http://web.ukonline.co.uk/michael.magee/awwls/00/wls138.html

EQ depends upon the ecological niche occupied by the animal. The three
dimensional environment of squirrels give
them a higher EQ than their rodent relatives, the rats. Insect eating
monkeys have a higher EQ than their fruit
eating cousins and the latter, in turn, have a higher EQ than leaf eating
monkeys. Animals surrounded by food, the
leaf eaters, need little brain power to seek it. The fruit eaters have to
hunt for their food and need intelligence to
find it. Insect eaters have to develop intelligent strategies to capture
their prey which itself has the sense to try
to escape. In general carnivores have a higher EQ than the herbivores upon
which they prey.