Nest-box orientation influences reproductive outcomes and consistency in the lesser kestrel

Artificial nest-boxes are now vital for countering cavity-nester declines from habitat loss, but the impact of nest-box design on long-term breeding success is still uncertain. Using 23 years of data from a Lesser Kestrel (Falco naumanni) colony in central Greece, we compared vertical and horizontal nest-box designs to assess effects on occupancy, breeding phenology, reproductive output, and particularly the repeatability of key breeding traits. Repeatability measures how much of a trait’s total variance is due to consistent, site-specific differences-like a stable microclimatic or nest-box structure–as opposed to random year-to-year variation. It shows what portion of variability is explained by persistent nest site features, versus what is due to chance. Vertical nest-boxes were used more often and had slightly higher average productivity. However, horizontal boxes had higher repeatability for clutch size and fledgling number. For both nest-box types, phenological traits like laying, hatching, and fledging dates -showed low repeatability, suggesting annual environmental changes were more influential than nest-site features. Our results indicate that the most-used nest boxes do not always provide the most consistent breeding conditions, emphasizing the need to assess both productivity and its temporal consistency in conservation programs.