DOI: 10.5061/dryad.rr4xgxdd6
title: Behavioral responses to a series of similar but distinct novel objects in house sparrows

description: Generalization refers to the process by which animals assign different
 stimuli into cognitive categories based on their similarity/dissimilarity
 to previously experienced stimuli. Stimuli which strongly deviate from
 previous experience may be avoided due to their novelty (i.e., neophobia),
 while stimuli which are sufficiently similar to a known/recognized cue may
 elicit the same response as that cue (i.e., generalization). While
 generalization has been widely researched, few studies have examined
 among-individual variance in its expression. Our study quantified
 among-individual variation in neophobia and generalization in house
 sparrows (Passer domesticus) by placing a series of different objects next
 to each subject’s food source on successive days and measuring the
 subject’s latency to approach the food source in the presence vs. absence
 of each object. Similarly to previous work, we found that house sparrows
 are neophobic on average and exhibit significant among-individual variance
 in neophobia. More interestingly, we found that the neophobic response
 declined across presentations of different novel objects. This implies
 that the sparrows generalized some aspect(s) of the objects. We also found
 significant among-individual variance in the rate at which approach
 latency changed across this series, possibly reflecting individual
 differences in propensity to generalize. These results raise new questions
 about how neophobia, habituation, and generalization are linked and about
 the potential for selection to act on these traits under different
 ecological conditions.
description: <em>Subjects and acclimation</em>
 We conducted experiments on 10 female and 8 male house sparrows
 (<em>Passer domesticus</em>) at the University of Kentucky’s
 Ecological Research and Education Center (38°4'52",
 -84°28'14”). We captured these subjects using mist nets from two
 sites in Lexington, KY: a backyard in a suburban housing development
 (38°0'28", -84°30'39") and the seed warehouse of a
 farm store in an industrial/commercial area (38°0'52",
 -84°26'29"). Eleven of the subjects (5 female, 6 male) we
 captured between January and March 2017 and assayed between May and
 September 2017, while the other seven (5 female, 2 male) we captured and
 assayed during the same time frames in 2018. All subjects were
 developmentally adults (i.e. after hatch year), but their exact ages were
 unknown. The choice of 18 subjects was based on practical constraints
 including the amount of available aviary space and the time needed to
 conduct a full set of behavioral assays; no a priori sample size
 calculation was conducted. No captured subjects were excluded from the
 experiment, nor did we have any a priori criteria for doing so. One
 captured subject (a sixth female captured in 2017) escaped from the
 experimental aviary before the completion of the full set of behavioral
 assays and was thus excluded from the final dataset/analysis.
 Following capture, subjects were tagged with a unique combination
 of colored plastic leg bands for visual ID; these are standard for birds
 and do not impede normal behavior. Between capture and commencement of
 behavioral assays, we held the subjects in mixed-sex flocks in outdoor
 aviaries (3.7 x 2.4 x 2.4m), each having a wooden frame with 1 x 1 cm wire
 mesh enclosing it on all sides except for the ends, which were solid
 plywood. Each aviary contained a tree and two elevated platforms (attached
 to the back wall) on which we placed dishes of water and food (a mix of 3
 parts white millet and 1 part chicken starter mix), both provided ad
 libitum. For the behavioral assays, we moved each subject to one of four
 “experimental aviaries,” identical to the housing aviaries, where it
 stayed for the duration of the assays. Experimental aviaries had six
 platforms, four on one wall and two on the opposite wall. Each of these
 four platforms contained a specialized feeding board on an aluminum tray;
 under one board was a balance used to obtain subject mass. For symmetry,
 we placed wooden spacers that matched the height of the scale under the
 other three boards. The two platforms on the opposite wall contained a
 water dish (bottom platform) and a camera tripod for filming experimental
 trials (top platform). After moving each subject from
 the group holding aviary to the experimental aviary, we gave it a variable
 period of two to five days to acclimate to its new surroundings with
 minimal disturbance (with the exception of the first two subjects tested,
 which had 33 acclimation days). The number of acclimation days is included
 in the data file. After acclimation, we trained each subject for the
 behavioral assays as described below.
 <em>Training protocol</em> The
 novel object presentations which comprise this data set were embedded in a
 set of trials designed to assess other behaviors, addressing other
 questions unrelated to neophobia and generalization. Our full trial set
 required the birds to be trained to find food on the feeding boards, each
 of which contained eight wells. A fully trained subject would find food by
 flipping a lightly weighted paper lid off of a well and digging through
 sand to find millet seed that was buried there. Subjects experienced sand
 and lids from the moment they entered the aviary, but food was slowly
 buried in sand, and the sand was covered by the lids over a 4-day period.
 We began the full sequence of behavioral assays on the 5th day after
 training started. <em>Behavioral
 assays</em> The first two days of behavioral
 assays involved assessing subjects’ preference for particular boards given
 a difference in the distribution of seed among wells on each board. This
 distribution was continued through all trials, including those analyzed
 here. In addition, subjects’ feeding boards were refilled four times per
 day, at about 8am, 12pm, 3pm, and 6pm. The third day marked the beginning
 of our neophobia trials, for which we modified the feeding schedule to
 include a 1hr deprivation period (in which all four boards were completely
 removed from the aviary) prior to the 12pm and 3pm feedings. This
 deprivation functioned to increase and roughly standardize the subjects’
 feeding motivation during the subsequent trials. At the 12pm (“control”)
 trial, we reintroduced the (refilled) food boards as usual and filmed the
 subject’s response over the following hour. At the 3pm (“novel object”)
 trial, we reintroduced the boards with a novel object placed immediately
 next to the same corner (front right from camera view) of each board. We
 then filmed the subject’s response over the following hour. The
 timing/order of the control and novel object trials were the same for each
 subject because our goal was to uncover pre-existing individual
 differences in the processing of cues, and this requires reducing
 differences in stimuli received during the experiment. 
 We repeated this schedule over the following three days, using
 the first four (different) novel objects from a sequence of eight. We
 constructed these novel objects using Mega Bloks® such that each object
 was of a similar size but differed in shape and/or color. Each subject
 experienced one of three predetermined orders of objects. To enable the
 assessment of individual differences (as with trial order) it would have
 been ideal for each subject to experience the same object presentation
 order. However, practical constraints on time and materials prevented
 this, so we account for this potential confound in our data with the
 variable “object order.” After the four neophobia
 assays, we devoted the following three days to further assays of board
 preference which included two days of reduced food across all three boards
 with food. Following this was a recovery day during which birds had access
 to their boards as before but were disturbed only when the boards were
 changed. We then repeated the novel object trials as before but with the
 remaining four objects in the sequence. Each subject therefore experienced
 a total of eight neophobia trials, with a six-day interval between the
 fourth and fifth trials. Upon completion of this second round of trials,
 we released our subjects back into the wild.
 <em>Video scoring</em> We scored
 video sessions by recording each subject’s “latency to land,” defined as
 the time in seconds between (a) the door being closed behind the last
 board placed in the aviary and (b) the first time that the bird had both
 feet touching down on any part of a feeding platform, board, or aluminum
 tray. All video recordings were started before the boards were placed so
 that this could be timed precisely. If a bird did not land on any part of
 a platform, board, or tray during the approximately 1-hour session, its
 latency to land was recorded as the time between door closure and the end
 of the video (N = 13 of 288 trials, 3600–3900 seconds). All videos were
 scored by A.L. McLaughlin. Because latency to land (as defined) was
 relatively objective and easy to observe, intercoder reliability was not
 measured, and scoring was not blind with respect to subject ID or novel
 object presence/ID (which would be difficult to accomplish given that both
 are readily visible in the videos).  <em>Data
 processing</em> Latency to land was
 log-transformed for all statistical analyses to reduce its skewness and
 treated as a Gaussian variable. Details of our statistical analysis
 (conducted in R version 3.5.1 and SAS 9.4®) may be found in the associated
 manuscript (McLaughlin and Westneat in press, Ethology manuscript number
 ETH-22-0172). 
description: Microsoft Excel is required to open our main data file
 (“Novelty_Data_DRYAD_version.xlsx”); open-source alternatives are Google
 Sheets and Microsoft Office Excel Online. Our ReadMe file (“ReadMe.txt”)
 may be opened in any text editor.