Do chickens out number rats in the world?

Not necessarilly.

I would bet on the rats.

No one seems to know an exact figure on the wild rat population globally but many studies estimate it to be a little more than one per human - that would be around 8 Billion rats. And given the little buggers abillity to procreate those numbers can explode if given the right set of factors. So the number goes up and down. They are able to breed at three to four months of age, produce up to seven litters a year, each containing 6 to 22 young. A female rat is back in heat within 12 hours after giving birth. Now thats sex drive!

In Myanmar, when the bamboo blooms (Melocanna baccifera, every 48 years), the rat population skyrockets - When that bloom occurs it attracts rats which feed on the flowers and seeds. And a well fed rat makes lots of babies! Last explosion of the rat population in that area of the world was in the 1950's causing a serious famine. This bamboo can bloom for four or five years - it's actually a very dangerous situation.

Chickens are easier to count because they are domesticated. The global estimate ironically is about 1.25 chickens per human on the planet which means about the same amount of chickens as rats. Go figure.

Believe it or not, there is a game online that challenges you to guess the top 30 countires in order by chicken population - http://www.sporcle.com/games/worldchickenpopulation.php I didn't do as well as I thought I would - I only got like 10 out of the 30! so let me know how you do :)