The typical generalizations (or guidelines) have stated, for instance: That bats will not take flight, or leave their temporary (or permanent) roosts, unless the outdoor temperature is at least 50 Deg. F. Those of you who (like me) read all the bat books, texts, and scientific papers that you can get your hands on; will have also read: That bats will not fly if it is too windy, or raining.
To put it nicely: Many of us have already discovered that these guidelines (or "Rules") are incorrect. The interesting thing, is that many modern documents also echo these guidelines.
I've found that a fascinating (and fun) activity, is to actually set-out to prove that these recommendations are incorrect. So, if possible - Place one of your detectors out if:
Temperatures are below 50 degrees Fahrenheit
It's raining lightly - And you're able to do so without getting the unit wet - Please make sure that your detector's microphone element doesn't get wet!
It's windy...Not too windy, mind you! Bats certainly will not fly if winds are over 15mph.
Remember to take notes! - Especially if you get any recordings of bats.
Together, we hobbyists will be able to prove a lot of those old texts wrong. And, be able to share new (and interesting) findings/updates. I keep a separate journal (notebook) especially for this purpose. I have already proven that the 50 Deg. F "rule" is not accurate : )
For intermediate or advanced hobbyists:
There is something else. Especially during this Winter - If you capture bat recordings at night, or at dusk/dawn; and it happens to be the "dead of Winter" - It would be good, to try to positively verify the species. This may be done, using the usual/conventional means: Studying various facets of the recordings, studying/comparing the resulting sonograms, etc.
If for instance, you determine that the species recorded; are of a type that should positively be hibernating at that date/time. There is a possibility, that you have picked up bats that are suffering from WNS. Of course, this is a very sad topic for most of us. Depending on your situation, location, (and perhaps other variables) you may be able to share your findings with your local Wildlife Authorities. You may even be instrumental in saving the lives of some bats.
Just keep in mind, that there are some bat species, which are known to be active (even in December) and it is not abnormal. You'll have to use your discretion.
Happy bat detecting!