I've never known starlings to take pelargonium leaves, but I do know that they are one of the birds which select certain leaves for their nest which have disinfectant and anti pest qualities - perhaps that's why, I'm not sure.

Olfactory cues ( scents and smells) are exactly what starlings use to select some of their nesting materials. As Bamboo says some leaves are better as anti-pest controls than others. And there is some research that suggests that nestlings will choose those specific leaves when adults. They seem to have learnt the smell or the scent that they will need. Haven't read about pelargoniums being used before though.

Interesting thanks......definately a starling,caught in the act they are very quick,think they are nesting in next doors roof as they did last year.