<p>Whole-organism performance in relation to ornamentation is often examined to evaluate the cost of ornamentation under the assumption that high performance is favored by viability selection. These studies typically involve experimental manipulations of ornamentation, which can disrupt phenotypic integration with compensatory traits, making it difficult to clarify performance function of ornamentation. Here, I adopted an alternative approach, macroevolutionary analysis, and examined the flight performance of swallows (Aves: Hirundininae) in relation to the tail fork depth to clarify the evolutionary force driving the ornamentation. I found that a measure of flight performance, the presence of notable non-straight flight (including maneuvering, turning, and swerving), peaked at an intermediate fork depth, which “appears to” support viability selection for moderately forked tails. However, the quadratic relationship was found only in males, and hirundines with high opportunities for extrapair mating had a higher probability of non-straight flight, indicating the presence of sexual selection for non-straight flight. Furthermore, I did not find support for the assumption that high performance is favored by viability selection, because the evolutionary association between non-straight flight and prey size, which have been thought to drive the evolution of the maneuverable flight of hirundines, was far from significant. Although the presence of other evolutionary drivers (e.g., predator avoidance) was not completely excluded, the current findings indicate that the flight performance of hirundines evolved, at least partially, through sexual selection. Thus, flight performance in relation to forked tails does not clarify the viability cost of ornamentation. Careful interpretation of whole-organism performance is required to deduce the evolutionary driver of ornamentation and its accompanying effect on the diversification of animal performance.</p>