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‘Urban’ ibis habits diverging from their wilder cousins

New study looks at how food sources in coastal cities help change movement patterns

 

With their long legs and curved beaks, ibis are fixtures in coastal and wetland areas across Florida and much of the Southeast.

But just as they can be found in the wild, poking their beaks among the tall grasses and marshy soil where few humans tread, the birds are also becoming increasingly common in neighborhoods, searching for food in freshly irrigated lawns or taking advantage of bread tossed to them.

There are consequences to adapting to these urban environments, though, says University of Georgia professor Jeff Hepinstall-Cymerman. With plentiful, reliable food sources, these typically nomadic birds are traveling less than their cousins living in the wild. That translates to less diverse food sources, concerns about diseases, changes in the birds’ natural breeding seasons and, possibly, longer-term effects on their offspring.

In a study recently published in the journal PLOS ONE, Hepinstall-Cymerman, a professor at the UGA Warnell School of Forestry and Natural Resources, investigates the differences in daily and seasonal movement patterns and nomadic habits between wild and urban ibis. By tracking the movements of birds in Palm Beach County, Florida, where birds have easy access to both urban and wild habitats, the authors found the wild ibis continued their typical nomadic movement patterns, rotating to new places as dictated by natural water levels and breeding seasons.

But the birds living in urban areas were less likely to move. Even during breeding season, when ibis move inland to seek suitable food and nesting spaces for their young, they seemed to wait until the last minute to leave their lawns, says Hepinstall-Cymerman.

“Our hypothesis was that during non-breeding season, these urban birds would be urban. But during the breeding season, they would behave more like wildland birds,” he says. While this pattern was proven true, a distinct difference emerged between the wild and urban birds.

“So, the urban birds, they zip up, they breed, and they go straight back to where they were before,” he adds. “Those birds clearly know a stable resource.”

This is in stark contrast to wild birds, which move all over Florida and into Georgia and other southeastern states throughout the year, following rain patterns, wetland depth and the drive to breed. The urban birds, though, would not only retreat back to their human environment as soon as their young were old enough, but they would return often to the same park they left just a few weeks before.

Lawn sprinklers, it turns out, create short-term wetlands. So, instead of flying from place to place as natural water levels rise and fall, urban ibis have adapted to jumping from lawn to lawn to find food. This, in addition to accepting food from humans and scavenging fish bait from docks and waterways, is fundamentally changing how the birds sustain themselves.

This can have an effect on the birds’ diet, the health of their offspring and, in the longer term, their overall survival rate.

The National Science Foundation-funded study is part of a larger body of research looking at ibis health and well-being. Because the birds have adapted to urban environments, they may be used as a bellwether for issues such as environmental contaminants, animal-borne diseases and species’ overall success.

“The long-term implication is, how does this affect fitness?” noted Hepinstall-Cymerman. In Australia, for example, the Australian ibis has adapted to the point where they might grab food out of a person’s hand. “At some point, if they’re going to be a nuisance, and if they’re carrying diseases, that’s going to be a problem.”

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