Key points are not available for this paper at this time.
Rowan Lockwood, John P. Swaddle, Jeremy M. V. Rayner, Avian Wingtip Shape Reconsidered: Wingtip Shape Indices and Morphological Adaptations to Migration, Journal of Avian Biology, Vol. 29, No. 3 (Sep., 1998), pp. 273-292
Lockwood et al. (Tue,) studied this question.