In 2016 I joined the Limpopo Dwarf Mongoose Project as a Research Assistant. This is a long term behavioural study. Mongoosers (an informal title) work 6 days a week collecting data and carrying out experiments. The work is with habituated mongoose groups so you can really observe them closely. Dwarf mongooses are cooperatively breeding social mammals with loads of interesting behaviours and complex group structures.
For the sake of ease I have formatted this in the same way as previous reviews of volunteer experiences, but it was more like a job (without the payment aspect, I suppose).