Bird geek mode on: the paper cited is about starlings, specifically the European Starling, Sturnus vulgaris, not sparrows. They are not the same thing. Starlings (members of the Sturnidae family) are probably one of the more intelligent passerine families, though likely not as intelligent as the Corvids (Jays and Crows). Sparrows, both Old World (Passeridae) and New World (Emberizidae), are not generally known for their intelligence.
Oh...thanks! I seem to have made a rather large number of tiny factual errors in posting this link, for some reason.
You walk into a store that sells two identical candies. Would you buy the candy that ordinarily costs $2 at 50% off (for one dollar), or the candy that ordinarily costs 10$ for 80% off (for one dollar)?
In an isomorphic situation, sparrows preferred the latter deal.
http://users.ox.ac.uk/~kgroup/publications/pdf/kacelnik_marsh_2002_animbehav_costs.pdf