Kittens are found daily and taken to local shelters and that includes Berkeley Animal Center. We ask that finders please wait and do not remove kittens from their nest. Most of the time the mom cat is out looking for food, and if she sees you she will not return and may run away in fear.
Please wait, one thing you can do is make a 2inch ring around the nest with flour and then wait 8-12 hours before checking to see if mom returned. If so great, you can leave food for mom daily and then once the kittens are big enough that they are playing and walking around the area you can trap mom and then turn the entire family into the shelter.
Kittens do best when raised by their mothers. The shelter environment is not safer for them compared to being with their mom. At the shelter they are exposed to many stray cats that often times carry airborn illnesses that threaten small kittens lives.
Please wait, let mom cat raise her babies till they are old enough to eat on their own.