Nicole Johnsey Burke says birds and squirrels bite into tomatoes to drink the juice, not eat the fruit. Put a water source like a birdbath or pot next to your plants and they'll drink from that instead.
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If birds and squirrels are eating your tomatoes before you do, this is a trick that's going to help. Have you ever gone to pick a tomato out of your garden and there's just one little bite out of it? Like they had the nerve to start to eat your tomato but not finish the whole thing? Chances are they didn't actually want your tomato; they wanted your tomato juice, and you can keep them from eating your tomato by adding a water feature to your garden. Fill up a little pot with some water, add some rocks in it. You could get a birdbath or even a fountain. The trick is to always have fresh, clean water right next to your plants. That the wildlife are always finding their hydration from here, not here. If you want my guide on how to prevent all kinds of pests in your garden naturally and organically without the sprays, check the caption.