Variable Expression of Sexually Mosaic Plumage in Female Lesser Kestrels

Abstract

Estacih Bioldgica de Dofiana, C.S.I.C., Avda. M. Luisa s/n, Pabellh de1 Per%, 41013 Sevilla, Spain, e-mail: Tella@cica.es Key words: plumage coloration; Lesser Kestrel: Falco naumanni. The Lesser Kestrel (Falco naumanni) is sexually di- morphic with respect to plumage coloration (Cramp and Simmons 1980). Adult males have a gray-blue head, rump, tail and upper wing-coverts, unspotted chesnut mantle and scapulars, pink-buff to cream with some dark brown marks on the breast, belly and flanks, and a black subterminal tail band. Yearling (i.e., sec- ond-calendar year) males differ because upper wing coverts are brown with dark bars, showing variable extension of gray and brown in the head and tail. Fe- males are completely brownish, independent of age, with dark bars on the head, back and tail, and stripes on the breast and belly. Nestlings show sexual dimor- phism in the rump, and sometimes in tail color (grayish in males, brownish in females) (Negro and Hiraldo 1991, Tella et al. 1996a). Both sexes have a partial post-juvenal molt (October-May), and a complete post- breeding molt (June-January) in yearling and older birds. Between 1993 and 1995, we captured and color banded 389 female Lesser Kestrels in Los Monegros (NE Spain, Tella et al. 1996b). Most of them had al- ready been banded as nestlings in the previous five years, enabling us to determine their exact age. Looking for plumage variability of these females, we found two of them showing male and female plumage expressed in a mosaic fashion. The first one (OM), a three-year-old female, was caught on 1 May 1993. The left half of its head was like that of a male (gray) and the right side like that of a female (striped brown), and the rest of its plumage was normal. The same female was recaptured on 7 April and 21 June 1994, and it showed no male color patches. However, we trapped OM again on 26 May and 7 June 1995, and again it showed partial male coloration. On this occassion, we photographed the bird to add to our detailed descriptions. The head was bilaterally colored, gray in the left and striped brown in the right. Moreover, the left wing was more similar to that of yearling males than to that of females, with almost unspotted chestnut lesser and middle wing co- verts, and banded greater covers. The tail also had one grayish central rectrix. The rest of the plumage was