travelling round eastern europe and france i noticed platic balls attached to pylons above the road. why?

why do they have these. They are always above roads . They are round ,about the size of footballs and usually red or white. They don't have them in england. I think i might know ,but want to confirm it. Thanks.
p.s just to be clear , they are on overhead power cables that run across the land and the balls are only attached where they cross a road.

If they are only over the roads, then it is likely to provide greater visibility to the drivers of high vehicles, but sometimes in the UK you find them in use other than over roads, simply to warn off birds.

To prevent flocks of birds from flying into the cables.

They are there to identify utility wires. This can be for a number of reasons, like high vehicles, birds and low-flying pilots. Some countries also use them as location markers for their highway system, to designate main roads. They are also found away from roads, but tend to be in locations that are open and thus more likely for fliers. The balls are easily visible against the background of a road from overhead. They actually do have them in UK (I've seen them in Scotland, at least) and everywhere else I've lived.