The zoological term sexual dimorphism doesn’t define anything as weird as one might think. Translated to common speak it means male and female birds have different colored feathers.
In general, the boys sport the brightly colored plumage. Think about how flashy a male tanager is in the spring, or an oriole, or the fire-headed vermillion flycatcher. And why all the showy feathers? To attract a mate.
But as with most things in the natural world there are no absolutes. The sexual dimorphic markings of the Belted kingfisher (Megaceryle alcyon) are reversed. The female wears the colors – a rusty brown stripe across its chest. The same reversal is true of the Red-necked phalarope (Phalaropus lobatus) which was spotted this month at the Merced National Wildlife Refuge.
The kingfisher is no rare visitor like the phalarope. It can be seen throughout California, and North and Central America generally. Both male and female birds are blue-gray with a white collar and blue breast band but only the female sports the chestnut stripe.
The male Belted kingfisher is a homebody. It doesn’t typically migrate from more moderate climates like the Central Valley but stays through the winter defending prime nest territory near water which can range for a distance more than half a mile. The female heads south for the winter and doesn’t return until it’s time to find a mate and hatch chicks.
No one knows for sure why Belted kingfisher females are more brightly colored than males of the species but there are some plausible ideas.
From an adaptive point of view, because the birds live apart for much of the year and the male is defending territory from other male kingfishers year round may be why the female is more brightly marked – so the male can immediately see he should not attack the female as an intruder but instead court her.
Another supposition is that the female kingfisher has brighter markings than the male because she has higher than normal levels of testosterone. That would also account for the bird’s unusually aggressive countenance near her nesting territory. The female red-necked phalarope’s role reversal due to elevated testosterone levels is so complete that besides laying the eggs she has nothing to do with incubation or chick rearing other than to defend the nest while the male keeps the eggs warm.
The kingfisher is easy to spot and perches in the open on telephone lines of tree branches overlooking open water. If it spots a fish near the surface or a crayfish moving about, it will dive into the water with its eyes closed to catch its prey in its massive beak.
The bird’s diet is almost exclusively aquatic but, in a pinch, the kingfisher will quit fishing and snare a reptile or an insect for lunch. It will also eat small mammals or young birds.
Its own young while in the nest can digest fish and crayfish scale, bones, invertebrate shells and all. Adult kingfishers don’t do that but instead disgorge pellets of fish skeletons and crayfish carapaces. Scientists dissect those pellets when determining what the birds are eating.
The Belted kingfisher doesn’t nest in trees. It builds its nest by tunneling into earthen canal banks or other steep-sided ground near water and forming a nest chamber at the end. The tunnels slope upward to keep water out and may extend as much as eight feet in length. It sometimes nests with bank swallows.
Kingfishers are ancient birds. Pleistocene fossils of Belted kingfishers have been found in the southern United States. A two-million-year-old fossil of the kingfisher genus was found in Florida.
One doesn’t need a rock hammer and shovel when looking for Belted kingfishers locally. They’re alive above ground here, easy to spot and fun to watch as they dive for fish.
The San Luis National Wildlife Refuge, Merced National Wildlife Refuge and the San Joaquin River National Wildlife Refuge comprise the San Luis National Wildlife Refuge Complex. Its headquarters and visitor center are located just north of Los Banos off Highway 165 at 7376 South Wolfsen Road.
The refuges are open to visitors daily from one half-hour before sunrise to one half-hour after sunset. The visitor center is open Monday through Friday except federal holidays from 8 a.m. to 4:30 p.m.
