Permanent urban legends patrol blind albino crocodile patrols New York City sewers. These mythical crocodiles are ingrained in city lore, with some New Yorkers even celebrating the crocodile on Sewer Day every February.
But in Florida, sewer crocodiles are not a myth. Reptiles routinely find their way into the municipal drainage channel. In late January, a 10½-foot gator was rescued at Cape Coral after being trapped in a rainwater drain.
And not all crocodiles accidentally fall into sewerage. A study recently published in the Journal of Urban Naturalists reveals that crocodiles and nearly 30 other species safely cross urban environments in one urban area of Florida using stormwater sewer systems Masu.
“It's like something from the 'Teen Mutant Ninja Turtles',” said PhD Alan Ivory. University of Florida students led the research. “The abundance of animals there was amazing.”
There has been a thorough study of rats in sewer systems, but it is not much documented what other animals are doing on the streets. Ivory and his colleagues suspected that these underground mazes, built to deflect rainwater and separated from the sewage system, serve as important routes for urban animals.
Ivory and his colleagues focused on stormwater sewer systems under the city of Gainesville. Scientists equipped a motion-activated trail camera with a magnetic mount and secured it under the manhole cover. Overall, 39 cameras were deployed in 33 storm drains.
The cameras were left alone for 60 days, but not all of them survived that long. Some were wiped out by storm waters, while others were stolen by bandits with sticky feet.
“We're going to let raccoons steal cameras from time to time,” Ivory said. “They climbed the ladder and ripped it out of the manhole.”
Despite the best efforts of these masked marauders, the team was able to retrieve most of the cameras, recording about 3,800 sightings of 35 animal species. Sewer residents included regular suspects, such as possums and rats. But there was a surprise: wooden frogs containing Carolina lenses, armadillos and 12 species of birds. These small birds were observed in six different storm drains, sometimes towed by nesting materials.
Mammals were the most common creatures in the sewer system. The raccoon has been captured over 1,800 times on camera. The second spotted animal was a bat in the southeastern myeloid, which was observed nearly 700 times. These small bats were used to forage insects using sewers, and Ivory said they appeared to roost under the species' first manhole.
Several large species, such as whitetail deer and bobcats, were recorded milled near the sewer system. However, apart from the crocodile, few giants ventured inside.
The team recorded 50 alligator sightings. Most appeared to use the sewer as the slope between the ponds. However, the team also sometimes swim towards dead ends in fish hunting. “It's like they're chasing fish to this dead end, and they use human infrastructure to help them forage,” Ivory said.
Scientists have only studied the Gainesville area, but believe that similar species use stormwater sewer systems in urban Florida. The state has built tunnels to help the Florida Panthers avoid busy streets.
Jocchen Jeger, a researcher who studies landscape ecology at Concordia University in Montreal and has not been involved in the new study, is already suspected that some species use storm drains. However, he said the paper shows the extent to which urban animals adopted these human structures.
In his own work, Dr. Jaeger examined how wild mammals, including black bears and moose, crossed underground passages like dark verts across busy highways in Quebec's mountainous regions. Modifying these often covered tunnels through dry routes makes wildlife more accessible.
Ivory and his colleagues believe that Florida's stormwater sewer could be improved as well. During the investigation, the team observed that snakes and toads were often washed away by sewers during heavy rains and sometimes struggled to return. Installing a lamp near a storm drain will help trapped creatures escape safely.
These changes are also essential for other sewer residents. Southeastern myotis bats hanging from the manhole are at risk of being trapped without an additional escape hatch. And some of these bat groups are declining due to the lack of a cave environment suitable for urban Florida.
“If the sewer system acts as an artificial roost, these systems can be extremely valuable,” Ivory said. “But if there's a flood when there's a roost bat, they could be washed away.”
