Nest site selection and breeding biology of Western House Wrens (Troglodytes aedon parkmanii) using natural cavities in Western Canada

House Wrens (Troglodytes aedon Vieillot, 1809) are among the best studied songbirds in North America, but most of what is known about this model species derives from studies using artificial nestboxes. Consequently, we know comparatively little about the natural breeding biology of House Wrens and whether it corresponds to patterns reported from nestboxes. To address these issues, we report a study of nest site selection and breeding phenology in Western House Wrens (Troglodytes aedon parkmanii Audubon, 1839) using natural cavities in aspen forests in southwest Alberta, Canada. A total of 96 breeding pairs, representing 77 different banded males, were studied across a 4 year period (2011-2014). In total, 78% of arriving males paired, with 52% of nests successfully fledging. More than 30% of males attempted polygyny, but only 8% succeeded. Distinct patterns were observed for many characteristics of the nest site and cavity, including the type of tree used, as well as the cardinal direction and dimensions of the cavity entrance, its location on the nest tree, and its height above the ground, some of which were related to pairing and breeding success. Results are compared with studies of House Wrens using artificial nestboxes with broader application to many other model species likewise studied primarily using nestboxes.