Theory predicts that males should mate with as many females as possible and females with the best... more Theory predicts that males should mate with as many females as possible and females with the best male available; thus for both sexes, if nothing else is important, polygyny would be their preferred mating system. Monogamy constrains mate choice of both sexes, and molecular techniques, not surprisingly, revealed that in most socially monogamous species, some or most individuals indeed seek fertilizations outside their pair bond, called ‘extra-pair fertilizations,’ with frequencies of extra-pair young reaching 70% in some populations. Extra-pair copulations seem to be a strategy males use to increase their reproductive success, and females to obtain benefits. Numerous hypotheses try to explain variation in extra-pair paternity, but there is still no way to significantly predict whether it occurs in a species or not. We conclude that more attention should be given to the behavioral interactions between actors involved in the extra-pair paternity phenomenon.
Nest predation is considered a prime determinant of avian reproductive success (Ricklefs 1969, Ma... more Nest predation is considered a prime determinant of avian reproductive success (Ricklefs 1969, Martin 1992, 1993a,b) and natural selection should favour ha-bitat and nest site selection that reduces predation risk (Martin 1998). Habitat preferences for nest site loca-tion have ...
IntroductionThe differential allocation hypothesis (DAH) predicts that individuals should adjust ... more IntroductionThe differential allocation hypothesis (DAH) predicts that individuals should adjust their parental investment to their current mate’s quality. Although in principle the DAH holds for both sexes, male adjustment of parental investment has only been tested in a few experimental studies, revealing contradictory results. We conducted a field experiment to test whether male blue tits (Cyanistes caeruleus) allocate their parental effort in relation to female ornamentation (ultraviolet colouration of the crown), as predicted by the DAH.ResultsWe reduced the UV reflectance in a sample of females and compared parental care by their mates with that of males paired to sham-manipulated control females. As predicted by the DAH our results demonstrate that males paired with UV-reduced females invested less in feeding effort but did not defend the chicks less than males paired with control females.ConclusionsTo our knowledge, this is one of the first studies providing support for male...
Hoarding behaviour in birds is well known, but some aspects, like variation in hoarding among clo... more Hoarding behaviour in birds is well known, but some aspects, like variation in hoarding among closely related species, have received little attention. To explain this variation would help understand the evolution of hoarding and ecological aspects related to prey storing. Shrike species are ideal for this purpose, because hoarding is widespread in them but apparently varies too. Here we analyse impaling in one of these species, the lesser grey shrike, and try to unravel experimentally factors triggering and constraining such behaviour. Field data show that the lesser grey shrike seldom stores food under natural conditions. Longterm food surplus of valuable prey did not stimulate food storing. Hoarding was induced experimentally by offering birds a transient, spatially clumped food surplus. Repeated exposure of birds to experimental food surplus significantly increased the impaling rate. This suggests that low caching rates may be partly caused by lack of experience. Foraging success...
To nest in the same breeding area, territory or even nest-site in successive years may provide a ... more To nest in the same breeding area, territory or even nest-site in successive years may provide a possibility to look at mechanisms involved in breeding habitat selection and could also be an important tool for conservation, management and restoration attempts. In this study we examine site fidelity towards the breeding area as well as the nesting site in a dense and stable population of the Lesser Grey Shrike Lanius minor, a long-distance migrant and highly endangered passerine species, at its present northern border of its breeding range. Overall we recovered 48 out of 146 (32.8%) adults between 1996 and 2000. Recovery rate is significantly higher for males (31 of 77, 40.25%) than for females (17 of 69, 24.6%). Recovery rate of nestlings is much lower since only 51 of 790 (6.5%) were recovered and there is no significant sex difference. Furthermore, our results from 1989 to 2000 revealed that more than 30 % (97/319) of the nests were built in the same nest tree in successive years ...
While the function of ornaments shaped by sexual selection is to attract mates or drive off rival... more While the function of ornaments shaped by sexual selection is to attract mates or drive off rivals, these signals may also evolve through social selection, in which the social context affects the fitness of signallers and receivers. Classical 'mate choice' experiments often reveal preferences for ornaments, but few studies have considered whether these are strictly sexual or reflect general social preferences. Indeed, an alternative possibility is that ornaments evolve through 'non-sexual social selection' (hereafter 'social selection'). We examined the role of ornamentation (yellow ventral patch) and familiarity (individuals recognize group mates with which they have had previous interactions) on mate choice (opposite-sex stimuli preference) and social choice (same-sex stimuli preference) in both male and female white-eyed bulbuls (Pycnonotus xanthopygos). In the mate choice test, females preferred unfamiliar males with increased yellow. There were no biolog...
Several studies have investigated how individuals’ social status or behavioural and physiological... more Several studies have investigated how individuals’ social status or behavioural and physiological traits affect social organisation in group-living species, but the potential role of ornamental traits has been rarely studied. Here, we analysed initiator–follower interactions in relation to experimentally manipulated sexually selected ornaments in captive flocks of male bearded reedlings (Panurus biarmicus). We manipulated beard length or tail length on the most and least frequently followed individuals in unisex flocks and examined how trait manipulation affected social prestige (i.e. frequency of being followed) and centrality (i.e. frequency of following others) of these individuals. We found that prestige/centrality after manipulation was significantly positively associated with their before-manipulation measure, whereas body condition did not affect social position within flocks. Similarly, the manipulation of the ornamental traits had no significant effect on the social positions of the manipulated individuals. Both social prestige and centrality were significantly positively correlated with the frequency of allopreening interactions, but not related to fighting success, i.e. the number of won/total fights in the flocks. Our findings indicate that the level of influence male bearded reedlings exert on social cohesion is not related to ornamental traits, and birds are likely to have a consistent social position, at least in the short term, within their flocks.
Theory predicts that males should mate with as many females as possible and females with the best... more Theory predicts that males should mate with as many females as possible and females with the best male available; thus for both sexes, if nothing else is important, polygyny would be their preferred mating system. Monogamy constrains mate choice of both sexes, and molecular techniques, not surprisingly, revealed that in most socially monogamous species, some or most individuals indeed seek fertilizations outside their pair bond, called ‘extra-pair fertilizations,’ with frequencies of extra-pair young reaching 70% in some populations. Extra-pair copulations seem to be a strategy males use to increase their reproductive success, and females to obtain benefits. Numerous hypotheses try to explain variation in extra-pair paternity, but there is still no way to significantly predict whether it occurs in a species or not. We conclude that more attention should be given to the behavioral interactions between actors involved in the extra-pair paternity phenomenon.
Nest predation is considered a prime determinant of avian reproductive success (Ricklefs 1969, Ma... more Nest predation is considered a prime determinant of avian reproductive success (Ricklefs 1969, Martin 1992, 1993a,b) and natural selection should favour ha-bitat and nest site selection that reduces predation risk (Martin 1998). Habitat preferences for nest site loca-tion have ...
IntroductionThe differential allocation hypothesis (DAH) predicts that individuals should adjust ... more IntroductionThe differential allocation hypothesis (DAH) predicts that individuals should adjust their parental investment to their current mate’s quality. Although in principle the DAH holds for both sexes, male adjustment of parental investment has only been tested in a few experimental studies, revealing contradictory results. We conducted a field experiment to test whether male blue tits (Cyanistes caeruleus) allocate their parental effort in relation to female ornamentation (ultraviolet colouration of the crown), as predicted by the DAH.ResultsWe reduced the UV reflectance in a sample of females and compared parental care by their mates with that of males paired to sham-manipulated control females. As predicted by the DAH our results demonstrate that males paired with UV-reduced females invested less in feeding effort but did not defend the chicks less than males paired with control females.ConclusionsTo our knowledge, this is one of the first studies providing support for male...
Hoarding behaviour in birds is well known, but some aspects, like variation in hoarding among clo... more Hoarding behaviour in birds is well known, but some aspects, like variation in hoarding among closely related species, have received little attention. To explain this variation would help understand the evolution of hoarding and ecological aspects related to prey storing. Shrike species are ideal for this purpose, because hoarding is widespread in them but apparently varies too. Here we analyse impaling in one of these species, the lesser grey shrike, and try to unravel experimentally factors triggering and constraining such behaviour. Field data show that the lesser grey shrike seldom stores food under natural conditions. Longterm food surplus of valuable prey did not stimulate food storing. Hoarding was induced experimentally by offering birds a transient, spatially clumped food surplus. Repeated exposure of birds to experimental food surplus significantly increased the impaling rate. This suggests that low caching rates may be partly caused by lack of experience. Foraging success...
To nest in the same breeding area, territory or even nest-site in successive years may provide a ... more To nest in the same breeding area, territory or even nest-site in successive years may provide a possibility to look at mechanisms involved in breeding habitat selection and could also be an important tool for conservation, management and restoration attempts. In this study we examine site fidelity towards the breeding area as well as the nesting site in a dense and stable population of the Lesser Grey Shrike Lanius minor, a long-distance migrant and highly endangered passerine species, at its present northern border of its breeding range. Overall we recovered 48 out of 146 (32.8%) adults between 1996 and 2000. Recovery rate is significantly higher for males (31 of 77, 40.25%) than for females (17 of 69, 24.6%). Recovery rate of nestlings is much lower since only 51 of 790 (6.5%) were recovered and there is no significant sex difference. Furthermore, our results from 1989 to 2000 revealed that more than 30 % (97/319) of the nests were built in the same nest tree in successive years ...
While the function of ornaments shaped by sexual selection is to attract mates or drive off rival... more While the function of ornaments shaped by sexual selection is to attract mates or drive off rivals, these signals may also evolve through social selection, in which the social context affects the fitness of signallers and receivers. Classical 'mate choice' experiments often reveal preferences for ornaments, but few studies have considered whether these are strictly sexual or reflect general social preferences. Indeed, an alternative possibility is that ornaments evolve through 'non-sexual social selection' (hereafter 'social selection'). We examined the role of ornamentation (yellow ventral patch) and familiarity (individuals recognize group mates with which they have had previous interactions) on mate choice (opposite-sex stimuli preference) and social choice (same-sex stimuli preference) in both male and female white-eyed bulbuls (Pycnonotus xanthopygos). In the mate choice test, females preferred unfamiliar males with increased yellow. There were no biolog...
Several studies have investigated how individuals’ social status or behavioural and physiological... more Several studies have investigated how individuals’ social status or behavioural and physiological traits affect social organisation in group-living species, but the potential role of ornamental traits has been rarely studied. Here, we analysed initiator–follower interactions in relation to experimentally manipulated sexually selected ornaments in captive flocks of male bearded reedlings (Panurus biarmicus). We manipulated beard length or tail length on the most and least frequently followed individuals in unisex flocks and examined how trait manipulation affected social prestige (i.e. frequency of being followed) and centrality (i.e. frequency of following others) of these individuals. We found that prestige/centrality after manipulation was significantly positively associated with their before-manipulation measure, whereas body condition did not affect social position within flocks. Similarly, the manipulation of the ornamental traits had no significant effect on the social positions of the manipulated individuals. Both social prestige and centrality were significantly positively correlated with the frequency of allopreening interactions, but not related to fighting success, i.e. the number of won/total fights in the flocks. Our findings indicate that the level of influence male bearded reedlings exert on social cohesion is not related to ornamental traits, and birds are likely to have a consistent social position, at least in the short term, within their flocks.
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