Ruby-throated hummingbird (female)

Adult females of this species have an average mass of only 3.5 grams, adult males just 3 grams. Despite their tiny size, many of these birds fly nonstop across the Gulf of Mexico during fall and spring migration, a round-trip of more than 1,600 km. To accomplish this, individuals often double their body mass by fattening on nectar and insects prior to departure.