No matter the weather.
In over 50 years I never took them in the rain, but I never brought them back home if it did rain after I took them. In the 80s when birds went to the racepoint every week (no cancelled races or put back 24hrs) it was common for birds to be up if dry at the racepoint but rain was forecast on route. I clocked many times in the rain. Returns were erratic but often returns were very good. Learnt that rain doesn't lose birds, it only slows them down.