DOI: 10.5061/dryad.t4b8gtj9q
title: Personality composition affects group cohesion of homing pigeons in response to novelty and predation threat

description: Understanding how and why animal groups behave collectively is a central
 question in behavioural and social sciences. Variation in the phenotypic
 composition of the individuals within a group can lead to differences in
 group attributes and performance. However, whether and how individual
 personalities translate into group performance is not yet fully understood
 because experiments that test such hypotheses in realistic set-ups are
 still scarce. We explored how between-group variation in personality
 composition affected flock cohesion during homing flights of homing
 pigeons, Columba livia. Based on consistent individual
 differences, we established flocks of either ‘more reactive’ (MR flocks)
 or ‘less reactive’ (LR flocks) pigeons naïve to homing. Cohesion of flocks
 was tested in three distinct challenges: (1) first-ever collective homing
 experience (novelty); (2) release from a novel site (novel site homing);
 and (3) hunt by a robotic peregrine falcon (predation threat), with the
 latter two challenges performed with flocks trained for homing. MR flocks
 were more cohesive than LR flocks in the novelty challenge, but showed
 similar levels of cohesion during the novel site homing challenge.
 Predation threat decreased cohesion in both flock types, with a stronger
 effect in LR flocks. These results indicate that differences in the
 composition of personalities of group members can produce detectable
 differences in collective performance, and highlight the importance of
 accounting for individual-level behavioural variation when studying
 collective patterns in nature.
description: <strong>Personality</strong> Each
 bird was subjected to three behavioural tasks to define its personality
 traits: Flight Initiation Distance (FID), Escape Reaction Time (ERT) and
 Exploration Propensity (EXP). To assess the consistency of individual
 responses over time, we performed two replicas of each test. The second
 replica took place 1 week after the completion of the first one. The
 sequence of tests was randomized for each individual in each replica. The
 repeatability of the response of the birds to the first and second
 replicas of each test was assessed using mixed effect models through
 package rptR 0.9.22 (Stoffel et al., 2017) with 1000 bootstraps. The
 repeatability was adjusted taking into account the level of experience of
 tested birds, which could affect the response. The
 personality identified for each pigeon was used to assort monotypic flocks
 constituted of four individuals (only more reactive or less reactive). To
 assess the bird personality, we firstly ranked individual responses to
 each test at their first replica based on their reactivity, assigning the
 lowest rank to the least reactive individual. For each test, the ranks
 were then transformed into a three-level score based on the tertiles of
 the rank distribution. The first, the second and the third tertiles were
 scored as 0, 1 and 2, respectively. The scores of the three tests were
 then summed to obtain an Overall Personality Score (OPS). Subjects with
 OPS ≥ 4 were classified as ‘more reactive’ (MR pigeons), provided that the
 FID score was greater than 0 (i.e. took off at greater distances from the
 experimenter). Subjects with OPS ≤ 2 were classified as ‘less reactive’
 (LR pigeons), provided that the FID score was ≤ 1 (i.e., individuals
 seemed less intimidated by humans and took off only when the experimenter
 was close to them). Where these criteria were not fulfilled the birds were
 excluded from homing trials. <strong>Homing
 flights</strong> All birds of the flock were
 equipped with GPS data loggers to record their homing route. Monotypic
 flocks were exposed to three functional challenges: novelty (first release
 of the newly established monotypic flock), novel site homing (established
 flock released from a new unknown release site) and predation threat
 (established flock released from familiar release site and attacked by a
 robotic falcon - RobotFalcon). Each flock was released 7 times from the R1
 site and one time from a non familiar release site (R2 or R3). At the 7th
 release from R1 pigeons were attacked by the RobotFalcon. The tracks have
 been preprocessed in order to remove locations collected between the time
 the pigeon had reached the home loft after completing the homing flight
 (the first time crosses a distance &lt; 100 m from the home loft) and
 the time the GPS was retrieved from the bird.
 <strong>Assess degree of flock cohesion and identify first
 flock split event</strong> “Flock cohesion was
 assessed only for flocks with complete GPS recording for all four birds
 until at least one pigeon entered a 100 m buffer around the home loft. For
 each flock in each homing trial, the number of GPS locations used for
 assessing cohesion was the number of data points of the track of the bird
 that homed first. A cohesion index was computed for each homing trial as
 follows. The distance of each pigeon from all the others in the group was
 computed for each sampling step. If the distance between two individuals
 was equal to or higher than 500 m, we set a cutoff value of 500 m. These
 distances were summed, and this sum was divided by the sum of the
 theoretical maximum distances if the pigeons were flying alone (3000 m;
 i.e. all six pairwise distances were at the cutoff value of 500 m). The
 resulting value was then subtracted from 1. Therefore, the cohesion index
 varies from 0, when pigeons fly separately, to 1, when pigeons fly in
 group. To examine potential differences in flock splitting between flock
 types, we measured the time elapsed since a flock's release (TR) and
 the distance to home (DH) when the first split occurred (if any). A split
 was defined as at least one pigeon leaving the flock, with a separation
 threshold of 20 m (Biro et al. 2006).” (extracted from paper, Cerritelli
 et al. 2025). “We considered two types of splits: (1)
 to stop and rest before completing the journey (‘split-to-rest’); (2) to
 follow a different homing path from the rest of the flock
 (‘split-to-fly’). In the novelty challenge we performed the analysis
 considering both types of split behaviour in order to detect potential
 biases due to stress or physical fatigue potentially affecting flight
 performances. In the other two challenges, we considered only
 ‘split-to-fly’ individuals, given that an individual showed
 ‘split-to-rest’ behaviour in only two cases (one for the novel site
 challenge and one for the predation threat challenge).” (extracted from
 paper, Cerritelli et al. 2025)
 <strong>Statistical Analyses</strong>
 “For analysing cohesion responses to the novelty challenge and
 the novel site homing challenge in relation to flock type, we fitted a
 generalized linear model (GLM) with beta error distribution, with the
 cohesion index as the response variable and flock type (two-level factor:
 MR and LR) as predictor. The effect of flock type on the time since
 release (TR, log-transformed) and distance to home (DH) at the location of
 the first split was tested using linear models (LM). For the novelty
 challenge, the analyses were performed both including and excluding those
 groups containing ‘split-to-rest’ individuals. Flock cohesion of MR and LR
 flocks during the predation threat challenge was assessed using a
 generalized linear mixed model (GLMM) with beta error distribution. The
 cohesion index of each flock during the homing flight after exposure to
 the RobotFalcon (RobotFalcon flight) was compared to the cohesion index of
 the last available training release without predator exposure (control
 flight). Predictors included predator treatment (control versus
 RobotFalcon flight), flock type (MR versus LR) and their interaction as
 fixed effects, and flock identity as random intercept. Similar GLMMs were
 fitted to test the effect of the RobotFalcon on first flock split after
 release (TR and DH), using a negative binomial and a Gaussian
 distribution, respectively, and flock identity as random intercept.”
 (extracted from paper, Cerritelli et al. 2025)
 <strong>References</strong> Biro,
 D., Sumpter, D. J. T., Meade, J., & Guilford, T. (2006). From
 compromise to leadership in pigeon homing. Current Biology, 16(21),
 2123e2128. https://
 doi.org/10.1016/j.cub.2006.08.087 Stoffel, M. A.,
 Nakagawa, S., & Schielzeth, H. (2017). rptR: repeatability
 estimation and variance decomposition by generalized linear mixed-effects
 models. Methods in Ecology and Evolution, 8(11), 1639e1644. https://doi.org/10.1111/ 2041-210X.12797
description: # Personality composition affects group cohesion of homing pigeons in
 response to novelty and predation threat We have submitted our raw data
 (**ERT_test_results.csv, FID_test_results.csv and EXP_test_results.csv**)
 with results of personality tests for the three replicas, the deployment
 information on monotypic flock releases (**deployments.csv**), the
 coordinates of release sites and home loft location
 (**release_loc_2022.csv**), the cleaned tracking data for all homing
 flights – both from familiar release site (**data_clean_releases_R1.csv**)
 and not familiar release sites (**data_clean_releases_NoFamiliar.csv**).
 Empty cells (Nas) in the datasets are due to not available data. We have
 included R scripts to perform the analyses with:
 01.Repetability_Response.R; 02.SplitsEvaluation.R (which requires files:
 **MonoFlock_complete_data_20231222.rds**and
 **MonoFlock_complete_data_NF_20240122.rds**); 03.Statistical_Analysis.R
 (which requires files: **split_flock4.rds; split_flock4_NF.rds**). In
 order to run some of the R scripts four custom function were also
 included: **flock_comp_time.R, cum_interind_coord.R,
 cumulative_interindividual_distances_5.txt, first_split_4flock.R.** ##
 **Descriptions** ### *Personality tests results* **ERT_test_results** *
 *Anello*: animal id (unique for each individual) * *Test_rep*: number of
 repetition of the test * *Data*: date when the test was performed *
 *Rilevatore*: name initials of experimenter who performed the test *
 *secs*: time in seconds taken by the pigeon to escape the box; NA
 indicates that the test was not be performed (the pigeon was not found in
 the loft) **FID_test_results** * *Anello*: animal id (unique for each
 individual) - *Test_rep*: number of repetition of the test - *Data*: date
 when the test was performed - *Operatore*: name initials of experimenter
 who performed the test (was walking towards the pigeon) - *Distanza*:
 distance in cm between experimenter and pigeon at which the bird fled
 away; NA indicates that the test was not be performed (the pigeon was not
 found in the loft) #### **EXP_test_results** * *Anello*: animal id (unique
 for each individual) * *Test_rep*: number of repetition of the test *
 *DataOra*: datetime when the test was performed * *Operatore*: name
 initials of experimenter who performed the test * *Ex_punteggio*: score
 assigned to the exploration activity of the pigeon in the maze; NA
 indicates that the test was not be performed (the pigeon was not found in
 the loft) ### *Tracking dataset* #### **deployment** * *bandiera*: unique
 identifier of each flock - *anello*: animal id - *gps*: number of gps. it
 should be formatted as text. - *tipo*: type of release (A = training, C =
 control, F = with RobotFalcon) - *luogo_rilascio*: release site identifier
 (R1, R2 or R3) - *familiare*: familiarity of the pigeon to the release
 site (1 = familiar, 2 = non familiar) - *Nome_lancio*: name of release
 site (CAL, CAM e GUA ); the number indicates how many times the flock
 homed from that release site, i.e., the level of experience of the flock
 to home from a specific release site. - *data*: date of release -
 *ora_rilascio*: time of release - *dati_completi*: complete homing route
 of the individual is available (1) or not (0) - *dati_completi_recupero*:
 indicating whether the data for the individual is available until the
 first bird of the group reaches the loft (1) or not (0). ####
 **release_loc_2022** * *x*: longitude - *y*: latitude - *id_RS*: release
 site id - *RS*: name of release site. CASA is the home loft. - *name_RS*:
 release site identifier; Arnino is the home loft. ####
 **data_clean_releases_R1 and data_clean_releases_NoFamiliar** The data has
 been cleaned in order to remove all the locations obtained between the
 time the pigeon reached the home loft (the first time the pigeon is less
 than 100 m from the home loft). The two datasets have the same data
 structure. * *gruppo*: unique identifier of each flock - *lancio*: name of
 release. CAL stands for R1. The number associated, indicates the number of
 releases the pigeon homed from that release site, i.e., level of
 experience from the release site - *animal_id*: animal id - *personalita*:
 type of personality associated to each individual basing on the results
 obtained in the three personality tests. - *ts*: datetime of the location
 - *latitude*: latitude of the location - *longitude*: longitude of the
 location - *speed*: speed calculated from the data logger (km/h) - *RS*:
 name of the release site (CAL, GUA or CAM) - *exp_RS*: level of pigeon
 experience to home from a release site. The number indicates how many
 times the pigeon homed from that release site - *dati_completi*: complete
 homing route for the pigeon is available (1) or not (0) -
 *dist_from_home*: distance between location position and home loft in (m)
 - *dist_from_RS*: distance between location position and release site (m)
 #### **MonoFlock_complete_data_20231222.rds** * *gruppo*: unique
 identifier of each flock * *lancio*: name of release site. CAL stands for
 R1. The number associated, indicates the number of releases the pigeon
 homed from that release site, i.e., level of experience from the release
 site * *animal_id*: animal id * *personalita*: type of personality
 associated to each individual basing on the results obtained in the three
 personality tests (Non reattivi = Less reactive; Reattivi = More Reactive)
 * *ts*: datetime of the location * latitude: *latitude* of the location *
 *longitude*: longitude of the location * *speed*: speed calculated from
 the data logger (km/h) * *RS*: name of the release site (CAL, GUA or CAM)
 * *exp_RS*: level of pigeon experience to home from a release site. The
 number indicates how many times the pigeon homed from that release site *
 *idfix*: unique identifier of each location collected * *exp_dymmy*: level
 of pigeon experience to home * *idnum*: numeric unique identifier for each
 animal id * *id_lancio*: string reporting animal id and name of release *
 *dati_completi*: complete homing route for the pigeon is available (1) or
 not (0) * *dist_from_home*: distance between location position and home
 loft in (m) * *dist_from_RS*: distance between location position and
 release site (m) * *treatment*: type of treatment for the release (C =
 control; F = with RobotFalcon exposure) ####
 **MonoFlock_complete_data_NF_20240122.rds** * *gruppo*: unique identifier
 of each flock - *lancio*: name of release site. CAM stands for R2 and GUA
 for R3. The number associated, indicates the number of releases the pigeon
 homed from that release site, i.e., level of experience from the release
 site. In this file are included only homing flights from unfamiliar
 release sites. - *animal_id*: animal id - *personalita*: type of
 personality associated to each individual basing on the results obtained
 in the three personality tests (Non reattivi = Less reactive; Reattivi =
 More Reactive) - *ts*: datetime of the location - latitude: *latitude* of
 the location - *longitude*: longitude of the location - *speed*: speed
 calculated from the data logger (km/h) - *RS*: name of the release site
 (CAL, GUA or CAM) - *exp_RS*: level of pigeon experience to home from a
 release site. The number indicates how many times the pigeon homed from
 that release site - *idfix*: unique identifier of each location collected
 - *exp_dymmy*: level of pigeon experience to home - *idnum*: numeric
 unique identifier for each animal id - *id_lancio*: string reporting
 animal id and name of release - *dati_completi*: complete homing route for
 the pigeon is available (1) or not (0) - *dist_from_home*: distance
 between location position and home loft in (m) - *dist_from_RS*: distance
 between location position and release site (m) #### **split_flock4.rds
 and** split_flock4_NF.rds * *ts*: datetime of the location * *n*: numeric
 unique identified of ts * *gruppo*: unique identifier of each flock *
 *lancio*: name of release site. The number associated, indicates the
 number of releases the pigeon homed from that release site, i.e., level of
 experience from the release site. * *personalita*: type of personality
 associated to each individual basing on the results obtained in the three
 personality tests (Non reattivi = Less reactive; Reattivi = More Reactive)
 * *animal*: animal id * *longitude*: longitude of the location * latitude:
 *latitude* of the location * *flock_composition*: represents how is
 arranged the flock in that timestamp: compact flock (4 pigeons flying
 together = “uniti”); 3 pigeons flying as a compact flock and one separated
 from the group that flyes alone ("3+1"); two couples of pigeons
 homing separately ("2+2"); a couple of pigeons and two pigeons
 homing as singletons ("2+1+1"); all four pigeons separated and
 homing alone ("1+1+1+1") * id.separato: when flock_composition
 is "3+1" or "2+1+1", in this column is reported the
 pigeon that flies alone, separated from the group. Therefore, the cells
 can assume NA values when the flock assumes a different composition. *
 *id.separato2*: when flock_composition is "2+1+1", in this
 column is reported the second pigeon that flies alone separated from the
 group. Therefore, the cells can assume NA values when the flock assumes a
 different composition * *nfix*: unique identifier of each location
 collected. * change_group_status: unique identifier of stable flock
 compositions * Rts: timestamp of release * *dist_from_home*: distance
 between location position and home loft in (m) * *dist_from_RS*: distance
 between location position and release site (m) * *secpassed_from_R*: time
 passed from release (sec) ## **Code/Software** R is required to run the
 scripts which were created using version 4.4.1. Annotations are provided
 throughout the script through 1) library loading, 2) dataset loading , 3)
 analyses, and 4) figure creation. R scripts may recall specific functions
 or tables, which are also provided. The custom functions provided were
 used to estimate the cohesion index
 (cumulative_interindividual_distances_5.txt) and evaluate first split
 event (cum_interind_coord.R, first_split_4flock.R, flock_comp_time.R).