Yep, I had one on the manifold of my New Holland loader tractor the other day. It's used for at least an hour every single day.
I posted about it the other week under the title 'Fire Hazard' or something similar.
Had the same on my NH tractor. I’d removed the half built nest twice before, but this time it was built and eggs laid . The tractor was parked up for about a week. Did the same on a different tractor last year as well. It’s a pied wagtail. Unfortunately I had to remove the nest, but hoped she’d find them in a box nearby, as needed the tractor again.
Very common cause of tractor fires. Needs to be added to pre start checks in spring and summer really. Amazing how small a gap they get through on some machines.
A bit of road work often helps the fire get going. Seen a few burnt out on the road side a km or so from farm drives.
Don't know for sure but I'd guess that's what happened to this one.
Black birds are good at that, I reckon they can build a nest in a day or two that's how long the defender stood there for, next thing a ruddy blackbird had built a nest under the bonnet blow me if it didn't do the same thing the following year in the same defender!!!