What's nesting in our truck's engine? (Shallow Thoughts)

What's nesting in our truck's engine?

We park the Rav4 outside, under an overhang. A few weeks ago, we raised the hood to check the oil before heading out on an adventure, and discovered a nest of sticks and grass wedged in above the valve cover. (Sorry, no photos -- we were in a hurry to be off and I didn't think to grab the camera.)

Pack rats were the obvious culprits, of course. There are lots of them around, and we've caught quite a few pack rats in our live traps. Knowing that rodents can be a problem since they like to chew through hoses and wiring, we decided we'd better keep an eye on the Rav and maybe investigate some sort of rodent-repelling technology.

Sunday, we got back from another adventure, parked the Rav in its usual place, went inside to unload before heading out for an evening walk, and when we came back out, there was a small flock of birds hanging around under the Rav. Towhees! Not only hanging around under the still-warm engine, but several times we actually saw one fly between the tires and disappear.

Could towhees really be our engine nest builders? And why would they be nesting in fall, with the days getting shorter and colder?

I'm keeping an eye on that engine compartment now, checking every few days. There are still a few sticks and juniper sprigs in there, but no real nest has reappeared so far. If it does, I'll post a photo.