Friends,
I have a bat question. I am not an ADC trapper. In March we heard scratching in the attic; I investigated and did not find anything out of the ordinary. The first week of June an adult Big Brown Bat was found in the ground floor of the house (in the ceiling). I returned to the attic to find a maternity colony of approximately 20-30 adults, juveniles were also present. Shortly after that a juvenile entered the bottom floor from a crack in the foundation. The juvenile was approximately 2/3rds the size of the adult, very mobile but I am not certain if it could fly.
I have done some work to seal off the attic from the rest of the house and seal off entry points to the lower levels of the house. I have not done anything to the colony or tried to exclude the colony from the attic.
I have found an adult dead under the exit/entry point (where the chimney meets the soffit). We have not heard anymore scratching in the last 10 days. The past few weeks we have been approaching 100 degrees. I went into the attic today and cannot find any bats, there are 2 dead juvenile bats where they were roosting but that is it.
So finally my question is what is the chance the colony relocated?

Thanks Sean

If the conditions as far as the comfort zone goes gets intolerable they may have moved to a more comfortable area of the house or completely left to another site. But with the juveniles present as you stated most likely they have moved to another area of the soffit or part of the home where it is cooler.

Do a watch around the perimeter of the home before dark with 2-3 people to determine if they are still there.

That is not common around here, but it does happen. I inspected a home in early June. There was a colony of about 100 Freetail Bats with pups. A large quantity of guano had to be swept off of the driveway each morning. I checked it again last week. Now there are only about 10 bats with pups in the vent. Very little guano is being deposited on the driveway. There is another home about 200 yards away that has bats in three gable vents. It is in a more shaded area. It wouldn't surprise me if the first colony is moving to the cooler location.

In your situation, I would conduct an evening and morning bat watch. Maybe even place an old sheet on the ground below the entrance to see if any guano is being deposited. Even if no indication of bats is found, I would not be in a rush to close the entrance. There could be a couple of bats still there. I would concentrate on sealing all potential entrances into the home. About the 1st of August, install an excluder, leave it for a few days, then seal the entrance.

Now, let's see other opinions. I know we all have one! I am interested in reading about other ideas.

EDIT: Bob J. types faster than I do!

It has been such a cool spring and summer here, that it wouldn't surprise me to see all of our bats relocating to Washington D.C. for some of that global warming.

I do see colonies move as the young become flighted and am seeing it now.
Completed a job first of the week. At inspection (after the cutoff date) no young were present but the ladies were VERY pregnant. They were in a gable vent with an INTACT interior screen. Exclusion approved by DNR. Upon my return I found newborns so I used my own best judgement and decided to wait to hang a valve. I did seal all other areas of the home and verified that the bats were confined to only the outer portion of the vent. As of tuesday this week the bats have left of their own accord.