We investigated the effect of spatial autocorrelation on heritability (h2) estimates of laying date and clutch size in a population of great tits Parus major. We found that h2 of laying date, but not clutch size, declined significantly with increasing distance between the nestbox of mothers and daughters. This decline was caused by a decreasing effect of spatial autocorrelation in laying date, rather than by the existence of genotype–environment interactions (GEI). After correcting for the effect of spatial autocorrelation, h2 of laying date was low (0.16 ± 0.07), but significant, and surprisingly consistent with increasing distance between parental and offspring environments. The h2 of clutch size was not much affected by spatial autocorrelation.
Most previously published estimates of the heritability of laying date include various degrees of common environment effects, which can bias estimates both upwards and downwards. We suggest that using techniques that take spatial autocorrelation into account might be a fruitful approach to estimate h2 of traits that show a high degree of plasticity.