Emi Arai

Mating Advantage of Multiple Male Ornaments in the Barn Swallow Hirundo Rustica Gutturalis

Abstract The maintenance of multiple ornaments by animals can be explained when those multiple ornaments are sexually selected. However, there have been only a few studies of sexual selection on multiple ornaments. We investigated sexual selection on two ornaments, plumage coloration and white spots in the tail, in a population of Barn Swallows Hirundo rustica gutturalis in Japan. There was sexual dimorphism in throat coloration and in the size of the white spots in the tail. Males with a less saturated (colourful) throat and larger white spots in the tail bred earlier than others, indicating a mating advantage for these males. These trends are what would be expected if these ornaments were indeed sexually selected.

Female mate choice based on territory quality in barn swallows

Female mate choice based on territory quality is difficult to study because territories often contain many resources, which are difficult to quantify. Here, using the barn swallow (Hirundo rustica gutturalis) breeding at an outdoor breeding site in Japan, where each male defends only a small territory containing old nests, we studied whether females choose social mates based on territory quality. Since the territories of this species contain few other resources, territory quality can easily be assessed by quantifying old nests in the territory. We made the following four observations: (1) male swallows displayed old nests in their territories to females; (2) the old nests used for the first clutch were less broken than the other old nests within the same territory; (3) territory quality, defined by the number of old nests weighted by the intactness of each old nest, predicted the productivity of the territory; and (4) males with better territories paired with females earlier, and hence bred earlier, than those with inferior territories. The relationships remained significant even after controlling for male morphological traits. Based on these results, we can infer that female swallows choose their mates based, in part, on territory quality.

Methods for correcting plumage color fading in the Barn Swallow

Abstract It is necessary to correct plumage color fading when comparing the plumage coloration of birds captured at different times during the breeding season. We proposed two methods for correcting plumage color fading and compared them using the throat feathers of the Barn Swallow (Hirundo rustica gutturalis). One method uses the color shift of feathers on live birds during the same breeding season (the field method). The other method uses longitudinal color measurements of feathers placed on the open ground (the experimental method). This method has an advantage of not capturing the birds twice. The field and experimental methods estimated similar rates of fading of hue and brightness. Saturation was predicted to fade with time in the experimental method, which is unrealistic because there was no effect of time on saturation in live birds. Using the field method, we derived an equation for correcting plumage color fading in Barn Swallows. When assessing changes in plumage color, the field method should be used whenever possible since this method estimates plumage color fading in live birds.

Low Level of Extra-Pair Paternity in a Population of the Barn Swallow Hirundo Rustica Gutturalis

Abstract On average, male birds other than social father sire more than 10% of all offspring. Levels of extra-pair paternity below 5% of offspring are rarely found and are now considered worthy of explanation in monogamous birds. We recorded the lowest levels of paternity loss ever reported in a population of Barn Swallows Hirundo rustica. The levels of extra-pair paternity were below 5% of offspring (7/243 in 2005 and 1/53 in 2006). We discuss our results in relation to the density-dependence of extra-pair paternity.

Divorce and asynchronous arrival in Barn Swallows Hirundo rustica

Capsule Divorce in Barn Swallows could be explained by the mechanism of asynchronous arrival of mates.

Colourful males hold high quality territories but exhibit reduced paternal care in barn swallows

The European barn swallow, Hirundo rustica rustica, is a model system of female mate choice for indirect benefits. Its long tail, which is the target of female mate choice, is positively related to the genetic quality of males, whereas direct benefits in terms of territory quality and paternal care are unimportant in the choice of long-tailed males. However, the situation may differ in other subspecies where male ornaments other than tail length are elaborate and appear to be the main target of female choice. Here we studied whether throat colouration, a sexually selected trait, provides direct benefits in terms of territory quality and parental care in a population of Japanese barn swallows, H. r. gutturalis, which have short tails and large throat patches. We compared dyads of males occupying neighbouring territories to study the relationship between male ornamentation and territory quality in our sparse population. Males with higher quality territories had more colourful throat patches than males with lower quality territories, indicating a positive relationship between male throat colouration and the quality of their territory. In contrast, male feeding rate decreased with increasing colourfulness of male throat patch without confounding with female feeding rate. These results are consistent with previous studies showing a positive association between plumage colouration and testosterone levels. The trade-off between the two direct benefits of mate choice, i.e., territory quality and paternal care, can explain sexual selection for colourful throat patches rather than long tails in our sparse outdoor population, a typical breeding habitat in Japan, whereas it predicts a reverse pattern in dense indoor populations as found in Europe.

Differential Female Access to Males with Large Throat Patches in the Asian Barn Swallow Hirundo rustica gutturalis

Intersexual selection results from several processes, such as differential allocation and differential access, in addition to mating skews by mate choice. These processes can contribute to the evolution, maintenance, and geographic differentiation of male ornamentation, although the importance of these processes in male ornamentation remains poorly understood. The Asian barn swallow Hirundo rustica gutturalis is a socially monogamous songbird that exhibits biparental care and has red throat patches twice as large as those of the nominate H. r. rustica. Our previous study showed that females paired to males with large throat patches had higher reproductive output in terms of multiple broods, although the underlying process resulting in selection for a large throat patch remained unclear. In the present study, we analyzed differential female access to males with large throat patches in H. r. gutturalis. We observed that males with large throat patches acquired older and fatter females, independent of male age class. In addition, females that mated to males with large throat patches returned to the study site more compared with others, indicating the high viability of these females, supporting differential access but not differential allocation. No other measures of male ornaments (i.e., tail length, white tail spots, or throat color value) were linked to female qualities. As these female qualities were associated with female reproductive output, males with large throat patches would obtain reproductive advantages, as found in our previous study. The current findings suggest the importance of differential access for the evolution of a large throat patch in this subspecies.

High Incubation Investment of Females Paired to Attractive Males in Barn Swallows

Abstract Differential parental investment is the sexual selection process in which females that have acquired an attractive male invest relatively more in his offspring than females that are paired to an unattractive male. However, it is often difficult to distinguish between differential parental investment and compensation for a decrease in parental investment by an attractive mate. Using Barn Swallows Hirundo rustica gutturalis, in which males rarely participate in incubation, we investigated differential incubation investment of females. We made the following four observations: (1) Females participate in 94% of total nest attentiveness (time that eggs were incubated). (2) Female nest attentiveness was positively correlated with the ornamentation of their mates, the size of white spots in the tail, which is a measure of male attractiveness in this population. (3) Male nest attentiveness was not related to male ornaments. (4) Total nest attentiveness was positively correlated with the size of white spots in the tail. These results are consistent with differential parental investment, but not with compensation for a decrease in parental investment by a mate. Therefore, we conclude that female Barn Swallows that have acquired an attractive male invest differentially in incubation.

Male viability is positively related to multiple male ornaments in Asian Barn Swallows

AbstractThe European Barn Swallow Hirundo rustica rustica is a model system for studying female mate choice for indirect benefits, as the long tail of males, the target of female mate choice, is positively related to male viability. However, situations may differ in other subspecies where male ornaments other than tail length are prominent and seem to be the targets of female choice. In this study, similar to previous studies on European populations, we determined the relationship between male viability and male ornaments, including tail length, in a Japanese population of the Asian Barn Swallow H. r. gutturalis, which have short tails, a whitish ventral plumage, and a large red throat patch. We observed that males with longer tails and larger and more colored (i.e., lower saturation values) throat patches were more likely to return to the study area than other males, independent of their age. Of these ornaments, information on viability of male tail length partially overlapped the information on viability by throat coloration. Because females choose mates, either directly or indirectly, based on their throat coloration, female mate preference for tail length had few benefits for the choosers. This may explain why female mate preference for tail length was not observed in this population. In addition, differing from a previous study in a European population, male throat patch size may serve as a good indicator of male viability, independent of tail length and throat coloration in this population. We discuss the possible explanations for the observed patterns.ZusammenfassungDie Qualitätder Männchen ist positiv korreliert mit mehreren männlichen Ornamenten bei Asiatischen Rauchschwalben Die Europäische Rauschschwalbe Hirundo rustica rustica ist ein Modelorganismus zur Untersuchung der weiblichen Partnerwahl hinsichtlich indirekter Vorteile, da der lange Schwanz der Männchen, Auswahlkriterium der Weibchen bei ihrer Partnerwahl, positiv korreliert ist mit der Qualität der Männchen. Allerdings kann dies bei anderen Unterarten abweichen, wo andere männliche Ornamente als die Länge der Schwanzfedern prominenter sind und als Auswahlkriterien der Weibchen dienen. Ähnlich wie bei früheren Studien an europäischen Populationen untersuchten wir in dieser Studie das Verhältnis zwischen der Männchen-Qualität und der männlichen Ornamentik, inklusive der Schwanzlänge, in einer japanischen Population der Asiatischen Rauchschwalbe H. r. gutturalis. Asiatische Rauchschwalben haben kurze Schwanzfedern, eine weißliche Unterseite und einen großen roten Kehlfleck. Wir beobachteten, dass, unabhängig ihres Alters, Männchen mit längeren Schwanzfedern sowie größeren und stärker gefärbten Kehlflecken (d. h. geringere Farbsättigungswerte) eher in das Untersuchungsgebiet zurückkehrten als andere Männchen. Bei diesen Ornamenten überlagerte die Information zur Männchen-Qualität mittels der Schwanzlänge teilweise die Information zur Qualität mittels der Kehlfärbung. Da die Weibchen ihre Partner, entweder direkt oder indirekt, auf Basis der männlichen Kehlfärbung wählen, hatte die weibliche Präferenz für die Schwanzlänge der Männchen weniger Vorteile. Das könnte erklären, warum die Präferenz der Weibchen für die Länge der Schwanzfedern bei den Männchen in dieser Population nicht beobachtet werden konnte. Darüber hinaus, abweichend von früheren Studien in europäischen Populationen, könnte in dieser Population die Größe des männlichen Kehlfleckes ein guter Indikator für die Qualität der Männchen sein, unabhängig von der Schwanzlänge und der Kehlfärbung. Wir diskutieren mögliche Erklärungsansätze für die beobachteten Muster.

Reproductive advantages of multiple female ornaments in the Asian Barn Swallow Hirundo rustica gutturalis

AbstractRecent research has increasingly focused on female ornamentation, with several studies having investigated female ornaments in relation to reproduction. However, most previous studies have focused on single female ornaments, while females of numerous species, particularly birds, possess multiple ornaments. It is still unclear whether multiple female ornaments are linked to reproductive performance, though this information is crucial for understanding how these ornaments have been maintained. In this study, we examined the signaling function of multiple female ornaments in the Asian Barn Swallow Hirundo rustica gutturalis in Japan. First, females with previous breeding experience in the study population had longer tails and more colorful throat patches than other females. This indicates that these ornaments can provide information about the breeding experience of females to conspecifics. In contrast to males, the size of white tail spots was not significantly related to breeding experience in females, partly because females with larger white spots were less likely to return to breed after a failed clutch. Second, females with longer tails and more colorful throats started breeding earlier than others, even after controlling for confounding factors, and they paired with attractive males (thereby obtaining their direct and indirect benefits too), suggesting a mating advantage for females with such ornaments. In addition, males paired with long-tailed females invested more in paternal care. These observed patterns differed from those of males, for whom the throat coloration and the size of white tail spots, rather than tail length, were significant predictors. In fact, a sex-combined analysis of breeding date demonstrated significant interactions of sex in relation to tail length and the size of white tail spots, indicating differential selection between the sexes. Our data suggest that selection on females may facilitate the evolution and maintenance of some female ornaments, partially independently of male ornaments.ZusammenfassungFortpflanzungsvorteile multipler weiblicher Ornamente bei der asiatischen Unterart der Rauchschwalbe (Hirundo rustica gutturalis) In letzter Zeit hat sich die Forschung zunehmend auf Ornamentierung bei Weibchen konzentriert, und mehrere Studien haben weibliche Ornamente in Bezug auf die Fortpflanzung untersucht. Die meisten vorherigen Studien haben sich jedoch auf einzelne Weibchenornamente konzentriert, während die Weibchen vieler Arten, insbesondere bei Vögeln, mehrere Ornamente besitzen. Nach wie vor ist unklar, ob multiple Weibchenornamente mit der Fortpflanzungsleistung in Verbindung stehen, obwohl diese Information entscheidend ist, um zu verstehen, wie diese Ornamente aufrechterhalten worden sind. In dieser Studie haben wir die Signalfunktion multipler Weibchenornamente bei der asiatischen Unterart der Rauchschwalbe (Hirundo rustica gutturalis) in Japan untersucht. Erstens hatten Weibchen mit vorheriger Bruterfahrung im Untersuchungsgebiet längere Schwänze und buntere Kehlflecken als andere Weibchen. Dies deutet darauf hin, dass die Ornamente Artgenossen über die Bruterfahrung von Weibchen informieren können. Anders als bei Männchen hing die Größe der weißen Schwanzflecken bei Weibchen nicht mit der Bruterfahrung zusammen, z.T. weil Weibchen mit größeren weißen Flecken nach einer erfolglosen Brut mit geringerer Wahrscheinlichkeit zum Brüten zurückkehrten. Zweitens begannen Weibchen mit längeren Schwänzen und bunteren Kehlflecken früher mit der Brut als andere, selbst wenn die statistische Analyse Störfaktoren berücksichtigte. Zudem waren diese Weibchen mit attraktiven Männchen verpaart (und erlangten auf diese Weise auch noch direkte und indirekte Fitnessvorteile), was darauf hindeutet, dass Weibchen mit solchen Ornamenten einen Paarungsvorteil besitzen. Des Weiteren investierten Männchen, die mit langschwänzigen Weibchen verpaart waren, mehr in die Brutpflege. Diese beobachteten Muster unterschieden sich von denen für Männchen, bei denen die Kehlfärbung und die Größe der weißen Schwanzflecken (und nicht die Schwanzlänge) als signifikante erklärende Variablen fungierten. In der Tat zeigte eine beide Geschlechter berücksichtigende Analyse des Brutdatums signifikante Interaktionen von Geschlecht in Bezug auf Schwanzlänge und Größe der weißen Schwanzflecken, was auf unterschiedliche Selektionsdrücke bei den Geschlechtern hindeutet. Unsere Daten lassen darauf schließen, dass auf Weibchen wirkender Selektionsdruck die Evolution und Aufrechterhaltung einiger Weibchenornamente fördern könnte, und zwar z.T. unabhängig von männlichen Ornamenten.