“…Moult begins immediately subsequent to, or in some cases during, breeding (Hussell, 1983). The species’ wide distribution and resilience to study has led to their extensive use in ecological applications such as impact assessment, where physiological biomarkers would be useful tools (Ghilain and Bélisle, 2008; Harms et al ., 2010; Custer, 2011; Paquette et al ., 2013; Cruz-Martinez et al ., 2015). Finally, tree swallow flight feathers are uniformly dark, preventing confounding effects of pigment differences when comparing feather CORT levels (Jenni-Eiermann et al ., 2015).…”