Homebrewing - Beer, Mead, Wine, Cider

I've had plenty of pellicle lately despite not changing anything in my routines. I even have it in some bottles with a small head of air. I'm not worried but I'm curious about the cause. I've done a few brews with brettanomyces that are more prone to pellicle but even several without have had a thin white surface. Could it be brett living in the air contaminating or the spring times have naturally more wild yeasts of which some are more sensitive?