THE CARE OF ORPHANED MAMMALS (not including deer, bears, or other very large ones)
If you find an injured or orphaned baby mammal then the first thing you must do is make sure it is truly orphaned. Is it in a den? Is it cold? is it crying for food? is it malnourished? Is it injured? Did your pet dog or cat bring it to you? Are there others in the litter? Can it walk or not? What species is it?
Often the mother will hide while humans are around and you may think the baby is alone for that reason. For example, a squirrel or rabbit that is out of the nest and able to walk around is likely able to survive even if its mother has died.
Pros are the best choice when it comes to wildlife care, but sometimes you have to do first aid or no one is available to help at the time, so you have to take things into your own hands. If you see that the animal is too thin, cold, injured, you cannot find its nest (your pet brought it too you and you looked but couldn't find it), its mother has been killed (such on the road or by your pet), or some other issue such as this, take the baby and get it warm first. If you think it may be sick handle with a towel or gloves to avoid contact and tuck it under your shirt or somewhere else where it will feel warm and secure but not over-heat. If it is still unable to walk (so for most mammals somewhere under 3 weeks of age) it is far easier to care for them. Any older and it may be aggressive and lash out at you, which is a risk of contracting disease, in which case getting them into a crate is important. Any animal old enough to eat and use the bathroom on its own can be kept in a pen with minimal contact and fed until they are large enough to survive on their own, then released where they were found (if legal in your area).
For now lets talk about truly little babies, the kind that have closed eyes or just opened their eyes. After getting them warm stimulate them to use the bathroom by taking your finger or a damp cloth and stroking their belly in the direction of their tail. Have a cloth under you, as it can be messy when this happens. If you don't do this they can get sick and die.
Next you want to check for any injuries. Look for broken bones, open wounds, bleeding, bruising, ect. If there are injuries, you likely won't be able to help it. Small wounds can be treated but broken bones or large wounds need a vets attention. Worms and parasites can also be a problem in wild animals.
Once you get the young animal home set up a box with a towel in it. This box will be its den. If there is more then one keep them together, as this is very comforting and will allow the animals to feel more at home. Young animals are at risk of the cold and the heat, so whatever source of warmth you use make sure the babies can crawl away from it if they want.
Prepare an electrolyte solution for any baby that is dehydrated. If its mother just died and it is still well-fed, you can use a milk replacer right form the beginning. Puppy milk replacers can work for a short time, but generally cat milk replacers or supplemented goats milk are the best choices. Again, if the young is dehydrated, feed it electrolyte solution first and gradually switch to milk. A good temperature for hairless babies (such as mink, rabbits, ect) is 85-95 F (depending on species) while haired babies with eyes still closed can be kept at 90 F. Slowly reduce this by 5 F per week once the yes open until they are at room temperature.
To feed young animals use a syringe (of course with no needle), plastic bag with a hole cut in a corner, or a kitten bottle. A syringe with a nipple attached can be used, but you might not have one handy. Generally mammals (besides rabbits) eat every 1-3 hours, even during the night, and so should be fed in this manner. As they get older they can slowly be fed less during the night and then gradually switched to only 4-5 times a day and learning to eat solid foods.
To get them drinking the milk place a drop on their tongue or lips while the animal is held-upright (to avoid choking) and let them taste it. Don't hold the animal on its back but either hold it upright or on its belly with its head slightly higher then its body. A towel beneath it will help clean up the mess, as most mammals are messy eaters on a bottle.
Put drops of milk on its lips until they begin to lick or suck and then you can start feeding a little more. Make sure not to feed too fast as young animals are prone to inhaling the milk, choking, or getting too much in their mouth. If bubbles appear at the nose or the infant opens its mouth wide stop feeding immediately and tilt the infant head down to let the milk drain from it. Let the baby recover and then start feeding again, but more slowly this time.
Clean up the babies face when it is done eating. Stimulate it to use the bathroom either before or after feeding (before tends to be better) and before their nap).
Weigh the babies daily to make sure they are gaining weight. They may loose some during the first few days, but they should make up for this once they learn to feed from a bottle.
At any time you can still get this baby to a rehabber and it is best to do so, as it can be illegal to keep wild animals, even orphans, and equally illegal to release them. Rabies-vector species (such as raccoons, squirrels, opossums, foxes, bobcats, weasels, ect) are often given stricter laws then fawns, rabbits, baby birds, or other rodents. If you can, minimize handling of a species that may be in danger of bonding to people before release. A bird doesn't need this, as they are not a danger to people. However, if a raccoon approaches a person then that person will think they have rabies and may kill them.
If the baby seems lonely, you can try raising it with an orphaned kitten, puppy, or have a dog that helps to mother it so that an animal teaches it how to behave and not a human.
To wean an animal, continue feeding it from a bottle but offer milk in a dish. When they begin drinking from a dish start mixing in with it ground up cat food or meat (for carnivores) or place some greens, hay, or grass into their enclosure (for rabbits and other herbivores). Squirrels may enjoy some other fun treats as well. Gradually give more and more of the soft baby food and less of the milk from the bottle. They can continue to drink milk from a dish as it offers calcium for their bone development.
Keep records of when they eat, use the bathroom, their weight, and any health issues so that you can tell if something is going wrong.
Inappropriate nutrition from poor quality or the wrong type of milk replacer can lead to constipation or diarrhea, poor weight gain, poor coat, allergies, and death. Make sure they get the right vitamins, minerals, calcium, fat, and protein. Make sure the milk is not too cold or too warm (it should be the temperature that the mother's body naturally would be, generally 95-100 F or so.
Introduction to their natural environment helps build immunity and may give some species access to needed minerals in the soil (such as deer).
You animals like dark, warm, snuggly places so a soft, clean blanket is great bedding.
You can use a heat light (this can be dangerous), warm water bottle (monitor regularly), heat pad, incubator (for poultry), or other such things to warm up a baby and to keep it warm. Get them warm, but try not to shock them with a temperature change, as it can be dangerous.
Make sure that the baby can still breath and is not suffocated by bedding
You can gently massage some baby animals to get them to burp out any access air. Others may not need this.
Babies sleep a lot when young, so let them do so without disturbing them.
Newborn babies need the antibodies provided by colostrum and are unlikely to survive without it.
I hope this helps. : )