Figure 1. We interpreted significance in GLMM model outputs where 95%
credible intervals did not span zero (red bars; otherwise black bars
denote non-significant results), and points denote posterior mean. Our
observed results (A1-2) suggest that female birds who divorce social
partners regularly engage with more extra-pair males than those who
maintain social monogamy. Likewise, the number of broods initiated also
significantly predicted an increase in extra-pair males, without
affecting the proportion of extra-pair offspring, presumably by virtue
of opportunity (A2; red bars). Simulated breeding events (B1-2), where
extra-pair males and extra-pair offspring were permuted between females
in our system were not significant. Random effects are given in the
shaded box (Dam and Cohort) for each model. Intercept and residuals for
each model are not shown in the figure: A1, intercept -1.65 (-2.12 –
-1.1), residuals 0.61 (-2.11 – 0.92); A2, intercept -1.65 (-2.11 –
-1.8), residuals 0.53 (3.47 – 0.72); B1, intercept -0.5 (-8.78 –
-0.14), residuals 0.81 (6.54 – 0.95); B2, intercept 1.26 (8.53 –
1.66), residuals 1.06 (9.37 – 1.2).
Discussion
We empirically tested an assumption of the intrasexual antagonistic
pleiotropy hypothesis - that extra-pair behaviour is linked to another
trait beneficial to female fecundity, in this case, solicitation of
social partners (Halliday and Arnold 1987; Wang et al. 2020), which we
measured as the rate of divorce within years. Our results suggested that
female divorce is linked with females engaging more extra-pair males.
However, we found no effect of divorce on the proportion of extra-pair
offspring. We also found a link between the number of broods initiated
and female engagement of extra-pair males, which we consider a
by-product of the opportunity for more extra-pair paternity over a
longer breeding period.
Opportunity has been demonstrated to increase extra-pair behaviour in
several systems (see Maldonado-Chaparro et al. 2018), including
empirical studies suggesting that extra-pair copulations may be
obligate, where they are facilitated by opportunity (Fossøy, Johnsen,
and Lifjeld 2006). Liker, Freckleton, and Székely (2014) suggested that
the sex ratio of the wider social environment also influences the
divorce rate, driven by female-biased sex ratios and infidelity, by
male-biased sex ratios (but also Culina, Hinde, and Sheldon 2015).
However, opportunity cannot explain what drives extra-pair
decision-making, instead, that must come from selective advantage to
those who engage in extra-pair copulations. Our results support the
suggestion by Wang et al. (2020) that female social solicitation
behaviours are linked with extra-pair mate solicitation, and therefore,
support intrasexual antagonistic pleiotropy as a mechanism for female
extra-pair behaviour. However, we suggest that other, probably
post-copulatory, processes control the proportion of extra-pair
offspring born to females within a breeding year. Equivalent attention
has also been given towards intersexual pleiotropic effects, where
female extra-pair behaviour may be linked with a trait which benefits
male reproductive success, these studies have found little support in
captivity (Wang et al. 2020), or in wild populations (Zietsch et al.
2015; Reid and Wolak 2018). Where quantitative genetic studies have
sought to demonstrate a heritable basis for male extra-pair behaviour,
required for intersexual pleiotropy to drive female extra-pair
behaviour, estimates are low (Reid et al. 2011; Reid and Wolak 2018;
Grinkov et al. 2020). However, Dobson et al.. (2023) found that the
inclusion of social partner indirect genetic effects (those derived from
the behaviour of another) improved model fit for the heritability of
both male and female extra-pair behaviour, implying a role for the wider
social environment in the plasticity of extra-pair behaviour.
We used divorce rate within a female breeding year, between multiple
broods, as a measure of solicitation, but not between breeding years -
more akin to a classic definition of divorce behaviour. Divorce is more
broadly defined as where both partners are alive, and at least one of
them has paired with a new social partner (Black and Hulme 1996; but
also see Culina, Radersma, and Sheldon 2015). However, the motivations
for female sparrows to divorce social partners between broods may be
like those described elsewhere for divorce, which has been demonstrated
to represent an adaptive strategy between sexes across monogamous
birds (Choudhury 1995; Culina, Radersma, and Sheldon 2015; Mercier,
Yoccoz, and Descamps 2021; Wilson, Nguyen, and Burley 2022). Previous
works have also considered divorce and extra-pair behaviours as linked
traits in the context of indirect benefits (Cezilly and Nager 1995;
Choudhury 1995), that is, both provide females with a mechanism to
improve the quality of their social partner, by divorcing or cuckolding,
lesser quality males. However, empirical evidence for indirect benefits
derived from extra-pair behaviours is scarce (Akçay and Roughgarden
2007; Arct, Drobniak, and Cichoń 2015), and multi-paternity broods were
not linked to the divorce rate Ramsay et al. (2000).
Although we consider our data to be near-complete, our phenotypic study
is still subject to some bias (Hadfield 2008). For example, we sampled
chicks for paternity at day two, (see Dunning et al. 2023), but this may
still exclude an invisible fraction of those pairs, females (Kidd et al.
2015) or eggs (Yuta et al. 2018; Assersohn et al. 2021) who fail early.
As a result, our study measures extra-pair paternity, and not extra-pair
copulations, which could be more frequent than is reflected in paternity
analysis (Fossøy, Johnsen, and Lifjeld 2006; Girndt 2018). Females that
exhibit extra-pair behaviours may not always produce extra-pair
offspring, but their within-pair offspring will inherit her genes, which
may determine the extra-pair behaviour. Future work may support
intrasexual pleiotropy as a mechanism for female extra-pair behaviour by
either including measures of copulation attempts (rather than paternity)
or, through further quantitative genetic methods.
We demonstrate that females who swap mates more frequently within
breeding years engage more extra-pair males, but do not have greater
proportions of extra-pair offspring. Our study contributes an empirical
example to the growing body of research that supports non-adaptive
phenomena as mechanisms for why females engage in extra-pair behaviours.
Bibliography
Akçay,
Erol, and Joan Roughgarden. 2007. “Extra-Pair Paternity in Birds:
Review of the Genetic Benefits.” Evolutionary Ecology Research 9
(5): 855.
Arct, Aneta, Szymon M
Drobniak, and Mariusz Cichoń. 2015. “Genetic Similarity Between Mates
Predicts Extrapair Paternity—a Meta-Analysis of Bird Studies.”Behavioural Ecology 26 (4): 959–68.
Arnqvist, Göran, and
Mark Kirkpatrick. 2005. “The Evolution of Infidelity in Socially
Monogamous Passerines: The Strength of Direct and Indirect Selection on
Extrapair Copulation Behaviour in Females.” The American
Naturalist 165 (S5): S26–37.
Assersohn, K, AF
Marshall, F Morland, P Brekke, and N Hemmings. 2021. “Why Do Eggs Fail?
Causes of Hatching Failure in Threatened Populations and Consequences
for Conservation.” Animal Conservation 24 (4): 540–51.
Bates, Douglas M. 2010.
“Lme4: Mixed-Effects Modeling with r.” Springer New York.
Beck, Kristina B, Damien R
Farine, and Bart Kempenaers. 2020. “Winter Associations Predict Social
and Extra-Pair Mating Patterns in a Wild Songbird.” Proceedings
of the Royal Society B 287 (1921): 20192606.
———. 2021. “Social
Network Position Predicts Male Mating Success in a Small Passerine.”Behavioural Ecology 32 (5): 856–64.
Beck, Kristina B, Mihai
Valcu, and Bart Kempenaers. 2020. “Analysis of Within-Individual
Variation in Extrapair Paternity in Blue Tits (Cyanistes Caeruleus)
Shows Low Repeatability and Little Effect of Changes in Neighborhood.”Behavioural Ecology 31 (6): 1303–15.
Birkhead, TR. 1995.
“Sperm Competition: Evolutionary Causes and Consequences.”Reproduction, Fertility and Development 7 (4): 755–75.
Blomqvist, Donald,
Malte Andersson, Clemens Küpper, Innes C Cuthill, János Kis, Richard B
Lanctot, Brett K Sandercock, Tamás Székely, Johan Wallander, and Bart
Kempenaers. 2002. “Genetic Similarity Between Mates and Extra-Pair
Parentage in Three Species of Shorebirds.” Nature 419 (6907):
613–15.
Bolund, Elisabeth, Holger
Schielzeth, and Wolfgang Forstmeier. 2012. “Singing Activity Stimulates
Partner Reproductive Investment Rather Than Increasing Paternity Success
in Zebra Finches.” Behavioural Ecology and Sociobiology 66 (6):
975–84.
Brommer, Jon E, Jussi
S Alho, Clotilde Biard, Joanne R Chapman, Anne Charmantier, Amelie
Dreiss, Ian R Hartley, et al. 2010. “Passerine Extrapair Mating
Dynamics: A Bayesian Modeling Approach Comparing Four Species.”The American Naturalist 176 (2): 178–87.
Brommer, Jon E, Peter
Korsten, Karen M Bouwman, Mathew L Berg, and Jan Komdeur. 2007. “Is
Extrapair Mating Random? On the Probability Distribution of Extrapair
Young in Avian Broods.” Behavioural Ecology 18 (5): 895–904.
Brouwer, Lyanne, and Simon
C Griffith. 2019. “Extra-Pair Paternity in Birds.” Molecular
Ecology 28 (22): 4864–82.
Cockburn, Andrew.
2006. “Prevalence of Different Modes of Parental Care in Birds.”Proceedings of the Royal Society B: Biological Sciences 273
(1592): 1375–83.
Culina, Antica, Camilla A Hinde, and Ben C Sheldon. 2015. “Carry-over
Effects of the Social Environment on Future Divorce Probability in a
Wild Bird Population.” Proceedings of the Royal Society B: Biological
Sciences 282 (1817): 20150920.
Dawson, Deborah A,
Gavin J Horsburgh, Andrew P Krupa, Ian RK Stewart, Sigrun Skjelseth,
Henrik Jensen, Alexander D Ball, et al. 2012. “Microsatellite Resources
for Passeridae Species: A Predicted Microsatellite Map of the House
Sparrow Passer Domesticus.” Molecular Ecology Resources 12 (3):
501–23.
Drobniak, Szymon M,
Aneta Arct, and Mariusz Cichoń. 2015. “Extrapair Paternity and Genetic
Similarity—We Are Not Quite There Yet: A Response to Comments on Arct
Et Al.” Behavioural Ecology 26 (4): 973–74.
Dobson, Sarah, Jamie Dunning, Terry Burke, Heung Ying Janet Chik,
and Julia Schroeder. 2023. “Indirect genetic effects improve female
extra-pair heritability estimates”
Evolution: In press.
Dunning, Jamie, Terry Burke,
Alex Hoi Hang Chan, Heung Ying Janet Chik, Tim Evans, and Julia
Schroeder. 2022. “Opposite-Sex Associations Are Linked with Annual
Fitness, but Sociality Is Stable over Lifetime.” bioRxiv .
https://doi.org/10.1101/2022.01.04.474937.
Firth, Josh A, and Ben C
Sheldon. 2016. “Social Carry-over Effects Underpin Trans-Seasonally
Linked Structure in a Wild Bird Population.” Ecology Letters 19
(11): 1324–32.
Forstmeier,
Wolfgang. 2007. “Do Individual Females Differ Intrinsically in Their
Propensity to Engage in Extra-Pair Copulations?” PLoS One 2 (9):
e952.
Forstmeier, Wolfgang,
Katrin Martin, Elisabeth Bolund, Holger Schielzeth, and Bart Kempenaers.
2011. “Female Extrapair Mating Behaviour Can Evolve via Indirect
Selection on Males.” Proceedings of the National Academy of
Sciences 108 (26): 10608–13.
Forstmeier, Wolfgang,
Shinichi Nakagawa, Simon C Griffith, and Bart Kempenaers. 2014. “Female
Extra-Pair Mating: Adaptation or Genetic Constraint?” Trends in
Ecology & Evolution 29 (8): 456–64.
Fossøy, Frode, Arild
Johnsen, and Jan T Lifjeld. 2006. “Evidence of Obligate Female
Promiscuity in a Socially Monogamous Passerine.” Behavioural
Ecology and Sociobiology 60 (2): 255–59.
Germain, Ryan R,
Matthew E Wolak, and Jane M Reid. 2018. “Individual Repeatability and
Heritability of Divorce in a Wild Population.” Biology Letters14 (6): 20180061.
Girndt, Antje, Charlotte Wen
Ting Chng, Terry Burke, and Julia Schroeder. 2018. “Male Age Is
Associated with Extra-Pair Paternity, but Not with Extra-Pair Mating
Behaviour.” Scientific Reports 8 (1): 1–10.
Griffith, Simon C.
2015. “Genetic Similarity Is Broadly Associated with Genetic Polyandry
in Birds: A Comment on Arct Et Al.” Behavioural Ecology 26 (4):
970–71.
Griffith, Simon C, and
Simone Immler. 2009. “Female Infidelity and Genetic Compatibility in
Birds: The Role of the Genetically Loaded Raffle in Understanding the
Function of Extrapair Paternity.” Journal of Avian Biology 40
(2): 97–101.
Griffith, Simon C, Ian PF
Owens, and Katherine A Thuman. 2002. “Extra Pair Paternity in Birds: A
Review of Interspecific Variation and Adaptive Function.”Molecular Ecology 11 (11): 2195–2212.
Grinkov, Vladimir
G, Andreas Bauer, Helmut Sternberg, and Michael Wink. 2022.
“Understanding Extra-Pair Mating Behaviour: A Case Study of Socially
Monogamous European Pied Flycatcher (Ficedula Hypoleuca) in Western
Siberia.” Diversity 14 (4): 283.
Hadfield, Jarrod D. 2010.
“MCMC Methods for Multi-Response Generalized Linear Mixed Models: The
MCMCglmm r Package.” Journal of Statistical Software 33: 1–22.
Hadfield, Jarrod D.
2008. “Estimating Evolutionary Parameters When Viability Selection Is
Operating.” Proceedings of the Royal Society B: Biological
Sciences 275 (1635): 723–34.
Halliday, Tim, and
Stevan J Arnold. 1987. “Multiple Mating by Females: A Perspective from
Quantitative Genetics.” Animal Behaviour .
Hamilton, William D,
and Marlene Zuk. 1982. “Heritable True Fitness and Bright Birds: A Role
for Parasites?” Science 218 (4570): 384–87.
Hanson, Haley E, Noreen S Mathews, Mark E Hauber, and Lynn B Martin.
2020. “The House Sparrow in the Service of Basic and Applied
Biology.” Elife 9: e52803.
Hsu, Yu-Hsun, Julia
Schroeder, Isabel Winney, Terry Burke, and Shinichi Nakagawa. 2014.
“Costly Infidelity: Low Lifetime Fitness of Extra-Pair Offspring in a
Passerine Bird.” Evolution 68 (10): 2873–84.
———. 2015. “Are
Extra-Pair Males Different from Cuckolded Males? A Case Study and a
Meta-Analytic Examination.” Molecular Ecology 24 (7): 1558–71.
Hsu, Y-H, Mirre JP Simons, Julia
Schroeder, Antje Girndt, Isabel S Winney, Terry Burke, and Shinichi
Nakagawa. 2017. “Age-Dependent Trajectories Differ Between Within-Pair
and Extra-Pair Paternity Success.” Journal of Evolutionary
Biology 30 (5): 951–59.
Ihle, Malika, Bart
Kempenaers, and Wolfgang Forstmeier. 2015. “Fitness Benefits of Mate
Choice for Compatibility in a Socially Monogamous Species.” PLoS
Biology 13 (9): e1002248.
Kempenaers, Bart, and
Emmi Schlicht. 2010. “Extra-Pair Behaviour.” In Animal
Behaviour: Evolution and Mechanisms , 359–411. Springer.
Kidd, Lindall R, Ben C
Sheldon, Emily G Simmonds, and Ella F Cole. 2015. “Who Escapes
Detection? Quantifying the Causes and Consequences of Sampling Biases in
a Long-Term Field Study.” Journal of Animal Ecology 84 (6):
1520–29.
Kirkpatrick, Mark,
and NH Barton. 1997. “The Strength of Indirect Selection on Female
Mating Preferences.” Proceedings of the National Academy of
Sciences 94 (4): 1282–86.
Lebigre, Christophe,
Peter Arcese, and Jane M Reid. 2013. “Decomposing Variation in Male
Reproductive Success: Age-Specific Variances and Covariances Through
Extra-Pair and Within-Pair Reproduction.” Journal of Animal
Ecology 82 (4): 872–83.
Lifjeld, Jan T, and
Raleigh J Robertson. 1992. “Female Control of Extra-Pair Fertilization
in Tree Swallows.” Behavioural Ecology and Sociobiology 31 (2):
89–96.
Liker, András, Robert P Freckleton, and Tamás Székely. 2014. “Divorce
and Infidelity Are Associated with Skewed Adult Sex Ratios in
Birds.” Current Biology 24 (8): 880–84.
Maldonado-Chaparro,
Adriana A, Pierre-Olivier Montiglio, Wolfgang Forstmeier, Bart
Kempenaers, and Damien R Farine. 2018. “Linking the Fine-Scale Social
Environment to Mating Decisions: A Future Direction for the Study of
Extra-Pair Paternity.” Biological Reviews 93 (3): 1558–77.
Matysioková, B, and
V Remeš. 2013. “Faithful Females Receive More Help: The Extent of Male
Parental Care During Incubation in Relation to Extra-Pair Paternity in
Songbirds.” Journal of Evolutionary Biology 26 (1): 155–62.
Mingju, E, Ye Gong, Jiangping
Yu, Siyu Zhang, Qianxi Fan, Yunlei Jiang, and Haitao Wang. 2017. “Low
Level of Extra-Pair Paternity Between Nearest Neighbors Results from
Female Preference for High-Quality Males in the Yellow-Rumped Flycatcher
(Ficedula Zanthopygia).” Plos One 12 (3): e0172713.
Moiron, Maria, Anne
Charmantier, and Sandra Bouwhuis. 2022. “The Quantitative Genetics of
Fitness in a Wild Seabird.” Evolution .
Møller, Anders Pape. 2000.
“Male Parental Care, Female Reproductive Success, and Extrapair
Paternity.” Behavioural Ecology 11 (2): 161–68.
Nakagawa, S, DOS
Gillespie, BJ Hatchwell, and T Burke. 2007. “Predictable Males and
Unpredictable Females: Sex Difference in Repeatability of Parental Care
in a Wild Bird Population.” Journal of Evolutionary Biology 20
(5): 1674–81.
Nakagawa, Shinichi, Nancy
Ockendon, Duncan OS Gillespie, Ben J Hatchwell, and Terry Burke. 2007.
“Does the Badge of Status Influence Parental Care and Investment in
House Sparrows? An Experimental Test.” Oecologia 153 (3):
749–60.
Nakagawa, Shinichi, Julia
Schroeder, and Terry Burke. 2015. “Sugar-Free Extrapair Mating: A
Comment on Arct Et Al.” Behavioural Ecology 26 (4): 971–72.
Ockendon, Nancy,
Simon C Griffith, and Terry Burke. 2009. “Extrapair Paternity in an
Insular Population of House Sparrows After the Experimental Introduction
of Individuals from the Mainland.” Behavioural Ecology 20 (2):
305–12.
Oh, Kevin P, and Alexander
V Badyaev. 2010. “Structure of Social Networks in a Passerine Bird:
Consequences for Sexual Selection and the Evolution of Mating
Strategies.” The American Naturalist 176 (3): E80–89.
Petrie, Marion, and Bart
Kempenaers. 1998. “Extra-Pair Paternity in Birds: Explaining Variation
Between Species and Populations.” Trends in Ecology & Evolution13 (2): 52–58.
Poissant, Jocelyn, Alastair
J Wilson, and David W Coltman. 2010. “Sex-Specific Genetic Variance and
the Evolution of Sexual Dimorphism: A Systematic Review of Cross-Sex
Genetic Correlations.” Evolution: International Journal of
Organic Evolution 64 (1): 97–107.
Raj Pant, Sara, Maaike
A Versteegh, Martijn Hammers, Terry Burke, Hannah L Dugdale, David S
Richardson, and Jan Komdeur. 2022. “The Contribution of Extra-Pair
Paternity to the Variation in Lifetime and Age-Specific Male
Reproductive Success in a Socially Monogamous Species.”Evolution .
Reid, Jane M. 2012.
“Predicting Evolutionary Responses to Selection on Polyandry in the
Wild: Additive Genetic Covariances with Female Extra-Pair
Reproduction.” Proceedings of the Royal Society B: Biological
Sciences 279 (1747): 4652–60.
———. 2015. “What Can We
Really Say about Relatedness and Extrapair Paternity: A Comment on Arct
Et Al.” Behavioural Ecology 26 (4): 969–70.
Reid, Jane M, Peter
Arcese, Rebecca J Sardell, and Lukas F Keller. 2011. “Heritability of
Female Extra-Pair Paternity Rate in Song Sparrows (Melospiza Melodia).”Proceedings of the Royal Society B: Biological Sciences 278
(1708): 1114–20.
Reid, Jane M., and Matthew E.
Wolak. 2018. “Is There Indirect Selection on Female Extra-Pair
Reproduction Through Cross-Sex Genetic Correlations with Male
Reproductive Fitness?” Evolution Letters 2 (3): 159–68.
https://doi.org/https://doi.org/10.1002/evl3.56.
Reid, Jane M, and Matthew E
Wolak. 2018. “Is There Indirect Selection on Female Extra-Pair
Reproduction Through Cross-Sex Genetic Correlations with Male
Reproductive Fitness?” Evolution Letters 2 (3): 159–68.
Sánchez-Tójar,
Alfredo, Julia Schroeder, and Damien Roger Farine. 2018. “A Practical
Guide for Inferring Reliable Dominance Hierarchies and Estimating Their
Uncertainty.” Journal of Animal Ecology 87 (3): 594–608.
Sardell, Rebecca J, Peter
Arcese, Lukas F Keller, and Jane M Reid. 2012. “Are There Indirect
Fitness Benefits of Female Extra-Pair Reproduction? Lifetime
Reproductive Success of Within-Pair and Extra-Pair Offspring.”The American Naturalist 179 (6): 779–93.
Schlicht, Lotte, Mihai
Valcu, and Bart Kempenaers. 2015. “Male Extraterritorial Behaviour
Predicts Extrapair Paternity Pattern in Blue Tits, Cyanistes
Caeruleus.” Behavioural Ecology 26 (5): 1404–13.
Schmoll, Tim, Frank M
Schurr, Wolfgang Winkel, Joerg T Epplen, and Thomas Lubjuhn. 2009.
“Lifespan, Lifetime Reproductive Performance and Paternity Loss of
Within-Pair and Extra-Pair Offspring in the Coal Tit Periparus Ater.”Proceedings of the Royal Society B: Biological Sciences 276
(1655): 337–45.
Schroeder, Julia,
Terry Burke, M-E Mannarelli, DA Dawson, and Shinichi Nakagawa. 2012.
“Maternal Effects and Heritability of Annual Productivity.”Journal of Evolutionary Biology 25 (1): 149–56.
Schroeder, Julia,
Yu-Hsun Hsu, Isabel Winney, Mirre Simons, Shinichi Nakagawa, and Terry
Burke. 2016. “Predictably Philandering Females Prompt Poor Paternal
Provisioning.” The American Naturalist 188 (2): 219–30.
Schroeder, Julia,
Shinichi Nakagawa, Mark Rees, Maria-Elena Mannarelli, and Terry Burke.
2015. “Reduced Fitness in Progeny from Old Parents in a Natural
Population.” Proceedings of the National Academy of Sciences 112
(13): 4021–25.
Sheldon, Ben C. 1994.
“Male Phenotype, Fertility, and the Pursuit of Extra-Pair Copulations
by Female Birds.” Proceedings of the Royal Society of London.
Series B: Biological Sciences 257 (1348): 25–30.
Simons, Mirre JP, Isabel
Winney, Shinichi Nakagawa, Terry Burke, and Julia Schroeder. 2015.
“Limited Catching Bias in a Wild Population of Birds with Near-Complete
Census Information.” Ecology and Evolution 5 (16): 3500–3506.
Smith, Susan M. 1988.
“Extra-Pair Copulations in Black-Capped Chickadees: The Role of the
Female.” Behaviour 107 (1-2): 15–23.
Team, R Core et al. 2022. “R: A
Language and Environment for Statistical Computing.”
Vedder, Oscar. 2022.
“Experimental Extra-Pair Copulations Provide Proof of Concept for
Fertility Insurance in a Socially Monogamous Bird.” Proceedings
of the Royal Society B 289 (1976): 20220261.
Wang, Daiping, Wolfgang
Forstmeier, Katrin Martin, Alastair Wilson, and Bart Kempenaers. 2020.
“The Role of Genetic Constraints and Social Environment in Explaining
Female Extra-Pair Mating.” Evolution 74 (3): 544–58.
Westneat, David F,
Veronika Bókony, Terry Burke, Olivier Chastel, Henrik Jensen, Thomas
Kvalnes, Ádám Z Lendvai, et al. 2014. “Multiple Aspects of Plasticity
in Clutch Size Vary Among Populations of a Globally Distributed
Songbird.” Journal of Animal Ecology 83 (4): 876–87.
Westneat, David F, and
Paul W Sherman. 1997. “Density and Extra-Pair Fertilizations in Birds:
A Comparative Analysis.” Behavioural Ecology and Sociobiology 41
(4): 205–15.
Wetton, Jon H, and
David T Parkin. 1991. “An Association Between Fertility and Cuckoldry
in the House Sparrow, Passer Domesticus.” Proceedings of the
Royal Society of London. Series B: Biological Sciences 245 (1314):
227–33.
Yuta, Teru, Daisuke Nomi,
Malika Ihle, and Itsuro Koizumi. 2018. “Simulated Hatching Failure
Predicts Female Plasticity in Extra-Pair Behaviour over Successive
Broods.” Behavioural Ecology 29 (6): 1264–70.