1) Certify that this is a baby sparrow. It's easy to get confused between mature and immature birds.
2) There are certain species of birds that typically rear their babies on the ground-- though I don't think the sparrow is one of them, you may want to ensure that this isn't the case.
3) Make sure it's actually a sparrow.
4) If it is a baby bird, then it's really unlikely it'll survive out there if the parents don't come. I'd say keep a close eye on it for the next 10-15 minutes or so, and if the mom doesn't come, then take them in.
Just to help you identify the age of the sparrow:
-If the sparrow's eyes are still closed, it's likely less than a week old.
-By 12-14 days of age, it should have a majority of its feathers erupted but not fully unfurled (A.K.A, still in pinfeather form).
-By 16-20 days it should be completely feathered.
You can visit the source of the information I'm currently supplying as to why it may be a bad idea to do this, but if you decide that you should put the bird back into its nest somewhere, here's what you should do:
If the entire nest blew down, you can try to tie or wire it back where it was- or close by to where it was. But parents often abandon such nests. If they are not seen feeding the chicks within 1- 1.5 hours, it didn't work.
If the baby is close to fully feathered but not yet able to perch, you can place it in a shoe box, woven basket or similar container lined with hay or dry leaves in a safe, elevated, shaded area and wait 1- 2 hours to see if its parents begin feeding it. I look for containers with sides twice as high as the original nest. Another technique that works well for babies old enough to grasp your finger tightly is to place it in a leafy bush with many low and high branches. The thick leaves will conceal the baby from cats, and the many branches allow the baby to gradually hop to the top - out of harm's way. Its parents will locate it by its cheeping. If the bird is too frightend to stay where you put it - try placing it in the bush or tree again at night. Baby birds are clumsy, hyperactive and excitable.
Baby birds of a younger age are not good candidates for this technique because parent birds do not usually feed younger babies in two different locations.
If the baby is weak, injured, soiled , sleepy, or dehydrated do not attempt to return it. These re-introductions succeed best when the parent birds are still hovering about, concerned about their missing junior. After your attempt, observe only from a distance that does not cause the parents concern.
If you decide to take care of the bird:
You will need a secluded area. It need not be large, but it should be airy, clean, uncluttered, well-lit and amenable to temperature regulation. It should not be accessible to your pets or children. You will need plenty of time. You will need to get organized and follow a schedule. You will need ingenuity because you will face unexpected situations.
If I keep on adding information to this, then this answer is going to explode, and I don't want it to be one of those answers that you need to scroll down halfway down the page to read. I suggest just clicking the source link. Hope it works out!
Take him in. If he was on the ground, he either tried to fly or he fell. The crow will just kill him. In about a week, see if he is strong enough to fly.
I saw him in the bushes this afternoon and I thought he'd be fine, his mom would come. But I went to check and he's still there, it's getting dark out and there's a crow watching. I was wondering if there's anything I could do like food or water or take him in
