# Carnivore coexistence without competition: giant otters are more nocturnal around dens than sympatric neotropical otters

## TL;DR

Giant otters become more active at night near dens when neotropical otters are nearby, suggesting a strategy to avoid competition.

## Contribution

First documentation of den use and nocturnal behavior in sympatric giant and neotropical otters in the Amazon.

## Key findings

- Giant otters showed significantly more nocturnal activity near dens compared to neotropical otters.
- Sympatric otters used the same dens but not at the same time, suggesting temporal partitioning.
- Nocturnal behavior in neotropical otters may depend on the presence or absence of giant otters.

## Abstract

Nocturnal activity of tropical otters is rarely reported. To date no studies have documented den use by sympatric giant (Pteronura brasiliensis) and neotropical otters (Lontra longicaudis). We used camera-traps to monitor den use by sympatric otters along an equatorial Amazonian river. Camera-traps provided evidence that giant otters were more nocturnal around dens than sympatric neotropical otters. Nocturnal activity was recorded in 11% of giant otter photos (n = 14 of 125 photos), but was recorded only once for neotropical otters. Den use by giant and neotropical otters overlapped spatially and temporally but not concurrently. We hypothesize that previously reported nocturnal activity in neotropical otters is facilitated by the absence or low density of giant otters. Our results also underscore the need to use complementary techniques together with den counts for monitoring otters as sympatric species can use the same dens.