Today we have the special Sunday bird-themed collection of photos by John Avise. John’s IDs and comments are indented, and you can enlarge his photos by clicking on them.
In the scientific literature, “sex-role reversal” is defined as any situation in which the intensity of sexual selection is stronger on females than on males. Although the phenomenon is very rare in birds, it does characterize some shorebirds known as phalaropes. In these sex-role-reversed avian species, the following features are also present: brighter breeding plumages in females than in males (resulting from the intense sexual selection on females); active courtship and mating solicitation by females; polyandry, in which females often mate with multiple males but each male typically has only one mate; nest-tending and incubation duties are solely by males; and in general a reversal of what we typically might think of as “normal” roles for the two sexes. This week’s photos show the world’s only three phalarope species, but I’ve also included the Spotted Sandpiper because it too shows some behavioral (though not plumage) tendencies toward a milder degree of sex-role reversal.
Several plausible scenarios have been envisioned for the evolution of sex-role reversal in phalaropes. For example, under the “fluctuating-food hypothesis” the ancestral condition was biparental offspring care, but then, under the harsh tundra conditions where phalaropes breed, some birds faced severe food shortages such that females were physiologically exhausted after laying a clutch of eggs. Faced with an incapacitated mate, a male phalarope in effect would have no choice but to tend the nest and young. Males thereby became “captured” into a high-investment reproductive strategy. If food resources then improved, any rejuvenated female could perhaps maximize her genetic fitness by courting other males and laying additional clutches. Repeated over time, this process presumably eventuated in the evolution of sex-role reversal that we see today in extant phalarope populations.
The phalaropes are also of interest because of their peculiar feeding behavior, which entails rapid spinning on the surface of shallow water, thereby creating a vortex that brings up food items that they then pick from the water’s surface. All of my pictures were taken near my home in Southern California, where the birds were in migration.
Red-necked Phalarope (Phalaropus lobatus), female in breeding plumage:
Red-necked Phalarope, male in breeding plumage:
Red-necked Phalarope, non-breeder swimming:
Red-necked Phalarope, non-breeder flying:
Wilson’s Phalarope (Phalaropus tricolor), female in breeding plumage:
Wilson’s Phalarope, male in breeding plumage:
Wilson’s Phalarope pair (with female behind):
Wilson’s Phalarope, non-breeding plumage:
Wilson’s Phalarope, juvenile:
Wilson’s Phalarope, non-breeder flying:
Wilson’s phalarope group:
Wilson’s Phalarope, two females spin-swimming:
Red Phalarope (Phalaropus fulicaria), male in breeding plumage:
Red Phalarope, another view (a breeding female would be even brighter red):
Red Phalarope flying:
Spotted Sandpiper (Actitis macularia) breeding plumage:
Spotted Sandpiper, non-breeding plumage:
Spotted Sandpiper flying: