Circulation of zoonotic flaviviruses in wild passerine birds in Western Spain.

We explore the presence of zoonotic flaviviruses (West Nile virus (WNV) and Usutu virus (USUV)) neutralizing antibodies in rarely studied passerine bird species. We report, for the first time in Europe, WNV-specific antibodies in red avadavat and cetti's warbler, and USUV in yellow-crowned bishop. The evidence of WNV and USUV circulating in resident and migratory species has implications for both animal and public health. Future outbreaks in avian reservoir hosts may occur and passerines should be considered as priority target species in flavivirus surveillance programmes.

Environmental conditions during winter predict age- and sex-specific differences in reproductive success of a trans-Saharan migratory bird.

Previous studies have linked winter habitat with subsequent breeding phenology and physical condition of migratory birds, but few have found delayed effects of winter habitat on subsequent reproductive success. The aim of this study was to test if African winter habitat is related to subsequent reproductive success of house martins (Delichon urbicum) breeding at a colony in Spain. We measured stable isotope (δ2H, δ13C, δ15N) values from feathers moulted in West Africa and used confirmatory path analysis to test if isotopic values of winter-grown feathers were related to reproductive success through the mediation of breeding phenology and body condition. We conducted separate analyses for males, females and age classes (yearlings vs ≥ 2 years old). Experienced males wintering in habitats of higher rainfall (as inferred from lower feather δ2H values) were in better body condition and produced more offspring during the subsequent breeding season. In contrast, we did not find any effect of winter habitat on reproductive success of young males or females. These findings provide evidence consistent with a complex causal link between winter habitat quality and subsequent breeding success of long-distance migratory songbirds.

Geographical variation in reproductive ageing patterns and life-history strategy of a short-lived passerine bird.

We investigated differences in ageing patterns in three measures of breeding performance in populations of barn swallows Hirundo rustica L. from Spain and Denmark differing in breeding latitude and hence migration distance and duration of the breeding season. We found differences in ageing patterns between populations. Generally, young (i.e. yearling) and old females (i.e. ≥ 5 years of age) laid their first eggs later and produced smaller clutches than middle-aged females (i.e. 2-4 years of age) in both populations. The southernmost population (i.e. Spanish) showing the shorter migratory distance experienced a greater within-individual increase in timing of breeding and clutch size in early life and a greater within-individual decrease in laying date but not in clutch size during senescence compared with the northernmost population (i.e. Danish). We also found that the number of fledglings produced annually was related to the age of the two members of the breeding pairs with pairs composed of young and old females performing less well than breeding pairs composed of middle-aged females. We did not find reproductive senescence for the age of the male while controlling for the age of the female on the number of fledglings produced annually by the breeding pair. Differential survival between individuals did not explain age effects on laying date or annual clutch size in neither population. However, the increase in the number of fledglings produced annually with age was partly explained by the disappearance of poor-quality members of the pairs, mainly poor-quality males. Age-related breeding success (i.e. number of fledglings) was similar for barn swallows from Spain and Denmark. Therefore, the study of ageing patterns and life-history strategies in free-ranging animals from more than a single population can throw new light on life-history theory, population dynamics and evolutionary studies of senescence.

Quantitative genetics of migration syndromes: a study of two barn swallow populations.

Migration is a complex trait although little is known about genetic correlations between traits involved in such migration syndromes. To assess the migratory responses to climate change, we need information on genetic constraints on evolutionary potential of arrival dates in migratory birds. Using two long-term data sets on barn swallows Hirundo rustica (from Spain and Denmark), we show for the first time in wild populations that spring arrival dates are phenotypically and genetically correlated with morphological and life history traits. In the Danish population, length of outermost tail feathers and wing length were negatively genetically correlated with arrival date. In the Spanish population, we found a negative genetic correlation between arrival date and time elapsed between arrival date and laying date, constraining response to selection that favours both early arrival and shorter delays. This results in a decreased rate of adaptation, not because of constraints on arrival date, but constraints on delay before breeding, that is, a trait that can be equally important in the context of climate change.

Determinants of age-dependent change in a secondary sexual character.

Many secondary sexual characters vary in a systematic way with the age of individuals, with young and old individuals displaying at lower levels than individuals of intermediate age. Analyses quantifying the within-individual and among-individual components of phenotypic variation can help partition effects of phenotypic plasticity and selective mortality. We analysed phenotypic variation in the expression of a secondary sexual character, tail length, in male and female barn swallows Hirundo rustica from four European populations studied during 11-26 years, using linear mixed effect models to describe age-related expression. Tail length increased from yearlings to intermediate aged birds with a subsequent decrease at old age. In males, this age-related pattern was because of both within-subject and between-subject effects, with no difference among populations. Males having longer lifespan had shorter tails when young than those having shorter lifespan. Females showed similar patterns of age-related variation as males, with no difference among populations. The major difference between sexes was that the between-subject effects (i.e. disappearance effects or selection) were much more important for males compared to females for which lifetime variation in tail length was mainly because of a within-subject effect (i.e., a plastic response). These findings suggest that whereas males trade greater expression of the secondary sexual character at young age against longevity, that was not the case for females. This is consistent with tail length being more costly in males than in females, with the cost of long tails potentially being offset by elevated mating success, whereas that is not the case in females.

Senescent sperm performance in old male birds.

Senescence is the deterioration of the phenotype with age caused by negative effects of mutations acting late in life or the physiological deterioration of vital processes. Birds have traditionally been assumed to senescence slowly despite their high metabolic rates, high blood sugar levels and high body temperature. Here we investigate the patterns of age-related performance of sperm of a long distance migrant, the barn swallow Hirundo rustica, varying in age from 1 to 6 years, analysed by the computer-assisted sperm analysis equipment. Sperm showed deteriorating performance in terms of linear movement, track velocity, straight line velocity and reduced proportions of rapidly moving, progressive and motile sperm with age. In a second series of experiments, we assessed performance of sperm from the same males in neutral medium and in medium derived from the reproductive tract of females in an attempt to test if sperm of old males performed relatively better in female medium, as expected from extra-pair paternity being negatively related to male age, but not to female age. Older males showed consistently better performance in female medium than in neutral medium in terms of track velocity, straight line velocity and reduced proportions of rapidly moving, progressive and motile sperm, whereas young males showed better performance in neutral medium. These results provide evidence of declining sperm performance for important reproductive variables not only with age, but also with the sperm of old males performing differentially better in female medium than young males.

Effects of malaria double infection in birds: one plus one is not two.

Avian malaria parasites are supposed to exert negative effects on host fitness because these intracellular parasites affect host metabolism. Recent advances in molecular genotyping and microscopy have revealed that coinfections with multiple parasites are frequent in bird-malaria parasite systems. However, studies of the fitness consequences of such double infections are scarce and inconclusive. We tested if the infection with two malaria parasite lineages has more negative effects than single infection using 6 years of data from a natural population of house martins. Survival was negatively affected by both types of infections. We found an additive cost from single to double infection in body condition, but not in reproductive parameters (double-infected had higher reproductive success). These results demonstrate that malaria infections decrease survival, but also have different consequences on the breeding performance of single- and double-infected wild birds.

Elevated frequency of abnormalities in barn swallows from Chernobyl.

Ever since the Chernobyl accident in 1986, that contaminated vast areas in surrounding countries with radiation, abnormalities and birth defects have been reported in human populations. Recently, several studies suggested that the elevated frequency of such abnormalities can be attributed to poverty and stress in affected human populations. Here, we present long-term results for a free-living population of barn swallows, Hirundo rustica, demonstrating the presence of 11 morphological abnormalities in populations around Chernobyl, but much less frequently in an uncontaminated Ukrainian control population and three more distant control populations. The presence of these abnormalities in barn swallows is associated with reduced viability. These findings demonstrate a link between morphological abnormalities and radiation in an animal population that cannot be attributed to poverty and stress. The most parsimonious hypothesis for abnormalities in animal and human populations alike is that the effects are caused by the same underlying cause, viz. radiation derived from the Chernobyl accident.

The design of complex sexual traits in male barn swallows: associations between signal attributes.

Variation in the expression of sexually selected traits among individuals is widely investigated on the premise that these traits evolved to signal male quality. Significant repeatabilities of sexual signals and their associations with condition, mating success, survivorship and age may be the signatures of sexual selection. However, little is known about the relationship between these sexual attributes. Here we studied 28 acoustic and visual traits in the barn swallow, Hirundo rustica, that may potentially function in sexual selection. Based on effect sizes calculated at the between-individual level, we assessed the relationship between repeatability, condition-dependence, attractiveness, age-dependence and viability indicator value of sexual traits using sexual signals as the units of analyses. Those traits that showed high within-year repeatability also showed high between-year repeatability, indicating that between-individual variation is consistent within and among seasons. In addition, age-dependence of traits, probably causing between-year variation, was negatively related to between-year repeatability. Condition-dependence was negatively correlated with effect sizes for the extent to which traits predicted viability. Therefore, traits that are positively related to immediate condition are those that are negatively related to survival, which may be the signature of a trade-off between current and future reproductive success ultimately reflecting signal reliability. No other significant relationship was found between trait attributes. We conclude that multiple sexual signals reflect different aspects of male quality in the barn swallow.

An analysis of continent-wide patterns of sexual selection in a passerine bird.

Patterns of selection are widely believed to differ geographically, causing adaptation to local environmental conditions. However, few studies have investigated patterns of phenotypic selection across large spatial scales. We quantified the intensity of selection on morphology in a monogamous passerine bird, the barn swallow Hirundo rustica, using 6495 adults from 22 populations distributed across Europe and North Africa. According to the classical Darwin-Fisher mechanism of sexual selection in monogamous species, two important components of fitness due to sexual selection are the advantages that the most attractive males acquire by starting to breed early and their high annual fecundity. We estimated directional selection differentials on tail length (a secondary sexual character) and directional selection gradients after controlling for correlated selection on wing length and tarsus length with respect to these two fitness components. Phenotype and fitness components differed significantly among populations for which estimates were available for more than a single year. Likewise, selection differentials and selection gradients differed significantly among populations for tail length, but not for the other two characters. Sexual selection differentials differed significantly from zero across populations for tail length, particularly in males. Controlling statistically for the effects of age reduced the intensity of selection by 60 to 81%, although corrected and uncorrected estimates were strongly positively correlated. Selection differentials and gradients for tail length were positively correlated between the sexes among populations for selection acting on breeding date, but not for fecundity selection. The intensity of selection with respect to breeding date and fecundity were significantly correlated for tail length across populations. Sexual size dimorphism in tail length was significantly correlated with selection differentials with respect to breeding date for tail length in male barn swallows across populations. These findings suggest that patterns of sexual selection are consistent across large geographical scales, but also that they vary among populations. In addition, geographical patterns of phenotypic selection predict current patterns of phenotypic variation among populations, suggesting that consistent patterns of selection have been present for considerable amounts of time.

Yolk androgens in the barn swallow (Hirundo rustica): a test of some adaptive hypotheses.

Maternal effects such as androgen in avian eggs can mediate evolutionary responses to selection, allowing manipulation of offspring phenotype and promoting trans-generational adaptive effects. We tested the predictions of two adaptive hypotheses that have been proposed to explain female variation in yolk androgen allocation in birds, using the barn swallow Hirundo rustica as a model. We found no support for the first hypothesis proposing that yolk androgen varies as a function of breeding density in order to prepare offspring for different breeding densities. However, we found experimental support for the hypothesis that female yolk androgen allocation depends on mate attractiveness and that it constitutes an example of differential allocation. Females increased the concentration of androgens in their eggs when mated to males with experimentally elongated tails. Female phenotypic quality as measured by arrival date and clutch size was positively related to egg androgen concentration, consistent with the hypothesis that this is a costly investment, constrained by female condition. We found correlative evidence of a direct relationship between egg androgen concentration and performance of offspring as measured by mass increase.

Geographic variation in the G matrices of wild populations of the barn swallow.

In this paper, we present an analysis of genetic variation in three wild populations of the barn swallow, Hirundo rustica. We estimated the P, E, and G matrices for six linear morphological measurements and tested for variation among populations using the Flury hierarchical method and the jackknife followed by MANOVA method. Because of nonpositive-definite matrices, we had to employ 'bending' to analyse the G and E matrices with the Flury method. Both statistical methods agree in finding that the P and G matrices are significantly different but comparison between the analysis of the P matrices and pairwise analyses of the P, E, and G matrices suggests caution in interpreting the Flury results concerning differences in matrix structure. The significant variation among the populations in the G matrices appears to be due in large measure to the most geographically distant population.

Physiological and haematological consequences of a novel parasite on the red-rumped swallow Hirundo daurica.

Parasite virulence has been hypothesised to increase with the degree of host sociality because highly social hosts have a greater probability of encountering horizontal transmission of parasites and experiencing infections with multiple strains of the same parasites than do solitary hosts. As compared with the defences of closely related social host species, we predicted that solitary hosts should have relatively weak defences against parasites, thus being relatively more affected when parasitised by a novel parasite. We tested this prediction by either experimentally infesting 12 nests of the solitarily nesting red-rumped swallow Hirundo daurica with 50 individuals of the generalist martin bug Oeciacus hirundinis or by fumigation of nine nests. Nestlings 13 days old from the parasite addition group experienced increased mortality, attained lower body mass and tended to have shorter tarsi compared to nestlings from fumigated nests. Surprisingly, nestlings from the parasite addition group had higher packed cell volume (cellular fraction of blood) and lower levels of heat shock proteins (HSP60) than nestlings from the fumigation group. A measure of immunocompetence was not significantly affected by treatment, but its magnitude was positively related to packed cell volume and negatively related to level of HSP60. Solitary hosts like the red-rumped swallow have weak immune responses and low levels of heat shock proteins when infested with ectoparasites while highly social hosts have strong immune responses and high levels of heat shock proteins when infested. These findings partially support the hypothesis that potential host species with weak defences are more susceptible to infection and the deleterious effects of evolving parasites than potential hosts with strong defences.

Genetic and environmental components of phenotypic variation in immune response and body size of a colonial bird, Delichon urbica (the house martin).

Directional selection for parasite resistance is often intense in highly social host species. Using a partial cross-fostering experiment we studied environmental and genetic variation in immune response and morphology in a highly colonial bird species, the house martin (Delichon urbica). We manipulated intensity of infestation of house martin nests by the haematophagous parasitic house martin bug Oeciacus hirundinis either by spraying nests with a weak pesticide or by inoculating them with 50 bugs. Parasitism significantly affected tarsus length, T cell response, immunoglobulin and leucocyte concentrations. We found evidence of strong environmental effects on nestling body mass, body condition, wing length and tarsus length, and evidence of significant additive genetic variance for wing length and haematocrit. We found significant environmental variance, but no significant additive genetic variance in immune response parameters such as T cell response to the antigenic phytohemagglutinin, immunoglobulins, and relative and absolute numbers of leucocytes. Environmental variances were generally greater than additive genetic variances, and the low heritabilities of phenotypic traits were mainly a consequence of large environmental variances and small additive genetic variances. Hence, highly social bird species such as the house martin, which are subject to intense selection by parasites, have a limited scope for immediate microevolutionary response to selection because of low heritabilities, but also a limited scope for long-term response to selection because evolvability as indicated by small additive genetic coefficients of variation is weak.

Nest building is a sexually selected behaviour in the barn swallow.

Females may use male nest building to assess male parental quality, and nest size would then be a sexually selected trait. In the barn swallow, Hirundo rustica, females select their partner by his tail length, a character believed to signal good genes. Both sexes participate in nest building, although male participation is negatively related to his attractiveness as reflected by tail length. We tested the hypothesis that nest building is a sexually selected trait: females paired with males of high parental quality (as shown by the male during nest building) may obtain a mate providing large amounts of parental investment, while, as has been shown previously, females mated to attractive (long-tailed) males will acquire mates with good genetic quality. Therefore, since nest building in barn swallows occurs after mating, we predicted a postmating sexual selection process by which the female invests differentially in reproduction depending on the male's nest-building effort (reflecting his willingness to invest in reproduction). The volume of material in a nest was related to the male's contribution to nest building and, in agreement with our hypothesis, in a multiple regression analysis, male tail length and nest material volume were negatively related to laying date and positively to female investment in reproduction (total number of eggs laid during the breeding season). Moreover, females paired with long-tailed males (which contribute very little to nest building), but using the same amount of nest material as females paired with short-tailed males, reduced the thickness of the nest and hence increased its capacity. Therefore, in the barn swallow two different traits appear to be sexually selected: tail length of males owing to the good genes process and nest-building ability owing to the good parent process. (c) 1998 The Association for the Study of Animal Behaviour.

Parasitism, immune response and reproductive success in the house martin Delichonurbica.

Parasites often exert strong selection pressures on their hosts that have evolved anti-parasite defences to counter the negative effects of parasites. We studied the relationship between intensity of parasitism, one aspect of host immune response, and host reproductive success, using the house martin bug Oeciacushirundinis and its house martin Delichonurbica host as a model system. Experimental manipulation of parasite load of nests during laying of the first clutch altered the intensity of parasitism. Parasites reduced the reproductive success of their hosts measured in terms of body condition and survival of nestlings. Host immune response, measured as the concentration of gammaglobulins and total plasma proteins, was positively associated with parasite reproduction, estimated as the number of juvenile parasites, but was only weakly related to the intensity of adult parasites. The concentration of gammaglobulins was negatively related to nestling body mass, implying a trade-off between immune function and body condition. Parasite reproduction thus exerts a cost on hosts by increasing the immune response.

Increase in a heat-shock protein from blood cells in response of nestling house martins (Delichon urbica) to parasitism: an experimental approach.

Heat-shock proteins (HSPs) are synthesized by animals and plants in response to various stressors. The level of the HSP60 stress protein was measured from the cell fraction of peripheral blood obtained from nestling house martins (Delichon urbica) to test whether ectoparasitism increased the concentration of stress protein. We assessed HSP from nestlings raised in nests previously treated with an insecticide or infested with 50 martin bugs (Oeciacus hirundinis). In addition, haematozoa infections were checked in blood smears. Nestlings from parasite-infested nests, or nestlings infected with trypanosomes, had increased levels of HSP in their blood cells. Nestling growth as determined from wing length was negatively related to HSP60 levels and within-brood variation in wing length increased with increasing levels of the stress protein independently of treatment and infection by trypanosomes. These results suggest HSPs may play a role in host-parasite interactions, and that they can be used reliably for measuring physiological responses to parasites.

Ectoparasites and host energetics: house martin bugs and house martin nestlings.

We measured the energy cost of ectoparasitism in an experimental study of the house martin bug Oeciacus hirundinis and its main host, nestlings of the house martin Delichon urbica. Nests were randomly assigned to inoculation with 0 (control) 10, or 100 bugs during egg laying, and this resulted in statistically significant differences in parasite loads following fledging of nestlings. Parasite loads negatively affected house martin nestlings as estimated from their body mass at age 16 days and from mass loss estimated over 1 day late in the nestling period. Daily energy expenditure (KJ/d), average daily metabolic rate (ml CO2/g h), and mass independent daily energy expenditure (kJ/mass0.67d) did not differ significantly between experimental treatments. However, average daily metabolic rate increased with increasing intensities of ectoparasitism. Mass independent daily energy expenditure also increased with higher levels of parasite infestation. These results demonstrate that the bug imposes an energy cost on its host by elevating the level of metabolism.