Hummingbirds draw nectar into their bills using long tongues that act like tiny pumps.
It was long thought that liquid travels passively up the birds' tongues without suction. But Alejandro Rico-Guevara and his colleagues at the University of Connecticut in Storrs found a different mechanism when they captured slow-motion films of 18 species of hummingbirds feeding from transparent artificial flowers (pictured is Anthracothorax nigricollis). The videos showed that two long grooves in the birds' tongues are squashed closed by the tip of the bill as the tongue protrudes. When dipped into the nectar, the grooves spring back open, creating a force that draws the liquid in.
This pumping technique allows the animals to sip nectar much faster than the passive action.