North American porcupine
The North American porcupine has a long gestation period relative to other rodents, an average of 202 days. By contrast, the North American beaver, which is comparable in size, has a gestation period of 128 days. The eastern grey squirrel ("Sciurus carolinensis") has a gestation period of just 44 days. Porcupines give birth to a single young. At birth, they weigh about 450 g, which increases to nearly 1 kg after the first two weeks. They do not gain full adult weight until the end of the second summer about 4.5 kg. Their quills harden soon after birth.