I know that at these wolf crossings, they sometimes leave food there to teach them or show them the way.

I think in the case of Singapore, these wild animals already intuitively know that there is food on the other side of the expressway. Which is why they risked their lives and made the pilgrimage before the wildlife crossing was built. Maybe the chemical pheromones they release or something?

cryotosensei

I always wondered about how these things work. In the US there are signs posted on the side of the road reading deer crossing, bear crossing, turtle crossing, etc, but no way I can see to protect the animals besides the sign! People joke about wondering how to teach the animals to read. I have never seen one like depicted above. That would be effective.