Could be slugs. They make a round hole. Birds make a v-shaped hole.

Lots of bugs will chomp on strawberries if they are resting on the ground. Mold and fungus can get a foothold as well. I prop my berries up with plastic forks. The handle sticks in the ground and the berry stems rest in the tines. I'm not a huge fan of using plastic in the garden beds, but this is one case that I make an exception for.

As for bugs, go out at night with a flashlight and poke around the bed. Get ready to do some smashing or drowning in soapy water. For birds, spare no expense and buy the cheapest birdblock that money can buy. :)

the fork idea is very interesting, but my strawberry bed must have close to 15 dozen berries that are ripening.

I mulch with pine needles from Christmas trees and wreathes, seem to do a good job at keeping out slugs and keeping the berries off the ground

"I mulch with pine needles "

Me too! My in-laws in upper Michigan have about 300 pine trees on their property. I bring home 2-3 yard waste bags of it every visit!

Hope it's okay to add a question about another strawberry pest. Has anyone else noticed small, clear worms inside the berries? They are very hard to see, but the berries they are in are softer than those that are unaffected. The first year I planted my strawberries I didn't see any, the second year there were some, and the third year at least half of the berries were affected. What are they and what should I do about them?

When the strawberries come in contact with the ground I've seen earwigs, pillbugs, and ants inside holes where the fruit touches the ground (the ants probably come after someone else made the hole).

I put plastic mulch over my natural mulch around the berries and it has helped. Also the later strawberries seem to be higher up on the plants, no ground contact and don't get the damage.

I wish breeders would pay more attention to developing strawberries that hold their fruit higher off the ground.

But because all the commercial growers are using plastic, there seems to be insufficient demand for this.

MoleX:
Just prop up the berries that need it. Also, you can stack up multiple berry stems on each fork. It doesn't have to be a 1:1 berry to fork ratio.

peachymomo:
Hard to say for sure what those worms are, maybe fruit fly larvae? Having various bugs, worms and such is generally a sign of healthy soil.

ltilton:
Let's keep plant breeders focused on berry quality such as flavor, yields, size, etc. :)
That said, there may be some varieties that ride higher than others naturally.