First of all best wishes to every one. Take it easy on the gulls this year for a change

Today I went to Scheveningen, the Netherlands, where I observed several Kittywakes in three age groups. Pink-legged Kittywakes were in the majority

Anyway, I noticed an adult in flight with some plastic on the left tarsus. At first glance I thought it was ringed, but it wasn't a CR. When I got a better view I thought it could be a datalogger. But the bird had no metal ring on the other leg and I assume birds with loggers are ringed as well. But the plastic seems to be attached on purpose. Any one any idea? Or just garbage plastic after all?
Cheers, Vincent