Relationship between testes mass and testosterone (T) levels before handling (baseline), post-handling, and after a GnRH injection. Relationship between testes mass and testosterone (T) levels before handling (baseline), post-handling, and after a GnRH injection. Orange data points represent control birds; gray data points indicate chronically disturbed birds; shaded areas denote 95% confidence interval for the slope of the regression line. Mikus Abolins-Abols et al. J Exp Biol 2018;221:jeb180869 © 2018. Published by The Company of Biologists Ltd