This is the accepted version of the following article: Lee, A. M., Reid, J. M. and Beissinger, S. R. (2017), Modelling effects of nonbreeders on population growth estimates. J Anim Ecol, 86: 75–87., which has been published in final form at doi:10.1111/1365-2656.12592. This article may be used for non-commercial purposes in accordance with the Wiley Self-Archiving Policy [http://olabout.wiley.com/WileyCDA/Section/id-828039.html].