What is an indication of an occupied prairie falcon eyrie?

An indication of an occupied prairie falcon eyrie is the presence of blow flies and whitewash. The whitewash, which is a type of fecal matter left behind by the birds, is a clear sign that the area is being used and is actively occupied by these birds. Additionally, blow flies are often attracted to the nesting sites of birds, especially if there are remnants of food or waste present. Their presence can indicate that the eyrie has been in use, as the birds may be feeding and thus producing waste that attracts these flies. In contrast, the other options may describe signs of activity but are not as definitive indicators of occupancy as the combination of blow flies and whitewash. For instance, raptor calls could be made by many types of birds, nesting materials may not be exclusively linked to nesting activity, and the presence of other birds might not directly indicate that the prairie falcon's eyrie is occupied.