As you approach the equator, you find fewer and fewer crepuscular animals. Any idea why?

As a process of elimination, you can look at the reasons creatures are crepuscular. The two (at meast the most common two) reasons are to avoid the midday heat while using light, or as a defense mechanism to avoid the usual cycles of natural predators. Since the tendancy for equatorial areas is to be of a hotter climate, we can eliminate the avoidance of heat, as that would encourage there to be more crepuscular animals. The answer must be a lack of direct predators for the animals in the areas, there is another less common factor for the cause, or that the statement itself is false in one way or another (counting mammals as opposed to all animals).

I hope this pointed you in the right direction!