What is the primary factor cited for the apparent population increase and range expansion of the Eastern Phoebe?

Answer

The availability of man-made structures like bridges, culverts, and barns.

The availability of man-made structures provides abundant, secure, sheltered niches, correlating directly with human activity and allowing the population to potentially better cope with environmental pressures.

What is the primary factor cited for the apparent population increase and range expansion of the Eastern Phoebe?
raritybirdPhoebe