I don't think there is one but if they are struggling why do you wish to deprive them of food. the food you put out for all the birds is of benefit to all of them. if the starlings are eating the fat balls then the other food is left for all the other birds.
they don't rationalise it. I 'm not keen on the pigeons but I cant stop them eating [even when they are eating flowers grrr:o( ]

There are other feeders for the starlings so I'm not depriving them but they clearly prefer fat balls these days. I'm happy to give them food, they're entertaining to say the least, but want them to leave some for the small birds which they aren't doing.

The answer is simple: Take down your fat-balls. Birds don't need fat at this time of year - they need the high energy that fat-balls provide during the cold winter months, not during the summer.

I have always fed my birds fat balls and since the RSPB has said to feed all year that's exactly what I do. So I have no intention of depriving the smaller birds.

I don't understand. I feed the birds all year round, but I only put fat out during the winter, when the birds need a high-energy boost. The rest of the year, they're fed on seeds and nuts, which starlings aren't nearly so interested in. Fat is not a food recommended by the RSPB at this time of year.

Here's a link you should find helpful:

http://www.rspb.org.uk/makeahomeforwildlife/advice/helpingbirds/feeding/whentofeed.aspx