Most mammals can become pregnant several times during adulthood, but for the vast majority, there is a healthy pause after each birth, while mothers nurse their babies. For some, of course, it’s normal to only have one or a couple offspring in a lifetime.

But swamp wallabies, small hopping marsupials found throughout eastern Australia, are far outside the norm: New research suggests that most adult females are always pregnant. As described in a paper published March 2 in the Proceedings of the National Academy of Science, the animals typically conceive one to two days before giving birth.

Like all marsupials, swamp wallabies (Wallabia bicolor) give birth to tiny, immature babies that crawl to a special pouch where they nurse on their