how impactful of a problem are birds, even small birds, to travel with?

someone said to ask here and that someone here would know about travelling with birds?

https://www.reddit.com/r/birding/comments/bkw7u7/how_impactful_of_a_problem_are_birds_even_small/

submitted by /u/bestminipc
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from Pets https://www.reddit.com/r/Pets/comments/bl8jjs/how_impactful_of_a_problem_are_birds_even_small/