sometimes cross birds are backlit and black. That transition black change much because it detects the black as a value to calculate and produce a flicker.
so does some reflections all white, firing calculations and produce luma flicker in the sequence.

You can add a minimum and maximum values ​​to discriminate and not considered in the render?

Gracias
Y disculpas por mi mal inglés.

I understand that you are talking about the deflickering. Please use the reference area to set a proper reference, like I explained it in the deflicker tutorial (see tutorials).

Well, but the birds cross some time and break the luma.
the area selected is crossed by birds.

Thnaks.

There is not too much I can do about that - choose another area ;-)
Always remember it's better to take care of flickering while shooting, then you don't need to deflicker!