The most widely discussed research on rat culture was performed by Joseph Terkel in 1991 on a species of black rat that he had originally observed in the wild in Israel. Terkel noticed that the rats he observed exhibited a unique kind of feeding behavior — they systematically stripped off pine cone scales from pine cones, a favorite food, prior to eating. After further study revealed that this group of rats did not exhibit this behavior unless they were taught by other rats, it was evident that the behavior was indicative of culture.
The behavior of all these different animals is evidence that animal culture is probably far more widespread among mammalian species than acknowledged. As scientists perform more definitive studies looking for culture among other mammals, this list could become a lot longer.