Body condition and head size in snakes

On several occasions during my many years of working with various snake species, I observed a significant positive relationship between body condition and head size (the former calculated from residual scores from a general linear regression of ln-transformed mass on ln-transformed snout-vent length). Based on results from my long-term study of water pythons (Liasis fuscus) this relationship is, however, most likely caused by a condition-dependent bias when recording snake snout-vent length (SVL). Water pythons in good condition were recorded as being "shorter" and hence having relatively larger head size, whereas snakes in poor condition were recorded as being "longer" with concomitant smaller head relative head size. Such a systematic bias may lead to spurious conclusions concerning the adaptive significance of the relationship between snake body condition and head size. © Koninklijke Brill NV, Leiden, 2011.