Does retreating from going to a location at night due to fear of Jinn after hearing a nocturnal bird's sound and assuming a connection between it and the Jinn count as "Tatayyur" (superstitious belief in omens) and pessimism?

At-tiyarah (omen-taking) is a form of shirk, and it is being pessimistic about something seen, heard, or known. It contradicts Tawhid because the one who takes omens severs his reliance on Allah and depends on other than Him, attaching himself to something that has no reality.

As for a person's fear that the sound of a bird might indicate that he has seen a jinn, this does not fall under at-tiyarah. Rather, it is a feeling of dread of the place for fear of harm from the jinn. The hadith "If you hear the crowing of roosters... and if you hear the braying of donkeys..." testifies to the possibility of animals seeing jinn, just as harm from jinn to humans is possible.

Whoever fears this must not exaggerate their delusions and must rely on Allah. The sound of a bird has no indication of seeing jinn; this is merely a waswasah (whispering/obsessive thought) that must be treated.