the family Paridae (tits and chickadees). The cytochrome b data further suggest that Pseudopodoces may be closest to the Great Tit Parus major species group. Pseudopodoces is the only species of parid whose distribution is limited to treeless terrain. Its evolutionary relationships were long obscured by adaptations to open habitat, including pale, cryptic plumage; a long, decurved bill for probing in crevices among rocks or in the ground; and long legs for terrestrial locomotion. Despite these accommodations to a novel adaptive zone, its evolutionary affinity with the Paridae is clearly expressed in comparative osteology and genetics, and is supported by its habit of nesting in cavities.