Size isn't the criteria...species preference is. Those feeders are on the market because that's the preferred seed choice and one which can be fairly inexpensively mass produced.

I don't know if the seeds of gerbera daisies are a good food source for birds, or not. What are your observations? You might consider removing the feeders for a while to encourage the finches to forage in the garden. There are so very many plants going to seed at this time of year. Finches are going crazy in my perennial gardens right now.

I would simply leave the dry flower heads on the plants, let the feeders run dry, and see if the birds will use the flower heads. Leaving the seeds on the plant allows for more access by a greater number of animals, also. They don't have to wait for the feeder to clear out.

Martha

Thank you!

I would have loved to leave the flower heads on the plant, however I needed to remove it.

I have de-seeded many of the heads into the feeder and I'm waiting for a few dry days before I put it back out. It is a tall feeder with two levels for the birds to land on. There is still nyjer in the bottom, which they loved, and I am trying the daisy seed on top.

Fingers crossed for happy birds!