Tonight, the ratio of Eastern Red Bats to Big Brown Bats recordings was 129 to 38, where last week it was an even split. But I don't know if it was a change in the number of bats or if the Eastern Reds just hung out longer. Last week, the Eastern Red Bats came out early, followed by the Big Brown Bats. Tonight, the Eastern Red Bats stayed until it was very dark.
I have no idea if the number of bats has changed or if the food sources changed. Unlike Bird Watching, which has a long history of citizen science and great databases (eBirds, Christmas Bird Counts, etc.), there are almost no resources for bats. There are no hot spot maps for bats for example! Or online records of when to expect different bat species to be present in Central Park. This is going to take time to figure out!