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.     

Current distribution and population size of the Blue Swallow Hirundo atrocaerulea in the southern Tanzanian highlands

Two surveys of Blue Swallows were conducted in the southern Tanzanian highland grasslands in order to determine the habitat preferences and estimate the size of this subpopulation. During the 2008/09 and 2012 surveys, a total distance of 3 635?km was travelled in search of Blue Swallows (at an altitude of above 1 400?m above sea level). Blue Swallows showed no preference for any altitude range above 1 400?m. The Blue Swallows showed a preference for natural pastures and for rural villages interspersed with crops and natural pasture. The buildings in the rural villages provide the nesting sites and, in close proximity, the crops, natural pastures, livestock and their dung possibly provide the food source for the aerial arthropods on which the Blue Swallows feed. In total, 151 Blue Swallows were recorded consisting of 62 males, 68 females and 21 unsexed individuals at 62 localities. These data along with environmental variables were used to construct an ecological niche model for the Blue Swallow. It was estimated that a mean of 12 791 km2 of suitable habitat was available for Blue Swallows. The 151 Blue Swallows recorded within the maximum perpendicular distance of 262?m on either side of the survey route resulted in a subpopulation estimate of 1 014 (338 to 507 pairs) Blue Swallows in the southern Tanzanian highland grasslands (12 791 km2). Mean densities were 0.023 to 0.035 pairs km???2. A density of 0.13 pairs km???2 recorded on a cattle farm consisting primarily of grasslands and wetlands was similar to the density of pairs found on sites in South Africa and Swaziland of compara- ble size and with matching characteristics to this site in Tanzania. Based on this new information the global Blue Swallow population estimate is updated to between 1 169 and 1 338 pairs.     

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.     

Facultative prioritization of wing growth in the Welcome Swallow Hirundo neoxena

Bird species adapted to variable environments tend to have slow lean tissue growth rates and high fat deposition rates, allowing survival during food shortages. This emphasis on fat deposition may be a fixed physiological trait. Alternatively, tissue allocation may be adjusted facultatively according to the proximate food supply. We consider two models of facultative adjustment that could account for the emphasis on fat deposition: (1) the fat-priority model, in which no lean growth occurs when food is scarce, and (2) the lean-priority model, in which a minimal level of lean growth always occurs but nutrients are otherwise allocated to fat deposition. We tested these two models using Welcome Swallows Hirundo neoxena , a species we show to have a variable food supply that is influenced by weather. We reduced food supply to chicks experimentally, by enlarging broods or excluding parents from chicks, and tested for reduction in wing growth (an indicator of lean growth) and mass growth (an indicator of fat deposition). Mass growth was retarded by both manipulations, but not wing growth, corroborating the lean-priority model. This growth strategy may function not to cope with violent variation in food supply, but to maintain development and symmetry of wings and feathers in the face of moderate variation in food supply. Our results contrast with those of a similar experiment on the Black Noddy Anous minutus , a species with more severe variation in food supply.     

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.     

家燕和金腰燕的卵胚胎心率比较

胚胎心率是衡量胚胎新陈代谢速率的重要指标。鸟类的胚胎心率随新陈代谢的增加而呈上升趋势。对早成性鸟类的种间比较发现,胚胎心率平均值随卵重量的增大而减小,卵体积小的种类具有相对较高的胚胎心率。国内有关野生鸟类胚胎心率的研究较少。2014年5~8月,在黑龙江扎龙国家级自然保护区,利用红外胚胎心率测量仪对两种近缘鸟类家燕(Hirundo rustica,n=14)和金腰燕(Cecropis daurica,n=14)的卵胚胎心率及其变化进行了测量与比较。两种燕均在孵卵的第2天开始出现胚胎心率,并随胚龄增加心率呈上升趋势,但在第8天及第11~14天家燕的胚胎心率显著低于金腰燕(第8天:z=﹣2.602,P=0.009;第11天:z=﹣2.497,P=0.013;第12天:z=﹣2.354,P=0.019;第13天:z=3.424,P=0.001;第14天:z=﹣3.380,P=0.001)。家燕卵胚胎日均增长心率(19.0±3.1)次/min,金腰燕卵胚胎日均增长心率(16.1±3.4)次/min,二者差异不显著(z=﹣1.792,P=0.073)。两种燕的胚胎心率与卵容量和卵重均不存在显著相关性[家燕:卵容量(1.73±0.09)cm3,r=0.192,P=0.511;卵重(1.74±0.09)g,r=0.128,P=0.663。金腰燕:卵容量(1.74±0.08)cm3,r=0.040,P=0.891;卵重(1.51±0.09)g,r=0.054,P=0.855]。这可能表明,卵大小和卵重量对家燕与金腰燕的胚胎心率均影响不明显。     

Frequency and consequences of feather holes in Barn Swallows Hirundo rustica

The relationship between feather quality, estimated through the prevalence and intensity of feather holes, and the breeding performance and survival of the Barn Swallow Hirundo rustica was studied over a 5-year period. In addition, we present some indirect data on the role of chewing lice in producing the feather holes. The balanced distribution of feather holes (high prevalence, low aggregation) corresponds with the pattern of distribution of lice on colonial birds, and in the Barn Swallow. Feather holes were significantly and positively associated with the arrival dates of the birds, as both males and females with an increased number of feather holes started laying later. Females that survived the winter had significantly fewer holes than non-surviving females, whereas there was no difference in feather hole number between surviving and non-surviving males. Given that there was no association between the number of feather holes and body condition indices, except for the tail length of male Barn Swallows, we suggest that the negative effect of feather holes on the fitness of the birds is mainly apparent during periods of intensive locomotor activity, such as migration. Alternatively, if feather holes are an indicator of quality, those birds with a high intensity of feather holes may have been of poor quality. These birds may have been less able to cope with the environmental conditions, resulting in the lower survival and later arrival of the birds to the breeding grounds. The negative relationship between the length of the outermost tail feathers of males and the incidence of feather holes suggests that the tail is a condition-dependent secondary sexual characteristic.     

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.     

哈尔滨家燕mandschurica亚种繁殖生态特征

许多鸟种因具有较强的适应性而分布广泛,例如家燕(Hirundo rustica)。在不同纬度地区研究其繁殖生态学特征有助于了解家燕对不同环境的适应。家燕mandschurica亚种在国内仅分布于黑龙江省,且该亚种的繁殖资料少有报道,为此,于2016和2017年每年的4至10月,在哈尔滨对其繁殖生态特征开展研究,并与国内目前已发表的家燕gutturalis亚种繁殖生态特征进行对比。家燕mandschurica亚种4月底或5月初迁来哈尔滨,9月下旬或10月初南迁;窝卵数为4～6枚(n=19);卵长径(18.7±1.4)mm(15.9～22.5 mm)、卵短径(13.0±0.5)mm(12.2～14.2 mm),卵重(1.6±0.1)g(1.3～1.9 g),n=35;孵卵期为(16±2)d(14～18 d,n=19);育雏期为(17±1)d(16～18 d,n=6)。雏鸟的体长、翅长及尾羽长的生长曲线能与Logistic较好地拟合;体重、嘴峰和跗跖在5日龄左右生长最快,体长和翅长在7日龄左右增长最快,雏鸟的生长模式符合能量分配假说。与我国南方的家燕gutturalis亚种相比,在哈尔滨繁殖的mandschurica亚种的卵更小、更轻,二者孵卵期相似,但后者育雏期更短。这或许与不同地区食物丰富度及亲鸟喂食策略有关。     

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.     

Contrasting sensitivity of nestling and fledgling Barn Swallow Hirundo rustica body mass to local weather conditions

Local weather can influence the growth and development of young birds either indirectly, by modifying prey availability, or directly, by affecting energetic trade-offs. Such effects can have lasting implications for life history traits, but the nature of these effets may vary with the developmental stage of the birds, and over timescales from days to weeks. We examined the interactive effects of temperature, rainfall and wind speed on the mass of nestling and fledgling Barn Swallows Hirundo rustica both on the day of capture and averaging weather across the time since hatching. At the daily timescale, nestling mass was negatively correlated with temperature, but the strength of this association depended on the level of rainfall and wind speed; nestlings were typically heavier on dry or windy days, and the negative effect of temperature was strongest under calm or wet conditions. At the early lifetime timescale (i.e. from hatching to pre-fledging), nestling mass was negatively correlated with temperature at low wind speed. Fledgling body mass was less sensitive to weather; the only weather effect evident was a negative correlation with temperature at the daily scale under high rainfall that became slightly positive under low rainfall. These changes are consistent with weather effects on the availability and distribution of insects within the landscape (e.g. causing high concentrations of flying insects) and with the effects of weather variation on nest microclimate. These results together demonstrate the impacts of weather on chick growth, over immediate (daily) and longer term (nestling/fledgling lifetime) timescales. This shows that sensitivity to local weather conditions varies across the early lifetime of young birds (nestling–fledgling stages) and illustrates the mechanisms by which larger scale (climate) variations influence the body condition of individuals.     

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.