Niger seed (nyjer seed or thistle seed) is known to be a favourite of finches, due to the shape and structure their beaks, which are suitable for a smaller type of bird seed.
“Each year when the Goldfinches arrive I have many many in my garden each day as they "fight" each other to get to the Niger seeds from Vine House Farm. I have 6 feeding positions and these are regularly full with others waiting. The seeds are clearly in good condition and the delivery very good. I thoroughly recommend them. They are also at a good price.”