Figure 5 from: Yosef R, Pande S, Pawashe A, Mahajan M, Mahabal A, Dahanukar N (2011) Biometry based ageing of nestling Indian Spotted Owlets (Athene brama brama). ZooKeys 132: 75-88. https://doi.org/10.3897/zookeys.132.1346

Figure 5 - Flight formula for different age groups of nestling Spotted Owlets (Athene brama brama). Box plot of flight formula index are plotted for different age groups. When the flight formula approaches unity birds are ready to fly.