# Flight initiation distance differs among eumelanin-based color morphs in feral pigeons

A. Frantz, M. Baneux, L. Pichon, S. Renier, J. Vilanova

► To cite this version:

A. Frantz, M. Baneux, L. Pichon, S. Renier, J. Vilanova. Flight initiation distance differs among eumelanin-based color morphs in feral pigeons. Journal of Zoology, 2025, 325 (2), pp.115-123. 10.1111/jzo.13235 . hal-04958549

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ORIGINAL RESEARCH

# Flight initiation distance differs among eumelanin-based color morphs in feral pigeons

A. Frantz<fnref n="1" /> ID, M. Baneux<fnref n="1" />,*, L. Pichon<fnref n="1" />,*, S. Renier<fnref n="1" />,† & J. Vilanova<fnref n="1" />,<fnref n="2" />,† ID

**Keywords**

urbanization; birds; FID; habituation; melanin; color morphs; *Columba livia*.

**Correspondence**

Adrien Frantz, Institut d'Écologie et des Sciences de l'Environnement de Paris, iEES Paris, Sorbonne Université, 4 place Jussieu, case courrier 237, Paris Cedex 05 F-75005, France.
Email: adrien.frantz@sorbonne-universite.fr

*These authors contributed equally.

Editor: Hazel Nichols
Associate Editor: Desire Dalton

Received 18 July 2024; revised 23 September 2024; accepted 11 October 2024

doi:10.1111/jzo.13235

**Abstract**

Organisms facing anthropogenic activities usually exhibit phenotypic responses assumed to enhance coping with disturbance. These responses include a decreasing degree of reaction toward potentially risky situations (“behavioral tolerance”) with increasing disturbance. Though melanin is associated with many phenotypic traits, including pigmentation and behavior, the potential relationship between behavioral tolerance and melanin has never been explored. Such relationship may potentially result from either direct association between melanin and behavior (e.g., genetic correlation) or indirectly through a coloration-dependent behavior-modulating factor (e.g., differential predation or human preferences in cities toward color morphs). Feral pigeons (*Columba livia*) represent an ideal biological system to test for these hypotheses, due to their presence in cities worldwide, their considerable variation in eumelanin-based coloration, ranging from white to black plumage, and their close proximity to humans. We measured Flight Initiation Distance (FID, classically used for behavioral tolerance assessment) of feral pigeons of 4 different eumelanin-based color morphs in sites differing in their urbanization rate and pedestrian traffic within the restricted scale of a city center (Paris). Urbanization rate and pedestrian traffic had no effect on FID, maybe because of the small spatial scale considered. FID varied with eumelanin-based coloration: white pigeons had lower FID (104.6 cm; i.e., higher behavioral tolerance) than darker morphs (232.3 cm for Blue bar, 184.4 cm for T-pattern & Checker, and 181.8 cm for Spread color morphs). Though the exact underlying causes remain to be identified, we propose different possible mechanisms for this relationship that remain to be investigated in future work.

**Introduction**

Anthropogenic activities and human disturbances increasingly affect ecosystems worldwide (Smith et al., 2024). Growing urbanization worldwide acts as environmental filters favoring certain phenotypic traits in individuals, populations, and communities (Alberti et al., 2017; Cheptou et al., 2008; Johnson & Munshi-South, 2017; Lambert et al., 2021; Kern & Langerhans, 2019; Szulkin et al., 2020), including body coloration (Chatelain et al., 2016a; Leveau, 2024; Leveau & Kopp, 2024; Turak et al., 2022). Phenotypic responses to perceived risk of human activities, including increased behavioral tolerance toward disturbance (i.e., the degree of reaction toward a potentially risky situation; Çapkun-Huot et al., 2024), are increasingly documented in animals (Pollack et al., 2022; Smith et al., 2021, 2024).

A classic proxy to assess perception of risk, including in human-dominated habitats, is Flight Initiation Distance (FID),

corresponding to the distance at which an organism flees from a perceived approaching predator (Szulkin et al., 2020). FID is assumed to be adaptive, resulting from the cost-benefits balance associated with escape (Blumstein, 2003; Bonenfant & Kramer, 1996; Ydenberg & Dill, 1986). Decreasing FID (i.e., increasing behavioral tolerance of animals allowing closer approach) with increasing disturbance has been evidenced in various taxa facing diverse types of disturbance, including urbanization and anthropogenic presence (several bird species, Carrete & Tella, 2011; Díaz et al., 2013; Møller, 2008; Møller & Tryjanowski, 2014; Anolis sagrei, Lapiedra et al., 2017; Morelli et al., 2018; fox squirrels *Sciurus niger* McCleery, 2009; gray squirrels *Sciurus carolinensis* Engelhardt & Weladji, 2011; yellow-bellied marmots *Marmota flaviventris* Li et al., 2011; blue-tailed skinks *Emoia impar* McGowan et al., 2014; mule deer *Odocoileus hemionus* Price et al., 2014; Samia et al., 2015; Feral pigeons *Columba livia*, Carlen et al., 2021; Nubian ibex *Capra nubiana* Zukerman & Berger-

<footnote n="1">¹CNRS, INRA, IRD, Institute of Ecology and Environmental Sciences, Sorbonne Université, Université Paris-Est Créteil, Paris, France</footnote>

<footnote n="2">²Department of Biology, Concordia University, Montreal, QC, Canada</footnote>
Tal, 2024). This pattern has been widely assumed to result from plastic behavioral habituation (i.e., a progressive reduction in response to neither aversive nor beneficial stimuli; Bejder et al., 2009), but other hypotheses have recently challenged this view (Sol et al., 2013). Indeed, decreasing FID with increasing disturbance may alternatively result from natural selection on genetically based behaviors (Winchell et al., 2020), where different levels of tolerance would be favored depending on the balance between their respective costs and benefits (Blumstein, 2003; Bonenfant & Kraemer, 1996; Ydenberg & Dill, 1986) as a function of disturbance-induced lethality (Cooper & Frederick, 2007, 2010). This hypothesis has gained support from heritable variation in FID suggested in 20 European bird species (Mikula, 2014) and from genetically based anti-predator behavior (in the spider *Agelenopsis aperta*; Riechert & Hedrick, 1990). Most recently, the hypothesis that decreased FID with increasing disturbance (or any other phenotype-environment correlation; Edelaar et al., 2019) may result from differential settling of individuals in habitats matching their tolerance to disturbance has been proposed (Carrete & Tella, 2010) and supported in burrowing owl *Athene cunicularia* (Carrete & Tella, 2010) and in dunnock *Prunella modularis* (Holtmann et al., 2017).

Behavioral tolerance in general and FID in particular may be further directly or indirectly modulated by individual phenotypic characteristics. Direct influence of individual phenotype on FID (hereafter “direct association” hypothesis) may result from genetic effect of pleiotropic genes on behavior. Indirect effects (hereafter “indirect association” hypothesis) may be generated by any external factor differentially affecting the behavior of individuals depending on their phenotype. In particular, since optimal FID is theoretically expected to further depend on predator-induced lethality (Cooper & Frederick, 2007, 2010), or more generally on the fitness costs associated with disturbance, differential regularity of interactions with predators between individual phenotypes may differently influence their optimal FID. Previous studies have found that tolerance covaries with several traits such as sex (e.g., Kalb et al., 2019; Petelle et al., 2013), morphology (e.g., tail length Møller, 2014; body length Bell et al., 2019), pterin- and carotenoid-based color morph (e.g., Brock & Madden, 2022), and other life history traits (e.g., Møller, 2014). It is, however, not clear whether such phenotype-behavior covariances result from direct or indirect associations.

Among phenotypic traits potentially affecting directly or indirectly FID, melanin is of particular interest. It is the most common pigment in animals, exhibits heritable variation, and is associated with a large number of phenotypic traits (through pleiotropic effects of melanogenic genes), including organ and tegument pigmentation and behavior (Ducrest et al., 2008; Roulin, 2004). In species with interindividual variation in melanin-based coloration, more melanic individuals are generally bolder than their paler conspecifics (e.g., Mafli et al., 2011); therefore, more melanic individuals could directly exhibit a lower FID than paler individuals within the same environmental range of disturbance intensity (“direct association” hypothesis). Alternatively, behavioral tolerance could be

indirectly associated with melanin-based coloration through the influence of external phenotype-dependent factors (“indirect association” hypothesis), including interspecific interactions. In particular, melanin-based coloration can be involved in camouflage (Leveau, 2019, 2021) and influence the regularity of encounters with predators, consequently impacting the opportunities for increased behavioral tolerance (i.e., decreased FID) in more camouflaged relative to less camouflaged phenotypes (Cooper & Frederick, 2007, 2010).

In addition to predators, animals in the cities experience diverse interactions with humans, which may cause either zero or very low fitness costs (e.g., chasing by humans) or even fitness benefits (e.g., feeding by humans). FID is thus expected to decrease with increasing regularity of interactions with humans, as predicted when lethality is low (Cooper & Frederick, 2010). Moreover, animal melanin-color morph is culturally non-neutral; any differential human perception of, and behavior toward, differentially colored animals (Prokop & Fančovičová, 2013; Williams et al., 2024) would exacerbate the opportunities for habituation and modulate their behavioral tolerance toward humans. Generalizing the predictions of Cooper and Frederick (2010), FID may thus decrease among phenotypes gaining fitness advantages (e.g., preferentially fed phenotypes) or experiencing more opportunities for habituation to non-lethal stimuli (e.g., more chased phenotypes). However, to our knowledge, the relationship between FID and melanin-based coloration has never been explored.

Here, we investigated FID in relation to pedestrian traffic and urbanization rate among feral pigeons of different eumelanin-based color morphs in a restricted spatial scale (city of Paris). Feral pigeons (*Columba livia*) represent an ideal biological system to explore these hypotheses: they live in urban habitats worldwide in high proximity to humans and exhibit a considerable variation in melanin-based coloration, ranging from total white to fully black (eumelanin) or red (pheomelanin) plumage (Johnston & Janiga, 1995), associated with a series of phenotypic traits (Aouissi et al., 2021; Chatelain et al., 2016a, 2016b; Corbel et al., 2016; Jacquin et al., 2011, 2012; Jacquin, Haussy, et al., 2013; Jacquin, Récapet, et al., 2013). They adjust their behavior to different stimuli (Stephan & Bugnyar, 2013) and to past experience (Belguermi et al., 2011; Stephan et al., 2012). Their behavioral tolerance has been shown to increase with pedestrian traffic and urbanization (Carlen et al., 2021). Moreover, melanin-based colors in Feral pigeons are culturally not neutral to humans: black individuals are usually considered dirty while white individuals bear symbols of peace, potentially further shaping FID in relation to color morph.

The aim of this study was to investigate whether FID differs between different eumelanin-based color morphs and according to pedestrian traffic or urbanization at this fine spatial scale. More specifically, we expected FID to decrease with increasing urbanization and pedestrian traffic and to either increase (as predicted by the “direct association” hypothesis) or to decrease (as predicted under the hypothesis of human preferences toward white pigeons) with increasing eumelanin-based coloration. FID was not associated to either urbanization rate or pedestrian traffic, but we did find different FID according to color morphs,
with white pigeons exhibiting a lower FID than other color
morphs. Though the exact causes remain unknown, we propose
several underlying mechanisms that may generate the pattern
observed, which however requires further investigation.

**Materials and methods**

Species and study sites

The Feral pigeon *Columba livia* is a worldwide resident bird
species present in cities year-round. It exhibits a considerable
variation in melanin-based coloration resulting from genetic
differences at two loci (Johnston & Janiga, 1995), which can
be reliably classified into several color morphs (Jacquin
et al., 2011). Here, we visually classified individuals into 4 dif-
ferent melanin-based color morphs (Fig. 1), following previous
categorization (Jacquin et al., 2011; Johnston & Janiga, 1995;
Récapet et al., 2013): “White” morph (completely white plum-
age), “Blue bar” (gray mantle, two black bars across the

wings), “Checker and T-pattern” morph (from gray mantle with
black spots to black mantle with gray spots), and Spread
(completely black plumage). Checker and T-pattern are some-
times distinguished (Récapet et al., 2013), though the variation
appears a bit continuous; according to the hypotheses tested in
our work, such distinction did not appear relevant. Addition-
ally, we attributed a quantitative color score to each color
morph, following Jacquin et al. (2011): 0 (“White”), 1 (“Blue
Bar”), 3 (“Checker & T-pattern”), and 4 (“Spread”).

Flight initiation distance

We measured FID of feral pigeons in several sites within the
center of Paris intramuros (Fig. S1) following Blumstein (2003).
Because FID can vary between breeding and non-breeding sea-
sons (Novčić & Parača, 2022), we measured all FIDs within a
short period of time (from January 18 to February 1, 2021) of
the non-breeding season. These sites were chosen to cover a
range of environmental conditions in the city, distant enough
to avoid exaggerated autocorrelations while remaining in the
city center at a restricted geographical scale (maximum dis-
tance between sites was 8 km). When a pigeon flock was visu-
ally encountered, one of us walked toward an individual
pigeon at constant pedestrian speed (approximately 1.5 m.s⁻¹,
from a distance of approximately 15 m) and stopped when the
pigeon started to escape, whether by walking, running, or tak-
ing off. Then, using a tape measure, we measured the distance
to the nearest centimeter between the position of the experi-
menter and the last position of the pigeon before escape. To
standardize our data and avoid time of the day as a confound-
ing factor (Ferguson et al., 2019), we limited measurements to
9 AM to 12 AM in all sites.

Geographical coordinates, urbanization rate,
and pedestrian traffic

We determined geographical coordinates of each individual
FID measurement on https://www.gps-coordinates.net/. To
determine urbanization rate, we downloaded landcover data
from https://www.institutparisregion.fr/mode-doccupation-du-
sol-mos/, and extracted landcover around each site for 900 m
buffer using QGIS (QGIS Development Team, version 3.36
Maidenhead; QGIS.org, 2024). We chose this radius because it
likely corresponds to the typical range of daily displacement of
feral pigeons in cities (Rose et al., 2006; Frantz et al., 2012).

Within this buffer, we then calculated the urbanization rate
as the proportion of its surface occupied by urban features
(individual and collective housing, activities, transports,
quarries, landfills, and building sites) as opposed to non-urban
features (forests, semi-natural and agricultural habitats, water,
and open artificialized areas).

We also extracted street pedestrian traffic information
(from https://opendata.apur.org/datasets/Apur:troncon-voie-paris/
about). Within a 900 m buffer, we calculated the proportion of
each pedestrian traffic intensity, hereafter called “relative
pedestrian traffic,” as the ratio [street length with a given
pedestrian traffic intensity within the buffer]/[total street lengths
within the buffer].

<figure><img src="image_2.png" /><figcaption>**Figure 1** Estimated marginal means of flight initiation distance (± SE) for the best model fitted according to eumelanin-based color morph. Open circles represent raw data (slightly horizontally displaced to avoid overplotting), and black circles represent mean (± SE). Mean FID with different letters (a or b) are statistically different at α = 0.05. (Pigeon drawings by Adrien FRANTZ).</figcaption></figure>
## Statistical analyses

First, we explored potential associations between environmental variables (urbanization rate and relative pedestrian traffic) that may lead to collinearity issues in the models, using Pearson's correlation coefficients *r*. Relative pedestrian traffic of low intensity appeared highly correlated to relative pedestrian traffic of high intensity (*r* = -0.83) and moderately to relative pedestrian traffic of medium intensity (*r* = -0.60), while no correlation was found between relative pedestrian traffic of medium and of high intensities (*r* = 0.06). No correlation was observed between urbanization rate and any relative pedestrian traffic (low: *r* = -0.14; medium: *r* = -0.00; high: *r* = 0.18), nor between eumelanin-based color morph (transformed as quantitative melanin score) and any relative pedestrian traffic (low: *r* = -0.09; medium: *r* = -0.01; high: *r* = 0.11) nor urbanization rate (*r* = -0.08).

Given these correlations and the questions raised in our work, we then tested for relationships between FID and environmental variables with linear mixed-effects models with FID as a dependent variable, color morph, urbanization rate, and relative pedestrian traffic of high intensity as fixed effects, and geographical coordinates as random effects. To investigate whether taking into account the heterogeneity in FID variance improved model fit, we fitted several models with different structures of the residual variance of FID (Pinheiro & Bates, 2000; Zuur et al., 2009): Var ($ε_i$) = $σ^2$ with homogeneity of variance assumption (i.e., homoscedasticity); Var ($ε_{ij}$) = $σ_j^2 δ_{morphij}^2$ in "Different variances per morph" structure (varIdent in R), where $δ$ is a vector of variance parameters, allowing different FID variances between morphs *j*; and var ($ε_i$) = $σ^2$ × $e^{2δ_{morphij} urbanizationij}$ in "Exponential of covariate" variance structure (varExp in R) with different variations of FID variance along urbanization between morphs (Pinheiro & Bates, 2000; Zuur et al., 2009 for more details). We compared their AIC and selected the model(s) with the lowest AIC, from which we estimated marginal means with multivariate *t*-distribution adjustment for pairwise comparisons between color morphs.

Finally, we investigated potential spatial correlation in the final model(s) by plotting the standardized residuals in both a "bubbleplot" versus their spatial coordinates (longitude and latitude) and in a semi-variogram that assumes isotropy (see Zuur et al., 2009).

Statistical analyses were performed using R (ver. 4.1) and RStudio (ver. 1.4.1717), with packages car (which function Anova allows extracting $χ^2$ associated with global effects), dplyr (Wickham et al., 2023), ggplot (Wickham, 2016), ggeffects (for predicted values in the figures; Lüdecke, 2018), ggsignif (Ahlmann-Eltze & Patil, 2021), nlme (Pinheiro et al., 2024) and emmeans (Lenth, 2024).

## Results

We measured the FID of 82 individuals: 7 individuals of "White" morph (8.5%), 26 of "Blue bar" morph (31.7%), 35 of "T-pattern & Checker" morph (42.7%), and 14 of "Spread" morph (17.1%).

The model with variance structure varExp(form = ~Urbanization|Morph) had a lower AIC (AIC = 986.1) than models assuming either homoscedasticity (AIC = 993.4) or varIdent(form = ~1|Morph) (AIC = 987.7). No spatial correlation appeared in either "bubbleplot" or the semi-variogram (Fig. S2). This model indicated a significant relationship between FID and color morph ($χ^2_3$ = 14.21, *P* = 0.003) and no significant relationship between FID and urbanization rate ($χ^2_1$ = 1.23, *P* = 0.27) or pedestrian traffic ($χ^2_1$ = 0.01, *P* = 0.91). Pairwise comparisons showed that "White" pigeons had significantly lower FID (mean ± *se* = 104.6 cm ± 17.3) than "Blue bar" (232.3 cm ± 34.4; *t* ratio = -3.04, *P* = 0.021), "Checker & T-pattern" pigeons (184.4 cm ± 21.4; *t* ratio = -2.83, *P* = 0.035), and "Spread" pigeons (181.8 cm ± 31.6; *t* ratio = -2.90 *P* = 0.029); all other differences were insignificant ("Blue bar" vs. "Checker & T-pattern": *t* ratio = 0.62, *P* = 0.92; "Blue bar" vs. "Spread": *t* ratio = 0.37, *P* = 0.98; "Checker & T-pattern" vs. "Spread": *t* ratio = -0.16, *P* = 0.99; Fig. 1).

## Discussion

In agreement with our hypothesis, we did find different FID between pigeons of different color morphs: "White" pigeons had lower FID (i.e., higher behavioral tolerance) than other morphs ("Blue bar," "Checker & T-pattern," and "Spread"). Different FID between phenotypically different individuals may have different underlying mechanisms, linking either directly or indirectly behavior to phenotypes. Direct association could result from the pleiotropic effects of the genes on which eumelanin-based coloration relies, linking coloration to a series of other phenotypic characteristics, including behavior (Ducrest et al., 2008), which may be involved in different reactions to a given stimulus and explain the relationships observed. However, two results were unexpected under this simple hypothesized mechanism of direct association.

First, the pattern observed did not support a monotonous relationship between FID and eumelanin-based coloration, as it opposed "White" to other morphs. Assuming that genes governing melanin intensity are indeed the driver of boldness, this suggests that the main difference in melanin content (or any genetically associated factor) opposes "White" to non-white pigeons (suggesting a kind of threshold response to melanin).

Second, the lower FID of "White" pigeons contradicts the prediction that boldness would increase (i.e., FID would decrease) with the amount of melanin in the feathers, as expected from the "direct association" hypothesis that we formulated from the general observation that more melanic individuals are bolder than paler conspecifics (e.g., Mafli et al., 2011). Alternatively, the association between FID and melanin-based coloration may be indirectly driven by external factors ("indirect association" hypothesis), such as differential behaviors of ecological interactors, including predators or humans. For instance, eumelanin-based coloration may be involved in predator-prey interactions through camouflage. Interestingly, camouflage has been proposed as a main factor responsible for the predominance of gray species in Argentinian cities (Leveau, 2019), and species with camouflage exhibit lower FID than species without (Møller et al., 2019), while
pterin- and carotenoid-based color morphs (Andrade et al., 2019) of the wall lizard *Podarcis erhardii* differ in escape behavior, potentially due to predation (Brock & Maden, 2022). However, predators in Paris are scarce (mainly comprising Peregrine falcon *Falco peregrinus*, European herding gull *Larus argentatus*, and Carrion crow *Corvus corone*; Le Maréchal et al., 2013) and likely do not represent the main environmental driver of FID (e.g., Parisian feral pigeons rarely bear the white rump shown by Palleroni et al., 2005 to be adaptive against predation by Peregrine falcons *Falco peregrinus*). Moreover, “White” pigeons are most likely not better camouflaged on urban surfaces than other morphs. Camouflage is thus not likely the main driver for the pattern observed here in Parisian feral pigeons.

Other potential indirect causes for different FID between melanin-based color morphs may include human behaviors in the cities. Indeed, FID is assumed to be shaped by habituation to non-risky (i.e., without fitness costs) situations, as pedestrian proximity probably is, and is often used as a proxy to estimate perception of risk in human-dominated habitats (Szulkin et al., 2020). Therefore, any differential human behavior toward pigeons depending on their color may cause different habituation opportunities to neither costly nor beneficial stimuli (Bejder et al., 2009), such as chasing by children, distancing or warding off, or may cause direct learning and reduced fear from beneficial stimuli such as feeding by people. Animal color influences human emotions and willingness to protect (Prokop & Fančovičová, 2013), and the interactions people have with conspicuously colored wildlife (i.e., individuals that vary from their species-typical coloration), including melanin-based coloration, are influenced by a combination of scarcity, symbolism, lore, and individualism (Williams et al., 2024). Thus, animals may experience human behaviors nonrandomly according to their body color, due to biological causes (propensity to disproportionally focus on rare phenotypes, akin to anti-apostolic selection; Allen & Weale, 2005) and/or such cultural aspects. This may be even more pronounced in feral pigeons, where black individuals are usually considered dirty, while white individuals bear symbols of peace and are even given a separate name in some languages (the ambiguous French word “colombe” designates white birds from the Columbidae family and is symbolically distinct from “pigeon”), which is not neutral to human–wildlife relationships (Borkfelt, 2011). However, we did not find any study investigating differential human behavior toward pigeons according to their plumage coloration, which would modulate the regularity of stimuli favoring habituation and FID and may account for the pattern observed. Further work is thus needed to test these hypotheses linking human to synanthropic animal behaviors in the city.

We did not find any significant effect of either urbanization rate or pedestrian traffic. This was surprising, as FID adjustments to environmental conditions have been repeatedly documented in various taxa and diverse contexts: birds have been shown to adjust their alert and flight initiation distances with many environmental conditions, such as car speed limit (Legagneux & Ducatez, 2013), approach velocities of anthropogenic sounds (Lukas et al., 2022), urbanization (population

size, pedestrian traffic, abiotic environmental factors; Carlen et al., 2021), time since urbanization (Symonds et al., 2016), the proximity of predators (however in opposite directions depending on the predator; Carlen et al., 2021) including cat colonies (Díaz et al., 2022), distance to the nearest available refuge (Morelli et al., 2022), approach speed (Hammer et al., 2022), human behavior during bird escape (Tätte et al., 2020), season (breeding vs. non-breeding; Novčić & Parača, 2022) and weather (Hammer et al., 2022). In feral pigeons, Carlen et al. (2021) found that FID significantly decreased with increasing human population size, pedestrian traffic, and the proportion of urban features. The absence of effect of urbanization on FID in our work could be due to the range (from 0.69 to 0.95) or to the mean of urbanization rates (0.79 ± 0.01) and/or pedestrian traffic, or to the restricted spatial scale we considered: we measured FID of pigeons located in the urban center of a single city (Paris) and distant from less than 8 km within a surface of approximately 17 km², far smaller than the surface investigated previously (783 km² in Carlen et al., 2021). Though previous work suggested limited movements at this scale (Frantz et al., 2012; Rose et al., 2006), it is likely that pigeons are mobile enough not to adjust their FID at this spatial scale or within these ranges of environmental conditions.

Our work has some limitations that future studies should address. First, it was based on a small sample size (especially for “White” pigeons, due to their low proportion in Paris). Second, pigeons often live in groups and may use social cues to flee, such as flock size (“contagious fear”; García-Arroyo & MacGregor-Fors, 2020; Gupta & Saxena, 2024; Morelli et al., 2019) and/or flock composition. Though these factors were likely not confounded with color morph in our work (we never observed any relationship between melanin-based color morph and either flock size in these populations, we measured FID of a given color morph in different sites, and the output of the models did not indicate any substantial spatial correlation), they should further be included in future work.

Altogether, our work on a widely distributed synanthropic bird species provides, to the best of our knowledge, the first evidence for different behavioral tolerance between eumelanin-based color morphs. Although the exact causes underlying the pattern evidenced and the potential adaptive significance (i.e., fitness consequences) of such behaviors remain to be further explored, the ubiquitous melanin-based variation in wildlife (McNamara et al., 2021) makes such intraspecific associations between behavioral tolerance and melanin-based coloration likely to be common. Covariation between coloration and behavioral responses would have important implications for the growing interactions between humans and wildlife in an increasingly urbanizing world.

## Acknowledgements

We thank Magali CHIRAL for constructive comments and discussions on the results, and three anonymous reviewers for their useful comments. We thank the “équipe data” from the “Atelier parisien d’urbanisme APUR” (https://www.apur.org/en) for gently providing useful information on the availability of
environmental data in Paris. This work was supported by Sor-
bonne Université and the Ministère de l'Enseignement
supérieur, de la Recherche et de l'Innovation, MESRI.

Author contributions

All authors equally conceived the ideas and designed methodology; MB, LP, SR, and JV collected field data, under the supervision of AF; AF analyzed the data, led the writing of the manuscript, and drew the pigeons in the figures. All authors contributed critically to the drafts and gave final approval for publication.

Conflict of interests

We declare we have no conflict of interests.

Data availability statement

Supporting data can be accessed here: 10.5281/zenodo.13747910

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## Supporting Information

Additional Supporting Information may be found in the online version of this article:

**Figure S1.** Maps showing the location of France in the world, the location of Paris in France and the sites in Paris where Flight Initiation Distance (FID) of feral pigeons were measured, colored according to their values (in centimeters).

**Figure S2.** (a) “Bubbleplot”: standardized residuals obtained by the model plotted versus their spatial coordinates (black dots are negative residuals, and grey dots are positive residuals). (b) Semi-variogram of the standardized residuals obtained by the model. Both correspond to model with urbanization rate, relative pedestrian traffic of high intensity and color morph as fixed effects, with varExp(form=~Urbanization|Morph) structure of variance.