Lectures are a commonly used teaching method in higher education, but there is significant debate about the relative merits of different classroom practices. Various classroom observation tools have been developed to try to give insight into these practices, beyond the simple dichotomy of "traditional lecturing versus active learning". Here we review of a selection of classroom observation protocols from an ethological perspective and describe how this informed the development of a new protocol, FILL+. We demonstrate that FILL+ can be applied reliably by undergraduate students after minimal training. We analysed a sample of 208 lecture recordings from Mathematics, Physics, and Veterinary Medicine and found a wide variety of classroom practices, e.g. on average lecturers spent 2.1% (± 2.6%) of the time asking questions, and 79.3% (± 19%) of the lecture talking, but individuals varied considerably. The FILL+ protocol has the potential to be widely used, both in research on effective teaching practices, and in informing discussion of pedagogical approaches within institutions and disciplines.