Say what you will about the National Zoo, some animals definitely like it there and have showed their fondness by voting with their wings.
These are the black-crowned night herons, which return every spring to the zoo to breed, thus giving firm evidence of their affinities for the District, Rock Creek Park and the zoo.
But starting around this time of year, they fly off again, and just where they go has been a subject of ornithological uncertainty. But this year, authorities think that they will find out: They have attached miniature radio transmitters to six of the birds.
It happened on July 7. Using food as the attraction, scientists lured the herons from their perches, which were not in the birdhouse, but in the trees around it.
They briefly confined the birds, caught them, according to the zoo, and fitted them with custom-crafted backpack-style transmitters.
The birds are fine with the added baggage, the zoo said in an online account of the procedure. After being fitted, the birds were released again, and have been seen flying about with them.
If the past is a guide, the solar-powered radios will report back to scientists on the birds’ position after they take wing on their annual migration. This generally occurs some time after the start of August and is understood to involve days of flying over routes that cover hundreds of miles.
An effort was made last year to subject the herons to electronic monitoring in flight. That pilot study worked for a while, the zoo said.
At least three herons fitted with satellite transmitters were tracked for a time. One left on Sept. 22, and in six days flew to Fort Myers, Fla.
A second lingered in the Washington area (although not at the zoo) for about two months. Then after three weeks on the Chesapeake Bay’s eastern shore, on Nov. 6, it too, left for Florida.
The third left the breeding site at the zoo on Aug. 13, but as of Dec. 10 had also lingered in the Washington area, specifically at the Georgetown waterfront.
But after three months, the transmitters fell silent, and the birds’ whereabouts could not be specified.
This year’s monitoring is expected to work better, the zoo said.
The black-crowned night heron differs substantially from the stilt-legged blue heron that prowls wetlands around the metropolitan area, and occasionally takes to the air with a slow-flapping of its broad wings.
Instead, the black-crowned heron is a relatively compact sort of avian, which measures about two feet in length.
Most of its dimensions are commensurately shorter. This includes its bill, legs and neck.
Sometimes they may be seen in trees in wetland areas around the District, remaining almost immobile, with their bodies hunched, and bills tucked toward their chests.
Unsurprisingly, the adult birds have black feathers covering the tops of their heads, and black feathers down their backs as well.
None of the birds belong to the zoo’s formal collection, the zoo said. However, their informal connection to the zoo seems undeniable.
They have been arriving each spring for about 100 years to their breeding sites in the tall trees surrounding the birdhouse.
After the young birds emerge from their shells, and are up to flight, they dart around the zoo, free as any other of the world’s winged, feathered creatures.