The short answer
Warm, contained, dark and quiet, and nothing to eat or drink. That is the whole overnight protocol, and doing exactly that and no more is what gives the animal its best chance of surviving until someone qualified sees it.
Do not feed it. Do not give it water. Do not check on it repeatedly. Every one of those instincts is the wrong move.
The four things
1. Warmth first
A cold baby cannot digest, cannot absorb fluids, and will not respond to anything else you do. Warm it before you think about anything else, and warm it gradually.
Fill a bottle with hot tap water, cap it, wrap it in a towel, and put it alongside the animal. Or use a heating pad set to low under half the container — half, so the animal can crawl off if it gets too warm. A sock filled with uncooked rice, microwaved 30 to 60 seconds and tested on your wrist, works if you have nothing else.
If you have a heating pad with an auto-shutoff, it will turn itself off in the middle of the night. Set an alarm, or use the water bottle instead.
2. Containment
A cardboard box with air holes, or a plastic tub with a ventilated lid. Line it with fleece, a receiving blanket or an old T-shirt. Avoid loose-weave towels — toenails catch in the loops and animals deglove toes trying to pull free.
Put the lid on. A baby that seems immobile at 10pm can be surprisingly mobile at 3am, and animals loose in a house at night rarely end well.
3. Dark and quiet
Put the box somewhere warm, dark and away from household traffic. A closet, a bathroom, a spare room with the door shut. No pets in the room, no children showing friends, no lifting the lid to look.
This is genuinely hard for people and it matters enormously. To a wild animal you are a predator, and every look is a predator opening the den. Stress alone kills small mammals.
4. Nothing by mouth
No milk, no formula, no water, no eyedropper, no soaked bread. Overnight is exactly when people give in on this, and it is exactly when it does the most damage — cold gut, aspiration risk, and nobody awake to catch it.
Why feeding is the thing that kills them
In the morning
Text a photo to a rehabber first thing. In West Tennessee, 901-340-6534. Tell us the animal's rough size, where you found it, whether a cat or dog was involved, and how long you have had it.
If the animal is uninjured and it is a species that can still be reunited, morning is often the right time to put it back and let the mother collect it. Do not assume the night in your bathroom has ruled that out. It usually has not.
When it cannot wait until morning
Some things are genuine emergencies and a rehabber would rather be woken.
Active bleeding, an open wound, or an obviously broken limb.
Any contact with a cat or dog, even with no visible injury. Their saliva is an emergency.
Flies or fly eggs on the animal — small white grains that look like grated coconut.
Cold and unresponsive after an hour of warming.
A rabies vector species — raccoon, skunk, fox or bat — that has had bare-handed contact with a person.
In those cases, text anyway. We will answer if we are up, and we usually are.
Who is answering this
Out of the Woods Wildlife Rescue & Rehab is a TWRA-permitted wildlife rehabilitation nonprofit in Memphis, Tennessee, serving Shelby County and West Tennessee. There is never a charge to ask. Text 901-340-6534.