Sexual selection in the barn swallow Hirundo rustica. VI. Aerodynamic adaptations

Secondary sexual characters are assumed to be costly to produce and maintain, and this will select for morphological modifications that reduce the magnitude of such costs. Here we test whether a feather ornament, the sexually exaggerated outermost tail feathers of male barn swallows Hirundo rustica, a trait currently subject to a directional female mate preference, and other aspects of the morphology used for flight have been modified to increase aerodynamic performance. This was done by making comparisons among sexes within populations, among individuals varying in tail length within populations, and among populations from different parts of Europe. Male barn swallows experienced reduced drag from their elongated tail feathers by morphological modifications of the ornamental feathers as compared to females. Morphological features of the outermost tail feathers were unrelated to tail length in both males and females within populations. Wing and tail morphology (length of central tail feathers and wings, wing span, wing area, wing loading, and aspect ratio) was modified in males compared to females. Barn swallows with long tails had morphological tail and wing modifications that reduced the cost of a large ornament, and similar modifications were seen among populations. The costs of the exaggerated secondary sexual character were therefore reduced by the presence of cost-reducing morphological modifications. The assumptions of reliable signalling theory, that signals should be costly, but more so to low than to high quality individuals, were not violated because long-tailed male barn swallows had the largest cost-reducing morphological characters.     

Phenotypic quality and molt in the barn swallow, Hirundo rustica

Phenotypic quality may determine the development and expressionof secondary sexual characters. We studied the relationshipbetween molt and several measures of phenotypic quality in thesexually size-dimorphic barn swallow (Hirundo rustica) in itswinter quarters in Namibia. Males were in a more advanced stageof molt than females and juveniles, and the speed of molt asdetermined from the residual of the regression of the size ofthe gap in wings caused by missing and growing feathers on wingmolt score (residual wing raggedness) was also higher in malesthan in females and juveniles. Male barn swallows with longand symmetric tail feathers had a more advanced stage of moltand molted at a higher speed than males with short and asymmetrictails. Long-tailed females had a delayed molt, and females withasymmetric tails had less advanced molt and lower rates of feathergrowth than females with symmetric tails. Molt of secondariesin juveniles also appeared to be less advanced if they had longtails. Adult barn swallows molted their tail feathers in anirregular sequence with the longest, outermost tail featherusually replaced before the second or the third outermost feathers.Good body condition was positively associated with a high moltscore for some feather tracts and a rapid wing molt in adultfemales and tail molt in juveniles. Mallophaga were only weaklynegatively associated with primary and secondary molt scorein adult females and speed of wing molt in adult males. In conclusion,phenotypic quality of adult male barn swallows as reflectedby the expression of their secondary sexual character duringthe previous molt reliably reflected stage and speed of currentmolt.     

Experimental manipulation of tail length in female barn swallows (Hirundo rustica) affects their future reproductive success

Previous studies have shown no significant effect of experimentaltail length manipulation in female barn swallows (Hirundo rustica)at the beginning of a breeding season on reproductive successor behavior during that breeding season. In the present study,we investigate if tail length manipulation had any effect onreproductive performance the following year, the so-called long-termeffect, in contrast to the short-term effects already studied.We found that females with experimentally elongated externaltail feathers at the beginning of a breeding season producedless offspring during the breeding season the following yearthan did females with shortened or unmanipulated tails. Theseresults suggest that tail elongation caused flight deficienciesthat deteriorated the condition of females and eventually reducedreproductive success. The finding of long-term effects but nosignificant short-term effects for female tail elongation suggeststhat female barn swallows have the ability to adjust immediateparental investment. Detrimental effects of long tails in femalesin terms of decreased reproductive success might explain whyfemale tails are not as long as those of males. Finally, femalesmated to long-tailed (sexually attractive) males decreased theirreproductive success the following year more than did femalesmated to short-tailed males, possibly owing to differentialparental effort causing a deterioration of their condition.     

SEXUAL SELECTION IN THE BARN SWALLOW HIRUNDO RUSTICA. III. FEMALE TAIL ORNAMENTS

Male secondary sexual characters are often expressed in females, and the maintenance of the character in females can be due to either direct selection on females favoring the maintenance of the trait, or a correlated response to selection in males. Here I report on determinants of and phenotypic selection on tail length of female barn swallows Hirundo rustica. The homologous trait in males is under strong directional sexual selection. Female tail length was positively associated with several reproductive parameters including total seasonal reproductive success, even when controlling for year and age effects. A change in female tail length from one year to another was often associated with a change in the reproductive parameters correlated with absolute tail length. There was little evidence for an association between female tail length and the duration of the incubation period (only females incubate) and absolute and relative female provisioning rates of offspring, and subsequent size of offspring. Tail length of female barn swallows was positively correlated with that of their mates. Female tail length was a heritable trait as determined from regression of the tail trait of offspring on that of their mother and their father, and there was a positive genetic correlation between the tail trait in males and females. In conclusion, female tail length reliably reflects female reproductive potential, and the trait appears to be under directional selection, which may result in an evolutionary response to selection because of the heritability of the tail trait.     

Aerodynamic costs of long tails in male barn swallows Hirundo rustica and the evolution of sexual size dimorphism

Exaggerated tail feathers of birds constitute a standard exampleof evolution of extravagant characters due to sexual selection.Such secondary sexual traits are assumed to be costly to produceand maintain, and they usually are accompanied by morphologicaladaptations that tend to reduce their costs. The aerodynamiccosts for male barn swallows Hirundo rustica of having longtails were quantified using aerodynamics theory applied to morphologicaldata from seven European populations. Latitudinal differencesin tail length were positively correlated with differences inflight costs predicted by aerodynamics theory. A positive relationshipbetween aerodynamic costs of long tails and the degree of sexualsize dimorphism was found among populations. Latitudinal differencesin foraging costs may result in tail length being relativelysimilar in males and females in southern populations, whereasthe low foraging costs for males in northern populations mayallow them to cope with higher aerodynamic costs, giving riseto large sexual size dimorphism. Enlargement of wingspan inmales can alleviate but not eliminate the costs of tail exaggeration,and therefore differences in aerodynamic costs of male ornamentswere maintained among populations. Sexual size dimorphism in thebarn swallow arises as a consequence of latitudinal differencesin the advantages of sexual selection for males and the costsof long tails for males and females.     

DIFFERENTIAL COSTS OF A SECONDARY SEXUAL CHARACTER: AN EXPERIMENTAL TEST OF THE HANDICAP PRINCIPLE

The evolution of reliable signaling can be explained by the handicap principle, which assumes that (1) the cost of a signal guarantees its reliability, and (2) cheating is prevented because the cost of a unit of display is greater for low-quality than for high-quality individuals. A test of these two assumptions was performed using manipulations of the length of the outermost tail feathers of male barn swallows Hirundo rustica, a trait currently subject to a directional female mate preference. We found that survival decreased with tail elongation and increased with tail shortening of males, supporting the assumption that the secondary sexual character is costly. Naturally long-tailed males were better able to survive with an elongated tail, whereas naturally short-tailed males improved their survival following tail shortening. This observation supports the second assumption of a differential cost of a signal. One mechanism imposing differential costs on sexually signaling barn swallows is foraging. Males with elongated tails captured smaller, less profitable Diptera, whereas males with shortened tails captured large, profitable prey items. The conditions for reliable sexual signaling by the tail ornament of male barn swallows are thus fulfilled.     

Population differences in density and resource allocation of ornamental tail feathers in the barn swallow

Many organisms show well‐defined latitudinal clines in morphology, which appear to be caused by spatially varying natural selection, resulting in different optimal phenotypes in each location. Such spatial variability raises an interesting question, with different prospects for the action of sexual selection on characters that have a dual purpose, such as locomotion and sexual attraction. The outermost tail feathers of barn swallows (Hirundo rustica) represent one such character, and their evolution has been a classic model subject to intense debate. In the present study, we examined individuals from four European populations to analyze geographical variation in the length and mass of tail feathers in relation to body size and wing size. Tail feather length differed between sexes and populations, and such variation was a result of the effects of natural selection, acting through differences in body size and wing size, as well as the effects of sexual selection that favours longer tails. The extra enlargement of the tail promoted by sexual selection (i.e. beyond the natural selection optimum) could be achieved by increasing investment in ornaments, and by modifying feather structure to produce longer feathers of lower density. These two separate processes accounting for the production of longer and more costly tail feathers and less dense feathers, respectively, are consistent with the hypothesis that both Zahavian and Fisherian mechanisms may be involved in the evolution of the long tails of male barn swallows. We hypothesize that the strength of sexual selection increases with latitude because of the need for rapid mating as a result of the short duration of the breeding season at high latitudes. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 925–936.     

Sexual selection in the monogamous barn swallow (Hirundo rustica). II. Mechanisms of sexual selection

Mechanisms of sexual selection in the monogamous, sexually dimorphic barn swallow (Hirundo rustica) were studied during a seven-year period. First, the sex ratio of reproducing adults was male-biased, and mated males had significantly longer tail ornaments than unmated males. Secondly, some of the unmated individuals later committed infanticide and became mated with the mother of the killed brood. Fathers of killed broods had significantly shorter tails than other males, and there was a tendency for infanticidal males to have longer tail ornaments than other unmated males. Thirdly, long-tailed male barn swallows were more successful in acquiring extra-pair copulations than other males, and females involved in extra-pair copulations, as compared to females not involved in such copulations, had mates with shorter tail ornaments. Fourthly, male barn swallows having long tails as compared to short-tailed males acquired mates in better body condition. Females mated to long-tailed males reproduced earlier, laid more eggs and were more likely to have two clutches than were females mated to short-tailed males. Finally, females mated to long-tailed males put more effort into reproduction than did other females, as evidenced by their relatively larger contribution to feeding of offspring. Thus, at least five different components of sexual selection affected male reproductive success. Selection arising from differential success during extra-pair copulations, differential reproductive success and differential male reproductive effort thus accounted for most of the selection on tail ornaments in male barn swallows.     

Sexual selection and tail streamers in the barn swallow

The functional significance of elongated, narrow tips of the tail feathers of certain birds, so-called tail streamers, has recently been discussed from an aerodynamic point of view, and the effects of sexual selection on such traits have been questioned. We review our long-term field studies using observational and experimental approaches to investigate natural and sexual selection in the barn swallow, Hirundo rustica, which has sexually size-dimorphic outermost tail feathers. Experimental manipulation of the length of the outermost tail feathers has demonstrated sexual selection advantages of tail elongation and disadvantages of tail shortening, with opposite effects for natural selection in terms of foraging efficiency, haematocrit and survival. These findings are contrary to the prediction of a general deterioration from both shortening and elongation, if the tail trait was determined solely by its effects on aerodynamic efficiency and flight manoeuvrability. Patterns of sexual selection in manipulated birds conform with patterns in unmanipulated birds, and selection differentials for different components of sexual selection in manipulated birds are strongly positively correlated with differentials in unmanipulated birds. Age and sex differences in tail length, and geographical patterns of sexual size dimorphism, are also consistent with sexual selection theory, but inconsistent with a purely natural selection advantage of long outermost tail feathers in male barn swallows.     

Fork tails evolved differently in swallows and swifts

Whether sexual or viability selection drives the evolution of ornamental traits is often unclear because current function does not clarify evolutionary history, particularly when the ornamentation is a modified version of the functional traits. Here, using a phylogenetic comparative approach, we studied how deeply forked tails—a classic example of sexually selected traits that might also be a mechanical device for enhancing aerodynamic ability—evolved in two groups of aerial foragers, swallows (family: Hirundinidae) and swifts (family: Apodidae). Although apparent fork depth, the target of sexual selection, increases with increasing outermost tail feather length, fork depth can also increase with decreasing central tail feather length, which impairs the lift generated by the tail. Thus, we predicted that sexual selection, but not viability selection, should favour the evolution of short central tail feathers in species with deeply forked tails, particularly in swifts, which are less reliant on the lift generated by their tail than in swallows. We found support for these predictions because central tail feather length decreased with increasing tail fork depth, particularly in swifts. Instead, the increase in outermost tail feather length per unit tail fork depth was higher in swallows than in swifts, indicating that a similar sexual ornamentation (i.e. forked tails) differently evolved in these two aerial insectivores perhaps due to the differential cost of ornamentation. We also found support for an optical illusion that changes the relative importance of central and outermost tail feather length in sexual selection.     

SEXUAL SELECTION IN THE BARN SWALLOW (HIRUNDO RUSTICA). IV. PATTERNS OF FLUCTUATING ASYMMETRY AND SELECTION AGAINST ASYMMETRY

The patterns of variation in fluctuating asymmetry were studied in four morphological characters of the barn swallow Hirundo rustica. The level of absolute and relative asymmetry was larger in the secondary sexual character “outer tail length” than in three nonsexual morphological traits (wing, central tail, and tarsus length). The extent of individual asymmetry in outer tail length was negatively correlated with tail-ornament size, whereas the relationship between asymmetry of all other morphological characters and their size was flat or U-shaped. Asymmetry in outer tail length was unrelated to asymmetry in other morphological characters, whereas asymmetries in the length of wing, central tail, and tarsus were positively correlated. Male bam swallows exhibited larger asymmetry in outer tail length than females. Asymmetry of most morphological traits exhibited intermediate repeatabilities between years, with the exception of male and female outer tail length, which were highly repeatable. Tail asymmetry of offspring weakly, though significantly, resembled that of their parents. Asymmetry in wing and outer tail length was also significantly related to several fitness components. Male barn swallows that acquired a mate were less asymmetric in wing and outer tail length than unmated males. Females with more asymmetrical tails laid eggs significantly later. Annual reproductive success was unrelated to fluctuating asymmetry. Male barn swallows that survived were less asymmetric in wing and outer tail length than nonsurvivors, whereas female survivors were less asymmetric in outer tail length than nonsurvivors. These results suggest that levels of fluctuating asymmetry in barn swallows are associated with differences in fitness.     

AN EXPERIMENTAL STUDY OF PATERNITY AND TAIL ORNAMENTATION IN THE BARN SWALLOW (HIRUNDO RUSTICA)

Previous studies of the socially monogamous barn swallow (Hirundo rustica) have shown that males that most frequently engage in extrapair copulations and whose partners are least involved in copulations with extrapair males are those with long tail ornaments. In this study, through the use of three highly polymorphic microsatellite markers, we analyze the relationships between length of tail ornaments of male barn swallows and proportion of nestlings fathered in own broods, number of offspring fathered in broods of other pairs, and total number of offspring fathered, using both a correlational and an experimental approach. Consistent with our predictions, we show that males with either naturally long or experimentally elongated tails have higher paternity (proportion of biological offspring in own broods), and they produce more biological offspring during the whole breeding season than males with naturally short or experimentally shortened tails. Males with naturally long tails also had more offspring in extrapair broods than short-tailed males, but the effect of tail manipulation on the number of offspring fathered in extrapair broods, although being in the predicted direction, was not statistically significant. Cuckolded males that did not fertilize extrapair females had smaller postmanipulation tail length than cuckolders. We conclude that there is a causal, positive relationship between male tail length and paternity. Since female barn swallows have extensive control over copulation partners and heritability of tail length is high, this study shows that female choice is a component of selection for larger male ornaments. Benefits from extrapair fertilizations to females may arise because they acquire “good” genes for sexual attractiveness or high viability for their offspring.     

Effects of experimental tail shortening on the phenotypic condition of barn swallows Hirundo rustica: implications for tail‐length evolution

Some studies have suggested that tail streamers in the barn swallow Hirundo rustica may have been elongated 10–12 mm by sexual selection, but according to other studies, the length of these feathers is at the aerodynamic optimum or very close to it. To shed light on this issue, outermost tail feathers were experimentally shortened in male and female barn swallows by 1, 11 or 21 mm. Changes in four physiological parameters commonly used to estimate phenotypic condition in birds (weight, erythrocyte sedimentation rate, blood leukocyte concentration and heterophil/lymphocyte ratio) were checked one month later. Health improved (blood leukocyte concentration decreased) in the group of birds with tails shortened by 11 mm (both males and females), but body condition deteriorated (weight decreased) compared to the other two experimental groups. There was no significant effect of tail‐length manipulation on the other two physiological parameters. These contradictory results suggest trade‐offs between components of phenotypic condition. Possible negative relationships between condition‐related traits imply that using one or very few physiological parameters to estimate phenotypic condition might not be appropriate. The most plausible explanation for the turning point in phenotypic condition when streamers were shortened by 11 mm is that these feathers are 7–15 mm longer than the aerodynamic optimum in both sexes. Therefore, our results are consistent with the hypothesis that tail streamers have been elongated 10–12 mm by sexual selection. This conclusion disagrees with a previous study on the effect of experimental tail shortening on haematocrit, but the complexity of interpreting changes in haematocrit might account for this discrepancy.     

Experimental manipulation of female tail length did not cause differential allocation by males in the barn swallow

The evolution and maintenance of female ornamentation has attracted increasing attention, because the previous explanation, that is a non‐functional copy of functional male ornamentation, seems insufficient to explain female ornamentation. A post‐mating sexual selection, differential allocation, may be more common than pre‐mating sexual selection, but few studies have investigated differential allocation by males. Here, we studied differential allocation of incubation investment by male barn swallows Hirundo rustica, a model species for the study of sexual selection, because our previous correlative study demonstrated a positive relationship between female tail length and male incubation investment. We manipulated the length of the outermost tail feathers in females after clutch completion and examined whether males adjust incubation investment according to female ornamentation. Because extra‐pair paternity is virtually absent in the study population, we were able to study differential allocation based on the tradeoff between current and future reproductive investments, rather than the tradeoff between current paternal investment and additional mating effort. The experimental treatment had no significant effect on male nest attentiveness, whereas female tail length before manipulation predicted male nest attentiveness. The observed pattern is consistent with differential access; that is, well‐ornamented individuals have greater access to mates with high reproductive (parental) ability, rather than differential allocation during incubation. Alternatively, males can directly assess eggs in their nests, and thus, as seen in other species, males might adjust their incubation investment based on the egg characteristics of long‐tailed females.     

Sexual Dimorphism and Population Differences in Structural Properties of Barn Swallow (Hirundo rustica) Wing and Tail Feathers

Sexual selection and aerodynamic forces affecting structural properties of the flight feathers of birds are poorly understood. Here, we compared the structural features of the innermost primary wing feather (P1) and the sexually dimorphic outermost (Ta6) and monomorphic second outermost (Ta5) tail feathers of barn swallows (Hirundo rustica) from a Romanian population to investigate how sexual selection and resistance to aerodynamic forces affect structural differences among these feathers. Furthermore, we compared structural properties of Ta6 of barn swallows from six European populations. Finally, we determined the relationship between feather growth bars width (GBW) and the structural properties of tail feathers. The structure of P1 indicates strong resistance against aerodynamic forces, while the narrow rachis, low vane density and low bending stiffness of tail feathers suggest reduced resistance against airflow. The highly elongated Ta6 is characterized by structural modifications such as large rachis width and increased barbule density in relation to the less elongated Ta5, which can be explained by increased length and/or high aerodynamic forces acting at the leading tail edge. However, these changes in Ta6 structure do not allow for full compensation of elongation, as reflected by the reduced bending stiffness of Ta6. Ta6 elongation in males resulted in feathers with reduced resistance, as shown by the low barb density and reduced bending stiffness compared to females. The inconsistency in sexual dimorphism and in change in quality traits of Ta6 among six European populations shows that multiple factors may contribute to shaping population differences. In general, the difference in quality traits between tail feathers cannot be explained by the GBW of feathers. Our results show that the material and structural properties of wing and tail feathers of barn swallows change as a result of aerodynamic forces and sexual selection, although the result of these changes can be contrasting.     

Sexual selection for white tail spots in the barn swallow in relation to habitat choice by feather lice

Many bird species have white spots in their tails or wing feathers, and such characters have been hypothesized to be either reliable signals (handicaps) or amplifiers that facilitate the message of a signal. In barn swallows, Hirundo rustica, the size of the white spots in the tail feathers is sexually dimorphic and positively correlated with feather length. We tested whether such spots act as handicaps or amplifiers. These white spots affect sexual selection in barn swallows, as shown by an experiment in which we randomly subjected males to (1) a considerable reduction of the size of all the spots by the use of a black permanent marker pen, (2) a small reduction of the size of the spots, or (3) no reduction. There was a positive association between spot size and the number of offspring produced per season. The white tail spots were preferred by feather-eating Mallophaga as a feeding site: holes made by Mallophaga were more abundant in the white spots than expected by chance. A habitat choice experiment with Mallophaga on barn swallow tail feathers revealed that they preferred white spots over black parts of the tail feathers. We therefore expected long-tailed male barn swallows to have more Mallophaga than short-tailed males. However, the opposite relationship was observed, indicating that long-tailed males may reliably signal their quality by the presence of large white tail spots without parasite damage. Thus white tail spots in barn swallows appear to be a reliable signal of phenotypic quality. Copyright 1999 The Association for the Study of Animal Behaviour.     

The maintenance of phenotypic divergence through sexual selection: An experimental study in barn swallows Hirundo rustica

Previous studies have shown that sexual signals can rapidly diverge among closely related species. However, we lack experimental studies to demonstrate that differences in trait‐associated reproductive performance maintain sexual trait differences between closely related populations, in support for a role of sexual selection in speciation. Populations of Northern Hemisphere distributed barn swallows Hirundo rustica are closely related, yet differ in two plumage‐based traits: ventral color and length of the outermost tail feathers (streamers). Here we provide experimental evidence that manipulations of these traits result in different reproductive consequences in two subspecies of barn swallow: (H. r. erythrogaster in North America and H. r. transitiva in the East Mediterranean). Experimental results in Colorado, USA, demonstrate that males with (1) darkened ventral coloration and (2) shortened streamers gained paternity between two successive reproductive bouts. In contrast, exaggeration of both traits improved reproductive performance within H. r. transitiva in Israel: males with a combination treatment of darkened ventral coloration and elongated streamers gained paternity between two successive reproductive bouts. Collectively, these experimental results fill an important gap in our understanding for how divergent sexual selection maintains phenotype differentiation in closely related populations, an important aspect of the speciation process.     

Senescence in a short-lived migratory bird: age-dependent morphology, migration, reproduction and parasitism

1. Senescence reflects age-dependent changes in residual reproductive value. Annual survival rates of the barn swallow Hirundo rustica L. increased from 1- to 2-year-old individuals, but decreased among 5 years old or older individuals. Estimates of age-dependent reproductive value showed a similar pattern.
2. Longitudinal data from two long-term population studies were used to test whether a number of different measures of performance (condition-dependent morphological traits, migratory performance, reproductive success, intensity of parasitism) changed among individuals when reaching old age.
3. The length of the outermost tail feathers (a secondary sexual character) decreased among old individuals, while two measures of individual developmental instability increased with age. Migratory performance decreased in old barn swallows as reflected by a delay in spring arrival at the breeding grounds. Reproductive performance measured as seasonal reproductive success decreased with age. The intensity of infestations with an haematophagous mite and a mallophagous ectoparasite increased among old barn swallows.
4. These results suggest that the condition-dependent secondary sexual character, developmental stability, and measures of migratory and reproductive performance deteriorated, and the frequency of parasitism increased among old individuals. Ageing was thus associated with a general deterioration of performance.     

FEMALE REPRODUCTIVE EFFORT DEPENDS ON THE DEGREE OF ORNAMENTATION OF THEIR MATES

Sexual selection theory assumes that secondary sexual characters do not influence female reproductive effort. Female animals may invest relatively more in reproduction if they acquire mates of high phenotypic quality, because offspring sired by preferred males may be relatively more viable than offspring sired by less preferred males. Here we report for the first time in a field study that females of the monogamous barn swallow Hirundo rustica adjust their reproductive effort to the attractiveness of their mates. Experimental manipulation of male tail length, which is a trait currently subject to a directional female mating preference, affected the reproductive effort by females in single broods as well as their decision on the seasonal number of clutches. These results, and those of previous experiments, demonstrate that female barn swallows assess the quality of their mates throughout the reproductive season and adjust their reproductive decisions accordingly. This result has important implications for the theory of sexual selection and for the possibility of testing current models of female mate preferences, because the viability of offspring will be confounded by differential reproductive effort.     

Morphological and genetic predictors of parental care in the North American barn swallow Hirundo rustica erythrogaster

Sexually dimorphic traits often signal the fitness benefits an individual can provide to potential mates. In species with altricial young, these signals may also predict the level of parental care an individual is expected to provide to shared offspring. In this study, we tested three hypotheses that traditionally relate sexually dimorphic traits to parental care in two populations of North American barn swallows Hirundo rustica erythrogaster. The good parent hypothesis predicts a positive relationship between an individual's ornamentation and his or her care whereas the differential allocation (more care given by individuals when paired to high quality mates) and reproductive compensation (more care given by individuals when paired to low quality mates) hypotheses predict that an individual's level of parental investment is relative to the quality of their mate. Male and female North American barn swallows have colorful ventral feathers and elongated tail streamers, but there is evidence that ventral color, not tail streamer length, predicts measures of seasonal reproductive success. Accounting for the positive correlation between within‐pair feeding rates and other potentially confounding variables in all of our models, we found no support for the good parent hypothesis because in both males and females, traits shown to be under sexual selection did not predict feeding rates in either sex. However, our data reveal that male coloration, and not streamer length, predicted a female's provisioning rate to shared offspring (females fed more when paired with darker individuals) in two separate populations, supporting the differential allocation, but not the reproductive compensation hypothesis. Because genetic traits have also been shown to affect parental investment, we evaluated this variable as well and found that a male's paternity did not have significant effects on either male or female feeding rates. Overall, our results suggest that females do not pair with darker males in order to gain direct benefits in terms of his expected levels of parental care to shared offspring, but do themselves invest greater levels of care when paired to darker males. Further, our results are consistent with previous studies which suggest that ventral feather color, not streamer length, is a target of sexual selection in North American populations of barn swallow because females invested more in their offspring when paired to darker mates.