High brood patch temperature of less colourful,less pheomelanic female Barn Swallows Hirundo rustica

In birds, even a minor difference in egg temperature (1–1.5 °C) has been shown to affect the fitness of offspring by changing hatching success, incubation period and nestling quality. Female, but not male, passerines develop brood patches. Thus if there are traits, such as plumage ornamentation, that indicate optimal egg temperature, males should pair with females that exhibit those traits. However, no study has yet investigated the relationship between female brood patch temperature, which would directly affect egg temperature, and female plumage ornamentation. In this study, we examined the surface temperature of female brood patches during nocturnal incubation and examined its relationship with female plumage ornaments in Asian Barn Swallows Hirundo rustica gutturalis. After controlling for ambient air temperature, brood patch temperature was negatively associated with colour saturation of the female throat patch. No other female ornaments, such as tail‐length, white tail spots or throat patch size, predicted brood patch temperature. When oral (mouth) temperature was statistically controlled, females with less colourful throats and longer tails showed higher brood patch temperature, indicating that these females had hotter brood patches in relation to the temperature of other body parts. Furthermore, we found a negative relationship between pheomelanin pigmentation and brood patch temperature after controlling for ambient air temperature or oral temperature. To our knowledge, this is the first study to show that female ornaments can predict the absolute/relative thermal investment in brood patches. This relationship, together with other aspects of female quality, may affect male mate preference and female ornamentation.     

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.     

No evidence for adjustment of sex allocation in relation to paternal ornamentation and paternity in barn swallows

Sex allocation theory predicts that parents should adjust investment in sons and daughters according to relative fitness of differently sexed offspring. In species with female preference for highly ornamented males, one advantage potentially accruing to parents from investing more in sons of the most ornamented males is that male offspring will inherit characters ensuring sexual attractiveness or high-quality genes, if ornaments honestly reveal male genetic quality. Furthermore, in species where extra-pair fertilizations occur, offspring sired by an extra-pair male are expected to more frequently be male than those of the legitimate male if the latter is of lower quality than the extra-pair male. We investigated adjustment of sex ratio of offspring in relation to ornamentation of the extra-pair and the social mate of females by direct manipulation of tails of male barn swallows Hirundo rustica . Molecular sexing of the offspring was performed using the W chromosome-linked avian chromo-helicase-DNA-binding protein (CHD) gene while paternity assessment was conducted by typing of hypervariable microsatellite loci. Extra-pair offspring sex ratio was not affected by ornamentation of their biological fathers relative to the experimental ornamentation of the parental male. Experimental ornamentation of the parental males did not affect the sex ratio of nestlings in their broods. Female barn swallows might be unable to bias offspring sex ratio at hatching according to the quality of the biological father. Alternatively, fitness benefits in terms of sexual attractiveness of sons might be balanced by the cost of compensating for little parental care provided by highly ornamented parental males, if sons are more costly to rear than daughters, or the advantage of producing more daughters, if males with large ornaments contribute differentially more to the viability of daughters than sons.     

Rapid temporal change in frequency of infanticide in a passerine bird associated with change in population density and body condition

Sexually selected infanticide, whereby unmated males obtaina mate by killing the dependent offspring of an already matedfemale, is a common alternative reproductive strategy in manyanimals. I estimated the frequency of infanticide in a populationof barn swallows, Hirundo rustica, during the period 1977–2002.Population size decreased by more than a factor 10 during thisperiod, and this decrease was associated with an increase inmortality, selecting for adults with better body condition.Density-dependent effects acted on infanticide through the relationshipbetween the relative number of unmated males and populationsize. Because males in prime condition are better able to defendtheir nests against infanticidal males, the frequency of infanticidedecreased as mean tail length and mean body condition of malesincreased during the study period. Therefore, a rapid decreasein population size, a decrease in the abundance of unmated males,and a concomitant increase in body condition have changed theimportance of infanticide from being a major cause of mortalityaccounting for more than 25% of all nestling mortality to beingalmost completely absent during a period of 25 years.     

Rapid change in nest size of a bird related to change in a secondary sexual character

Among bird species in which males contribute to nest building,sexual selection has favored larger nests. I investigated determinantsof nest size in the barn swallow Hirundo rustica and how nestsize changed during the period 1977–2003, when tail length(a male secondary sexual character) increased by more than 1.2standard deviations. Males with short tails contributed moreto nest building than long-tailed males, signaling their futureinvestment in food provisioning of offspring. Pairs of barnswallows were consistent in nest size when build ing new neststhe same or different years, and level of phenotypic plasticityin nest size was small and could not account for temporal patternsin nest size. Offspring resembled their parents with respectto nest size, indicating a significant heritability of nestsize, independent of whether offspring were reared by theirparents or by foster parents, and there was a significant negativegenetic correlation between male tail length and outer nestvolume and amount of nest material. The temporal increase inmale tail length was associated with a decrease in nest size,with the amount of nest material in 2003 on average being lessthan a third of the amount used in 1977. Temporal change innest size could be accounted for by indirect selection on taillength causing change in nest size to match that predicted fromchange in tail length and the genetic correlation between maletail length and nest size.     

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.     

Earlier breeding,lower success: does the spatial scale of climatic conditions matter in a migratory passerine bird?

Following over 20 years of research on the climatic effects on biodiversity we now have strong evidence that climate change affects phenology, fitness, and distribution ranges of different taxa, including birds. Bird phenology likely responds to changes in local weather. It is also affected by climatic year‐to‐year variations on larger scales. Although such scale‐related effects are common in ecology, most studies analyzing the effects of climate change were accomplished using climatic information on a single spatial scale. In this study, we aimed at determining the scale‐dependent sensitivity of breeding phenology and success to climate change in a migratory passerine bird, the barn swallow (Hirundo rustica). For both annual broods, we investigated effects of local weather (local scale) and the North Atlantic Oscillation (NAO, large scale) on the timing of breeding and breeding success. Consistent with previous studies in migratory birds we found that barn swallows in Eastern Germany bred progressively earlier. At the same time, they showed reduced breeding success over time in response to recent climatic changes. Responses to climatic variation were observed on both local and large climatic scales, but they differed with respect to the ecological process considered. Specifically, we found that the timing of breeding was primarily influenced by large‐scale NAO variations and to a lesser extent by local weather on the breeding grounds. Conversely, climatic conditions on the local scale affected breeding success, exclusively. The observed decrease in breeding success over years is likely a consequence of scale‐related mismatches between climatic conditions during different breeding phases. This provides further evidence that a species' response of earlier breeding may not be enough to cope with climate change. Our results emphasize the importance of considering the response of ecological processes along different climatic scales in order to better understand the complexity of climate change effects on biodiversity.     

Modelling past and present geographical distribution of the marine gastropod Patella rustica as a tool for exploring responses to environmental change

A climate envelope approach was used to model the distributions of the intertidal gastropod Patella rustica , to test the robustness of forecast responses to climate change. The model incorporated variables that were likely to determine the abundance and the northern range limit of this species in the NE Atlantic. The model was built using classification and regression tree analysis (CART) trained with historical distribution data from the mid 1950s and a set of corresponding climatic and oceanographic variables. Results indicated air and sea temperature, in particular during the reproductive and settlement periods, as the main determinants of the Atlantic distribution of P. rustica . The model was subsequently fed with contemporary climatic data and its output was compared with the current distribution and abundance of P. rustica , assessed during a 2002–2003 survey. The model correctly hindcasted the recent collapse of a distributional gap in northern Portugal, as well as an increase in abundance at locations within its range. The predicted northward expansion of the northern range limit did not occur because the absence of the species was confirmed in a survey encompassing the whole Atlantic French coast up to Brest. Stretches of unsuitable habitat too long to be overcome by dispersal are the likely mechanism controlling the northern limit of the distribution of this intertidal species.     

Immune response covaries with corticosterone plasma levels under experimentally stressful conditions in nestling barn swallows (Hirundo rustica)

Traits related to fitness are often pleiotropically linked orotherwise constrained in their expression. Organisms thereforetrade between fitness components such as number and viabilityof their offspring. The physiological mechanisms mediating suchtrade-offs, however, have been poorly investigated. We manipulatedbrood size and satiation of nestling barn swallows, Hirundorustica, to simulate the effect of two kinds of natural stresses,i.e., long-term intense competition in a large brood and acutefood deprivation, and we measured their effect on body condition,T cell–mediated immune response, and corticosterone, themain hormone mediating the adrenocortical stress-response. Broodenlargement increased corticosterone levels compared with thosefor brood reduction, and brood enlargement depressed immuneresponse, body mass, and condition. Corticosterone levels markedlyincreased after food deprivation. Immune response negativelycovaried with corticosterone levels measured after long-termstress. Hence, living in a crowded nest and with food deprivationelicited a stress response mediated by corticosterone, and depressedan important component of offspring fitness such as T cell–mediatedimmunity. The negative covariation between circulating corticosteroneand immunity suggests that the trade-off between offspring numberand quality is mediated by variation in plasma levels of corticosterone,which has immunosuppressive effects.