Nyjer seeds

Hi all, I am relatively new and though I have had bird feeders for a while, I bought a Nyjer seed feeder and the seeds last week.

While the other feeders have been devoured, it appears that not one nyjer seed has been consumed :(

is there a reason for this? how often should I change the seeds even though they haven't been eaten and how long should I keep on my bird feed station before I give up and take down for good?