Two of the piping plovers' four chicks recently vanished from Montrose Beach Dunes and are presumed dead, said Louise Clemency, a field supervisor for the Chicago office of the U.S. Fish and Wildlife Service.
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The chicks were likely taken by predators that frequent the area, such as hawks or falcons, she told the Chicago Sun-Times.
WATCH: Chicago Piping Plovers welcome new chicks
Chicago Piping Plovers welcome new chicks
Clemency said volunteers tried to monitor all four chicks as they became "more mobile and adventuresome" and began using different parts of the habitat, but that's a difficult task.
The nesting pair, known as Monty and Rose, produced four eggs earlier this year. But in early June a skunk ate all four eggs by reaching through the nest's protective wire enclosure.
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The birds soon produced four more eggs, one of which was hatched by staff at the Lincoln Park Zoo when the pair neglected it after their three other eggs hatched. The birds quickly accepted that hatchling after it was returned to the nest site, and that chick is one of the two surviving offspring.
The loss of two of the chicks is not unexpected, said Judy Pollock, president of the Chicago Audubon Society.
"There are so many dangers to these little birds," she said. "If these two make it, Monty and Rose will already be beating the odds."
Meet Imani and Siewka
While it remains a mystery what happened to the missing chicks, the two remaining have been named.
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Chicago residents suggested names for the chicks and a panel of 10 made the final choice: Imani and Siewka.
Imani means faith in Swahili, a language spoken along the east African coast from northern Kenya to northern Mozambique. The name represents having fath in the efforts that there will be a future when Great Lakes Piping Plovers are no longer endangered, according to the Chicago Piping Plover organization.
Siewka (pronounced Shivka) is the word for plovers in Polish. This name was given to the chick hatched at the Lincoln Park Zoo. The name honors Chicago's large and well0established Polish population, which is said to be the largest outside of Poland.
The Associate Press contributed to this post.
The video in the player above is from an earlier report.