The following sentence can be categorized as what stage in the Scientific Method: Abraham notices that Saharan desert ants will take great distances when looking for food, however once return from their journey they will take the shortest distance possible (straight line) to get back to their niche.

Saharan desert ants is making observations

Explanation:

The Saharan desert ants are using every available opportunity to make observations in search of food and that's the reason why they take great distances. However, after getting food, they are always eager to return back to their niche as soon as possible.