This post accompanies: Is the Brown Creeper more than one species?
The songs of Brown Creepers do vary regionally, but the variation is subtle and complex and not very obvious (at least to our ears). Regional differences in song may offer the strongest support for splitting Brown Creeper into multiple species, but remain virtually unstudied.
Hejl et al (2002) report, anecdotally, differences in song between study sites in Idaho, coastal Washington, and California (note that the Washington and California samples would presumably both be part of the new Pacific group). Baptista and Johnson (1982) found differences between songs near San Francisco and a site only 140 km south. These results show that there are regional dialects within the potential new “Pacific” species, and similar dialects probably exist within the Rocky Mountain and Eastern populations as well, which will make it harder to detect differences between those larger populations.
Careful comparison of the recordings linked below (songs of Brown Creeper from Xeno-Canto) reveals differences, but much more study is needed to determine how consistent these differences are across populations. Most importantly, field studies are needed to determine whether the birds recognize any differences.