Cameras placed inside the storm drains of Gainesville, Florida recorded about 3,800 animal sightings from 35 species, and the alligators caught on film were swimming pond to pond beneath busy roads

The drain grate in the road looks like every other one on the block.

Below it, a trail camera bolted to a magnetic bracket points down into the pipe.

In Gainesville, Florida, cameras like that kept running for months.

What moved through the pipes was a great deal more than rainwater.

So the team pulled the footage, and the question was suddenly simple: where had all these animals been going?

How a concrete drain became a highway

Stormwater sewers are not the same as sanitary pipes: they exist to drain rainwater, and they connect ponds, creeks and drainage basins into a network of tunnels that loosely mimics natural waterways. For an alligator, the difference is everything. A road is a wall; a pipe is a passage.

The researchers reported alligators moving between ponds through those connected culverts rather than crossing the surface streets above. The pipe did not just drain rain. It quietly carried predators between habitats that pavement would otherwise keep apart.

The pipes also offer dark, enclosed space, and the two animals recorded most often inside them were raccoons and southeastern myotis bats. A follow up paper by the same group found that raccoon presence tracked most closely with how near the nearest exit was, while bat roosting related to how much paved surface sat overhead. Those drivers are proposed rather than settled; the authors themselves describe raccoon use as possibly exploratory, or limited by food and light.

What the cameras actually caught

The footage held about 3,800 sightings of 35 vertebrate species. Raccoons topped the count with more than 1,800 sightings on their own, which made them by far the most frequent traveler in the system.

Southeastern myotis bats showed up nearly 700 times, foraging for insects and roosting inside the structures. Mammals dominated the sample overall, which matters for how the rest of the list should be read.

And then came the alligators: 50 sightings in all. The American alligator was one of seven reptile species recorded, and it was documented at more separate sites than any other reptile in the dataset.

The 35 species nobody knew were down there

The study appeared in the journal Urban Naturalist. A doctoral student at the University of Florida, Alan Ivory, suspected that stormwater drains might act as covert corridors for urban wildlife. The team installed 39 motion activated trail cameras on magnetic mounts beneath manhole covers across 33 stormwater drains in Alachua County, running from February to May 2023. Some cameras were lost to floods, and raccoons climbed the ladders and tore others from their mounts.

Possums, armadillos, cats, black rats, squirrels, egrets, wrens and toads all appeared on camera, alongside frogs and lizards. Twelve bird species turned up in total, filling in a picture that few people had thought to look for.

The researchers acknowledge that amphibians and reptiles are likely underrepresented in the data, because the cameras trigger on body heat. Aside from alligators and one turtle species, most cold blooded animals were recorded only because a mammal happened to walk into frame at the same moment. The true species count is probably higher.

What the pipes can tell us about disappearing habitat

Cities reduce natural spaces for wildlife, but animals adapt by using human made structures in surprising ways. In Gainesville, the effect showed up cleanly because the pipe network connects water bodies, giving animals a reason to travel and a route that keeps them off the asphalt. The same pressure playing out for Great Lakes whitefish squeezed by invasive species is at work here too: habitat shrinks, and animals take whatever corridor remains.

But the same infrastructure can also work against them. Not every animal on camera arrived by choice; some appear to have been swept in by rain. Cigarette filters, which top litter tallies on California cleanup days, wash through grates like these and settle in the same pipes.

Habitat loss and flooding together can turn a culvert into a dead end for smaller animals that lack the strength to fight the current back out.

What a simple ramp could change

The gap between what these pipes do and what they could do is not large. Knowing that wildlife uses stormwater systems, city managers can weigh cheap retrofits when pipes are built or replaced. Jochen Jaeger, a landscape ecologist at Concordia University who was not involved in the work, has suggested that fitting often submerged tunnels with dry pathways would make them more usable by animals.

No alligator waited for a wildlife crossing to be built. It found the crossing that already existed and used it, turning concrete infrastructure into a route between ponds.

“The abundance of animals down there was surprising,” said Alan Ivory, who led the research. The team expects the documented species count to rise as better sensors reach the pipes, because a heat triggered lens in a dim culvert undercounts cold blooded animals.

What the footage already shows is enough: the urban grid has a second layer, running just below the asphalt, and it has been carrying traffic the whole time.