What else makes a senior developer different from their more junior colleagues?

Most senior developers have a much [wider range of extensive duties in addition to the normal work of software development. In particular, they are likely to be responsible for leading a team of developers, or for managing a number of teams of developers.

At one end of the leading/managing spectrum, the form of leadership may be more in the style of a Scrum Master. At the other end of the spectrum, the senior developer might be working on organizational issues or perhaps focusing on activities related to keeping the business profitable.