Habitat use patterns and diet of Lontra longicaudis (Olfers 1818) in urban streams of southern Brazil
This study demonstrates that the habitat use and diet of the Neotropical otter in urbanized southern Brazilian streams are primarily driven by the availability of favorable microhabitats like sandbanks and landscape connectivity rather than seasonal changes or riparian vegetation extent alone, highlighting the need to maintain functional aquatic connectivity for the species' conservation in anthropized landscapes.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
In the wetlands and rivers of Latin America, a small but vital predator patrols the water's edge: the Neotropical otter. These sleek, semi-aquatic mammals are more than just charismatic residents of the riverbank; they serve as a living barometer for the health of an ecosystem. Because they need clean water, abundant prey, and safe places to rest and mark their territory, their presence signals that a waterway is functioning well. When these animals disappear, it often means the environment has been degraded by pollution, habitat loss, or human disturbance. Understanding where otters choose to live and what they eat is therefore crucial for conservationists trying to protect not just the species, but the entire web of life it supports. This is especially true in coastal regions where cities are expanding, squeezing natural habitats into smaller and more fragmented spaces.
A team of researchers in southern Brazil recently set out to see how these animals are faring in a landscape increasingly shaped by human activity. They focused on three small streams in the municipality of Rio Grande, each representing a different level of urban development. One stream flowed through a relatively preserved area with dense vegetation, another wound through a neighborhood where nature and city life mixed, and the third cut through a heavily built-up urban zone. Over the course of a year, from August 2024 to July 2025, the scientists walked along the banks of these streams every month. Instead of chasing the elusive otters, they looked for the clues left behind: footprints in the mud, scratches on the sand, piles of droppings, and resting spots where the animals had paused. They also collected fecal samples to determine what the otters were eating, and used drone imagery to map the exact layout of the riverbanks, measuring how much vegetation, sand, and concrete surrounded the water.
The results revealed a surprising twist in how these animals interact with their environment. Conventional wisdom might suggest that the otters would be most abundant where the vegetation was thickest and the human impact was lowest. However, the data showed the opposite. The stream with the most lush, continuous green cover had the fewest signs of otter activity. In contrast, the stream running through the intermediate zone—where patches of grass and trees mixed with roads and houses—was teeming with evidence of otter life. The researchers found that the key to the otters' presence was not just the amount of greenery, but the physical structure of the riverbank. Specifically, the otters relied heavily on sandbanks. These sandy areas, which made up a small fraction of the total landscape, were where the animals walked, rested, and left their marks. In the most vegetated stream, the banks were often covered in thick grass that hid footprints and prevented the animals from leaving clear signs. In the intermediate stream, exposed sandbanks were plentiful, making it easier for the otters to use the space and for the researchers to find them.
The study also examined what the otters were eating across these different environments. The diet was remarkably consistent: fish were the main course, followed by crustaceans like crabs and shrimp, with birds appearing only rarely. This preference for fish held true regardless of whether the stream was in a quiet, protected area or a busy urban neighborhood. The researchers found no significant difference in the menu between the seasons or between the different streams. Even in the most urbanized stream, where the otters faced more noise, traffic, and potential conflict with people and dogs, they still managed to catch fish. This suggests that the species is highly adaptable, able to find food even in modified landscapes, provided that the water remains clear enough to support fish populations.
Perhaps the most critical finding was that the presence of the otters did not simply follow the amount of vegetation. The researchers concluded that the animals were balancing the need for food and shelter against the risks posed by human activity. In the most preserved stream, the dense vegetation might have offered cover, but the proximity to a highway and the presence of domestic dogs may have made the otters feel unsafe, causing them to avoid the banks or move through the area without leaving many traces. In the intermediate stream, the mix of sandbanks and vegetation offered a perfect balance: enough structure to leave signs and find food, but not so much disturbance that the animals fled. The most urbanized stream showed that even in a city, otters can persist if there are small pockets of suitable habitat, though their numbers were lower.
Ultimately, this research suggests that saving the Neotropical otter in coastal cities requires more than just planting trees along the river. It demands a deeper understanding of the physical landscape. Conservation efforts must focus on maintaining the connectivity between different water bodies and ensuring that the specific microhabitats these animals need—like sandy banks for marking territory—are preserved. It also highlights the need to manage human disturbances, such as traffic and free-roaming dogs, which can drive animals away from even the most beautiful stretches of river. By looking beyond the simple count of trees and paying attention to the complex interplay of sand, water, and human presence, we can better protect these vital indicators of a healthy ecosystem.
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