Once in a while, a doe will kindle "on the wire" which means that she gave birth anywhere other than the nest box. Or a kit will be attached to the doe's nipple only to let go once his mom has hopped out of the nest box.
This is just one reason that it's important to check on does (throughout the day) that are due to kindle (give birth) or have a new litter. Kits are born blind, deaf, and very, very naked.
They become chilled quickly and the exposure can kill them in minutes.
However, the baby has ended up on the wire, when they are very young, there's no way for the bunny to get back into the warm nest box.
Kits that can't get back into a nest box are very young, indeed, and have little to no fur covering their bodies. The odds are that he will die of exposure (usually from being cold). Does don't pick up their babies or in any way retrieve them like dogs or cats do.
How to Warm Up a Baby Bunny
There are a few things that you can do to warm up baby bunnies. The first thing that I do when I find what my husband affectionately refers to as a “Popsicle bunny” is to place the kit under my shirt up against my skin. The baby begins to warm up immediately and I often feel its feet moving even before I get from the rabbitry to the house.
1. First of all, don't panic (even if he is not moving). Take a good look at him.
If the kit is warm and moving about, he may have just recently wandered and simply needs to be placed back into the nest box with his siblings where he will warm up quickly.
2. If the bunny you find is cool or cold to the touch, don't immediately assume that he is dead. Kits will become very still when their temperature drops, preserving energy, which keeps them alive as long as possible.
3. Indoors a heating pad can be used to warm up the little one. Wrap the pad up in a towel and place it on the lowest setting. Put the heating pad/towel and the bunny inside a shoe box so the heat surrounds it. It's better to warm the bunny up slowly.
I suggest that you don't give into the urge to turn the pad up to the high setting. A newborn's skin is less than paper-thin and can burn easily. If I use a heating pad, I don't leave the bunny alone with it. I'm sure to feel the pad regularly to be certain the pad isn't getting too hot. After the baby is warmed up and wriggling, I place him back into the nest box with his littermates.
4. Another technique is to put warm water into a bowl on the counter. Place the kit into a storage baggie (be sure to leave the top open and hold it securely) and place the storage baggie so that the baby is laying against the warm water inside the baggie. The idea is not to let the water touch the kit, but to let the warm water heat its skin through the plastic bag.
5. You could also put hand towels into the dryer and when once they warm up (not hot!) simply hold the kit in your hands with the towel wrapped around him. Once the hand towel cools, wrap him in another warm towel from the dryer.
Do this until the bunny pinks up and is quite warm without the towels, then bring him back to the nest with his siblings.
Before returning the kit to the box with the rest of the litter, it really needs to be fully (and slowly) warmed up without any chill to its little body. If it's still cool, the other kits will wriggle away from it. Without their bodies around him to keep him warm, he could become chilled again and perish.
When a Kit Fails to Recover
Sometimes a baby can be brought back from the brink of death, only to gape and gasp and pass away anyway even though he warmed up. You have to realize that you've done your best, but some kits are just too far gone to be brought back. This is the not-so-fun part of rabbit raising.