- Elephants: 22 months (average)
- Giraffes: 15 months (average)
- Blue Whales: 10-12 months (average)
- Humans: 9 months (average)
- Chimpanzees: 8 months (average)
- Gorillas: 9 months (average)
- Orangutans: 9 months (average)
- Kangaroos: 30-40 days (gestation), then joey develops in pouch for 180 days
- Opossums: 12-13 days (gestation), then joeys develop in pouch for 60-70 days
- Dogs: 63 days (average)
- Cats: 63-65 days (average)
- Rabbits: 30-32 days (average)
- Mice: 19-21 days (average)
- Rats: 21-23 days (average)
- Hamsters: 16-21 days (average)
- Guinea Pigs: 63-70 days (average)
- Ferrets: 41-43 days (average)
- Horses: 340 days (average)
- Cows: 283 days (average)
- Pigs: 115 days (average)
- Sheep: 150 days (average)
- Goats: 150 days (average)
- Chickens: 21 days (average)
- Ducks: 28 days (average)
- Geese: 35 days (average)
- Turkeys: 28 days (average)