Optics & Laser Technology 38 (2006) 329–334 An analysis of optimal structural features in the peacock tail feather Stuart C. Burgess à , Andrew King, Rick Hyde Department of Mechanical Engineering, Bristol University, Bristol BS8 1TR, UK Available online 29 September 2005 Abstract This paper presents an analysis of the optimal structural features in the peacock tail feather. Peacock tail feathers are highly optimized in three respects. The feathers are highly efficient structures that can support their own weight in a deployed position. The feathers are also optimized for producing thin-film colours with a high degree of lustre. The feathers also have a structure which produces intricate patterns with a high degree of aesthetic merit. There are structural features that allow simultaneous optimization in the different areas of performance. In particular, the thin-film sandwich structure is ideal for producing optimal structural performance and optimal optical performance. r 2005 Elsevier Ltd. All rights reserved. Keywords: Thin-film sandwich structure; Thin-film interference; Structural efficiency 1. Introduction The peacock tail feather is one of the largest and most attractive display feathers in nature. During the breed- ing season, the peacock (male peafowl) will often display his tail feathers in order to attract a peahen (female peafowl). The peacock display consists of a ‘fan formation’ of feathers as shown in Fig. 1. The peacock tail feathers are of interest to researchers in several disciplines including structural engineering, optical physics and industrial (aesthetic) design [1,2]. The attractiveness of thin-film colours is such that they are now sometimes used on motorcar bodies as a key aesthetic feature. In automotive applications, small thin- film flakes are embedded in a binder and surrounded by pigment particles and metallic flakes [3]. This paper describes how the peacock tail feathers are optimized in three main ways: (1) The feathers have a structural function of supporting their own weight in a deployed position using minimal material, (2) the feathers have an optical function of producing thin-film colours with a high degree of lustre, and (3) the feathers have an aesthetic function of producing attractive patterns. The paper describes specific optimal features in each of these areas. It also shows how there are several features which allow simultaneous optimization in different areas. In particular it is shown that the thin- film sandwich structure of the feather barbule is very important to structural optimization as well as optical optimization. A sample of peacock tail feathers was analysed using a Leitz stereo optical microscope. Design analysis methods were used including structural effi- ciency analysis and functional analysis. 2. Background to the peacock tail feathers Most species of bird have two types of tail feather: flight feathers and tail-coverts. The flight feathers provide stability during flight, while the tail-coverts cover and protect the tail region of the bird. In the vast majority of birds, the tail-coverts are small feathers just a few centimetres long. However, some male birds like the peacock have very large decorative tail-coverts for the purpose of making an attractive display in the courtship process. The peacock tail feathers are some- times called decorative or ornamental feathers but they ARTICLE IN PRESS www.elsevier.com/locate/optlastec 0030-3992/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlastec.2005.06.021 à Corresponding author. Tel.: +44 117 928 8075; fax: +44 117 929 4423. E-mail address: s.c.burgess@bris.ac.uk (S.C. Burgess).