The corvids are the most intelligent birds. Yesterday I learned how to clean chimneys properly (most commercial sweeps are rip offs and I can save myself 70 Euro for their 'service'). Both chimneys had jackdaw nests that blocked them. Now we got all the soot, twigs, sheep hair and intriguingly blue
razors, clothes pegs and plastics. It was strange because no other colours were present. Why? jackdaws are the only member of the crow family that have blue eyes. So I reckon they use these plastic artefacts as a proxy, i.e. beware this nest is already in use by a jackdaw.
I came to the hypothesis/conclusion after having discovered a razor and clothes peg in the second chimney. A team of researchers from Cambridge reached the same conclusion in 2014. I could have done it for half the price.
After analysing 40 videos of jackdaws peeking into each other’s nest boxes, she found that compared with the other nest boxes, those that contained the picture of a jackdaw with its bright eyes was much more likely to deter the birds from landing on it, and that the birds spent less time near such a nest box.
So, jackdaws build scarecrows.