Swallow Calendar
riowang.blogspot.comThe article mentions the swallows arrived in early March, but sometimes as early as mid February, during the 18th century... that seems really early, which indicates the weather was actually warmer than today?
I wondered if the Julian/Gregorian adoption might have had something to do with it, but no, italian states were early adopters, having already swapped in the XVI.
https://upload.wikimedia.org/wikipedia/en/timeline/9pg7rf83a...
Not a meteorologist, but from my understanding that would be quite unlikely[1]. Furthermore, it seems odd that warmer temperatures in the area they are migrating to would trigger an early arrival (how would they know?). A more plausible hypothesis might be abnormally cool summer/early fall in the southern hemisphere, or other conditions local to the swallows southern nesting sites.
skip down (~40%?) to find the actual description of the calendario delle rondinelle.
Or start at the top and enjoy a gentle introduction to the place where this calendar is found.