There was an error published in J. Exp. Biol. 211, 3836-3849.

In Eqn 3 (p. 3838), the denominator in the ratio contained within the brackets was written incorrectly. The correct version of the equation is shown below.

The author apologises to readers for this error but confirms that the correct equation was used in the analyses and therefore the error does not affect the results or conclusions of the paper.