Timescapes of fear: Exogenous and endogenous control of moonlight-mediated circalunar foraging rhythms in a weakly electric fish

The timing of activity is fundamental to animal survival. For many nocturnal species, moonlight suppresses activity due to elevated predation risk. However, how animals track moonlight—with its complex nightly and monthly variation—remains poorly understood. We investigated the relative roles of exogenous and endogenous control in the moonlight-mediated foraging rhythm of the nocturnal electric sand knifefish (Gymnorhamphichthys rondoni) inhabiting Amazonian streams. Using continuous field recordings of electric organ discharge (EOD) paired with high-resolution moonlight measurements, together with laboratory experiments under recreated moonlight cycles, we quantified activity across the lunar month. Sand knifefish restricted foraging to moonless periods, closely tracking nightly shifting windows of darkness. Activity was strongly suppressed under moonlight but resumed when dense clouds blocked it, indicating exogenous masking. We also documented a daily “pre-em..., , # Timescapes of fear: Exogenous and endogenous control of moonlight-mediated circalunar foraging rhythms in a weakly electric fish

Dataset DOI: [10.5061/dryad.9p8cz8wwx](https://doi.org/10.5061/dryad.9p8cz8wwx)

## Description of the data and file structure

Wild sand knifefish data:

1. **wild_monthly_passage_rate.csv**
2. **wild_preemergence_rise.csv**

Captive sand knifefish data:

1. **captive_monthly_EOD_rate.csv**
2. **captive_preemergence_rise.csv**

### Files and variables

Dataset keys:

1. **wild_monthly_passage_rate.csv**: Data for plotting figure 2a, the wild sand knifefish passage rate actogram with field-measured moonlight ground illuminance shown as a heatmap.
* datetime: Timestamp in datetime format (M/D/Y h:mm), at 15-min intervals
* average_passage_rate: Number of sand knifefish passages per 15 min, averaged across the six EOD loggers (continuous)
* illuminance: Field measurements of ground illuminance (lux) at 15-min intervals (continuous): the light meter c...,