DOI: 10.5061/dryad.j3tx95xqw
title: Behavioral responses of crows to anthropogenic cues for food (Experiment 1 & 2)

description: Behavioral flexibility and the ability to respond appropriately to
 anthropogenic cues that signal potential threats or rewards may promote
 success of wild animals in the urban environment. Here, we examine the
 behavioral responses to anthropogenic cues of free-living American crows
 (Corvus brachyrhynchos), an opportunistic scavenger and common urban
 exploiter. Specifically, we tested the hypotheses that crows would more
 readily approach (1) novel objects and anthropogenic food when in close
 proximity to trash cans, and (2) paper bags with hidden food rewards when
 closer to a McDonald’s restaurant, due to their associations of food with
 these cues. In addition, we examined the preference of crows for bags
 marked with a McDonald’s logo versus unmarked bags, hypothesizing that
 crows closer to McDonald’s would be more likely to approach the labeled
 bag because of its familiarity. Consistent with our expectations, crows
 exhibited a lower approach latency to anthropogenic food and novel objects
 in close proximity to trash cans. Likewise, they were more likely to
 approach paper bags when in proximity to a McDonald’s restaurant, but they
 showed no preference for bags with a McDonald’s logo. Overall, we found
 evidence that the foraging behavior of crows varied in the presence of
 specific anthropogenic cues and that these responses depended on their
 probable cue familiarity. Their ability to use anthropogenic cues specific
 to the local environment, combined with their exploitation of human food
 resources, likely contributes to the success of the American crow in the
 city.
description: <strong>Experiment 1: Foraging behavior, urbanization,
 and presence of trash cans</strong>
   Behavioral responses to novel food and
 objects were recorded along an urbanization gradient at sites in Utica,
 Kirkland, New Hartford, and Rome, New York (USA) between October 2014 and
 March 2015 and September 2020 and April 2021 (Fig. 1). Sites were selected
 in parking lots in urban centers and on roadsides along agricultural
 fields in rural areas. Agricultural roadsides had minimal traffic; no cars
 drove past for the entire duration of most roadside trials (e.g.,
 Supplementary materials, Video S1). To characterize the degree of
 urbanization, we created buffers with a 50-meter radius surrounding each
 data collection site in QGIS 3.16. We calculated the percent impervious
 surface cover based on data from the 2016 National Land Cover Database
 (Percent Urban Imperviousness dataset), using the Zonal Statistics tool in
 QGIS to quantify the percentage of pixels covered by impervious surfaces
 within each buffer. We chose a 50-meter radius because it is a spatial
 scale relevant to the microhabitat and local associations of individuals
 in the immediate vicinity of each testing location. The percentage of
 impervious surface cover in these trials ranged from 0 – 87%  (mean: 31.96
 ± 4.99%; Supplementary materials, Fig. S1a). Qualitatively, sampling
 points in and surrounding Utica, NY (population = 64K; population density
 1500 people/km2), were relatively urban; points in the village of Clinton,
 NY (population = 1.7K; population density 1000 people/km2), were
 intermediate, and points surrounding Kirkland, NY (population = 10K;
 population density 116 people/km2), were relatively rural (Fig.
 1).   We chose sites for our
 trials along pre-selected routes, with exact locations based on the
 presence of unique groups of crows along these routes. At the start of all
 trials, the nearest crow was 15-25m from the experimental setup, a
 distance that we confirmed with a rangefinder (Nikon Monarch Gold). At
 this distance, birds did not fly away when we set up the experiment but
 were still close enough to observe the experimental setup. The
 experimental setup is shown in Fig. 2. We defined two contexts in which to
 compare the foraging behavior of crows encountered along these routes:
 sites at which a novel object and anthropogenic food items were placed
 within two meters of a trash can or dumpster ("trash treatment”) and
 sites at which a novel object and food items were placed out of view of
 the nearest trash can or dumpsters (i.e., at least 75m from the nearest
 trash can or dumpster; “control treatment”). At each site, we stepped out
 of the car, placed a video camera (the GoPro Hero 4 Black) on the
 pavement, and started recording with the GoPro. The GoPro served as the
 novel object in our experiment while simultaneously recording the crows’
 foraging behavior. We tossed 20 cheese puffs, a brightly colored food
 reward that is highly attractive to crows (Caffrey 2002) but with which
 they are likely to be unfamiliar, in the air in front of the GoPro to get
 the attention of the crows and returned to our car, moving it at least 20
 meters away from the experimental setup to observe and video record the
 responses of crows (Supplementary materials, Videos S1 and S2). Latency to
 approach (defined as the number of seconds that elapsed before any crow in
 the group made first contact with a food item, with the timing beginning
 immediately after parking our car &gt;20m from the experimental
 setup), the number of crows present at the start of the trial, amount of
 bait consumed, and GPS location were recorded for each trial. Trials were
 recorded for 20 minutes or until all the bait was gone. If no crows
 approached the bait within 20 minutes but were present for the entire 20
 minutes, we stopped the experiment and recorded 20 minutes as the latency
 to approach the bait for that trial. If crows dispersed from the area
 completely without having ever approached the experimental setup, the
 trial was discontinued and data were not recorded.* *Likewise, trials with
 human disturbance (e.g., pedestrians or vehicles; *n *= 6 trials) were
 discontinued and excluded from the sample. All trials were conducted
 within 2.5 hours of sunrise.  
 In total, ten sampling sites were established on roads along
 agricultural fields, seven on Hamilton College campus, and 20 in urban
 centers (Fig. 1). To minimize the likelihood that crows participated in
 multiple trials, agricultural sites were established ≥ 0.4 km apart and
 urban sites were located in separate parking lots at least 100m apart.
 Campus sites were established on known crow territories, and we only
 performed one test (i.e., trash treatment or control) within each
 territory.  
 <strong>Experiment 2: Urbanization and bag preference
 (labeled vs. unlabeled)</strong>
   To evaluate the extent to which crows
 use the McDonald’s logo as a cue for food resources (i.e., their
 preference for labeled bags vs. unmarked bags), we collected data in
 Kirkland, Rome, Oneida, Utica, and New Hartford, New York from October
 2019 to March 2020 and in November 2023. Twenty-four sites were
 established at pre-selected locations, at specific distances (0.5 km, 1.0
 km, and 1.5 km) from six different McDonald’s restaurants. Sites were
 pre-selected using Google Earth in parking lots of non-food establishments
 (e.g., automotive garages, gas stations, health centers, and schools) or
 street sides in residential neighborhoods. Seventeen additional locations
 were randomly selected in parking lots in urban centers or along roadsides
 in rural areas, based on the presence of unique groups of crows for
 testing. Crows were present at only 18 of the 24 pre-selected sites;
 therefore, the final sample included only 18 preselected sites and 17
 randomly selected sites (*n *= 35 sites). Only one trial was conducted at
 each location to minimize the likelihood that crows participated in
 multiple trials. As above, degree of urbanization was characterized as the
 percent impervious surface cover within a 50m radius around each testing
 site. The percent impervious surface cover in these trials ranged from
 0.13 – 85.13% (mean: 44.65 ± 4.42%; Supplementary materials, Fig.
 S1b)   Before each trial,
 one McDonald’s cheeseburger was placed inside a plain brown paper bag and
 one inside a McDonald’s bag. The burgers were immediately frozen after
 purchase and thawed overnight in the refrigerator prior to each trial.
 Bags containing burgers (one marked, the other unmarked) were placed on
 the ground two meters apart from one another, within five meters of a
 perched crow. Bags were oriented so that birds could not see their
 contents without approaching them closely (Fig. 3; Supplementary
 materials, Video S3). Observers then returned to their car, moving it at
 least 20 meters away from the experimental setup to observe the trial. The
 order that the bags were placed on the ground was randomly selected using
 an online sequence generator (random.org/lists). The bag (marked or
 unmarked) first approached by a crow was recorded at each location. Birds
 were allowed to remove and eat the burger from the first bag that they
 approached; trials were interrupted and bags collected before they were
 able to approach the second bag. Trials were ended if the crows did not
 descend to either bag within twenty minutes.
description: # Behavioral responses of crows to anthropogenic cues for food (Experiment
 1 & 2) Data for Corvus brachrhynchos behavioral responses to food and
 anthropogenic objects/ cues. Experiments were conducted along an
 urban-rural gradient in Oneida County, NY, USA. Contact Andrea Townsend
 ([[aktownse@hamilton.edu](mailto:aktownse@hamilton.edu)] with any
 questions. This manuscript has been accepted for publication Merz, M. R.,
 S. Cote, R. Weinberg, T. Malley and A. K. Townsend. "Can I have fries
 with that? Context-dependent foraging behavior in urban and rural American
 crows." Behavioral Ecology, Volume 36, Issue 1, January/February
 2025, arae098,
 [https://doi.org/10.1093/beheco/arae098](https://doi.org/10.1093/beheco/arae098) Data files include: Data files include: ## File: experiment1_ImperviousSurface_TrashBin.csv Variables Treatment_Type: whether or not a trash can is present (Y/N) Percent_impervious_50m: The percentage of impervious surface within a 50m radius around each test site Number_individ_at_start: The number of crows present at the start of each trail Bait_eaten: The number of pieces of food consumed during the trial seconds_to_approach: The number of seconds that elapsed before a crow first contacted the bait in each trial ## File: experiment2_McDonalds.Bag.csv  Variables Distance.to.McDonalds(km): Distance from the experimental trial to the nearest McDonald's restaurant (in km) impervious surface_50m: The percentage of impervious surface within a 50m radius around each test site Bag.Preference (C= control; M = McDonalds): Bag first closely approached by crows in a given trial, where control bags were unmarked and McDonald's bags had a McDonald's logo. NA: Not Applicable; birds did not descend to the ground or approach either bag during the trial period.  descended to bait (Yes/No): Whether or not crows descended to the ground during the trial period