Birds have been observed intentionally lining their nests with cigarette butts. While the nicotine in them is toxic to the birds, it’s a low enough dose that it it’s not a significant risk to them in the short term (they don’t live long enough for the long term effects to be a problem), and it kills parasites that may infect the chicks in the nest.

Crows have been observed stealing lit cigarette from ashtrays and wafting the smoke through their feathers to kill parasites.

And smaller bird species have been seen stealing anti-bird spikes from buildings and putting them in their nests like little palisade walls against other birds and predators. The smaller birds can get through the spikes easily, but it makes it more difficult for a predator like a hawk or a rat to get into the nest.