Why these dumpy water birds are masters of evolving into flightless island dwellers

Nature · Published 3 October 2026 Swipe more like this →

In short: Moorhens are compact, red-beaked rails that seem built for the water, yet they are surprisingly prone to losing the power of flight. While common moorhens can migrate thousands of kilometers, their island-dwelling cousins have repeatedly evolved to stay grounded, illustrating a strange, recurring pattern of adaptation in the rail family.

Moorhens belong to the genus Gallinula, a name derived from the Latin for 'little hen.' These birds are part of the Rallidae family, which includes coots and other rails. Physically, they are compact, ranging from 25 to 40 cm in length, characterized by their distinctive red and yellow bills and strong, unwebbed legs. Unlike many of their relatives that prefer the safety of dense reedbeds, moorhens are often found foraging in open water margins, making them relatively easy to observe.

The evolutionary trajectory of these birds is marked by a fascinating propensity for flightlessness, particularly among island populations. While the common moorhen is a capable migrant—sometimes traveling up to 2,000 km from Siberian breeding grounds—other species like the Gough moorhen have become almost entirely flightless. This trait has emerged independently across various island-dwelling gallinules, suggesting that once these birds colonize isolated environments, the high energy cost of flight becomes a disadvantage that natural selection eventually prunes away.

The history of the genus is deep, with fossil records dating back to the Late Oligocene. Scientists believe the genus originated in the Southern Hemisphere, specifically around Australia, before spreading globally by the Pliocene. Today, the genus includes five extant species, though human settlement has likely caused the extinction of several others. Beyond their evolutionary history, moorhens are opportunistic omnivores, feeding on everything from plant material and seeds to small rodents, amphibians, and snails. During the breeding season, they become aggressively territorial, yet they remain social enough to congregate in flocks on shallow, vegetated lakes during the rest of the year.

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