There is another reason that birds should be discouraged from nesting or setting up shop in a smithy. Especially in an indoor one. That extra reason is some very nasty fungal diseases, that are found in bird feces (xxxx).
San Joaquin Valley fever is found throughout the American southwest. It is a rare but very serious systemic disease. That fungus disease is Coccidioidomycosis.
Histoplasmosis is another very serious systemic fungal disease. It is found in bird feces, especially pigeon dung. That disease is common in the Mississippi River and St. Lawrence River valleys The fungus can remain as viable infectious spores in dust, for decades.
None of us needs bird dung build up in our work shops. (there are other nasty fungus diseases like Blastomyces, Nocardia, Aspergillus etc., but I've made the point.)
Permit me to be a little clearer. One bird and one nest should not be a problem. Many roosting birds and their poop is.
SLAG.