Mr. Wilson’s Phalarope Gender Role Reversal – Reflections of the Natural World

One Moment in Nature is a reflection back in time to a moment of discovery as I explored the natural settings around me. Through the sharing of this moment, is my hope that readers will become motivated to learn more about our environment and its inhabitants, and become passionate advocates for conservation. One Moment in Nature is a Reflections of the Natural World Blog Post Series by Jim Gain

THE WILSON’S PHALAROPE MOMENT

Ever since my first Golden Guide to Birds, my mind was trained to expect that boy birds had the pretty feathers and momma birds incubated the eggs in the nest. As I enrolled in the upper division Biology course of Ornithology 301, these gender specific traits had been ingrained in my neural network of expectations. Forty five years later at the Ceres Water Reclamation Facility, as I spied a beautifully colored fully alternate-plumaged Wilson’s Phalarope my mind lit up with the recollection from that Ornithology class that the male phalaropes weren’t the pretty ones, the females were! And in fact, all of the Wilson’s Phalaropes present that day were either females or newly fledged young birds, because the males were all still tending to the nests and recent fledglings back at the nesting grounds.

The next section dives into the science of sexual morphism and egg incubation strategies among most bird species.

SEXUAL DIMORPHISM

The majority of bird species are sexually monomorphic, meaning males and females appear visually identical or very similar. Over 60% of bird species are monomorphic showing little to no human-visible differences in appearance between sexes. Of those species that are clearly dimorphic (males and females have distinct differences in appearance), the vast majority are males featuring brighter colors and/or different sizes. A good example of that would be the male vs female Mallard.

EGG INCUBATION PARTICIPATION

While the prevalence varies significantly by species and even pairs within a species, male birds help with egg incubation in approximately 54% of bird families. In many species, both sexes share the incubation duties, with varying levels of male participation depending on the species, time of day, and incubation period. However, in roughly 25% of families, only the female incubates, and in about 6%, only the male does.

Biparental care is a common pattern, but the level of male contribution to incubation can differ significantly.

• In many species, parents take turns incubating the eggs.
• In some species, the female incubates at night and the male during the day.
• For some species the female incubates the eggs alone, while the male provides indirect care by delivering food to the incubating female.
• In about 54% of bird families, both sexes share incubation responsibilities.
• Across all bird species, males are not involved in egg incubation in approximately 8% of species
• In a smaller percentage of families (around 6%), only the male incubates the eggs.
• In species where only the female incubates, the male doesn’t develop a brood patch.

The development of a brood patch is a hormonal response to nesting, leading to feather loss and increased blood flow in the belly area to efficiently transfer heat to the eggs. While most female birds that incubate eggs will develop a brood patch, some species, like certain shorebirds or pelicans, do not have one, while others, like some ducks, line their nests with down rather than developing a bare patch. In species where only the female incubates, the male doesn’t develop a brood patch.

ABOUT THE WILSON’S PHALAROPE IN CENTRAL CALIFORNIA

In California’s Central Valley, the Wilson’s Phalarope is a striking seasonal migrant, most commonly observed during its southbound journey from breeding grounds in the northern Great Plains and Intermountain West. The Valley’s saline and freshwater wetlands—particularly those in the Sacramento and San Joaquin basins—serve as critical stopover sites, where large flocks gather to refuel. Peak occurrence typically spans from late July through early September, with smaller numbers appearing in spring. The species gravitates toward shallow ponds, evaporation basins, and flooded fields, often in areas with minimal vegetation and high invertebrate density.

Unlike most shorebirds, Wilson’s Phalaropes are highly gregarious during migration, forming dense feeding aggregations that can number in the hundreds. They are especially drawn to saline environments, such as managed wetlands and wastewater ponds, where they forage by spinning in tight circles to stir up aquatic prey. Their presence in the Central Valley is closely tied to water availability and wetland management—years with extensive flooding or well-timed drawdowns tend to support higher numbers. While not a breeder in California, their annual passage is a dependable feature of the Valley’s late summer shorebird assemblage.

Globally, Wilson’s Phalarope is listed as a species of Least Concern, with an estimated population of around 1.5 million individuals. However, its dependence on a network of inland wetlands during migration makes it vulnerable to habitat loss, water diversion, and declining water quality. In the Central Valley, conservation efforts that maintain seasonal wetlands, support saline habitat management, and regulate agricultural runoff are vital to sustaining this species’ migratory needs. Long-term monitoring suggests stable or slightly declining trends, though data gaps remain, especially in wintering areas and migration corridors.

Natural history reveals a bird of elegant contradictions. Though classified as a shorebird, Wilson’s Phalarope behaves more like a waterbird—swimming buoyantly, spinning to feed, and nesting in upland grasslands near shallow wetlands. Its mating system is polyandrous: females are larger, more brightly colored, and compete for mates, while males incubate the eggs and care for the young. During migration, both sexes undergo a complete molt and accumulate fat reserves for their transcontinental journey to South America. In the Central Valley, their brief but vivid presence offers a glimpse into one of the most unusual life histories in the shorebird world.

A PHOTO GALLERY OF OSPREY

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