The mod was included in a config pack called 'Pigeon Mod Pack' (or whatever), and it's outdated at the moment.
https://www.beamng.com/resources/pigeon-mod-pack.1642/ it was this one to be specific its unsupported but seeing as little was done to the pigeon it should still work
Imagine if someone added giant bird wings to the Pigeon, BeamNG can simulate that, I've seen flying creatures before