How can I block this venting from rodents?
The soffit vents are an important part of keeping airflow under your roof, lowering your cooling costs in the summer, and preventing ice dams in the winter.

You can screen over the gap, but I would look for a soffit vent strip that you can fit into the gap to give it a nice look and prevent any animals, or even insects, from getting in. My newest ridge vent included a plastic mesh underneath that wouldn't rot but would keep out any leaves and most insects. If you can find something like this for your soffit vent, that would be the best of both worlds: decent appearance without any bugs.