"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'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 k*lls parasites that may try to hide in the nest and infect the chicks.

Smaller bird species have been sighted stealing the anti-bird spikes that we put on buildings and lining their nests with them, like little palisade walls against other birds and predators. A small species like a songbird can navigate the spikes easily, but it makes it more difficult for a predator like a hawk or a rat to get to the nest.

Crows have also been observed stealing lit cigarettes from ashtrays and wafting the smoke through their feathers to k*ll parasites."