For what it is worth, I was the one who suggested it could just be for
decoration of the nest, or for repelling some insect/predator. Although I have
no evidence either way. I just would think it unlikely that the things would be
eaten later. This decoration idea is in the way that Diamond Firetails weave
flowers into their nest and if I remember that correctly Riflebirds use
snakeskin. My reason for suggesting a good biting would be the way the adult
birds immobilise caterpillars is because so many birds that eat caterpillars
either belt them against a branch or rock or whatever and/or give them a
thorough nibbling, before eating them and I couldn't imagine a chemical
retardant being used, as was suggested in Frank's original question. A very
good question by the way! I wonder how widespread the practice is and what
level of evidence there is that the birds eat the caterpillars. Is it just a
odd thing that has been copied from one book to many others?
As for someone doing a PhD about that. Imagine how much time would be spent
looking for the things to get any kind of usable data.
Philip
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