Male and female bands are different sizes and as such have a different series of numbers - there are 22 sizes of bands used in North America, they are numbered from 0 to 9 (with letters to help differentiate intermediate sizes). There are also bands for humming birds but they are like thin layers of aluminum foil and don't have a number.
Peregrines take sizes 6 and 7A/7B. The males wear size 6, females wear 7A/7B. I think all our females wear 7As, the 7Bs are probably more for use on tundrius birds, they are just that much larger in general.
Each band size has a unique prefix four digits. Currently the first four digits for our males is 816, for our females it is 1387. (note the 0 in 0816 is not impressed on the band, its implied). These numbers are not geographically distinct, rather they were the next numbers in sequence as banders restock their inventory. Radisson's chicks could also be 816/1387 as too could be birds in Nova Scotia. Canadian banders get their bands through the Cdn banding office, US banders from the US office.
Remember, each bird has a unique number, so no we won't have 7A bands (female) that start with 816 (a male 6 band prefix).
