DOI: 10.5061/dryad.k0p2ngfk6
title: Nocturnal but not diurnal threats shape stopover strategy in a migrating songbird

description: Songbird migration involves frequent migratory flights interrupted by
 several days of stopover to refuel. For first-year migratory birds, this
 entails stopping in unfamiliar locations to exploit local resources and
 maximize fuelling rates. However, stopovers also pose mortality risks due
 to predator presence. We investigated whether auditory cues from two avian
 predators with contrasting hunting strategies—the diurnal Eurasian
 sparrowhawk (Accipiter nisus), which captures prey in flight, and the
 nocturnal tawny owl (Strix aluco), which relies on pouncing
 attacks—trigger different anti-predator responses in the nocturnally
 migrating European robin (Erithacus rubecula). We found that robins react
 to the perceived risk of predation by the nocturnal predator but did not
 alter their strategy in response to diurnal predator cues. Robins reduced
 foraging activity under perceived predation risk at night and decreased
 their fuel deposition rates over the stopover period. Lower body condition
 after stopover can result in a slower migration pace and consequently
 later arrival to wintering areas, potentially affecting individual
 fitness. This novel study highlights the flexibility of avian migration
 programs in adapting to perceived predation risks based on predator
 activity time and hunting modalities, and how these adaptations
 differentially shape stopover strategies.
description: # Nocturnal but not diurnal threats shape stopover strategy in a migrating
 songbird Dataset DOI: [10.5061/dryad.k0p2ngfk6](10.5061/dryad.k0p2ngfk6)
 ## Description of the data and file structure This dataset contains daily
 measurements of mean food intake, body condition, activity levels, and
 departure time after sunset from juvenile European robins (*Erithacus
 rubecula*). Individuals were assigned to one of two separate experiments,
 each with control and treatment groups, to assess anti-predator responses
 triggered by auditory cues from two avian predators: the diurnal Eurasian
 sparrowhawk (*Accipiter nisus*) and the nocturnal tawny owl (*Strix
 aluco*). The accompanying R script used for data analysis and to produce
 the results reported in the associated article is also included. ### Files
 and variables #### File: Data.csv **Description:** Dataset containing
 daily average measurements for the two experiments and the two
 experimental groups. ##### Variables * *Experiment*: Factor with 2 levels:
 "Diurnal predator" or "Nocturnal predator". * *Group*:
 Factor with 2 levels: "Treatment" or "Control". *
 *Ring*: Factor with 48 levels indicating the bird’s ring number and used
 as a unique bird ID. * *Day*: Integer (1 to 14) representing the
 experimental day. * *Food.intake*: Numeric value indicating the amount of
 food in grams consumed by the bird. * *Body.condition*: Numeric value
 representing normalized body mass, scaled by wing length. *
 *Activity.day*: Numeric value representing the percentage of time the bird
 was active. 'NA' indicates missing data due to technical issues
 with video-recording equipment. * *Departure.after.sunset*: Numeric value
 representing the fraction of 20-minute intervals after local sunset when
 the bird departed. 'NA' are not available values on the last
 experimental day (14), when night-time data were incomplete, or when
 activity data were unavailable due to technical issues with
 video-recording equipment. #### File: R\_Script.txt **Description:** R
 script with in-line comments used for data processing and statistical
 analysis. The script performs the following steps: 1. Load and structure
 the data. 2. Build and inspect linear mixed-effects models. 3. Perform
 likelihood ratio tests. 4. Calculate estimated marginal means from the
 models. 5. Generate plots of estimated marginal means with 95% confidence
 intervals. ## Code/software R version 4.3.2