DOI: 10.5068/d1t978
title: Urban junco flight initiation distances correlate with approach velocities of anthropogenic sounds

description: Urban-dwelling birds face novel visual cues and soundscapes. To
 thrive in these challenging environments, individuals must correctly
 identify and calibrate threats posed by humans and their
 activities. We showed that Dark-Eyed Juncos (Junco hyemalis)
 residing in an urban habitat responded differently to the sounds that
 approaching people and objects make. A person approached juncos
 simultaneously playing the sounds of object types that normally move at
 different relative velocities: faster (bicycles), intermediate
 (skateboards and scooters), or slower (people walking). Juncos
 responded at significantly greater distances and moved further in relation
 to what sound cues would normally imply about the velocity of approach.
 Absolute stimulus volume was not a significant predictor of response
 across object type. The responses occurred without the presence
 of visual cues, suggesting that an auditory cue alone and without visual
 confirmation can produce an appropriate response. Overall, this
 shows that this population of urban juncos has the ability to respond
 appropriately to novel anthropogenic sound cues. The question
 remains as to how universal such abilities are across species, different
 urban situations, and in natural habitats.
description: The observer flushed birds on the ground that were foraging or
 otherwise at ease (e.g., not alarm calling or agitated near a nest), using
 standard protocols. The observer approached a focal individual in a
 straight line, dropping markers at locations where the approach began (the
 starting distance), where the observer was when the focal subject clearly
 moved away, and the distance to the spot from where that movement happened
 (the FID). Using the location from which birds flee avoids FID being
 confounded by incidental foraging movements. FIDs were measured based on
 converting steps between markers to meters (1 step = 0.85m, as measured
 during training before the experiment). To avoid eliciting further escape
 behavior, we visually estimated distance moved away in meters as the
 Euclidian distance determined by the horizontal and vertical distances the
 bird travelled. The immediate distance of targeted birds to cover (either
 bushes and trees, or structures such as walls and outdoor furniture) was
 recorded at the point in time when the approach began.
 Each bird experienced 9 different sound stimuli. Each recording
 (10-15 seconds in length) was made using the Voice Memos app for smart
 phones as an MPEG-4. KL recorded the sounds while riding a bike, scooter,
 skateboard, or walking, in the presence of ambient background noise (i.e.,
 without any extraneous sounds that might signal danger such as car horns,
 or singing or alarm-calling birds). Thus, the recordings themselves were
 of a constant activity and not of an object approaching or passing by.
 Hence, the sound of an ‘approaching’ stimulus was entirely created by the
 experimenter advancing towards the focal bird. Each stimulus type was
 replicated two to three times: in a quieter state when moving over smooth
 terrain such as a flat sidewalk, or a noisier state when moving over rough
 terrain such as a textured sidewalk or dry leaves. This captures a range
 of noise that such moving objects may often make in an urban
 setting. Playbacks were from the phone at same set volume level, held at
 same height, and perpendicular to the ground. Phones, rather than speakers
 or other large equipment, were used so that the advancing person would not
 look unusual. Because the played recordings would meld into the existing
 soundscape of the immediate area in UCLA where the approach occurred, the
 total auditory environment of each approach would not have been completely
 identical. Birds were not approached, however, in areas where construction
 or some other loud sound would have affected the ability to hear the
 recordings. Decibel X, a noise meter application (https://skypaw.com/decibel10.html). 30-130dba; time weightings 200-500 milliseconds), was used to determine the mean loudness of each noise type across the duration of the recording when played. For each approach, the sound was turned on at the start of the approach and off when the bird moved away, which always occurred before the recordings ended. All birds were approached 5 consecutive times in a given day with the same sound playing (= 9 days of trials with 45 total approaches per bird).
description: The data are all in a single Excel file.