sql 2005, transaction logs

I have sql 2005 server. I do a full backup of the db each night. During the workday from 7-5 I do hourly transaction log backups.

The first t-log backup of the day is always 2 to 4GB in size, but each one after that is no larger than 3MB. (management studio says the log file has 97% free space available – the mdf file is 2.2GB, ldf file is 6.6GB)

Is this normal? How can I get the log to come down to size? (I want to ftp the logs each hour to an offsite backup server)