European Barn Swallow Research Articles

Age-related changes in sperm traits and evidence for aging costs of sperm production in a sexually promiscuous passerine

In many animal species, organismal performance declines with age in a process known as aging or senescence. Senescence typically leads to a deterioration of physiological functionality and can impact the development of primary sexual phenotypes. Sperm production is a complex and costly process that is sensitive to changes in individual physiological state, yet remarkably little is known about age-related changes in sperm performance and aging costs of sperm production. Here we use a non-linear generalized additive mixed models (GAMM) modelling to evaluate age-related changes in postcopulatory sexual traits in the European barn swallow (Hirundo rustica rustica), a relatively short lived sexually promiscuous passerine species, where male extra-pair fertilization success has been shown to increase with age. We confirmed a positive relationship between sperm midpiece length and sperm velocity in this species. Within-male changes in sperm morphology and sperm velocity were in general absent, with only sperm length decreasing linearly with increasing age, although this change was negligible compared to the overall variation in sperm size among males. In contrast, the cloacal protuberance (CP) size changed nonlinearly with age, with an initial increase between the first and third year of life followed by a plateau. The results further indicate the existence of a trade-off between investments in sperm production and survival as males with large CP tended to have a reduced lifespan. This seems consistent with the idea of expensive sperm production and survival aging costs associated with investments in post-copulatory traits in this sexually promiscuous species.

Across the deserts and sea: inter-individual variation in migration routes of south-central European barn swallows (Hirundo rustica)

BackgroundThe spatiotemporal organization of migratory routes of long-distance migrants results from trade-offs between minimizing the journey length and en route risk of migration-related mortality, which may be reduced by avoiding crossing inhospitable ecological barriers. Despite flourishing avian migration research in recent decades, little is still known about inter-individual variability in migratory routes, as well as the carry-over effects of spatial and temporal features of migration on subsequent migration stages.MethodsWe reconstructed post- and pre-breeding migration routes, barrier crossing behaviour and non-breeding movements of the largest sample (N = 85) analysed to date of individual barn swallows breeding in south-central Europe, which were tracked using light-level geolocators.ResultsMost birds spent their non-breeding period in the Congo basin in a single stationary area, but a small fraction of itinerant individuals reaching South Africa was also observed. Birds generally followed a ‘clockwise loop migration pattern’, moving through the central Mediterranean and the Sahara Desert during post-breeding (north to south) migration yet switching to a more western route, along the Atlantic coast of Africa, Iberia and western Mediterranean during the pre-breeding (south to north) migration. Southward migration was straighter and less variable, while northward migration was significantly faster despite the broader detour along the Atlantic coast and Iberia. These patterns showed limited sex-related variability. The timing of different circannual events was tightly linked with previous migration stages, considerably affecting migration route and speed of subsequent movements. Indeed, individuals departing late from Africa performed straighter and faster pre-breeding migrations, partly compensating for the initial departure delays, but likely at the cost of performing riskier movements across ecological barriers.ConclusionsDifferent spatiotemporal migration strategies during post- and pre-breeding migration suggest that conditions en route may differ seasonally and allow for more efficient travelling along different migration corridors in either season. While highlighting patterns of inter-individual variability, our results support increasing evidence for widespread loop migration patterns among Afro-Palearctic avian migrants. Also, they suggest that carry-over effects acting across different phases of the annual cycle of migratory species can have major impacts on evolutionary processes.

Telomere length is highly repeatable and shorter in individuals with more elaborate sexual ornamentation in a short-lived passerine.

Quantifying an individual's state as a fitness proxy has proven challenging, but accumulating evidence suggests that telomere length and attrition may indicate individual somatic state and success at self-maintenance, respectively. Sexual ornamentation is also thought to signal phenotypic quality, but links between telomeres and sexual ornamentation have been little explored. To address this issue, we examined whether telomere length and dynamics are predicted by the expression of a sexually selected ornament, the length of the outermost tail feathers (streamers), using longitudinal data from a population of European barn swallows (Hirundo rustica). In 139 adult individuals, each measured twice, we further assessed associations of telomere length with age, sex, breeding status and survival. Telomere length showed high individual repeatability (R=.97) across years while shortening with age in both sexes. Telomere length and dynamics were not significantly associated with survival to the next year, remaining lifespan or reproduction status (comparing breeding and nonbreeding yearlings). Tail streamer length, a sexually selected trait in barn swallows, was negatively associated with telomere length, independent of sex. Thus, telomere length may reflect the costs of carrying an elaborated sexual ornament, although ornament size did not significantly predict telomere shortening. In conclusion, telomere length in adult barn swallows is a highly consistent trait that shows a negative relationship with sexual ornamentation, suggesting a trade-off between sexual ornamentation and telomere length.

Short Communication: Roosting behavior of Wintering Barn Swallow (Hirundo rustica) in Peninsular Malaysia

Abstract. Ismail NA, Jufri ABAK, Daud UNS, Nor SM, Mansor MS. 2020. Short Communication: Roosting behavior of Wintering Barn Swallow (Hirundo rustica) in Peninsular Malaysia. Biodiversitas 21: 661-665. The East Asian Barn Swallow Hirundo rustica gutturalis primarily breeds in China, Japan, and Korea, typically migrates to Southeast Asia during winter, including Malaysia. To date, knowledge regarding population of Barn Swallow are limited to their breeding grounds and other subspecies (e.g., European Barn Swallow Hirundo rustica rustica). A previous study on Barn Swallow wintering in Malaysia was conducted approximately 50 years ago and mainly focused on population dynamics. The objective of the present study was to investigate the roosting behavior of wintering Barn Swallows in a major roosting site, Bentong, central Peninsular Malaysia, from October 2018 to March 2019. Scan sampling at 5-min intervals was used to examine the roosting behavior of the swallows perching on service wires (i.e., electricity and telephone wires). We found that the swallows began to roost an average of 10 minutes after sunset and slept 55 minutes later. However, cloudy and rainy weather significantly affects swallow roosting period, leading them to perch earlier, 5 minutes before sunset. The pattern of roosting behavior was somewhat similar throughout the migration season, except in the early migration season (October), which was likely inconsistent due to their early adaptation to the town environment. Behavioral scan sampling revealed that swallows spend most of the time motionless, followed by preening. However, anthropogenic disturbances disrupt their behavior and sleep time. We also noted that this communally roosting bird behaved gregariously on wires, particularly at sites illuminated by light, which is likely an anti-predator mechanism.

Selection on multiple sexual signals in two Central and Eastern European populations of the barn swallow.

Variation in intensity and targets of sexual selection on multiple traits has been suggested to play a major role in promoting phenotypic differentiation between populations, although the divergence in selection may depend on year, local conditions or age. In this study, we quantified sexual selection for two putative sexual signals across two Central and East European barn swallow (Hirundo rustica rustica) populations from Czech Republic and Romania over multiple years. We then related these differences in selection to variation in sexual characters among barn swallow populations. Our results show that tail length and ventral coloration vary between populations, sexes, and age classes (first‐time breeders vs. experienced birds). We found that selection on tail length was stronger in first‐time breeders than in experienced birds and in males than in females in the Romanian population, while these differences between age groups and sexes were weak in Czech birds. We suggest that the populational difference in selection on tail length might be related to the differences in breeding conditions. Our results show that ventral coloration is darker (i.e., has lower brightness) in the Romanian than in the Czech population, and in experienced birds and males compared with first‐time breeders and females, respectively. The sexual difference in ventral coloration may suggest sexual selection on this trait, which is supported by the significant directional selection of ventral coloration in first‐time breeding males on laying date. However, after controlling for the confounding effect of wing length and tarsus length, the partial directional selection gradient on this trait turned nonsignificant, suggesting that the advantage of dark ventral coloration in early breeding birds is determined by the correlated traits of body size. These findings show that ventral coloration may be advantageous over the breeding season, but the underlying mechanism of this relationship is not clarified.

SMRT long reads and Direct Label and Stain optical maps allow the generation of a high-quality genome assembly for the European barn swallow (Hirundo rustica rustica).

BackgroundThe barn swallow (Hirundo rustica) is a migratory bird that has been the focus of a large number of ecological, behavioral, and genetic studies. To facilitate further population genetics and genomic studies, we present a reference genome assembly for the European subspecies (H. r. rustica).FindingsAs part of the Genome10K effort on generating high-quality vertebrate genomes (Vertebrate Genomes Project), we have assembled a highly contiguous genome assembly using single molecule real-time (SMRT) DNA sequencing and several Bionano optical map technologies. We compared and integrated optical maps derived from both the Nick, Label, Repair, and Stain technology and from the Direct Label and Stain (DLS) technology. As proposed by Bionano, DLS more than doubled the scaffold N50 with respect to the nickase. The dual enzyme hybrid scaffold led to a further marginal increase in scaffold N50 and an overall increase of confidence in the scaffolds. After removal of haplotigs, the final assembly is approximately 1.21 Gbp in size, with a scaffold N50 value of more than 25.95 Mbp.ConclusionsThis high-quality genome assembly represents a valuable resource for future studies of population genetics and genomics in the barn swallow and for studies concerning the evolution of avian genomes. It also represents one of the very first genomes assembled by combining SMRT long-read sequencing with the new Bionano DLS technology for scaffolding. The quality of this assembly demonstrates the potential of this methodology to substantially increase the contiguity of genome assemblies.

Loop migration, induced by seasonally different flyway use, in Northern European Barn Swallows

Seasonal variation in migratory routes seems to be a common trait among many Afro-Palearctic migrants, but there are only few examples of species or populations which shift between entirely different flyways in autumn and spring. To identify non-breeding regions and seasonal differences in migration strategies we tracked Barn Swallows (Hirundo rustica) from a Baltic breeding population by light-level geolocators. Using novel analytical tools, we provide the first full annual tracks for European swallows. The main non-breeding residency sites of the tracked individuals were located in Southern Africa and all birds followed a distinct counterclockwise loop migration pattern shifting from the central Afro-Palearctic flyway in autumn to the eastern Afro-Palearctic flyway in spring. Despite the elongated detour through the Arabian Peninsula and the Caucasus Mountains, spring migration was faster than autumn migration in all of the tracked males and one out of two females, implying favorable conditions en route that allow for more efficient and faster traveling.

Lifetime reproductive success, selection on lifespan, and multiple sexual ornaments in male European barn swallows.

Natural and sexual selection arise when individual fitness varies according to focal traits. Extra-pair paternities (EPPs) can affect the intensity of selection by influencing variance in fitness among individuals. Studies of selection require that individual fitness is estimated using proxies of lifetime reproductive success (LRS). However, estimating LRS is difficult in large, open populations where EPPs cause reallocation of biological paternity. Here, we used extensive field sampling to estimate LRS in a population of barn swallows (Hirundo rustica) to estimate selection on lifespan and ornamental traits of males. We found selection on lifespan mediated both by within- and extra-pair fertilization success and selection on tail length mediated by within- but not extra-pair fertilization success. In addition, we found selection on tail white spots via extra-pair fertilization success after controlling for selection on other traits. These results were not confounded by factors that hamper studies of LRS, including nonexhaustive sampling of offspring and biased sampling of males. Hence, natural and sexual selection mediated by LRS operates on lifespan, tail length, and size of the tail white spots in barn swallows.

Disruptive selection without genome-wide evolution across a migratory divide.

Transcontinental migration is a fascinating example of how animals can respond to climatic oscillation. Yet, quantitative data on fitness components are scarce, and the resulting population genetic consequences are poorly understood. Migratory divides, hybrid zones with a transition in migratory behaviour, provide a natural setting to investigate the micro-evolutionary dynamics induced by migration under sympatric conditions. Here, we studied the effects of migratory programme on survival, trait evolution and genome-wide patterns of population differentiation in a migratory divide of European barn swallows. We sampled a total of 824 individuals from both allopatric European populations wintering in central and southern Africa, respectively, along with two mixed populations from within the migratory divide. While most morphological characters varied by latitude consistent with Bergmann's rule, wing length co-varied with distance to wintering grounds. Survival data collected during a 5-year period provided strong evidence that this covariance is repeatedly generated by disruptive selection against intermediate phenotypes. Yet, selection-induced divergence did not translate into genome-wide genetic differentiation as assessed by microsatellites, mtDNA and >20000 genome-wide SNP markers; nor did we find evidence of local genomic selection between migratory types. Among breeding populations, a single outlier locus mapped to the BUB1 gene with a role in mitotic and meiotic organization. Overall, this study provides evidence for an adaptive response to variation in migration behaviour continuously eroded by gene flow under current conditions of nonassortative mating. It supports the theoretical prediction that population differentiation is difficult to achieve under conditions of gene flow despite measurable disruptive selection.

Brood parasitism and quasi-parasitism in the European barn swallow Hirundo rustica rustica

We studied patterns of extra-pair maternity (EPM) in 245 nests (225 nests belonging to 120 females of known identity) of sexually promiscuous European barn swallows (Hirundo rustica rustica) over a 3-year period. At least one EPM nestling was identified in 54 nests (22.0 %), representing 5.7 % of a total of 1060 nestlings. Up to 28.3 % of all EPM nestlings resulted from quasi-parasitism (QP), whereby nest-attending males sired parasitic offspring. Nests of quasi-parasitic females were never in close proximity to the host nest. Our data thus indicate nonrandom QP patterns in our population suggesting that QP can be considered a third alternative reproductive strategy alongside extra-pair paternity (EPP) and intraspecific brood parasitism (IBP). Of several socioecological factors evaluated, only number of simultaneous egg-laying females in the population proved a good predictor for EPM occurrence. Whereas parasitic females produced more offspring per breeding attempt than was the population average, both QP and IBP affected host female reproductive output, being associated with a reduced number of her offspring produced from the nest. On the contrary, QP resulted in an increase in the number of offspring produced by nest-attending males, suggesting that males may benefit from cooperating with parasitic females at the expense of their social partners.

Transcontinental migratory connectivity predicts parasite prevalence in breeding populations of the European barn swallow.

Parasites exert a major impact on the eco-evolutionary dynamics of their hosts and the associated biotic environment. Migration constitutes an effective means for long-distance invasions of vector-borne parasites and promotes their rapid spread. Yet, ecological and spatial information on population-specific host-parasite connectivity is essentially lacking. Here, we address this question in a system consisting of a transcontinental migrant species, the European barn swallow (Hirundo rustica) which serves as a vector for avian endoparasites in the genera Plasmodium, Haemoproteus and Leucocytozoon. Using feather stable isotope ratios as geographically informative markers, we first assessed migratory connectivity in the host: Northern European breeding populations predominantly overwintered in dry, savannah-like habitats in Southern Africa, whereas Southern European populations were associated with wetland habitats in Western Central Africa. Wintering areas of swallows breeding in Central Europe indicated a migratory divide with both migratory programmes occurring within the same breeding population. Subsequent genetic screens of parasites in the breeding populations revealed a link between the host's migratory programme and its parasitic repertoire: controlling for effects of local breeding location, prevalence of Africa-transmitted Plasmodium lineages was significantly higher in individuals overwintering in the moist habitats of Western Central Africa, even among sympatrically breeding individuals with different overwintering locations. For the rarer Haemoproteus parasites, prevalence was best explained by breeding location alone, whereas no clear pattern emerged for the least abundant parasite Leucocytozoon. These results have implications for our understanding of spatio-temporal host-parasite dynamics in migratory species and the spread of avian borne diseases.

Male viability is positively related to multiple male ornaments in Asian Barn Swallows

The European Barn Swallow Hirundo rustica rustica is a model system for studying female mate choice for indirect benefits, as the long tail of males, the target of female mate choice, is positively related to male viability. However, situations may differ in other subspecies where male ornaments other than tail length are prominent and seem to be the targets of female choice. In this study, similar to previous studies on European populations, we determined the relationship between male viability and male ornaments, including tail length, in a Japanese population of the Asian Barn Swallow H. r. gutturalis, which have short tails, a whitish ventral plumage, and a large red throat patch. We observed that males with longer tails and larger and more colored (i.e., lower saturation values) throat patches were more likely to return to the study area than other males, independent of their age. Of these ornaments, information on viability of male tail length partially overlapped the information on viability by throat coloration. Because females choose mates, either directly or indirectly, based on their throat coloration, female mate preference for tail length had few benefits for the choosers. This may explain why female mate preference for tail length was not observed in this population. In addition, differing from a previous study in a European population, male throat patch size may serve as a good indicator of male viability, independent of tail length and throat coloration in this population. We discuss the possible explanations for the observed patterns.

Prevalence and molecular characterization of Clostridium difficile isolated from European Barn Swallows (Hirundo rustica) during migration

BackgroundClostridium difficile is an important bacterial pathogen of humans and a variety of animal species. Birds, especially migratory passerine species, can play a role in the spread of many pathogens, including Clostridium difficile. Barn Swallows (Hirundo rustica) nest in close proximity to human habitats and their biology is closely associated with cattle farming. Therefore, we hypothesized that Barn Swallows can be the reservoir of Clostridium difficile.ResultsBarn Swallows (n = 175) were captured on their autumn migration across Europe to sub-Saharan Africa. Droppings were collected from juvenile (n = 152) and adult birds (n = 23). Overall prevalence of Clostridium difficile was 4% (7/175); 4.6% (7/152) in juvenile birds and 0/23 in adults. Clostridium difficile ribotypes 078, 002 and 014 were identified, which are commonly found in farm animals and humans. Three new Clostridium difficile ribotypes were also identified: SB3, SB159 and SB166, one of which was toxigenic, harbouring genes for toxins A and B.ConclusionsResults of this study indicate that Barn Swallows might play a role in national and international dissemination of Clostridium difficile and could serve as a source for human and animal infection. Clostridium difficile ribotype 078 was identified, which has been reported as an emerging cause of community-associated Clostridium difficile infection in humans. Based on this and other studies, however, it is more likely that Barn Swallows have a more indicative than perpetuating role in Clostridium difficile epidemiology.

Colourful males hold high quality territories but exhibit reduced paternal care in barn swallows

The European barn swallow, Hirundo rustica rustica, is a model system of female mate choice for indirect benefits. Its long tail, which is the target of female mate choice, is positively related to the genetic quality of males, whereas direct benefits in terms of territory quality and paternal care are unimportant in the choice of long-tailed males. However, the situation may differ in other subspecies where male ornaments other than tail length are elaborate and appear to be the main target of female choice. Here we studied whether throat colouration, a sexually selected trait, provides direct benefits in terms of territory quality and parental care in a population of Japanese barn swallows, H. r. gutturalis, which have short tails and large throat patches. We compared dyads of males occupying neighbouring territories to study the relationship between male ornamentation and territory quality in our sparse population. Males with higher quality territories had more colourful throat patches than males with lower quality territories, indicating a positive relationship between male throat colouration and the quality of their territory. In contrast, male feeding rate decreased with increasing colourfulness of male throat patch without confounding with female feeding rate. These results are consistent with previous studies showing a positive association between plumage colouration and testosterone levels. The trade-off between the two direct benefits of mate choice, i.e., territory quality and paternal care, can explain sexual selection for colourful throat patches rather than long tails in our sparse outdoor population, a typical breeding habitat in Japan, whereas it predicts a reverse pattern in dense indoor populations as found in Europe.

Induction of multiple criteria optimal classification rules for biological and medical data

To induce critical classification rules from observed data is a major task in biological and medical research. A classification rule is considered to be useful if it is optimal and simultaneously satisfies three criteria: is highly accurate, has a high rate of support, and is highly compact. However, current classification methods, such as rough set theory, neural networks, ID3, etc., may only induce feasible rules instead of optimal rules. In addition, the rules found by current methods may only satisfy one of the three criteria. This study proposes a multi-criteria model to induce optimal classification rules with better rates of accuracy, support and compactness. A linear multi-objective programming model for inducing classification rules is formulated. Two practical data sets, one of HSV patients results and another of European barn swallows, are tested. The results illustrate that the proposed method can induce better rules than current methods.

Male tail streamer length predicts fertilization success in the North American barn swallow (Hirundo rustica erythrogaster)

In socially monogamous species, extra-pair paternity has the potential to increase the variance in male reproductive success, thereby affecting the opportunity for sexual selection on male extravagant ornamentation. In the European barn swallow (Hirundo rustica rustica), the tail streamer length is a sexually selected male ornament and an honest indicator of viability. The North American barn swallow (Hirundo rustica erythrogaster) also shows sexual dimorphism in tail streamer length, but whether this trait holds the same signalling function in this subspecies is a controversial issue, and the available literature is presently scarce. Here, we present data on paternity in the North American barn swallow, including a complete sampling of extra-pair sires in four colonies. We analysed how extra-pair paternity affected the variance in male fertilization success and examined whether male tail streamer (i.e. the outermost tail feather) length correlated with fertilization success (n=86 males). Extra-pair paternity constituted 31% of all offspring and significantly increased the variance in male fertilization success. The number of offspring sired by extra-pair males accounted for almost half of the total variance in male fertilization success. Males with naturally long tail streamers had a higher fertilization success than males with shorter tail streamers, and this pattern was mainly caused by a higher extra-pair success for males with long tail streamers. Males with long tail streamers also paired with early breeding females in prime body condition. These results are consistent with the idea that there is directional sexual selection on male tail streamer length, possibly mediated through male extra-pair mating success or the timing of breeding onset.

Object classification under ignorance using CaRBS: the case of the European barn swallow

This article investigates the potential of a novel technique for object classification, called Classification and Ranking Belief Simplex (CaRBS), which is based on the Dempster-Shafer theory of evidence. As such, the classification of objects and the evidence from their characteristics have a level of ignorance associated with them. Its potential is exposited in the application of the classification of European barn swallows according to their gender. The classification of biological data in the presence of ignorance about such data sets is a common problem in biology. Comparisons of the results from CaRBS with those from multivariate discriminant analysis and neural networks are made. Also shown throughout the investigation is the interpretability of the results with the utilisation of the simplex plot method of representing data.

Plumage coloration, not length or symmetry of tail-streamers, is a sexually selected trait in North American barn swallows

Sexual adornments often vary markedly across a species' range, which presumably is owing to differences in local environmental conditions and the associated selection pressures, such as natural versus sexual selection or the relative signaling value of different ornamental traits. However, there are only a few reported examples in which the information content of mating signals varies geographically, and even fewer in which a set of secondary sexual traits serves different signaling functions in different populations. Classic studies of sexual selection in the European barn swallow (Hirundo rustica rustica) demonstrate that elongate tail-streamers provide several reproductive advantages to males and females and are used as reliable signals of mate quality. Here, we show that tail-streamers do not appear to confer these same benefits in a population of barn swallows from North America (Hirundo rustica erythrogaster). Instead, ventral plumage coloration, which is more exaggerated in North American swallows compared with their European counterparts, predicts patterns of assortative mating and annual reproductive success in H. r. erythrogaster. These observations support the idea that ornamental traits can serve different functions among animal populations and suggest that geographic variation in different sexual signals may facilitate population divergence, which may ultimately lead to speciation. Copyright 2004.

YOU CAN'T JUDGE A PIGMENT BY ITS COLOR: CAROTENOID AND MELANIN CONTENT OF YELLOW AND BROWN FEATHERS IN SWALLOWS, BLUEBIRDS, PENGUINS, AND DOMESTIC CHICKENS

Abstract The two main pigment types in bird feathers are the red, orange, and yellow carotenoids and the black, gray, and brown melanins. Reports conflict, however, regarding the potential for melanins to produce yellow colors or for carotenoids to produce brown plumages. We used high-performance liquid chromatography to analyze carotenoids and melanins present in the yellow and brown feathers of five avian species: Eastern Bluebirds (Sialia sialis), Barn Swallows (Hirundo rustica), King Penguins (Aptenodytes patagonicus), Macaroni Penguins (Eudyptes chrysolophus), and neonatal chickens (Gallus domesticus). In none of these species did we detect carotenoid pigments in feathers. Although carotenoids are reportedly contained in the ventral plumage of European Barn Swallows (Hirundo rustica rustica), we instead found high concentrations of both eumelanins and phaeomelanins in North American Barn Swallows (H. r. erythrogaster). We believe we have detected a new form of plumage pigment that gives penguin and d...

An illustration of variable precision rough set theory: the gender classification of the European barn swallow ( Hirundo rustica)

This paper introduces a new technique in the investigation of object classification and illustrates the potential use of this technique for the analysis of a range of biological data, using avian morphometric data as an example. The nascent variable precision rough sets (VPRS) model is introduced and compared with the decision tree method ID3 (through a ‘leave n out’ approach), using the same dataset of morphometric measures of European barn swallows ( Hirundo rustica) and assessing the accuracy of gender classification based on these measures. The results demonstrate that the VPRS model, allied with the use of a modern method of discretization of data, is comparable with the more traditional non-parametric ID3 decision tree method. We show that, particularly in small samples, the VPRS model can improve classification and to a lesser extent prediction aspects over ID3. Furthermore, through the ‘leave n out’ approach, some indication can be produced of the relative importance of the different morphometric measures used in this problem. In this case we suggest that VPRS has advantages over ID3, as it intelligently uses more of the morphometric data available for the data classification, whilst placing less emphasis on variables with low reliability. In biological terms, the results suggest that the gender of swallows can be determined with reasonable accuracy from morphometric data and highlight the most important variables in this process. We suggest that both analysis techniques are potentially useful for the analysis of a range of different types of biological datasets, and that VPRS in particular has potential for application to a range of biological circumstances.