hmmm... strange birth but healthy pups

When i was away during the weekend, 3 of my hasmters gave birth. Two out of my suprise gave birth without a partner. 1 gave birth to 7pups and another gave birth to 3pupz. The other gave birth to 7. Just find it very strange Y without a partner it will still give birth. Anyone can give me an answer??? total 3 female pearl gave birth this way. which left me puzzled.