Last Saturday, on 5 March 2016, Erika and I encountered a Back-capped Chickadee giving a “gargling” call, with which we were unfamiliar. Gargles are poorly understood calls. They can be complex and variable, containing up to 23 syllable types. Gargles are components of aggressive displays and are often given in winter (Foote et al. 2010).
We are not sure if this chickadee was being aggressive towards us or to other chickadees. Perhaps the bird was defending sap dripping from a nearby branch. The chickadee made repeated visits to the branch, where it drank the sap. Curiously, the above-cited authors do not mention that chickadees drink sap. The behavior is well-known. Bazilchuk (in nasw.org) mentions that chickadees feed on sap icicles. Undoubtedly sweet sap contributes to the high energy needed to survive our cold and often barren winters.