It can be alarming to come across an unattended litter of kittens -- why would a mother abandon her babies? It's not uncommon for cats to leave their kittens at one time or another. Whether it's a stray cat or a pet, Mom has reasons to leave the nest sometimes.
Most cats are naturally good mothers. In most cases Mom will provide pretty intensive care for her babies during the first three weeks of their lives, when they're at their most vulnerable. If your cat has left her kittens, it could be because she's looking for a place to move them to -- or simply taking a break. Sometimes, however, a cat will find herself overwhelmed with her new responsibility and may need a helping hand getting started.
If you've ever come across a litter of stray or feral kittens mewing for comfort, you probably understand the inclination to rescue them. Most experts agree that you should wait and watch -- Mom is usually eating, searching for a new nesting spot or in the process of moving her babies. If the kittens are very young, with their eyes still closed, chances are Mom is close by.
Wait and Watch
If you come across a litter of kittens that looks abandoned, the best thing to do is wait and watch to see if Mom returns. If you move the kittens, she won't be able to find them when she returns. Take a quick look and see if the kittens seem generally healthy. Are they basically clean, alert (or sleeping contentedly) and nestled close together? This is an indication that Mom is in the middle of important business and that she'll be back soon enough. If so, watch from a distance to see if she returns.
If the kittens look lethargic, unkempt, scrawny and smell like urine or feces, this could be a sign that something has happened to Mom. If they are cold to the touch, look sickly (such as a runny nose or eyes) or are threatened by predators or weather, you should probably take action.
What to Do
If you think the kittens are sick, it's best to call either a vet or the local humane society and tell them what you see. If you've watched for several hours and Mom hasn't returned, it's possible that something has happened to her. Again, you can contact the local humane society or you can decide to try to take care of the kittens yourself. Caring for neonatal kittens is a significant commitment. For instance, they require bottle feeding of special formula (not cow's milk) and must be stimulated in order to go to the bathroom.