Hand-Wing Index as a surrogate for dispersal ability: the case of the Emberizoidea (Aves: Passeriformes) radiation

Abstract Measuring the dispersal ability of birds is particularly challenging and thus researchers have relied on the extended use of morphological proxies as surrogates for such ability. However, few studies have tested the relationship between morphological proxies and other dispersal-related traits. In this study, we test the relationship of the most commonly used morphological proxy for dispersal—the Hand-Wing Index (HWI)—with traits highly associated with dispersal abilities, such as geographic range size, migratory behaviour and migratory distances. We used the Emberizoidea superfamily to evaluate these relationships and measured the HWI of 2520 individuals from 431 species (almost half of all the species in the superfamily). We first estimated the phylogenetic signal of HWI and searched for the best evolutionary model to explain its variation. We then performed PGLS analyses to assess the relationships between HWI and dispersal abilities. Our results showed that HWI has a strong phylogenetic signal and is positively related to dispersal abilities. Our findings support the use of HWI as a viable morphological proxy for dispersal in birds.