The invention of hook tools greatly enhanced our ancestors’ foraging capacity through the development of productive fishing technologies and weapons of enhanced killing power. The New Caledonian crow is the only other species known to craft hook tools in the wild, providing insights into technological evolution. Hook tool manufacture in crows has been described as a complex, multi-stage process, although this was based on a few observations from a handful of birds. Here we ran experiments with a larger sample of wild-caught crows. We showed that hook manufacture by crows can be more variable than previously thought, and can involve two hitherto-undescribed behaviours: ‘pulling’ for detaching stems and bending of the tool shaft. Additional analyses suggested that the variation was at least partly due to seasonal changes in raw material properties. Our results indicated a plausible scenario for the evolutionary origins and the diversification process of hook tool manufacture in New Caledonian crows. Furthermore, our analyses of a link between raw-material properties and aspects of tool manufacture provides an alternative hypothesis for explaining regional differences in tool behaviours observed in New Caledonian crows, and some primate species.