Abstract
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.
Highlights
Most female altricial birds show important changes in body mass in the course of the breeding cycle, increasing in mass before egg laying to a maximum just at laying, maintaining partly this high mass during incubation and losing it afterCommunicated by S
The experimental reduction of nest building effort resulted in a significant increase in female body mass and wing loading and a subsequent increase in the occurrence of extra-pair paternity (EPP) and EPY in the experimental group
We found that the probability of a nest containing EPP and the proportion of EPY were negatively related to the extent of the female white wing patch and laying date
Summary
Most female altricial birds show important changes in body mass in the course of the breeding cycle, increasing in mass before egg laying to a maximum just at laying, maintaining partly this high mass during incubation and losing it afterCommunicated by S. Most adaptive explanations propose that females may obtain indirect benefits from EP behaviour (Møller and Birkhead 1994; Forstmeier et al 2014), e.g. through improving offspring viability trough the choice of more attractive extra-pair sires Under this point of view, the outcome of EPP depends on the interplay of two factors. On the female’s ability to evade mate guarding tactics (Alatalo et al 1987), which may depend on her size, age (Bouwman and Komdeur 2005; Ramos et al 2014), social dominance expressed through ornaments (Plaza et al 2018) or flight ability (Stutchbury and Robertson 1987) In this respect, a high female body condition would favour the capacity of females to evade the attention of their mates and fly in search of extra-pair mates, roaming more through the breeding area
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