Hey Dan,
Since you are in P.A. you are smack dab in the center of bats being devastated by white-nose syndrome. Not the only reason to try to mitigate
this problem without harming them but a good one even if they are a species not subject to the current losses.
The only good sound way to see them on their way is with solid exclusion, but knowing barns in the Northeast which is where I grew up, I can imagine that might not be possible with all the gaps and openings.
Summer is maternity season across North America and bats that have young can have young currently unable to fly, thus if you try to move or exclude the adults you can leave the pups to die off. That might not matter to the barn owner, but if it is possible to move forward in a rational way toward dealing with the problem, that would be great.
A few questions that may help others help you with advice.
1) How long have the bats been in this barn of his?
2) How many bats roughly are there (if you can see them in the rafters, etc...)?
3) Is his biggest complaint the guano (droppings)? (If so I get it, I have folks that rail about 10 little bits, folks with lots of bats get much much more and often don't appreciate the mess)
4) What kind of shape is the barn in? Old, missing siding, or newer with few openings? Type of roof, etc...?
The more info the better, while I wish everyone could find a way to exclude bats I know there are structures where it isn't going to happen either financially or due to other constraints, but if you can work with your neighbor there might be ways you could modify the roosting area after bats leave later this fall so that it isn't a spot they like anymore, it can be done, but barns are full of pitfalls.
Please throw some details on here so we can better address your question, pics are great too if you have any, even of the barn itself and description of where the bats are in the barn structurally speaking...
Bats fill an awesome ecological role, but most folks including myself are brought up to fear and loathe them. Now I spend all my time trying to flip the switch on folks back to the other side and at least get them neutral or in best cases positive about bats and finding ways to move them at the right time of year with the right methods.
Sorry for the rambling, in my nature....
Justin
