Obviously it's time to be feeding the birds. I feed birds in my yard all year round, but a lot of people only feed in winter. One of the most popular seeds to feed the birds is Niger (often spelled Nyjer). Did you know that Niger seed can dry out. Niger is an oily seed and when left out for a long period it will dry out. The oil provides the fat content in the seed which the birds enjoy, but once the oil dries the seed is no longer attractive to the birds. So only buy the amount that you will use in about a month's time, thus preserving the freshness of the seed.
As small as it is, a niger seed does have a shell. If you think birds aren't eating the seed because you see some on the ground, examine it more closely: you may be seeing mostly the thin niger hulls.
Niger is an agricultural crop imported primarily from India, Ethiopia, Nepal and Burma (Myanmar). Niger is not the typical niger you see along roadsides. The niger used for feeding birds is imported and must be heated to sterilize the seed so it will not propagate.
Niger is also vulnerable to spoilage while in the feeder. It should be changed every 3-4 weeks. The birds are able to tell that the seeds are bad and if you notice the birds are not eating the seed throw it away and refill with fresh seed. I'm sure you are aware that Goldfinches love niger but other birds will also be attracted to it. Pine Siskins, which associate with goldfinches, also love it, as do both Common and Hoary Redpoll. Occasionally, chickadees and nuthatches will also eat the niger.