Logs are disappearing

I have IP logging turned on for my poll. The logging is working, however, the list appears to be being purged. I noticed that we didn’t have a matching number of voters and logs after 1 day of voting. And over the next two days, I’ve watched the size of the logs actually decrease while voting has continued. The oldest entries appear to be the ones that are disappearing. Is this the intended behavior? Is there a setting I’m missing that is causing our logs to be purged?