J Anim Ecol. 2025;94:1461–1473.
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1461wileyonlinelib a y.com/jou nal/jane
Recei ed: 24 Ma ch 2024
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Accep ed: 15 May 2025
DOI: 10.1111/1365-2656.70077
RESEARCH ARTICLE
Global pa e ns o colou a ion complexi y in he Pa idae:
E ec s o clima e and species cha ac e is ics ac oss
body egions
Da id López- Idiáquez1,2,3 | Clai e Dou elan 2 | Pe e B. Pea man1,4,5
This is an open access a icle unde he e ms o he C ea i e Commons A ibu ion-NonComme cial License, which pe mi s use, dis ibu ion and ep oduc ion
in any medium, p o ided he o iginal wo k is p ope ly ci ed and is no used o comme cial pu poses.
© 2025 The Au ho (s). Jou nal o Animal Ecology published by John Wiley & Sons L d on behal o B i ish Ecological Socie y.
1Depa men o Plan Biology and Ecology,
Facul y o Sciences and Technology,
Uni e si y o he Basque Coun y (UPV/
EHU), Leioa, Bizkaia, Spain
2CEFE, Uni e si é de Mon pellie , CNRS,
EPHE, IRD, Mon pellie , F ance
3Depa men o Biology, Edwa d
G ey Ins i u e, Uni e si y o Ox o d,
Ox o d, UK
4IKERBASQUE Basque Founda ion o
Science, Bilbao, Spain
5BC3 Basque Cen e o Clima e Change,
Scien i ic Campus o he Uni e si y o he
Basque Coun y, Leioa, Bizkaia, Spain
Co espondence
Da id López- Idiáquez
Email: da id.lopez- idiaquez@biology.
ox.ac.uk; da [email protected]
Funding in o ma ion
Eu opean Commission, G an /Awa d
Numbe : GB- TAF- TA3- 027 20; Basque
Coun y Go e nmen , G an /Awa d
N u m b e : P O S - 2 0 1 9 - 1 - 0 0 2 6
Handling Edi o : Bea iz Willink
Abs ac
1. A ian plumage colou a ion is an iconic example o ai a iabili y among species.
Sexual, social and na u al selec ion, and he en i onmen al a iables modula ing
hem a e he main d i e s o his a iabili y.
2. So a , mos esea ch explo ing en i onmen al e ec s on he a iabili y o plumage
colou a ion has ocused on he a ia ion in o e all plumage da kness. Resea ch
on o he aspec s o colou a ia ion, such as he di e si y o colou s exhibi ed by
a species (i.e. colou complexi y), is limi ed and has p oduced inconsis en esul s.
Fu he mo e, colou complexi y has mos ly been analysed a he whole- plumage
le el, despi e he possibili y ha he colou complexi y o di e en plumage
pa ches may be sensi i e o di e en en i onmen al ac o s.
3. He e, we quan i y male and emale colou a ion in 58 species o he amily
Pa idae, and use mul i- p edic o Bayesian phylogene ic mixed models o es ima e
he ela ionship o colou a ion wi h bio ic and clima ic a iables ha quan i y
en i onmen , and wi h se e al species- speci ic cha ac e is ics. We conside bo h
he colou a ion o he whole plumage and he colou a ion o ou sepa a e colou
pa ches (head, ches , back and wing).
4. We ind ha Pa idae species in clima es wi h in e media e empe a u es
p esen mo e complex colou a ion han do species in wa me /colde clima es.
In addi ion, males, ela i ely small species, and species wi h ela i ely g ea e
sexual dich oma ism ha e mo e complex plumage colou a ion. We ind ha he
numbe s o p eda o s and sympa ic conspeci ics a e mo e associa ed wi h emale
colou a ion han wi h male colou a ion. Finally, he s eng h o he associa ions
wi h colou complexi y is speci ic o each plumage egion: species ecogni ion,
beak size and clima e a iables ela ed o compe i ion o ep oduc i e esou ces
(i.e. p ecipi a ion seasonali y) a e mo e s ongly associa ed wi h colou a ion
complexi y o he head and b eas han wi h ha o he back and wing.
5. O e all, ou esul s illus a e he impo ance o clima ic and social a iables, he
link be ween colou complexi y and dich oma ism in bo h sexes, and he analysis
1462
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LÓPEZ-IDIÁQUEZ e al.
1 | INTRODUCTION
Unde s anding he ac o s ha p omo e in e speci ic pheno ypic
di e si ica ion is a majo aim o ecology and e olu ion. A ian plum-
age colou a ion is an iconic example o ai a iabili y, wi h some
species being dull and homogeneous and o he s colou ul, a ied
and complex (Cooney e al., 2022; Dale e al., 2015). Plumage co-
lou a ion exhibi s di e se unc ions, including signalling (Te ill &
Shul z, 2022), camou lage (Koskenpa o e al., 2020) and he mo-
egula ion (Rogalla e al., 2022), which a e a iously in luenced
by na u al, sexual and social selec ion (Delhey, Valcu, Muck,
e al., 2023b; Gomez & Thé y, 2007). The speci ic unc ions and
associa ed e olu iona y p ocesses a y among plumage pa ches
(Te ill & Shul z, 2022). Fo ins ance, head and ches colou s a e
usually in ol ed in communica ion and a e p obably mo e s ongly
in luenced by sexual selec ion han is back colou a ion, which is
o en in ol ed in camou lage and likely e ol es unde na u al se-
lec ion (Gomez & Thé y, 2007; Te ill & Shul z, 2022). Howe e ,
ou knowledge o he associa ions be ween he colou a ion o
di e en plumage a eas and en i onmen al condi ions is limi ed.
Thus, unde s anding he p ocesses ha p omo e species di e -
ences in colou a ion equi es examina ion o how en i onmen al
ac o s and species ai s a e associa ed wi h cha ac e is ics o
bo h he en i e plumage and dis inc plumage a eas.
Resea ch explo ing en i onmen al e ec s on he a iabili y o
plumage colou a ion has mos ly ocused on he associa ion be ween
di e en abio ic and bio ic en i onmen al a iables and he exp es-
sion o a ce ain colou componen , like b igh ness o hue (Delhey,
Valcu, Muck, e al., 2023b; Shul z & Bu ns, 2013). Fo ins ance, many
s udies ha e analysed he alidi y o Gloge 's ule, usually ind-
ing ha he plumage o a ian species in we e and wa me a eas
ends o be da ke han ha o species in d ie and colde a eas
(Delhey, 2019; Passa o o e al., 2022). Some esea ch has also been
conduc ed on he e olu ion o ca o enoid- based colou s, showing
ha hey a e mo e likely o e ol e in a eas wi h highe p ima y p o-
duc i i y (Delhey, Valcu, Dale, e al., 2023a). Howe e , he ole o
en i onmen al ac o s in shaping a ia ion in he di e si y o colou s
exhibi ed by a species, ha is i s colou complexi y, has ecei ed less
a en ion.
Va ia ion in empe a u e, p ecipi a ion and hei seasonali y
a e likely associa ed wi h colou complexi y h ough hei e -
ec s on esou ce a ailabili y and compe i ion o ep oduc i e
esou ces. Fo ins ance, esou ce a ailabili y in seasonal en i-
onmen s usually occu s in pulses, limi ing he du a ion o he
b eeding season and enhancing compe i ion o ma es and e i-
o ies (Bo e o & Rubens ein, 2012; Macías- O dóñez e al., 2013).
These condi ions imply ha sexual selec ion should be s onge
in seasonal han in aseasonal en i onmen s (Ba be e al., 2024)
and, hus, species inhabi ing seasonal en i onmen s should exhibi
mo e complex colou a ion (Macedo e al., 2022). In addi ion o he
e ec s o clima e on esou ce a ailabili y and a iabili y, clima e
can also impose di ec cons ain s on colou a ion h ough he
physiological demands o he mo egula ion and he ad an ages o
camou lage (Delhey e al., 2019; Gal án e al., 2018). Colou a ion
complexi y, o example, could be limi ed in cold and a id clima es,
whe e camou lage agains snowy and/o b own/monoch oma ic
su oundings and a oidance o o e hea ing a ou ligh o homo-
geneous colou a ion, leading o a non- linea ela ionship be ween
colou complexi y and empe a u e (Delhey e al., 2019; Gal án
e al., 2018).
S udies es ing he associa ion be ween clima e and colou
complexi y ha e, howe e , p esen ed mixed esul s when examin-
ing whole- plumage colou a ion. Tempe a u e, o ins ance, is pos-
i i ely associa ed wi h colou complexi y in acan hizid ho nbills
(F iedman & Remeš, 2017), in all passe ines (Cooney e al., 2022),
and in emale, bu no male, an bi ds (Macedo e al., 2022).
P ecipi a ion is posi i ely linked o whole- plumage colou com-
plexi y in male, bu no emale, an bi ds (Macedo e al., 2022), in
ho nbills (F iedman & Remeš, 2017) and in all passe ines (Cooney
e al., 2022). Finally, clima e seasonali y is posi i ely associa ed
wi h mo e complex, whole- plumage colou a ion in ho nbills
and emale an bi ds, bu no in male an bi ds o in honeyea e s
(F iedman & Remeš, 2017; Macedo e al., 2022). The lack o con-
sis en esul s in he ew a ailable s udies highligh s he po en ial
o a ia ion in he links be ween clima e and plumage colou a-
ion complexi y. Fu he cla i ica ion o he ela ionship be ween
clima e and colou complexi y could bene i om mo e nuanced
quan i ica ion o clima e a ia ion, an allowance o non- linea as-
socia ions be ween clima e a iables and colou complexi y, and
examina ion o he associa ion be ween clima ic a iables and co-
lou complexi y in dis inc plumage a eas.
In addi ion o clima e, he di e si y o habi a s used by a
species is likely in ol ed in he e olu ion o colou complexi y.
Selec ion can ac o maximise camou lage in a pa icula habi a
o ac o inc ease he conspicuousness o ce ain colou pa ches
gi en needs o communica ion and he habi a con ex (Gomez &
Thé y, 2007). Fo ins ance, o es - dwelling passe ine bi ds usually
exhibi mo e complex colou a ion han do species in open habi a s
o dis inc plumage a eas o unde s anding global pa e ns o colou a ion
complexi y and he p ocesses ha p omo e hem.
KEYWORDS
bi d colou a ion, clima e, colou complexi y, Pa idae, sexual dich oma ism, sexual selec ion,
signalling, he mo egula ion
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LÓPEZ-IDIÁQUEZ e al.
(Cooney e al., 2022). S ill, he in luence o he di e si y o hab-
i a s used by bi ds on hei colou a ion complexi y emains li le
explo ed. Al hough some bi d, ep ile and mo h species wi h b oad
habi a use ha e g ea e in e speci ic colou complexi y han do
habi a specialis s (Fo sman & Åbe g, 2008; Fo sman e al., 2020;
Passa o o e al., 2018), mo e esea ch is needed o con i m he
gene ali y o his pa e n.
In addi ion o en i onmen al in luences, a a ie y o bio ic ac-
o s, including sexual selec ion, compe i ion and p eda ion and spe-
cies cha ac e is ics, such as body and beak size, a e likely in ol ed
in he e olu ion o plumage colou a ion complexi y (Table 1). Fo
example, colou a ion plays an impo an ole in signalling quali y
o po en ial ma es, and sexual dich oma ism, which can pa ly e-
lec sexual selec ion in ensi y, is associa ed wi h g ea e colou
complexi y in males (Cooney e al., 2022). Fu he , di e gence in
colou ai s among species can con ibu e o he main enance o
ep oduc i e isola ion (Wes - Ebe ha d, 1983). Species ha co-
occu wi h ela i ely many con amilial species exhibi mo e com-
plex colou a ion han hose co- occu ing wi h ewe con amilials,
likely because he o me species ace g ea e isk o he e ospe-
ci ic ma ing han do he la e (Dou elan e al., 2016; Simpson
e al., 2021). In addi ion, se e al s udies documen ha high p e-
da ion p essu e is associa ed wi h educed colou complexi y in
bi ds (Blia d e al., 2020). I smalle a ian species ace weake
p eda ion p essu e han do la ge species, we expec a nega i e
associa ion be ween colou complexi y and body size, due o con-
s ain s placed by he need o camou lage (Cooney e al., 2022,
bu see Dale e al., 2015).
He e, we analyse plumage colou a ion complexi y in he am-
ily Pa idae (A es: Passe i o mes), a widely dis ibu ed axon, he
species o which ha e de eloped ample a ia ion in colou a ion
complexi y (Figu es 1 and 2). We use he Pa idae o examine he
associa ion o clima e, li e his o y, habi a use, sexual dich oma-
ism and bio ic in e ac ions wi h colou a ion complexi y. We use
da a on he whole plumage and on ou speci ic a eas o he plum-
age (head, ches , back and wing) in modelling sex- speci ic associa-
ions o he e ec s o sympa y, p eda ion and social and sexual
selec ion, as he associa ions may di e be ween males and e-
males (Cooney e al., 2022; Dou elan e al., 2020; Fa ge ieille
e al., 2023). We expec o ind g ea e colou a ion complexi y in
smalle , mo e dich oma ic species ha li e in seasonal clima es,
while encoun e ing low p eda ion p essu e and ela i ely many
sympa ic con amilial species (Table 1). Fu he , we expec (a)
head and ches colou complexi y o be associa ed wi h a iables
linked o sexual/social selec ion, due o hei ole in communica-
ion and (b) he complexi y o he colou a ion o he back and wing
o be associa ed wi h ac o s linked o na u al selec ion, as hese
plumage a eas likely unc ion in p o iding camou lage and/o he -
mo egula ion. We examine hese associa ions by using da a on en-
i onmen and species anges om public sou ces and da a on bi d
ai s and beha iou om published sou ces and measu emen o
museum specimens. The analyses a e conduc ed in a causal ame-
wo k using a di ec ed acyclical g aph o in o m he selec ion o
app op ia e co a ia es, and phylogene ic mixed models o accoun
o he non- independence o con amilial species.
2 | METHODS
2.1 | E hical no e
Since his s udy did no in ol e he use o li e specimens, e hical ap-
p o al was no equi ed.
2.2 | Spec ome y and a ian isual models
We measu ed he plumage colou a ion o 58 ou o he 63 Pa idae
species (Johansson e al., 2018) a he Na u al His o y Museum
a T ing, Uni ed Kingdom, using a spec ome e (AVASPEC- 2048,
A an es, Apeldoo n, Ne he lands) wi h a deu e ium- halogen ligh
sou ce (AVALIGHT- DH- S lamp), co e ing a spec al ange o 300
o 700 nm and a 200 μm op ical p obe (FCR- 7UV200- 2- 45- ME). We
measu ed h ee males and h ee emales o each species, excep in
a ew ins ances whe e ewe we e a ailable (Table S1). We made
h ee eplica e measu emen s o 22 p ede ined plumage pa ches
(Figu e S1) in well- p ese ed adul specimens. When a specimen
had a pa ch including mo e han one colou , we measu ed all colou s
( ange: 22 o 27 pa ches, see Table S1 o u he de ail). All speci-
mens we e measu ed by a single pe son (DL- I).
We used he a e age o he h ee spec a aken in each pa ch
o each specimen o compu e colou complexi y o each specimen
using pa o ( . 2.7.1; Maia e al., 2019). We calcula ed ela i e co-
lou olumes espec i e o he a ian e ahed al space as he con-
ex hull ha included all pa ches in he cloud o poin s. We used
equal illuminances ac oss wa eleng hs and he blue i (Cyanis es
cae uleus) isual sys em (UV sensi i e) o econs uc how colou s
a e pe cei ed by conspeci ics (Fa ge ieille e al., 2023). Colou
olume is egula ly used as a p oxy o he di e si y o colou s
in a ian plumage, and la ge colou olumes indica e g ea e co-
lou complexi y (Cooney e al., 2022; Dou elan e al., 2016;
Fa ge ieille e al., 2023; Macedo e al., 2022). Finally, we used he
mean ch oma ic dis ance (dS) be ween alues o male and emale
pa ches wi hin a species as a measu e o sexual dich oma ism
(P ice e al., 2024).
2.3 | Clima e in o ma ion
We ob ained clima e da a wi hin he ange o each Pa idae species
om he bioclima ic a iables (BIO) a ailable om Wo ldClim ( .
2.1; Fick & Hijmans, 2017) a a 2.5- a c- minu e esolu ion using he
package as e ( . 3.5–29; Hijmans, 2022). We based ou geog aphic
analyses on a da ase o Pa idae ange maps p oduced by Bi dli e
In e na ional (2021). We esol ed he a ian axonomic and dis ibu-
ion di e ences be ween he Johansson ee (Johansson e al., 2018)
13652656, 2025, 7, Downloaded om h ps://besjou nals.onlinelib a y.wiley.com/doi/10.1111/1365-2656.70077 by Spanish Coch ane Na ional P o ision (Minis e io de Sanidad), Wiley Online Lib a y on [12/11/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License
1464
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LÓPEZ-IDIÁQUEZ e al.
and hose in he Bi dLi e maps by manually edi ing he dis ibu ion
ange maps. We ocused ou en i onmen al analysis on he b eed-
ing anges and egions inhabi ed (o p obably inhabi ed) by ou ocal
species, as done p e iously (Cooney e al., 2022). We ex ac ed om
wi hin each ange annual mean empe a u e (BIO1), iso he mali y
(BIO3), empe a u e seasonali y (BIO4), empe a u e annual ange
(BIO7), annual p ecipi a ion (BIO12) and p ecipi a ion seasonali y
(BIO15). In addi ion, we calcula ed annual p ecipi a ion ange as p e-
cipi a ion in he we es mon h (BIO16) minus p ecipi a ion in he
d ies mon h (BIO17).
We educed he dimensions o he clima ic a iables associ-
a ed wi h empe a u e and p ecipi a ion a iabili y using p incipal
componen analysis (PCA). We included he a iables iso he mal-
i y (BIO3), empe a u e seasonali y (BIO4) and empe a u e annual
ange (BIO7) o ep esen empe a u e a iabili y. We e ained he
i s axis o he PCA, explaining 95.0% o he a iance, in which
highe alues o he axis ep esen ed mo e seasonal empe a u es.
We success ully used p ecipi a ion seasonali y and p ecipi a ion
annual ange o ep esen p ecipi a ion a iabili y and conduc ed
a sepa a e PCA. We e ained he i s axis o his PCA, which ex-
plained 74.4% o he a iance. Highe alues on his axis ep esen
g ea e p ecipi a ion seasonali y (see Suppo ing In o ma ion S2 o
u he de ails on he PCAs).
2.4 | P eda ion p essu e
We used Bi dli e In e na ional species ange maps and he R package
as e (Hijmans, 2022) o es ima e p eda ion p essu e o each Pa idae
species. We es ima ed p eda ion p essu e as he numbe o sympa ic
a ian p eda o species ac oss i s ange, a me ic ha has been
success ully used as an index o p eda ion p essu e (Blia d e al., 2020;
Buckley & Je z, 2007; Valcu e al., 2014, 2023). P eda o densi ies o
es ima es o p eda o - d i en mo ali ies in ou s udied species would
p o ide mo e speci ic in o ma ion on he p essu e expe ienced
by a species; howe e , his in o ma ion is no a ailable o such a
TABLE 1 Explana o y a iables included in ou models and hei expec ed associa ions wi h colou complexi y. Fixed e ec s a e he
a iables included in he model o es each p edic ion.
Va iable P edic ion Fixed e ec s
Annual mean empe a u e ( ) Species li ing in a eas wi h in e media e empe a u es wi hin he Pa idae anges
will exhibi mo e complex colou a ion han species in colde /wa me a eas (1–3)
+ 2 + sex
Annual p ecipi a ion (p) Species li ing in a eas wi h highe p ecipi a ion will exhibi mo e complex
colou a ion (4–6)
p + + sex
Tempe a u e seasonali y ( s) Species in mo e seasonal a eas will exhibi mo e complex colou a ions (7–10) s + + sex
P ecipi a ion seasonali y (ps) ps + s + p + sex
Body size (bos) Smalle species will exhibi mo e complex colou a ions (5, 11, 12, bu see 27)bos + + sex
Beak size (bes) Beak size has been linked o di e en ecological and beha iou al aspec s o he
species ha can impose cons ain s and p essu es on bi d colou a ion, bu we do
no ha e a s ong expec a ion abou he di ec ion o his associa ion (13–17)
bes + bos + + sex
P eda ion (p ) Species unde s onge p eda ion p essu e will ha e less complex colou a ions,
and he e ec s will be s onge in males han in emales (18–21)
p + bos + sex + p × sex
Sympa y (sy) Species inhabi ing a eas wi h mo e con amilials will display mo e complex
colou a ion, wi h s onge e ec s in males han in emales. (22–26)
sy + bos + sex + sy × sex
Sex Males will display mo e complex colou a ion han emales (5, 27, 28)sex
Habi a b ead h (hb) Species wi h g ea e b ead h o habi a use will display mo e complex
colou a ion (29–31)
hb + ps + s + sex
Mig a ion (m) Mig an s will display less complex colou a ion han esiden s (32, 33)m + s + ps + sex
Sexual dich oma ism (sd) Mo e dich oma ic species will ha e g ea e complexi y han monoch oma ic
ones, wi h s onge e ec s in males han in emales (5, 28, 34)
sd + s + ps + sex + sd × sex
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28. C. R. Cooney., Na Commun. 10, 1773 (2019). 29. A. Fo sman, Ecology. 89, 1201–1207 (2008). 30. A. Fo sman, Ecog aphy. 43, 823–833 (2020). 31.
K. Delhey, J. E ol. Biol. 26, 1559–1568 (2013). 32. T. Ale s am, Oikos. 103, 247–260 (2003). 33. R. K. Simpson, P oc. R. Soc. B. 282, 20,150,375 (2015).
34. A. J. Shul z, E olu ion. 71, 1061–1074 (2017).
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la ge- scale s udy. A ian p eda o s o adul bi ds included species in he
o de s Accipi i o mes and Falconi o mes. Noc u nal a ian p eda o s
(S igi o mes) and mammals we e no included in he s udy because
we did no expec hem o impose s ong selec ion p essu es on
colou a ion. The e ina o S igi o mes species eyes con ains mos ly
od cells (Ha mening & Wagne , 2011), esul ing in weak colou ision.
Mammalian p eda o s a e mos ly blind o ul a iole and ha e poo
colou ision, as hey only ha e wo ypes o pho o ecep o s ( s. ou
in bi ds; Bowmake , 2008; Guil o d & Ha ey, 1998). Finally, al hough
he e a e se e al snake species ha eed on bi ds, we did no include
snakes in ou analyses, since he g ea majo i y o hem p eda e on
eggs and chicks in nes s (Ba ends & Ma i z, 2022; Wea he head
& Blouin- Deme s, 2004) and, hus, a e unlikely o impose selec ion
p essu e on a ian colou a ion. To con ol o po en ial size misma ches
be ween p eda o and p ey species (i.e. coun ing p eda o s wi h much
la ge o smalle p ey), we compu ed p eda o –p ey mass allome y
ela ionships, hen excluded hose Accipi i o mes and Falconi o mes
when size misma ches wi h po en ial p ey we e de ec ed, as p e iously
done by Valcu e al. (2014) and Blia d e al. (2020; see Suppo ing
In o ma ion S3 o u he de ails).
2.5 | Sympa y wi h o he Pa idae
Using he ange maps o he Pa idae and he package as e
(Hijmans, 2022), we calcula ed he deg ee o sympa y wi h o he
FIGURE 1 Va ia ion in plumage colou complexi y ac oss he Pa idae amily. O ange and blue ba s ep esen he a e age colou olumes
o males and emales, espec i ely. La ge olumes indica e g ea e colou complexi y. We plo ed he aw alues bu no e ha in he
analyses we ha e used a log- ans o med e sion o his a iable (see Sec ion 2). In Poecile hype melaena, he alue is he same in males and
emales as he sex o measu ed indi iduals was no de e mined and in Poecile da idi he e is no alue o emales as we only measu ed males.
The ed do s by ip names indica e he depic ed species. Colou complexi y alues ep esen he a e age o he h ee measu es aken in
each male and emale (see Sec ion 2). Species illus a ions by Hila y Bu n ©Lynx Edi ions.
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Pa idae species as he numbe o con amilial species wi h anges
o e lapping he ange o a ocal species.
2.6 | Mo phology
We ex ac ed da a on a sus, wing and ail leng hs, and body mass o
Pa idae species om he AVONET da ase (Tobias e al., 2022) and
he Handbook o he Bi ds o he Wo ld (Bille man e al., 2022). We
conduc ed PCA o hese da a o ob ain a p oxy o body size (he e-
a e body size). Speci ically, we e ained he species sco es on he
i s PCA axis, which explained 71.5% o he a iance in hese da a.
Addi ionally, one o us (DL- I) measu ed beak leng h and wid h ( o he
nea es 0.1 mm) om he museum specimens using a digi al callipe .
We used PCA o summa ise hese wo a iables as a single p oxy o
beak size (he e a e beak size). We e ained species sco es on he
i s axis o his PCA, which explained 81.0% o he da a a ia ion (see
Suppo ing In o ma ion S2 o u he in o ma ion on he PCAs).
2.7 | Habi a b ead h
We compu ed habi a b ead h by compiling in o ma ion abou he
gene al habi a (e.g. o es ) and sub- habi a (e.g. empe a e o bo eal)
om he Habi a Classi ica ion Scheme o he IUCN (IUCN, 2022).
B ie ly, we calcula ed habi a b ead h using an in ege alue co e-
sponding o he numbe o gene al habi a s a species occupies and
a decimal igu e o he numbe o sub- habi a s i occupies ( o u -
he de ails see Suppo ing In o ma ion S4 and Es ada e al., 2018).
Thus, highe alues o his a iable ep esen species inhabi ing a
mo e di e se se o en i onmen s.
2.8 | Mig a ion
We ob ained in o ma ion abou he mig a o y beha iou o ou ocal
species om he IUCN (IUCN, 2022). Speci ically, we classi ied spe-
cies in o wo ca ego ies based on whe he hey exhibi al i udinal
mig a ion o no , as he species wi hin he Pa idae amily do no pe -
o m long- dis ance mig a o y mo emen s.
2.9 | S a is ical analyses
To explo e he associa ion be ween colou a ion complexi y and
ou p edic o a iables (Table 1) we i ed mul i- p edic o Bayesian
phylogene ic mixed models using he b ms package ( . 2.34;
Bü kne , 2017) in R ( . 4.2.0, R Co e Team, 2022). The models in-
cluded a phylogene ic andom e ec o con ol o phylogene ic
non- independence o he species wi hin he Pa idae amily, based on
he Pa idae ee published by Johansson e al. (2018). This ee was
cons uc ed using Bayesian in e ence and was s ongly suppo ed,
wi h mos nodes achie ing p obabili ies o 1.00 ( o u he de ails,
see Johansson e al., 2018). We also included species as a andom
e ec o con ol o he non- independence o he measu es aken in
di e en specimens o he same species.
We i ed sepa a e models o he colou a ion complexi y o
he en i e plumage and each plumage a ea (i.e. head, ches , back
FIGURE 2 Maps illus a ing he geog aphical dis ibu ion o (a) Pa idae mean colou a ion complexi y (scaled), (b) Pa idae species ichness,
(c) mean annual empe a u e (BIO1) and (d) empe a u e seasonali y (BIO4) wi hin he Pa idae dis ibu ion ange. Annual mean empe a u e
and seasonali y ep esen he in o ma ion ob ained om Wo ldClim (see me hods). In A, we ha e plo ed he aw colou complexi y alues
bu no e ha in he analyses we ha e used a log- ans o med e sion o his a iable (see Sec ion 2).
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LÓPEZ-IDIÁQUEZ e al.
and wing; Figu e S1). The dependen a iable in hese models was
he colou olume, which was log- ans o med o achie e no mal-
i y (Fa ge ieille e al., 2023). To selec he ixed e ec s uc u e
o he models, we buil a di ec acyclical g aph (DAG) using he
package DAGi y ( . 0.3–4, Tex o e al., 2016). A DAG is a diag am
o he causal ela ionships be ween he a iables in a s udy and
allows iden i ica ion o he minimal se o a iables o inclusion
in a model o in e ing causal ela ionships wi h he dependen
a iable (Tex o , 2023; o u he in o ma ion on he causal e-
la ionship be ween ou explana o y a iables see Suppo ing
In o ma ion S5). All explana o y a iables we e s anda dised o
a mean o ze o and s anda d de ia ion o one o acili a e com-
pa ison o e ec sizes (see Suppo ing In o ma ion S6 o u -
he in o ma ion on he a iabili y o he explana o y a iables).
In all models, we included sex as a co a ia e. The sex o he wo
measu ed Poecile hype melaena indi iduals was unknown. To in-
clude his species in he analysis, we andomly assigned he sex
o hese wo specimens and epea ed he analyses wi h all pos-
sible sex combina ions o con ol o he po en ial biases o ou
assignmen . The esul s o all models a e consis en , showing ha
ou andom assigna ion o sex did no bias any o ou esul s (see
Suppo ing In o ma ion S7). All models included de aul p io s,
wi h he excep ion o he ixed e ec s, which included a No mal
(0, 1) egula ising p io (Macedo e al., 2022). The models we e un
o 10,000 i e a ions ac oss ou chains, wi h a wa m- up o 2000
i e a ions and a hin o 10, excep he model o he associa ion
be ween head colou complexi y and empe a u e and p ecipi a-
ion seasonali y, which was un o 100,000 i e a ions ac oss ou
chains, wi h a wa m- up o 2000 i e a ions and a hin o 100. In
each case, he alues we e selec ed o ensu e model con e gence
and good e ec i e sample sizes, which we e assessed by inspec-
ion o ace plo s and he Gelman- Rubin con e gence diagnos-
ic. We es ima ed phylogene ic signal (λ) om models including
sex as a p edic o as he phylogene ic he i abili y (Lynch, 1991),
λ = σ2Phylo/(σ2Phylo + σ2
Res), whe e σ2Phylo and σ2
Res a e he a i-
ances due o phylogeny and unmodelled sou ces ( esidual a i-
ance), espec i ely (De F amond e al., 2025; de Villeme euil &
Nakagawa, 2014; Lynch, 1991; Macedo e al., 2022).
3 | RESULTS
We ind ha whole- body plumage colou complexi y shows a
non- linea associa ion wi h annual mean empe a u e, a nega i e
associa ion wi h body size and a posi i e associa ion wi h sexual
dich oma ism, p esen ing a s onge ela ionship in males han in
emales (Table 2, Figu e 3a). Females exhibi less complex whole-
body colou a ion han males do. Fu he , al hough he 95% c edible
in e als (CI) include ze o, he pos e io dis ibu ion o beak size
s ongly g a i a es owa ds posi i e alues o associa ion (i.e. >90%
o he pos e io dis ibu ion was posi i e; Figu e 3a). Simila ly, he
pos e io dis ibu ions o p eda ion and sympa y s ongly g a i a e
owa ds nega i e alues o associa ion o emales, indica ing lowe
TABLE 2 Pos e io means and 95% c edible in e als (in b acke s) om models linking explana o y e ms wi h plumage colou complexi y o he en i e body and o i e sepa a e plumage
pa ches.
Mean annual
empe a u e2Annual p ecipi a ion Tempe a u e seasonali y P ecipi a ion seasonali y Habi a b ead h P eda ion em P eda ionmal Sympa y em
Whole body −0.212 [−0.395, −0.023] 0.151 [−0.092, 0.399] 0.105 [−0.318, 0.523] 0.085 [−0.248, 0.430] 0.024 [−0.238, 0.292] −0.251 [−0.613, 0.121] −0.240 [−0.614, 0.134] −0.203 [−0.428, 0.027]
Head −0.046 [−0.286, 0.201] 0.166 [−0.157, 0.483] 0.083 [−0.410, 0.587] 0.293 [−0.070, 0.643] 0.092 [−0.200, 0.390] −0.273 [−0.704, 0.158] −0.282 [−0.726, 0.169] −0.317 [−0.604, −0.006]
Ches −0.226 [−0.529, 0.088] 0.158 [−0.229, 0.544] 0.311 [−0.375, 1.044] −0.124 [−0.614, 0.441] 0.231 [−0.175, 0.609] −0.556 [−1.150, 0.049] −0.297 [−0.917, 0.334] −0.164 [−0.520, 0.278]
Back −0.304 [−0.573, −0.036] 0.174 [−0.179, 0.521] 0.034 [−0.569, 0.648] 0.032 [−0.419, 0.477] −0.084 [−0.469, 0.326] −0.196 [−0.736, 0.326] −0.106 [−0.644, 0.448] −0.164 [−0.520, 0.278]
Wing −0.155 [−0.501, 0.177] 0.135 [−0.272, 0.550] 0.103 [−0.560, 0.776] 0.107 [−0.445, 0.719] 0.036 [−0.415, 0.502] −0.022 [−0.675, 0.646] 0.066 [−0.609, 0.753] −0.005 [−0.447, 0.403]
Sympa ymal Mig an yes Beak size Body size Sexual dich oma ism em Sexual dich oma ismmal Sex em λ
Whole body −0.092 [−0.319, 0.139] −0.135 [−0.886, 0.594] 0.109 [−0.017, 0.239] −0.212 [−0.398, −0.010] 0.692 [0.489, 0.901] 0.865 [0.665, 1.072] −0.185 [−0.262, −0.109] 45.46% [26.16, 62.84]
Head −0.164 [−0.502, 0.286] −0.851 [−1.662, 0.040] 0.254 [0.031, 0.488] −0.080 [−0.348, 0.193] 0.526 [0.271, 0.775] 0.811 [0.557, 1.064] −0.057 [−0.197, 0.085] 18.20% [4.95, 32.82]
Ches −0.117 [−0.511, 0.262] 0.030 [−0.967, 1.000] 0.276 [−0.047, 0.601] 0.013 [−0.402, 0.450] 0.675 [0.233, 1.124] 0.978 [0.557, 1.441] −0.180 [−0.381, 0.017] 29.59% [15.30, 42.63]
Back −0.198 [−0.527, 0.145] 0.150 [−0.831, 1.087] 0.173 [−0.094, 0.445] −0.435 [−0.751, −0.116] 0.725 [0.352, 1.110] 0.904 [0.530, 1.289] −0.237 [−0.411, −0.074] 21.11% [7.74, 35.53]
Wing −0.136 [−0.544, 0.275] −0.390 [−1.500, 0.704] 0.159 [−0.224, 0.527] −0.504 [−0.922, −0.080] 0.698 [0.184, 1.190] 0.589 [0.075, 1.083] −0.219 [−0.466, 0.023] 23.09% [12.27, 35.44]
No e: λ is he es ima ed phylogene ic signal (see Sec ion 2).
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emale colou complexi y in species ha co- occu wi h ela i ely
many con amilial species and p eda o s (Figu e 3a, see Tables S1–
S10 o u he de ails on model esul s).
The colou complexi y o dis inc plumage pa ches p esen s a
a ie y o associa ions wi h he en i onmen , species mo phology
and bio ic in e ac ions. Head colou complexi y shows a posi i e as-
socia ion wi h a ia ion in beak size and sexual dich oma ism, which
is s onge in males han in emales (Table 2, Figu e 3b). The colou
complexi y o he head o emales is nega i ely associa ed wi h he
numbe o sympa ic species, bu head colou complexi y o males
is no (Table 2, Figu e 3b). Fu he , he pos e io dis ibu ion o p e-
cipi a ion seasonali y s ongly ends owa ds a posi i e associa ion
wi h colou complexi y, while he pos e io dis ibu ions o mig a-
ion end owa ds nega i e associa ions, al hough his associa ion is
es ima ed wi h high unce ain y (Figu e 3b; see Tables S11–S20 o
u he de ails on model esul s).
Fo he ches pa ch, we ind ha colou complexi y shows a posi-
i e associa ion wi h sexual dich oma ism o bo h males and emales
(Table 2, Figu e 3c). The pos e io dis ibu ion o he quad a ic com-
ponen o mean annual empe a u e ends owa ds nega i e alues,
sugges ing highe ches colou complexi y a in e media e han a
colde /wa me empe a u es (Figu e 3c). The pos e io dis ibu ion
o empe a u e a iabili y s ongly ends owa ds posi i e alues,
while he pos e io dis ibu ions o bo h p eda ion and sex in e-
males end owa ds nega i e alues o associa ion (Figu e 3c; see
Tables S21–S30 o u he de ails on model esul s).
The colou complexi y o he back p esen s a non- linea asso-
cia ion wi h mean annual empe a u e (i.e. highe colou complex-
i y a in e media e empe a u e, as shown by a nega i e quad a ic
e m), a nega i e associa ion wi h body size and a posi i e associ-
a ion wi h sexual dich oma ism, which is s onge in emales han
in males (Table 2, Figu e 3d; see Tables S31–S40 o u he de ails
on model esul s).
The colou complexi y o he wing co a ies nega i ely wi h body
size and posi i ely wi h sexual dich oma ism (Table 2, Figu e 3e). Fo
sex, al hough he 95% CIs include ze o, he pos e io dis ibu ion
sugges s ha wings o emales end o ha e less complex colou a-
ion han do hose o males (Figu e 3e; see Tables S41–S50 o u -
he de ails on model esul s).
4 | DISCUSSION
Ou indings show ha a ia ion in plumage colou a ion complex-
i y among Pa idae species is associa ed wi h clima ic and ecologi-
cal a ia ion, as well as wi h ac o s ha a e in insic o he species.
Ou esul s also show ha he ela ionship o colou complexi y
wi h he en i onmen al a iables we included depends on he
plumage pa ch we conside ed and unde sco es he impo ance o
conside ing dis inc plumage a eas sepa a ely, in o de be e o
unde s and he ela ionship be ween en i onmen al a ia ion and
a ian colou complexi y.
FIGURE 3 Associa ions be ween he colou complexi y o he whole plumage (a), head (b), ches (c), back (d) and wing (e) wi h he
scaled p edic o s. Black do s and whiske s ep esen he mean ± 95% c edible in e als (CI), and he densi y cu e indica es he pos e io s
dis ibu ions o each p edic o . Densi y plo s wi h solid colou s ep esen associa ions in which he 95% CIs do no include ze o. Densi y
plo s wi h in e media e shading deno e associa ions in which he 95% CIs includes ze o bu s ongly g a i a e (>90% o he pos e io
dis ibu ions) owa ds posi i e o nega i e alues. Densi y plo s wi h anspa en colou s deno e non- suppo ed associa ions. Pu ple, blue
and da k o ange shades ep esen clima ic, bio ic and in insic a iables, espec i ely. G ey ep esen s sex.
(a) (b) (c) (d) (e)
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4.1 | Whole plumage
Resea ch explo ing he associa ion be ween plumage colou a-
ion complexi y and empe a u e a ia ion has yielded con as -
ing esul s as some s udies epo signi ican posi i e associa ions
(Macedo e al., 2022) while o he s udies do no (Cooney e al., 2022;
F iedman & Remeš, 2017). Un il now, he associa ion be ween em-
pe a u e and colou complexi y has been analysed assuming only
linea ends may exis . Ou indings, in con as , sugges ha he
associa ion is likely mo e complex han p e iously hough , in ha
colou complexi y is highe in Pa idae species in egions wi h in e -
media e empe a u es compa ed o hose species in wa me and
colde a eas wi hin he Pa idae dis ibu ion anges. This pa e n
esembles ha o p e ious esul s on plumage da kness, in which
passe ine species ha expe ience ex eme empe a u es wi hin
hei anges ypically exhibi ligh e colou a ion han o he pas-
se ines (Delhey e al., 2019). One explana ion o his is ha ligh e
plumages a e a ou ed in such a eas due o hei ole in p o iding
camou lage and aiding in he mo egula ion (Delhey e al., 2019;
Gal án e al., 2018). We belie e ha a compa able phenomenon
may explain ou esul s on colou complexi y. Fo ins ance, selec-
ion a ou ing uni o m colou a ion ha enhances concealmen
agains snowy su aces may cons ain he e olu ion o complex
colou a ion a high la i udes. A complemen a y explana ion is ha
he esou ces equi ed o exhibi complex colou s may be limi ed in
ex emely wa m o cold a eas. Fo example, ca o enoids a e likely
less a ailable in a eas wi h ex eme empe a u es due o limi ed
plan p oduc i i y (Zhang e al., 2017). Beyond being he p ima y
pigmen s o lashy a ian colou s (Thomas e al., 2014), ca o enoids
also se e as c ucial immune- enhance s and an ioxidan s (Wea e
e al., 2018). Na u al selec ion in a eas wi h ex eme empe a u es
may a ou alloca ion o ca o enoids o main aining obus an ioxi-
da i e and immune unc ions, a he han o de eloping colou ul
plumage pigmen a ion.
The ele ance o sexual selec ion as a d i e o plumage co-
lou a ion complexi y is highligh ed by ou esul s showing ha
g ea e dich oma ism is associa ed wi h mo e complex colou a ion.
This aligns wi h p e ious wo k on passe ines (Cooney e al., 2022)
and anage s (Shul z & Bu ns, 2017) in highligh ing he ole o sex-
ual selec ion as an e olu iona y d i e o colou a ion complexi y.
Howe e , while hese s udies epo signi ican esul s in males
and no emales, ou esul s o he Pa idae suppo he associa ion
be ween sexual dich oma ism and plumage colou complexi y in
bo h sexes. Thus, sexual selec ion in he Pa idae may also explain
among- species a ia ion in emale colou complexi y a he han
i being simply a by- p oduc o selec ion on males. The sensi i -
i y o emale colou a ion complexi y o sexual selec ion sugges s
ha emale colou a ion, a he han being a gene ic co ela e o
colou a ion in males, plays a signalling ole, some hing suppo ed
by s udies o species in he Pa idae (Dou elan e al., 2020; Thys
e al., 2020) and in o he bi d species (López- Idiáquez e al., 2016).
In he ypically ca i y- nes ing Pa idae, he e could be li le p es-
su e o he e olu ion o camou lage in emales and bi- pa e nal
ca e may a ou he e olu ion o emale ai s unde sexual selec-
ion (Fa ge ieille e al., 2023).
Ou esul s also show ha emales in he Pa idae display less
complex colou a ion han males, and despi e model suppo , we
obse e li le di e ence in plumage colou complexi y be ween
males and emales. This lack o s ong di e ence be ween sexes
can be explained by Pa idae biology. As a axon o socially mo-
nogamous species wi h mode a e le els o ex a- pai pa e ni ies
(B ouwe & G i i h, 2019), simila selec i e p essu e may ac on
o namen al ai s in bo h sexes. A a mo e gene al le el, he di-
e gence be ween ou esul s and hose epo ed o he O de
Passe i o mes (Cooney e al., 2022), he encompassing axon o
he Pa idae, e eals he impo ance o explo ing hese e olu ion-
a y pa e ns a di e en axonomic scales. Resul s om global
analyses including housands o species, despi e being app op i-
a e o in e ing b oad pa e ns, can be biased owa ds ends in
nume ically dominan axa. This may conceal ela ionships in less
di e se axa and, hus, limi unde s anding o p ocesses explaining
a ia ion a lowe axonomical le els.
In line wi h ou p edic ion, we ound ha smalle species ex-
hibi mo e complex colou a ion. These esul s align wi h hose o
Cooney e al. (2022) o he whole plumage in he passe ines. The
nega i e associa ion be ween colou complexi y and body size
could be explained by a physiological limi a ion on he exp ession
o complex colou s in la ge bi ds (Gal án e al., 2013) as, o in-
s ance, la ge bi d species ha e lowe ci cula ing ca o enoid con-
cen a ions han smalle species (Tella e al., 2004). An al e na i e
hypo hesis is ha he e may be di e ing communica ion equi e-
men s associa ed wi h body size di e ences (Kil ie, 2000). Fo
example, selec ion may a ou he p esence o a highe numbe
o di e en ly colou ed pa ches in smalle species, which commu-
nica e a sho e dis ances han in la ge species in which a la ge ,
uni o mly colou ed pa ch could be mo e e ec i e. Ou esul s also
show ha species wi h la ge beaks exhibi mo e complex colou a-
ions. As die a y niches and p e e ences a e linked bo h o he
empo and mode o e olu ion o c anial mo phology and beak size
(Felice e al., 2019; Olsen, 2017; Pigo e al., 2020), his associa ion
sugges s a link be ween colou complexi y and die . Fo ins ance,
species wi h la ge beaks could ha e access o ca o enoid- ich e-
sou ces una ailable o species wi h smalle beaks. Al e na i ely,
a ia ion in beak size and shape has also been linked o non- die a y
ac o s, such as song p oduc ion and he mo egula ion (F iedman
e al., 2019; Na alón e al., 2019), which we e no conside ed in
ou s udy and could be linked o colou a ion.
Finally, ou esul s sugges a nega i e ela ionship be ween
colou complexi y and bo h p eda ion in ensi y and sympa y
wi h con amilials. Fo p eda ion, he esul s pa ially align wi h
ou p edic ion o less complex colou a ion in species acing
s onge p eda ion p essu e, as sugges ed by p e ious s udies
on he ole o plumage colou a ion as a modula o o p eda ion
isk (Blia d e al., 2020; Huh a e al., 2003). While p eda ion can
explain among- species di e ences in plumage b igh ness (Huh a
e al., 2003) and di e ences in colou complexi y be ween island
13652656, 2025, 7, Downloaded om h ps://besjou nals.onlinelib a y.wiley.com/doi/10.1111/1365-2656.70077 by Spanish Coch ane Na ional P o ision (Minis e io de Sanidad), Wiley Online Lib a y on [12/11/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License
