Ground cavity nest temperatures and their relevance to Blue Swallow Hirundo atrocaerulea conservation

Blue Swallows Hirundo atrocaerulea are Critically Endangered within South Africa. They nest in natural underground holes in mist-belt grasslands. Temperature dataloggers were used to record ground cavity nest (T_n) and ambient temperature (T_a) for one artificial and 11 natural Blue Swallow nests. Mean ground cavity T_n was significantly different to mean T_a. T_n ranged from 17.0 ± 0.1 °C to 28.5 ± 0.3 °C and varied less than T_a (14.0 ± 0.2 to 47.7 ± 0.4 °C). Mean ground cavity T_n averaged 3.3 ± 0.9 °C warmer than mean T_a for 58% of nests, and mean T_a averaged 2.6 ± 0.5 °C warmer than mean ground cavity T_n for 42% of nests. There was no significant difference in mean ground cavity T_n for the aardvark-excavated holes (22.7 ± 1.6 °C) and sinkholes (21.5 ± 1.2 °C). Blue Swallows also nest in man-made holes, potentially a way to increase nesting sites. Mean aardvark-excavated T_n (19.2 ± 0.1 °C) was significantly warmer than mean artificial cavity T_n (18.5 ± 0.2 °C). Further investigation of breeding success of Blue Swallows in relation to T_n, incubation strategies and predation risk needs to be addressed in future studies for a better understanding of their reproductive ecology.     

Breeding habitat selection in the Swallow Hirundo rustica

This paper investigates the factors which influence nest site selection in Swallows. In years with peak numbers, more pairs settle on favoured farms rather than establish new 'colonies' at sub-optimal sites.     

The breeding biology of the Pacific Swallow Hirundo tahitica in Malaysia

The breeding biology of the Pacific Swallow was studied in Malaysia. Time-budgets and preliminary energy-budgets were calculated for different stages of the breeding cycle. Breeding was seasonal, the first eggs were laid in the first week of March from 1978 to 1982. The nest was a mud cup built under an overhang, often on man-made structures over water. The mean clutch size was 2.98 eggs. So more than two successful clutches were ever raised, although up to four sets of eggs can be laid if clutches are lost. The incubation period was 16.2 days and the nestling period 19–21 days. Nestling weights showed the typical hirundine recession before fledging. The mean brood size was 2.32 and there was no evidence of undernourishment in larger broods. Nesting success was lower than for temperate hirundines but high for a tropical passerine. Incubation duties were carried out by the female alone but both parents fed the brood. The male never delivered more than 44% of the total feeds. Daily energy expenditure varied from 3.44–4.9×BMR depending upon the stage of the breeding cycle.     

The timing of breeding and moult of the Lesser Striped Swallow Hirundo abyssinica

The Lesser Striped Swallow seems to have two different breeding populations. The birds south of 10°S breed largely during the spring and summer (July to April) and moult from about April to August. Birds further north breed throughout the year, but mainly during the first seven months of the year. Moult in the birds north of 10°S is from July to February when few birds are breeding. There seem to be two clearly defined moulting populations, with the southern breeding population moulting largely south of 10°S and the east African breeding population moulting largely north of the equator. In both populations moult and breeding seem to be separated in time, at least at the individual level.     

The timing of breeding and moult of the Lesser Striped Swallow Hirundo abyssinica

The Lesser Striped Swallow seems to have two different breeding populations. The birds south of 10°s breed largely during the spring and summer (July to April) and moult from about April to August. Birds further north breed throughout the year, but mainly during the first seven months of the year. Moult in the birds north of 10°s is from July to February when few birds are breeding. There seem to be two clearly defined moulting populations, with the southern breeding population moulting largely south of 10°s and the east African breeding population moulting largely north of the equator. In both populationsmoult and breeding seem to be separated in time, at least at the individual level.     

Sexual dimorphism in wing and tail length as shown by the Swallow Hirundo rustica

In both sexes of Hirundo rustica two metric traits are significantly different. One of these traits, tail length, shows a positive correlation between mates and a negative correlation with the date of first egg laying. On the other hand, wing lengths are not significantly related in any of the corresponding tests. Similar relations were recorded both for all analysed birds and for at least two-year-old individuals. It is suggested that sexual selection, as proposed by Darwin (1871) for monogamous birds, is responsible for sexual dimorphism in the tail length of the Swallow. It seems that intersexual difference in wing length could be a result of such mechanisms as stabilizing the body sizes of males and females at different energetically optimum levels by natural selection.     

A Trade-Off between Reproduction and Feather Growth in the Barn Swallow (Hirundo rustica)

Physiological trade-offs mediated by limiting energy, resources or time constrain the simultaneous expression of major functions and can lead to the evolution of temporal separation between demanding activities. In birds, plumage renewal is a demanding activity, which accomplishes fundamental functions, such as allowing thermal insulation, aerodynamics and socio-sexual signaling. Feather renewal is a very expensive and disabling process, and molt is often partitioned from breeding and migration. However, trade-offs between feather renewal and breeding have been only sparsely studied. In barn swallows (Hirundo rustica) breeding in Italy and undergoing molt during wintering in sub-Saharan Africa, we studied this trade-off by removing a tail feather from a large sample of individuals and analyzing growth bar width, reflecting feather growth rate, and length of the growing replacement feather in relation to the stage in the breeding cycle at removal and clutch size. Growth bar width of females and length of the growing replacement feather of both sexes were smaller when the original feather had been removed after clutch initiation. Importantly, in females both growth bar width and replacement feather length were negatively predicted by clutch size, and more strongly so for large clutches and when feather removal occurred immediately after clutch completion. Hence, we found strong, coherent evidence for a trade-off between reproduction, and laying effort in particular, and the ability to generate new feathers. These results support the hypothesis that the derived condition of molting during wintering in long-distance migrants is maintained by the costs of overlapping breeding and molt.     

Viability Is Associated with Melanin-Based Coloration in the Barn Swallow (Hirundo rustica)

Pigmentation of body surface in animals can have multiple determinants and accomplish diverse functions. Eumelanin and pheomelanin are the main animal pigments, being responsible of yellow, brownish-red and black hues, and have partly common biosynthetic pathways. Many populations of vertebrates show individual variation in melanism, putatively with large heritable component. Genes responsible for eu- or pheomelanogenesis have pleiotropic but contrasting effects on life-history traits, explaining the patterns of covariation observed between melanization and physiology (e.g. immunity and stress response), sexual behavior and other characters in diverse taxa. Yet, very few studies in the wild have investigated if eu- and pheomelanization predict major fitness traits like viability or fecundity. In this correlative study, by contrasting adult barn swallows (Hirundo rustica) matched for age, sex, breeding site, and year and date of sampling, we show that males but not females that survived until the next year had paler, relatively more eu- than pheomelanic pigmentation of ventral body feathers. Better performance of individuals that allocate relatively more to eumelanogenesis was expected based on previous evidence on covariation between eumelanic pigmentation and specific traits related to immunity and susceptibility to stress. However, together with the evidence of no covariation between viability and melanization among females, this finding raises the question of the mechanisms that maintain variation in genes for melanogenesis. We discuss the possibility that eu- and pheomelanization are under contrasting viability and sexual selection, as suggested by larger breeding and sperm competition success of darker males from other barn swallow subspecies.     

Early-Life Telomere Dynamics Differ between the Sexes and Predict Growth in the Barn Swallow (Hirundo rustica)

Telomeres are conserved DNA-protein structures at the termini of eukaryotic chromosomes which contribute to maintenance of genome integrity, and their shortening leads to cell senescence, with negative consequences for organismal functions. Because telomere erosion is influenced by extrinsic and endogenous factors, telomere dynamics may provide a mechanistic basis for evolutionary and physiological trade-offs. Yet, knowledge of fundamental aspects of telomere biology under natural selection regimes, including sex- and context-dependent variation in early-life, and the covariation between telomere dynamics and growth, is scant. In this study of barn swallows (Hirundo rustica) we investigated the sex-dependent telomere erosion during nestling period, and the covariation between relative telomere length and body and plumage growth. Finally, we tested whether any covariation between growth traits and relative telomere length depends on the social environment, as influenced by sibling sex ratio. Relative telomere length declined on average over the period of nestling maximal growth rate (between 7 and 16 days of age) and differently covaried with initial relative telomere length in either sex. The frequency distribution of changes in relative telomere length was bimodal, with most nestlings decreasing and some increasing relative telomere length, but none of the offspring traits predicted the a posteriori identified group to which individual nestlings belonged. Tail and wing length increased with relative telomere length, but more steeply in males than females, and this relationship held both at the within- and among-broods levels. Moreover, the increase in plumage phenotypic values was steeper when the sex ratio of an individual’s siblings was female-biased. Our study provides evidence for telomere shortening during early life according to subtly different dynamics in either sex. Furthermore, it shows that the positive covariation between growth and relative telomere length depends on sex as well as social environment, in terms of sibling sex ratio.     

Haematocrit correlates with tail ornament size in three populations of the Barn Swallow (Hirundo rustica)

1. Handicap models of sexual selection propose that male ornaments are indicators of male quality and that honesty is enforced by the costs imposed by the exaggerated ornamental traits. In long-distance migratory birds that feed on the wing, the aerodynamic cost of exaggerated ornamental characters should be particularly high because the size of the ornaments deviates from the natural selection optimum. During migration, birds are expected to raise their oxygen consumption in relation to the energetic demands imposed by their morphology. An increase of haematocrit is an adaptive response to enhance oxygen uptake and efficiency of transfer to the muscular tissues during spells of intense muscular activity.
2. The change of haematocrit of Barn Swallows ( Hirundo rustica ) after their arrival to the breeding sites, and the relationships between haematocrit values recorded after migration and the size of ordinary and sexually selected morphological characters in three Barn Swallow populations were analysed.
3. Males had higher haematocrit values than females. Individual haematocrit values declined after arrival to the breeding sites. Haematocrit values of males were significantly and positively correlated with the size of their ornamental tail but not correlated with other characters, thus suggesting that well-ornamented males, in order to arrive early, have to raise their haematocrit above the level of short-tailed males.
4. Males and females of similar tail length did not differ in their haematocrit, thus suggesting that sexual dimorphism in haematocrit might be functionally related to dimorphism in tail length.
5. Our results are consistent with the handicap principle because long-tailed males experience lower mortality and larger seasonal reproductive success compared with short-tailed males.     

Segregation in the African wintering ranges of English and Swiss Swallow Hirundo rustica populations: a stable isotope study

Capsule Stable isotope analysis of Swallow feathers, grown in Africa, revealed significant differences between populations breeding in Switzerland and England.

Aims To investigate the extent to which Swallow populations breeding in Switzerland and England are separated on their African wintering grounds.

Methods Swallows were caught at breeding colonies, biometric measurements were taken and feathers, grown in Africa, were collected. Feathers were combusted in a Carlo Erba C/N/S analyser and the δ¹³C and δ¹⁵N signatures were measured using a mass spectrometer.

Results The δ¹³C signatures of Swiss birds were significantly more depleted than those of birds from England. The δ¹⁵N signatures did not differ between the two populations.

Conclusion Birds from Switzerland and England probably winter in geographically distinct parts of Africa. The Swiss birds probably feed on prey that are more reliant on C₃ vegetation, from woodlands, than the prey of English birds, which are more reliant on C₄ vegetation, from grasslands.     

Sexual Dimorphism in Melanin Pigmentation,Feather Coloration and Its Heritability in the Barn Swallow (Hirundo rustica)

Melanin is the main pigment in animal coloration and considerable variation in the concentrations of the two melanin forms (pheo- and eumlanin) in pigmented tissues exists among populations and individuals. Melanin-based coloration is receiving increasing attention particularly in socio-sexual communication contexts because the melanocortin system has been hypothesized to provide a mechanistic basis for covariation between coloration and fitness traits. However, with few notable exceptions, little detailed information is available on inter-individual and inter-population variation in melanin pigmentation and on its environmental, genetic and ontogenetic components. Here, we investigate melanin-based coloration in an Italian population of a passerine bird, the barn swallow (Hirundo rustica rustica), its sex- and age-related variation, and heritability. The concentrations of eu- and pheomelanin in the throat (brown) and belly (white-to-brownish) feathers differed between sexes but not according to age. The relative concentration of either melanin (Pheo:Eu) differed between sexes in throat but not in belly feathers, and the concentrations in males compared to females were larger in belly than in throat feathers. There were weak correlations between the concentrations of melanins within as well as among plumage regions. Coloration of belly feathers was predicted by the concentration of both melanins whereas coloration of throat feathers was only predicted by pheomelanin in females. In addition, Pheo:Eu predicted coloration of throat feathers in females and that of belly feathers in males. Finally, we found high heritability of color of throat feathers. Melanization was found to differ from that recorded in Hirundo rustica rustica from Scotland or from H. r. erythrogaster from North America. Hence, present results show that pigmentation strategies vary in a complex manner according to sex and plumage region, and also among geographical populations, potentially reflecting adaptation to different natural and sexual selection regimes, and that some coloration components seem to be highly heritable.     

Parasite Infestation and Parental Care in the Barn Swallow Hirundo rustical a Test of the Resource-provisioning Model of Parasite-mediated Sexual Selection

Barn swallows, Hirundo rustica, are commonly infested by the haematophagous tropical fowl mite Omithonyssus bursa (Macronyssidae, Gamasida), which severely reduces various measures of reproductive success among the barn swallow hosts. Food provisioning rate by parent barn swallows, measured in terms of absolute feeding rate by males and females and relative feeding rate by males (percentage of food provided by the male parent), was not significantly related to natural levels of infestation of nests. Experimental manipulation of mite loads in nests during the egg-laying period of the first clutch, which also affected mite loads of parent barn swallows, significantly affected food-provisioning rates of single-brooded, but not of double-brooded barn swallows. These results suggest that effects of mites on the parenting ability of barn swallow hosts depend on host resistance towards parasites. This is consistent with the resource-provisioning hypothesis of parasite-mediated sexual selection, suggesting that females prefer parasite-free males because they are efficient parents, but also with the hypothesis that females prefer males with traits signalling genetic resistance to parasites.     

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.     

Fine structure of the down feather during its early development

The down feather of the chick embryo has been examined by electron microscopy during three distinct stages of its early development; the presumptive stage, represented by dorsal skin of an area from which the feather organ will arise; the thickening stage, during which areas of the basal epidermis form spurs projecting into the mesenchyme, and the latter condenses under a thickened area of the epidermis; the elevation stage, at which time the basal epidermis flattens, the entire epidermis increases in thickness, and the underlying mesenchyme becomes more compact. As development proceeds the rough endoplasmic reticulum of the epidermal cells dilates, but during the elevation stage begins to flatten, and Golgi is observed with increasing frequency. The mitochondria do not appear to differ except for those in the periderm during the presumptive stage, in which case they reveal a vacant matrix and irregular cristae. Evidence is presented for actual contact between basal epidermal spurs and filopodia of cells within the mesenchyme, some of which contain numerous vesicles. The basal epidermal spurs are also seen in intimate association with collagen and anchor filaments and a network of reticulin. Evidence is also presented for the presence of neuronal elements within the mesenchyme during the thickening stage. Cross sections of cell processes within the condensations of the mesenchyme resemble unmyelinated nerve fibers, and cross sections of filopodia similar to arborizing axons abound at and within the basal lamina of both the thickening and elevation stages. Further support for the presence of nerve fibers within the mesenchyme comes from positive staining results with Bodian's and Ungewitter's methods. This comparative study of three stages of early development of the feather organ serves as a basis for more detailed investigations of each stage.