Symbiosis ? Commensalism?

Cattle egrets and cattle - is the relationship symbiotic (where both the bird and the animal benefit) or is commensalism (where only the egret benefits) ?

The egret gets its food - insect, particularily grasshoppers , when the grass is disturbed by the cattle.

 And the cattle ? Freed of insects that might cause disease? warned in advance of approaching animals/humans?