Snell, C. L., LaZerte, S. E., Reudink, M. W., & Otter, K. A. (2016). Sympatric song variant in mountain chickadees Poecile gambeli does not reduce aggression from black-capped chickadees Poecile atricapillus. European Journal of Ecology, 2(1), 53-59. https://doi.org/10.1515/eje-2016-0006