Norway Rats reproduce quickly.
While rats can breed any month of the year, breeding is most active in the spring and autumn.
In a large rat population, several males will mate with a female sequentially, in the order of their social dominance.
A female Norway rat can have as many as 12 litters per year; although they average 4-6 litters per year.
Litters may number from four to 22 young; however litters of 6-12 are more typical.
Litters are born 21 to 23 days after mating.
Rats are born hairless with their eyes closed.
Rats can eat solid food at 2 ½ – 3 weeks.
Norway rat reaches reproductive maturity in 2-5 months.
Rats can live up to 18 months, but most generally live up to one year.