An experimental increase in female mass during the fertile phase leads to higher levels of extra-pair paternity in pied flycatchers Ficedula hypoleuca
Female mass in most altricial birds reaches its maximum during breeding at egg laying, which coincides temporally with the fertile phase when extra-pair paternity (EPP) is determined. Higher mass at laying may have two different effects on EPP intensity. On the one hand, it would lead to increased wing loading (body mass/wing area), which may impair flight efficiency and thereby reduce female’s capacity to resist unwanted extra-pair male approaches (sexual conflict hypothesis). On the other hand, it would enhance female condition, favouring her capacity to evade mate guarding and to search for extra-pair mates (female choice hypothesis). In both cases, higher female mass at laying may lead to enhanced EPP. To test this prediction, we reduced nest building effort by adding a completely constructed nest in an experimental group of female pied flycatchers (Ficedula hypoleuca). Our treatment caused an increase in mass and thereby wing loading and this was translated into a significantly higher EPP in the manipulated group compared with the control group as expected. There was also a significant negative relationship between EPP and laying date and the extent of the white wing patch, an index of female dominance. More body reserves at laying mean not only a higher potential fecundity but a higher level of EPP as well. This interaction had not previously received due attention but should be considered in future studies of avian breeding strategies.
While most research has been focused on determining possible criteria for extra-pair mate choice by females, less effort has been made on establishing if female traits are related to EPP and its intensity. One such trait is mass at laying which attains its highest level for breeding females of altricial birds. Our study indicates that a higher mass during the fertile phase not only has implications for female fecundity and predation risk but also for EPP in the resulting brood as more mass means a higher EPP.
KeywordsExtra-pair paternity Wing loading Flight ability Nest building costs Female traits
This study is a contribution to the research developed at “Ventorrillo” field station. We are very grateful to D. Gil for improving the manuscript with his comments and to A. Machordom for helping at the molecular Lab of Museo Nacional de Ciencias Naturales. We are also grateful to the referees, whose feedback substantially improved the manuscript.
This study was financed by project CGL2013-48193-C3-3-P and CGL2017-83843-C2-1-P to JM from Spanish ‘Ministerio de Ciencia, Innovación y Universidades’. MP was supported by FPI grant from ‘Ministerio de Ciencia, Innovación y Universidades’. AC is supported by a postdoctoral fellowship from Fundación Ramón Areces.
Compliance with ethical standards
Conflict of interest
MP has received research FPI grant from ‘Ministerio de Ciencia, Innovación y Universidades’. AC declares that he has no conflict of interest. JM declares that he has no conflict of interest.
We were legally authorized to capture and handle pied flycatchers by Consejería de Medio Ambiente de Castilla y León (competent regional authority, protocol number EP/SG/706/2016, according to Royal Decree 53/2013), and by J. Donés, director of “Centro Montes de Valsaín”, to work in the study area. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. The experiments comply with current Spanish laws, and grant holder and field researchers were officially licensed for animal manipulation following current EU regulations on animal manipulation (authorization types C and D with reference numbers CAP-T-0123-15 and CAP-T-0121-15). The study was ethically approved by the Ethical Committee of the ‘Consejo Superior de Investigaciones Científicas’ (CSIC).
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