Context-specific territorial behavior in urban birds: No evidence for involvement of testosterone or corticosterone

►Urban Curve-billed Thrashers and Abert's Towhees are more aggressive than desert conspecifics. ►Total nor free testosterone or corticosterone explains this aggressive behavior. ►Urban towhees are more aggressive in high population density areas. ►Urban thrashers are more aggressive in isolated patches of “desert-like” vegetation. ►Free-ranging birds may assess territorial quality and alter defensive behavior accordingly.