Feather trace element profiles in urban mountain chickadees differ from adjacent rural chickadees

Worldwide, urbanization has transformed natural habitats and introduced a range of threats to the species living therein, including exposure to trace elements, including heavy metals. In interior British Columbia, Mountain Chickadees (Poecile gambeli) live and breed in both rural and urban habitats. We asked whether trace element concentrations (Be, Mg, Al, V, Cr, Mn, Co, Cu, Zn, As, Se, Mo, Ag, Cd, Sb, Ba, Hg, Tl, Pb, and U) in the feathers of urban-dwelling chickadees differed from their rural counterparts and, if so, whether the concentrations of trace elements differed by sex or were associated with body size/condition or reproduction. Zn, Mg, Al, Ba, and Sb were all found in higher concentrations in the feathers of urban birds. In contrast, Be, V, Cu, and Se were found in lower concentrations in urban birds. Unlike other studies, we did not find differences in Pb, U, or Cd between rural and urban birds. We found no differences between sexes; however, birds with longer tarsi had higher levels of Sb, while birds in better condition (mass/tarsus) had lower concentrations of Be, Zn, and Se and higher concentrations of Ba and U. In addition, females with earlier first egg dates had higher concentrations of Sb and lower concentrations of Zn. Pb was marginally negatively associated with the number of eggs and fledglings. Despite being separated by short distances (<5km), our results indicate distinct differences in feather trace element profiles between urban and rural nesting mountain chickadees and indicate that future work on the role of Pb and Zn on the physiology and reproduction of urban mountain chickadees may be warranted.

Methods
Combination of field data (age, sex, morphometrics, breeding success) and trace element concentrations.