DOI: 10.5061/dryad.sn02v6x3x
title: Acoustic and visual stimuli combined promote stronger responses to aerial predation in fish

description: Bird predation poses a strong selection pressure on fish. Since birds must
 enter the water to catch fish, a combination of visual and
 mechano-acoustic cues (multimodal) characterize an immediate attack, while
 single cues (unimodal) may represent less dangerous disturbances. We
 investigated whether fish could use this information to distinguish
 between non-threatening and dangerous events and adjust their
 anti-predator response to the perceived level of risk. To do so, we
 investigated the anti-predator behavior of the sulphur molly (Poecilia
 sulphuraria), a small freshwater fish which is almost exclusively preyed
 on by piscivorous birds in its endemic sulfide spring habitat. In a field
 survey, we confirmed that these fish frequently have to distinguish
 between disturbances stemming from attacking birds (multimodal) and those
 which pose no (immediate) threat such as bird overflights (unimodal). In a
 laboratory experiment, we then exposed fish to artificial visual and/or
 acoustic stimuli presented separately or combined. Sensitivity was high
 regardless of stimulus type and number (&lt; 96% of fish initiated
 diving), but fish dove deeper, faster and for longer when both stimuli
 were available simultaneously. Based on the system’s high rates of bird
 activity, we argue that such an unselective dive initiation with
 subsequent fine-tuning of diving parameters in accordance to cue modality
 represents an optimal strategy for these fish to save energy necessary to
 respond to future attacks. Ultimately, our study shows that fish
 anticipate the imminent risk posed by disturbances linked to bird
 predation through integrating information from both visual and acoustic
 cues.
description: <strong>Topic:</strong> We investigated the
 importance of visual and acoustic stimuli in aerial predator avoidance of
 a small freshwater fish, the sulphur molly <em>Poecilia
 sulphuraria</em>. Our first aim was to explore the diversity of
 disturbances to which sulphur mollies are exposed in their natural
 habitat. We then tested whether fish increased their anti-predator
 response with the number of predator stimuli by presenting  a moving
 object above the surface (unimodal visual), a playback of an impact sound
 (unimodal acoustic) or both stimuli simultaneously (bimodal). 
 <strong>DATA_SI_BirdActivityField:</strong> Bird
 activity<br> We recorded all sightings of birds in the predefined
 study area within a 30-min period. For each bird, we determined species
 (to lowest feasible taxonomical level), entry and exit times, as well as
 the number of attacks. Bird sightings were categorized as either
 'stay' or 'overflight' (i.e. flying through the
 transect without landing or attacking). We calculated presence time as the
 mean time birds spent in the study area (excluding overflights) and
 attacks as the total number of bird attacks launched in a sampling
 period.  <strong>DATA_SI_DivingGroupmeans:
 </strong>Lab experiment – predator stimuli <br> We exposed
 fish to simulated bird attacks presenting them with one of three stimulus
 types: unimodal visual, unimodal acoustic or bimodal (visual + acoustic).
 In a laboratory setting, we tested a total of 5 groups (12 individuals
 each; n = 60). Data provided here is group-pooled, but individual tracks
 are available upon request.
 <strong>DATA_SI_DivingField:</strong> Supplement –
 predator stimulus validation<br> We assessed fish's dive
 reaction in response to simulated bird attacks using a focal shoal
 sampling approach. Six focal shoals were chosen along the sulphidic stream
 habitat (but in correspondance with sites reported in Culumber et al.
 2016). The application of the acoustic stimulus was not feasible under
 field conditions. We stimulated fish 10–12 times with a minimum of 60 s
 between exposures and recorded diving responses within a frame of interest
 that allowed for the detection of individual fish. As the information of a
 detected threat often propagates through a group, we determined the
 interval from the point that 50% of fish had initiated diving until 50%
 had resurfaced.  
 <strong>DATA_SI_DivingBodysize:</strong> Supplement –
 lab experiment<br> For the experiment, test fish were visually
 matched for size. To verify that groups did not significantly differ in
 size, body sizes were estimated from video images taken during the
 experiment. To minimize a systematic error introduced through fish’s
 distribution in the z-axis (i.e. distance to camera), measurements were
 only taken for individuals that were very close to the tank’s front glass
 and not occluded by another fish. Monitoring of water paramters (DO, Temp)
 was carried out prior to a group's first trial and repeated after the
 last trial. <strong>2021_Lukas_Multisensory.R
 </strong>(see 2021_Lukas_Multisensory_Report for a PDF
 version)<br> All analyses were performed in R (R Core Team, 2020,
 version 4.0.2).
 <strong>SIAudio_Stimulus_Impact.wav</strong><br> The acoustic stimulus consisted of an underwater recording of a projectile hitting the water (duration: 1 s)