Remember that part of veraison that begins ripening in general and includes the influx of sugar to the berry? Sugar content of the juice goes from approximately 0 preveraison, to about 25% (a winemaker decision) at harvest. To put that in perspective, a can of cola is about 10% sugar.
So, the grapes kind of taste good to us humans that tend to like sweet. Why not, it is fast energy. Turns out (and for the same reason), we are not the only animals that like sugar. BIRDS, in particular, like the sugary grapes and set their sights on the grapes as soon as they begin to color and accumulate sugar. [Actually this is the whole idea behind the grape putting sugar in the berry. The vine is hoping the sweet berries will attract the birds, the birds will eat the fruit and deposit the seeds elsewhere thus expanding the range of the species. We humans are actually disrupting the natural intent and design. Wine was never part of the plan.] If we feed the birds there will be less if not zero wine. What to do?
There are many approaches tried, recorded bird distress calls, sonic cannons, glittering strands of reflective tape, balloons that look like predators, on and on. Usually, after a couple days, the birds figure out that all those things are not harmful and go back to their party. The only thing we have found that reliably works is the physical barrier of a net.
In today’s photo are Pinot noir grapes at Peake Ranch just after netting.