Permanent female mimics in a lekking shorebird

Abstract

Female mimics are known from many species, but permanent, non-conditional, alternative mating strategies are only known from an isopod, a fish, a lizard and a bird. The single bird example refers to lek-breeding ruffs Philomachus pugnax, a shorebird for which two strategies (independent and satellite) have been known for over 50 years. Ruffs also provided the single case of an animal with two, rather than three, permanent alternative mating strategies. Here, we describe a rare female-like morph of ruffs: the 'missing' third alternative mating strategy, which we have called 'faeder'. Faeders are slightly larger than females and in late April have testes 2.5 time the size of testes of normal males. On leks in aviaries and in the wild they appear to combine feminine and masculine behaviours. Faeders may represent the ancestral, care-giving, male strategy, but their relatively large testes suggest that currently they behave as sneakers.

Figure 1

(a) A female mimic (or faeder), individually colour-ringed in The Netherlands on 10 April 2004, photographed while visiting a lek in Varanger, northern Norway, from 16 to 19 June 2004 (photo by J. and T. Champion). (b) On the left two female mimics, on the right an independent male and between them a single female in an aviary setting (photo by Y. Verkuil). (c) The individually colour-ringed female mimic is mounted by an independent male on a lek in Varanger, northern Norway, on 17 June 2004 (photo by J. and T. Champion).

Figure 2

(a) Relative frequency distribution of wing lengths of the three categories of ruffs captured during northward migration in the northern Netherlands (2001–2004). Of the 20 birds with wing lengths between 170 and 180 mm, 11 were bled and in all cases they were molecularly confirmed to be males; the sex of 25 additional females and 28 males was also molecularly confirmed. (b) Samples of breast feathers of the nuptial plumage of two typical males (top), two female mimics or ‘faeders’ (middle row) and two females (bottom) of ruffs staging in April in The Netherlands. In female mimics and females these feathers represent the original alternate plumage, in males an additional, supplementary plumage (Jukema & Piersma 2000).