Start Pigeon season
The start of the pigeon season is often at a different time in the various countries. There are countries where a start is already made in March, but also countries where people are more likely to wait for the warmer season. Cold can be disastrous for the pigeons.
That is easy to understand because a person can also catch a cold just a few days after he or she has had a freezing cold. The name cold says it all. Getting snotty and drooping from "catching a cold". These infections that one seems to get, who likely “fall out of the air”. Of course not.
Humans and all cary several infections with them that are innocently, or rather, patiently waiting for the circumstances to become suitable to take their hit.