Male Swallows Research Articles

Barn Swallows in East Asia show strong tolerance against nest mites

Abstract Hosts defend against parasites through two main strategies: resistance and tolerance. These two strategies have different influences on the parasite load of the host and so have variable effects on the fitness of parasites. In this study, we investigated the strategy used by the Barn Swallow (Hirundo rustica) to defend against a hematophagous mite (Dermanyssus hirundinis) in East Asia. For the first time, we found Barn Swallows were parasitized by D. hirundinis in Asia and, in northeastern China, over 60% of broods were parasitized. We examined whether swallows with better body condition or the males with more extravagant sexually selected traits (longer tail streamers or redder ventral plumage) showed stronger resistance or tolerance to these parasites. The results showed that males with more extravagant sexual ornaments had weaker resistance (heavier brood mite load) than males with less extravagant traits; however, the heavier mite load was likely to be a byproduct of larger brood size. Moreover, the Barn Swallow population showed strong tolerance against the parasite (i.e. the brood mite load did not affect brood size or nestling body mass). It is worth noting that male swallows with redder breast plumage showed weaker tolerance (lower seasonal reproductive success) than other males. Further, we conducted experimental ectoparasite manipulations in 46 Barn Swallow nests to verify the potential effect of these parasites on the body condition of nestlings. Neither the body mass nor the hemoglobin concentration differed between the designed groups; however, the hemoglobin concentration of nestlings decreased with mite load. We concluded that the Barn Swallow population in East Asia used the tolerance strategy, rather than resistance to defend against nest mites, and the ectoparasitic mite did not appear to be a strong selective factor for reproductive success owing to the strong tolerance of the studied Barn Swallow population.

Mechanisms involved in the production of differently colored feathers in the structurally colored swallow tanager (Tersina viridis; Aves: Thraupidae).

Non-iridescent, structural coloration in birds originates from the feather's internal nanostructure (the spongy matrix) but melanin pigments and the barb's cortex can affect the resulting color. Here, we explore how this nanostructure is combined with other elements in differently colored plumage patches within a bird. We investigated the association between light reflectance and the morphology of feathers from the back and belly plumage patches of male swallow tanagers (Tersina viridis), which look greenish-blue and white, respectively. Both plumage patches have a reflectance peak around 550 nm but the reflectance spectrum is much less saturated in the belly. The barbs of both types of feathers have similar spongy matrices at their tips, rendering their reflectance spectra alike. However, the color of the belly feather barbs changes from light green at their tips to white closer to the rachis. These barbs lack pigments and their morphology changes considerably throughout. Toward the rachis, the barb is almost hollow, with a reduced area occupied by spongy matrix, and has a flattened shape. By contrast, the blue back feathers' barbs have melanin underneath the spongy matrix resulting in a much more saturated coloration. The color of these barbs is also even along the barbs' length. Our results suggest that the color differences between the white and greenish-blue plumage are mostly due to the differential deposition of melanin and a reduction of the spongy matrix near the rachis of the belly feather barbs and not a result of changes in the characteristics of the spongy matrix.

Swallow mums push metabolic limits when they can keep cool

![Figure][1] Male tree swallow ( Tachycineta bicolor ) sitting on a birdhouse. Photo credit: Mykola Swarnyk [CC BY-SA ( )] Parenting is not for the faint hearted. Dedicated tree swallow mums and dads commit themselves to 16 h of exertion

Promiscuous copulation attempts and discriminate pairing displays in male barn swallows as revealed by model presentation

The current knowledge of male mate preferences based on female ornamentation is quite limited. Few experimental studies have been conducted; therefore, even basic information, such as male mate preferences for copulation and pairing, is lacking. Here we studied male mate preferences in Japanese barn swallows Hirundo rustica gutturalis, a socially monogamous passerine with biparental care, using a model presentation experiment. We presented each unmated male with a control female model that had typical whitish ventral feathers of this subspecies or with a chestnut model that had chestnut ventral feathers, which are found in other subspecies such as H. r. erythrogaster, and compared male behaviour towards these models. The number of male copulation attempts did not significantly differ between treatments. In contrast, the number of male pairing displays was significantly different between treatments: males courted less often towards a chestnut model than towards a control model. These results demonstrate indiscriminate copulation attempts but discriminate pairing displays in male swallows, which is consistent with Trivers’ classic theory. We discuss the causes and consequences of the observed patterns.

Experimentally reduced male ornamentation increased paternal care in the Barn Swallow

It has recently been demonstrated that male ornaments feedback on their physiological state and this is expected to be followed by behavioral alterations in paternal care. However, only a few studies have shown the effects of experimental manipulation of ornamentation on paternal care behavior. The present study investigated the effects of experimental manipulation of the size of a male ornament, the red throat patch, on the feeding rates of nestlings by male and female Barn Swallows (Hirundo rustica gutturalis). First, we observed a dynamic change in male throat patch height during the breeding season, indicating that behavioral alterations in response to changes in throat patch height may be beneficial for male Swallows. Second, males with an experimentally reduced throat patch, but not their mates, fed their nestlings significantly more often compared with control individuals. In addition, we found a significant interaction between treatment and male body size: i.e., the effects of a reduced throat patch height varied depending on male body size. Among males with a reduced throat patch, male feeding rate increased with body size, but this was not the case in control males. This interaction is consistent with the idea that small males have low behavioral flexibility, and might contribute on positive correlation between throat ornamentation and male body size, given that behavioral flexibility is adaptive. The current finding indicates that males can increase paternal care in response to a seasonal decrease in ornamentation and this differential behavioral flexibility among males may facilitate the honesty of ornamentation.

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.

Plasma Testosterone Concentrations in Adult Tree Swallows During the Breeding Season

We studied seasonal profiles of circulating testosterone concentrations among male and female adult Tree Swallows (Tachycineta bicolor) breeding in nest-box colonies near Ames, Iowa, USA. Mean plasma testosterone in males was elevated during nest establishment (0.63 ± 0.86 ng/ml) and incubation stages (0.28 ± 0.26 ng/ml), and was significantly lower after hatching (0.03 ± 0.05 ng/ml) when males began provisioning nestlings. Male swallows do not incubate and high testosterone during the incubation stage may facilitate pursuit of extra-pair matings. Female testosterone concentrations were an order of magnitude lower than those of males (nest establishment, mean = 0.06 ± 0.09 ng/ml) and did not change significantly over the breeding season. These testosterone profiles support the hypothesis that elevated testosterone in males is associated with defense behaviors and obtaining additional mating opportunities during the first part of the breeding season, but is incompatible with parental care once the eggs have hatched.

Change in body mass during breeding in Barn Swallows Hirundo rustica

Capsule The body mass of female Barn Swallows (Hirundo rustica) varies cyclically in relation to breeding attempts within breeding seasons. Aim To determine whether body mass declines in relation to the progress of incubation in female and male Barn Swallows and whether this differs between breeding attempts within a season. Methods Adult Swallows were caught and ringed at breeding sites as part of a long-term study to estimate survival rates. Measurements of body mass and size at the time of ringing were analysed in relation to the start of incubation, defined from detailed observations of the progress of breeding at each site. Results Wing length, hour of weighing, and time from the start of incubation contributed significantly to variation in female body mass. Body mass peaked 3 days before the start of incubation and declined linearly by 0.115 g per day during incubation and brood rearing in both breeding attempts within a season. For males, body mass declined by 0.026 g per day from the start of incubation during the first breeding attempt, but this was not apparent for the smaller sample of males in the second breeding attempt, possibly because such breeding-related changes may be masked by premigratory increases in mass later in the breeding season. Conclusion The body mass of female Swallows varied cyclically during the breeding season in relation to breeding attempts and there were clear differences between male and female Swallows in the magnitude of body mass changes as breeding progressed.

Differences in rates of nest-visitation and removal of faecal sacs by male and female White-rumped Swallows

Despite being a common and widespread species, the White-rumped Swallow (Tachycineta leucorrhoa) is one of the least-studied members of its genus. We examined the rates of nest-visitation and nest-sanitation of male and female White-rumped Swallows during the nestling period, in 23 nests, and compared them with those of the extensively studied Tree Swallow (Tachycineta bicolor). White-rumped Swallow pairs increased the rate of nest-visitation as nestlings grew older, as was found in Tree Swallows. Females made significantly more visits to the nest than males, and the asymmetry was maintained irrespectively of the age of nestlings. These results are similar to those reported from Tree Swallows in the eastern United States, but differ from the equality of roles found in Ontario, Canada. Female and male White-rumped Swallows removed faecal sacs at the same rate when nestlings were young (Day 4) but by Day 12 females had quadrupled their effort whereas the rate of sanitation by males remained constant. Overall, female White-rumped Swallows made a significantly larger parental investment than males (as measured by number of visits to nests and, thus, presumably rates of feeding, and in contribution to nest-sanitation) and, in this respect, the asymmetry in parental investment is greater than that reported for Tree Swallows.

Behavioural and Energetic Responses to Body State in Male and Female Barn Swallows (Hirundo rustica)

Females and males often have different roles when attending young. The factors responsible for shifts in the balance of effort when both sexes provision their young are not clear. This study asked if sex-specific behaviour and provisioning rules in barn swallows (Hirundo rustica) were dependent on individual body-state or affected by the state of their provisioning partner. To assess this male and female barn swallows underwent overnight warming manipulations whilst provisioning 10-14 day old nestlings, a time when energetic demands are maximal. The overnight warming treatment reduced thermoregulatory costs and provided birds with extra energy reserves at dawn. Only one member of a pair was manipulated in this way, whilst their partners were left un-manipulated to assess their response to their partner's elevated body-state. The energetic and behavioural responses to these manipulations were followed over the subsequent 24-h. I found that warmed male and female barn swallows increased their energy expenditure and nest visitation rates to the same extent after manipulation, implying a trade-off in resource allocation, which was biased towards reproductive effort. There was no effect of gender. Males paired with manipulated females showed no energetic or behavioural adjustments, however, females paired with manipulated males tended to increase both energy expenditure and nest visitation. This study provides evidence that energy reserves constrain behaviour, and that male and female swallows normally follow the same state-dependent rules when provisioning young.

Individual and Seasonal Variation in External Genitalia of Male Tree Swallows

Abstract The cloacal protuberance (CP) of passerines functions primarily to store spermatozoa. When gently squeezed, the CP of male Tree Swallows (Tachycineta bicolor) everts to expose a small papilla from which semen can be expressed. From 1994 to 1999, I examined individual and seasonal variation in CP dimensions and papilla length of mated male Tree Swallows in western Michigan. Male CP volumes were greatest when their mates were laying eggs and declined to the nestling period. Papilla lengths did not vary over the course of the breeding season. Cloacal protuberance dimensions and papilla length were not associated with the age class of a male's mate, the date she started laying eggs, or number of eggs she laid. The decrease in CP size over the course of the breeding season is consistent with the steady decrease in reproductive opportunities for male swallows. Although it seems likely, whether or not the papilla of Tree Swallows functions as an intromittent organ awaits further study of the anatomical ...

Examining the Cost of Experimentally Imitated Ornaments

Examining the Cost of Experimentally Imitated Ornaments

HEALTH OF TREE SWALLOWS (TACHYCINETA BICOLOR) NESTING IN PESTICIDE-SPRAYED APPLE ORCHARDS IN ONTARIO, CANADA. II. SEX AND THYROID HORMONE CONCENTRATIONS AND TESTES DEVELOPMENT

To investigate the effects of pesticides on wild birds, sex (17beta-estradiol; testosterone) and thyroid (triiodothyronine (T3) hormone concentrations, body mass, and testes mass were measured and the development of testes was evaluated in wild tree swallows (Tachycineta bicolor) nesting in four sprayed apple orchards and three nonsprayed sites in southern Ontario, Canada, in 1995-1996. In orchards, birds were exposed to as many as 11 individual spray events and five sprays of mixtures of chemicals. Residues of organochlorine pesticides, PCBs, lead, and arsenic concentrations were low and not variable among sites except p,p '-DDE concentrations, which ranged from 0.36 to 2.23 mug/ g wet weight in eggs. These persistent compounds were not correlated with any endocrine response measured in tree swallows. In 16-d-old male tree swallow chicks, body mass and concentrations of 17 -estradiol (estradiol), testosterone, and T3 in plasma showed no significant differences between sprayed and nonsprayed groups and among sites within those groups. However, T3 concentrations were slightly elevated in the sprayed group compared to the nonsprayed group, and there was a significant and positive correlation between T3 and the number of mixtures of sprays applied during egg incubation through chick rearing. In 16-d-old female chicks, there were no significant differences among spray treatments or sites and no correlations with spray exposure for testosterone, estradiol, or T3 in plasma. Body mass was correlated positively with T3 and negatively with estradiol but showed no differences among spray exposure groups or sites. Histology of testes of 16-d-old male chicks indicated there were no significant differences among sprayed and nonsprayed birds in testes mass, area, or diameter, or the presence of Leydig cells in the interstitium, the distribution of the Sertoli cells, or the occurrence of heterophils in the testicular interstitium. For the percentage of spermatogonia present on the basement membrane, there were significant differences among sites, but these differences were not specifically associated with spray exposure. However, there was a marginally significant trend between increasing occurrence of a disrupted Sertoli cell population on the seminiferous tubular basement membranes as the number of mixtures of pesticides sprayed during chick rearing increased. In adult male and female parent tree swallows, there were no differences in hormone concentrations between birds from sprayed and nonsprayed sites. Nor were there any significant correlations between the concentration of any hormone and collection date, body mass, or any type of spray exposure for adults. The correlations between increasing pesticide exposure and abnormal thyroid hormone and testes development in male chicks indicate that further reductions of pesticide use in orchards may benefit the health of birds that nest there. However, it is unclear which of these pesticides or spray mixtures are responsible for these effects, and

Testosterone correlates of mate guarding, singing and aggressive behaviour in male barn swallows,Hirundo rustica

Sexual and social behaviour in male birds is largely controlled by gonadal secretions, most notably testosterone. In this paper the relationships between natural testosterone plasma concentrations and mate guarding, singing and rates of aggression in male barn swallows are reported. Behaviour of individually marked male swallows was observed in three breeding colonies. Individual mate-guarding rate was positively correlated with individual testosterone plasma level adjusted for stage in the breeding cycle in which blood was sampled. Mean mate-guarding rates by males at different stages in the breeding cycle were also positively correlated with mean testosterone levels in the population. Individual singing and fighting rates did not show a significant correlation with testosterone but mean singing rate in the population was positively correlated with mean testosterone levels. Male tail length, which is a morphological trait currently under directional sexual selection, was inversely correlated with mate-guarding rates after controlling statistically for the effects of testosterone.

Food, feathers and fluctuating asymmetries

Nutritional, or energetic, stress has been implicated as a causal factor in the inter-individual differences in levels of fluctuating asymmetry in the elongated tails of male swallows (Hirundo rustica). However, there has been no direct experimental test of this hypothesis. We report results from an experiment that has investigated the effects of sequential food deprivations on levels of fluctuating asymmetry in primary feathers and chest plumage of the moulting female European starling (Sturnus vulgaris). Birds were housed individually and taken through their full moult by means of photoperiodic manipulation. During this period, some of the birds experienced food deprivations. At regular intervals, we recorded the length of every primary feather, quantified the chest plumage via video-image analysis, and recorded body mass and subcutaneous fat score measurements. We found that increasing levels of nutritional or energetic stress caused larger development asymmetries, which would appear to have increased fitness costs. Primary feather asymmetry showed a negative relation with amount of subcutaneous fat stored during moult and a positive relation with social dominance. This is the first study to show, directly, the importance of energetic stress in the production of feather and plumage asymmetries. Low levels of feather asymmetries were also associated with an indicator of reproductive status (chest `spottiness'). These findings support the recent literature, suggesting that degree of fluctuating asymmetry, even in traits under stabilizing selection, may reveal aspects of individual fitness value.

Size, condition, and territory ownership in male tree swallows (Tachycineta bicolor)

Male tree swallow (Tachycineta bicolor) territory owners and floaters were compared in terms of size and nutritional condition to test the resource holding potential hypothesis. Owners were larger than floaters when compared using six morphological measurements. There were no differences in dry mass, ash, or fat content, but territory owners were heavier and had larger protein reserves than floaters. Territory owners may be those individuals who win intrasexual conflicts for the possession of nest boxes, or those who, because of their better nutritional condition, can arrive at the breeding grounds earlier to secure a territory.

Female swallow preference for symmetrical male sexual ornaments.

Many secondary sexual characters are supposed to have evolved as a response to female choice of the most extravagantly ornamented males, a hypothesis supported by studies demonstrating female preferences for the most ornamented males. Comparative studies of elaborate feather ornaments in birds have shown that (1) ornaments have larger degrees of fluctuating asymmetry (small, random deviations from bilateral symmetry caused by an inability of individuals to cope with environmental and genetic stress during development of a character) than other morphological traits, and (2) the degree of fluctuating asymmetry is often negatively related to the size of the ornament. The negative relationship between ornament asymmetry and size suggests that ornament size reliably reflects male quality because the largest secondary sex traits demonstrate the least degree of fluctuating asymmetry. I manipulated tail length and tail asymmetry independently in male swallows (Hirundo rustica) to determine whether ornament size or asymmetry were used as cues in mate choice. Male swallows with elongated, symmetric tails mated earlier, and enjoyed larger annual reproductive success than did males with shortened tails and increased asymmetry. Females therefore prefer large as well as symmetric ornaments, which suggests that females in their mate choice use ornament asymmetry and size as reliable indicators of male quality.

Double broodedness and mixed reproductive strategies by female swallows

It has been hypothesized that female birds should alter their mixed reproductive strategy from being willing to engage in extra-pair copulations during first clutches to not being willing to do so during second clutches, because it is beneficial in terms of paternal care for females to be faithful to their mates once they have proven their quality as parents during the first clutch. Parental care for nestling and fledgling swallows, Hirundo rustica, from the first brood may overlap with the initiation of a second brood. Since male brood care interferes with the ability to mate guard, this juxtaposition may have implications for the ability of males to guard their mates during the fertile period of the second clutch. However, the intensity of mate guarding was not related to the duration of the interval between initiation of the first and the second clutch and thus the extent of brood overlap, indicating that mate guarding was not severely constrained by paternal care. The intensity of mate guarding during the presumed fertile period was as high during second as during first clutches. Accordingly, the frequency of extra-pair copulations by females was similar during first and second clutches. The magnitude of male parental investment in first versus second broods was compared. Male swallows fed first broods slightly more than second broods. Male brood defence against a human intruder was also similar for first and second broods. These data do not support the hypothesis that female swallows alter their reproductive strategy from the first to the second clutch.

Preferred males acquire mates of higher phenotypic quality

Several field studies have shown that ornamented males of both polygynous and monogamous animals gain an advantage in terms of mate acquisition. Male reproductive success is strongly positively related to the number of mates acquired, but differential quality of female mates may also play an important role. Darwin (The descent of man, and selection in relation to sex (1871)) and Fisher (The genetical theory of natural selection (1958)) suggested that preferred males of monogamous species should experience a reproductive advantage because of differences in female phenotypic quality. Good condition is supposed to allow females to breed early and to grant them high fecundity. Preferred males should acquire early-breeding females in good condition and for that reason have greater reproductive success. Several genetic models confirm the possible significance of this sexual selection mechanism. Alternatively, preferred males may acquire mates that invest more in reproduction because they have acquired males of higher quality. Field data on birds suggest that preferred males do acquire early-breeding mates, but it has never been shown that such mates are of a higher phenotypic quality in terms of condition. Long-tailed males of the monogamous swallow, Hirundo rustica , are preferred by females. In this study, observations using males with naturally varying and experimentally manipulated tails show that females mated to long-tailed males were heavier, bred earlier, produced more offspring per season and were much more likely to survive to the next breeding season that were females mated to short-tailed male swallows. This is the first demonstration that preferred males actually obtain mates of high phenotypic quality. Preferred males had a direct reproductive benefit of mating with long-lived females, because pairs consisting of mate-faithful individuals reproduced earlier and produced more offspring than did pairs without previous common experience.

Defence of offspring by male swallows, Hirundo rustica, in relation to participation in extra-pair copulations by their mates

Defence of offspring by male swallows against a stuffed little owl, Athene noctua, predator model was studied in relation to participation of the mate in extra-pair copulations. The frequency of extra-pair copulations was manipulated by temporarily detaining males during the fertile period of their mates. Experimental colonial females experienced more extra-pair copulations than control colonial ones. Detained males defended their offspring less intensely, staying away from the predator model, giving fewer alarm calls and spending less time near the predator than did their mates. Solitarily breeding experimental females did not experience more extra-pair copulations than did their controls. Temporary detention of a group of colonial males during the incubation period of their mates did not reduce the intensity of their brood defence compared to control males, suggesting that detention per se did not have a negative effect on brood defence. The frequency of extra-pair copulations, and therefore presumably certainty of paternity, thus affects amount of, and sex roles in, anti-predator defence.