Densities and distributions of commensal feather mites (Zachvatkinia caspica) among the primaries of Caspian Terns

Abstract

This study employed a means of indexing the abundance of Zachvatkinia caspica (Mironov, 1989), an analgoid feather mite, among the primary feathers of its host, the Caspian Tern (Sterna caspia Pallas, 1770) in a manner that allowed for quantification of overall mite densities as well as spatial distributions of mites throughout the feathers. These mite-density estimates were used to examine properties of the hosts that may influence mite distributions both among different birds and within individual wings. Mite densities correlated negatively with host size and body condition (as indicated by fat reserves). Additionally mite loads on male birds were approximately 30% greater than those on female birds. Regarding within-host (or within-wing) mite distributions, mite densities were greatest among the outer five primaries and on the outer half of each feather, which contradicts predictions of spatial distributions based on aerodynamic considerations but roughly corresponds with areas of greatest barb height within the wing. Finally, a comparison of mite loads on old and new feathers showed mite distributions were uninfluenced by feather age. In summary, this study indicated that Z. caspica exercises a high degree of microhabitat selection and showed that although Z caspica is regarded as having no effect on its host, the abundance of these mites may be linked to the physical state of the host or sex-specific behavior.