I typically see vole-sized mammals in the process of being torn to pieces by a White-tailed Kite or another raptor. These abundant little mammals, commonly known as field mice, are the mainstay of many feathered predators’ diet. So it was a surprise to see a vole above ground and in one piece. I almost stepped on it but my sharp-eyed wife called it to my attention. At first I thought it was dead, but then it stirred and soon scuttled away, not very fast; possibly it was sick or injured. I gave it space and left it alone. If it didn’t get underground soon, it would be lunch. Normally they spend their days in burrows and venture out only at twilight or in the dark.
I don’t know nearly enough about voles to identify this one with any confidence. It’s very likely a California Vole, Microtus californicus, and it could be the subspecies endemic to Alameda County, M. californicus paludicola.
Like other vole species, these reproduce prolifically. The Wikipedia writers say
California voles are able to breed almost year-round, although most breeding occurs during the middle of the wet season, from March to April. Males may breed with more than one female, although the species is not as strongly polygynous as some other voles. Copulation can be prolonged and repeated, and is followed by formation of a copulatory plug and by induced ovulation. Gestation lasts three weeks and results in the birth of up to 10 young, with four or five being most common. The female is ready to breed again with 15 hours of giving birth, and may give birth to several litters over the course of her life.
The young are born hairless and blind, weighing an average of 2.8 g (0.099 oz). They begin to grow fur within five days of birth, and their eyes open at 9 days, although they are capable of sensing light before this. The young are weaned at around two weeks of age, and have a full set of adult teeth by three weeks. Females reach sexual maturity after as little as three weeks, while males become sexually mature after six weeks. The lifespan is correspondingly short, with individuals living for less than a year, even in the absence of predators.https://en.wikipedia.org/wiki/California_vole
Read more about them in Wikipedia here.