She may be a mallard, but the mother-to-be who has built her nest on I Street NW can’t seem to duck a persistent egg thief.

Someone has been robbing the cradle — and animal protection officials suspect that the thief is human, and may want to eat the developing eggs.

Since the plucky duck built her nest in a planter outside a downtown office building, the eggs have been disappearing, according to Anne Lewis, the president of City Wildlife. The I Street mallard had nine eggs less than a month ago, and now, as her eggs are nearly ready to hatch, she is reportedly sitting on only two or three.

Lewis said rats and raccoons sometimes snatch eggs out of ducks’ nests in the wild, but a citified duck like this one would rarely see her eggs fall prey to a fellow animal. Instead, the culprit seems to be a human thief.

According to Lewis, a security guard at the office building at 1575 I Street spotted a man putting on gloves and approaching the nest on June 6. “She found this guy kind of sneaking up to the nest, putting on these gloves and looking as though he was going to steal the eggs.”

The mallard sits on her remaining eggs on Sunday. City Wildlife says passersby should not be giving her food and water. (Julie Zauzmer)

At that point, City Wildlife was already wondering what was happening to the duck’s eggs, which were dwindling each time volunteers peeked into the nest.

The organization keeps tabs on every duck nest that it hears about in Washington — 25 nests so far during this year’s nesting season, which currently is at its peak. Lewis said eggs do not seem to have been stolen from any other nests.

Ordinarily, the organization’s volunteers are watching out for ducks that foolishly make their nests on rooftops or in enclosed spaces that they later can’t get their chicks out of, once they hatch.

“They’re not the smartest of creatures,” Lewis said. The volunteers routinely pick up those trapped ducks and transfer them to a nearby body of water.

In the case of the duck on I Street, the nesting mother had wisely picked a spot she could easily waddle away from, though she doesn’t have much privacy. Her nest takes up most of a planter right in the middle of a sidewalk just half a block from the McPherson Square Metro station.

Of the many workers who rush past her every morning, two called City Wildlife to report that the mallard had taken up residence when they first noticed her nesting in mid-May.

At the time, City Wildlife noted that she was sitting on nine eggs. A typical clutch is 10 eggs; some ducks sit on 15 at a time.

By early June, the I Street duck was down to six. The nest bore no signs of an animal intrusion, and the City Wildlife volunteer tracking the nest was perplexed.

When the security guard approached the man with the gloves, he turned and left. But Lewis assumes that the man was responsible for taking the first three missing eggs. And since then, three or four more have gone missing.

Fertilized duck eggs are the basis of a delicacy called balut that is enjoyed boiled or fried in some parts of Asia and is sometimes sold in American specialty food stores. Consumers of Balut wait for the egg to develop to the desirable point — usually somewhere between 17 and 21 days into the 22- to 28-day duck incubation period. Then they eat the partially formed embryo.

Harvesting fertilized eggs from domesticated ducks for balut is perfectly legal, Lewis said. But mallards are a different type than the ducks raised on farms. And under the 1918 Migratory Bird Treaty Act, disturbing a nesting mallard or taking its eggs is a federal crime, Lewis said.

She has alerted the U.S. Fish and Wildlife Service to the possibility of a repeat offender on I Street, and the security guard has been keeping an eye on the duck. But soon the duck will no longer be a sitting target — her remaining eggs are due to hatch any day now.

And they’re going straight to the top: Lewis said that one of the nearest bodies of water, where the duck will likely march her hatchlings and raise them in peace, is the fountain at the White House.