FIGURE 1.

Relationship of variation in pectoralis muscle mass (ΔPectoralis Mass) with variation in summit metabolic rate (ΔM_sum) across a range of natural acclimatization (winter vs. summer in climate with cold or mild winters, migratory vs. non-migratory conditions) and experimental acclimation (cold vs. warm, flight training vs. control) for birds. A linear regression on these data indicated no significant relationship (F _1,17 = 1.918, p = 0.184), including after removal of the “Mild Winters” data point (F _1,16 = 2.775, p = 0.115), suggesting that despite increases in both M_sum and pectoralis muscle mass often occurring under conditions of increasing energy demand in birds, the two traits are not tightly coupled. Data from Swanson (1990), Swanson (1991), Swanson (1995), O’Connor (1995a), O’Connor (1995b), Cooper (2002), Cooper and Swanson (1994), Petit et al. (2014), Liknes and Swanson (2011), Sgueo et al. (2012), Swanson et al. (2014a,b), Milbergue et al. (2018), Noakes et al. (2020), DeMoranville et al. (2019), King et al. (2015), Zhang et al. (2015), Vézina et al. (2006).