Proc. R. Soc. B doi: 10.1098/rspb.2009.0090 (2009)

A flashy tail is often a way for a male bird to attract a mate, but the adornment has been assumed to make flying more arduous.

To find out whether this is true, Christopher Clark and Robert Dudley at the University of California, Berkeley, trained Anna's hummingbirds (Calypte anna) to fly in a wind tunnel with and without hugely elongated feathers from another species tacked onto their tail feathers. Elongated tails slowed the birds' average top speed from 15.1 to 14.6 metres per second. The increased metabolic cost of flight at high speeds was about 10%, but negligible at lower speeds.

The researchers suggest that by hiding tails aerodynamically in the wake of the body, diverse sexual signals can be kept relatively cost-free.