How to connect the vertices of two separate objects? While I was modelling a bird I ended up in a dead end and I do not know how to get out. I created the eyes of my bird as two separate objects using the mirror modifier, but now I can no longer connect the eyes vertices with those of the rest of the face because I have two different objects.

If I join the eyes vertices with the face/body vertices using Ctrl+J I will lose the mirror modifier, but I don't want to loose the mirror modifier for the eyes.  So I don't see a way out from this situation.
Could you not work with one eye and your faced joined up and mirror afterwards?.

Highlight the eye vertices in edit mode with  with C or B then separate by selection with P and apply the mirror to new object creating your second eye. As long as it lines up nice it would get you your mirror option back.