Beyond morphs: Inter-individual colour variation despite strong genetic determinism of colour morphs in a wild bird

Categorizing individuals into discrete forms in colour polymorphic species can overlook more subtle patterns in coloration that can be of functional significance. Thus, quantifying inter-individual variation in these species at both within- and between-morph levels is critical to understand the evolution of colour polymorphisms. Here we present analyses of inter-individual colour variation in the Reunion grey white-eye (Zosterops borbonicus), a colour polymorphic wild bird endemic to the island of Reunion in which all highland populations contain two sympatric colour morphs, with birds showing predominantly grey or brown plumage, respectively. We first quantified colour variation across multiple body areas by using a continuous plumage colour score to assess variation in brown-grey coloration as well as smaller scale variation in light patches. To examine the possible causes of among-individual variation, we tested if colour variation in plumage component elements could be explained by genotypes at two markers near a major-effect locus previously related to back coloration in this species, and by other factors such as age, sex and body condition. Overall, grey-brown coloration was largely determined by genetic factors and was best described by three distinct clusters that were associated to genotypic classes (homozygotes and heterozygote), with no effect of age or sex, whereas variation in smaller light patches was primarily related to age and sex. Our results highlight the importance of characterizing subtle plumage variation beyond morph categories that are readily observable since multiple patterns of colour variation may be driven by different mechanisms, have different functions and will likely respond in different ways to selection.     

Morphological variation of introduced species: The case of American mink (Neovison vison) in Spain

We studied the morphology of American mink Neovison vison in five out of the six introduced populations in Spain. The spatial and temporal variation of body weight (BW), body length (BL), tail length, hind-foot length and ear length were analysed. Temporal trends in BW and BL in relation to years since mink introduction were also analyzed. In addition, we tested the effect of sex, age (juvenile, subadult and adult) and age–sex interaction, on each parameter. Morphological parameters differed between populations, illustrating the high variability of body size of American mink in different environments, and the phenotypic plasticity of the species. Annual variations were synchronized between populations, suggesting a large-scale effect on all of them. BW and BL showed a decreasing trend in both males and females in relation to years since introduction. This decrease may be related to mink's diet. Differences in sex and age were found, pointing to sexual dimorphism in adults, subadults and juveniles. The dimorphism in non-adult individuals suggests that subadult males may have a competitive advantage from subadult females in feeding and/or hunting on bigger prey from an early age (resource partitioning hypothesis).     

Temporal variation in detection of marsh birds during broadcast of conspecific calls

ABSTRACT.   The decline in populations of several species of marsh birds in North America has prompted development of a monitoring protocol that involves the broadcast of conspecific calls to enhance detection of these secretive species. However, with a standardized protocol, temporal (seasonal) and geographic variation in responses to the broadcast of calls could lead to inadequate monitoring of migratory species with large ranges. Our objective was to examine temporal variation in the response of marsh birds to playback of conspecific calls in west-central and northern New York to determine if use of the current protocol would permit effective monitoring of their populations. From 11 April to 8 July 2005, we conducted 572 surveys at 143 survey points on 16 marshes and detected 663 individuals of our target species. Our results revealed more detections of American Bitterns ( Botaurus lentiginosus ) and Pied-billed Grebes ( Podilymbus podiceps ) early in our survey period, and more detections of Virginia Rails ( Rallus limicola ) and Least Bitterns ( Ixobrychus exil is) later in our survey period. Only 22% of Least Bitterns were detected before 28 May, whereas 76% of American Bitterns and 70% of Pied-billed Grebes were detected before 28 May. With the current recommended monitoring protocol, surveys are to be completed during a 44-day period that includes three 10-day sampling periods separated by 1 week. However, our results indicate that this protocol would lead to inadequate and inaccurate monitoring of marsh birds in New York. Given that the timing of peak detection of different species of marsh birds varies geographically, we recommend flexibility in the timing and duration of surveys so that surveys can be synchronized with location-specific peak-detection periods.     

Shell colour variation in Littorina saxatilis Olivi (Prosobranchia: Littorinidae): a multi-factor approach

The marine snail Littorina saxatilis is highly polymorphic for shell colour. It lives in the heterogeneous intertidal zone, where there are sharp transitions in a number of abiotic factors that may influence the relative fitness of morphs. We investigated the hypothesis of selected variation by relating the colour distribution to five factors (wave exposure, substratum, shore level, sex, snail age), and to interactions between them. We compared patterns from geographical areas in Sweden, Iceland and Russia. Cryptic morphs (tessellated and different dark colours) generally dominated (80–98%) while conspicuous morphs (white, yellow, red and banded) were less common (2–20%). The colour frequencies were often related to wave exposure, substratum and shore level. Frequencies rarely varied with age and never with sex. In order to test the assumption that the different colours are genetically determined we cross-bred snails from Iceland in the laboratory. Both the presence of bands and the ground colours of the shell were inherited, and we have tentative support for a one-locus two-allele model for banding. Our results support a model of selected inherited colour variation, involving a number of different selective agents, the importance of which may vary between populations on local and geographical scales.     

Iris colour of American kestrels varies with age,sex, and exposure to PCBs

For most species of birds, little is known about the pattern and significance of intraspecific variation in iris colour. In early winter, captive American kestrels could be subjectively placed into at least two age categories: 0.5-yr-old birds had all-brown irides, whereas those of older birds were red-brown. As part of a toxicological study on kestrels, we quantified iris colour objectively using a digital camera to examine potential variation due to age, sex, and exposure to polychlorinated biphenyls (PCBs). Red, green, and blue values, plus an overall measure of colour using principal components analysis (PC1), were derived for breeding and nonbreeding kestrels 1.5-6.5 yr old (fed PCBs), plus offspring 0.5 yr old (exposed to PCBs only in ovo). Age category (0.5, 1.5, and 2.5+ yr) and PCB exposure consistently had an effect on colour, while sex was significant only for red and almost so for PC1. ANOVA with age as a covariate revealed that the amount of red continued to increase throughout life, but PCBs suppressed the development of that colour.     

Relationship between dental morphology, sex, body length and age in Pontoporia blainvillei and Sotalia fluviatilis (Cetacea) in Northern Rio de Janeiro, Brazil

The relationship between dental morphology, sex, body length and age of small cetaceans can be used to determine ontogeny, sexual dimorphism and geographical variation. The objective of this study was to determine the relationship between dental morphology, sex, body size and age. A total of 91 specimens of P. blainvillei and 80 specimens of S. fluviatilis accidentally captured in fisheries or stranded in northern Rio de Janeiro (21 masculine37'-22 masculine25'S), from September 1988 to November 1996 were analysed. The teeth root diameter in P. blainvillei was significantly different between the sex; the values for females were larger than males. In neither species aid we observed significant in variations dimension and number of teeth, thickness of dentine and cemental layers and in the maximum width of cement as a function of body size. Age was related to increases in tooth length, root and cingulum diameters, and maximum width of cement in individuals of P. blainvillei, and tooth and crown lengths and maximum width of cement in individuals of S. fluviatilis. The observation of a linear growth between maximum width of cement and age in both species indicates that the equations obtained can be used to estimate relative age in P. blainvillei and S. fluviatilis in northern of Rio de Janeiro.     

大山雀身体大小的性二态及其季节变化

动物中普遍存在雌雄个体身体大小的性二态现象。了解近缘种之间身体大小性二态现象的差异，可为深入探讨身体大小性二态现象的潜在驱动机制提供证据。国外对欧亚大山雀（Parus major）的研究发现，其喙长、跗跖长、翅长等 6 项身体大小指标存在着明显的性二态，且喙长的性二态存在季节间差异。大山雀（P. cinereus）曾被作为欧亚大山雀的一个亚种，其形态和行为与欧亚大山雀存在着诸多相似之处。为探讨大山雀是否也存在身体大小性二态及季节性差异，本研究分析了 2018 至 2020 年间在河南董寨国家级自然保护区捕捉的 226 只（雌性 96 只和雄性 130 只）大山雀的喙长、头喙长、跗跖长、翅长、尾长和体长这 6 项体征指标的两性差异及其季节变化。结果显示，大山雀上述 6 项身体大小指标均存在不同程度的性二态现象，且雄性个体仅喙长与雌性的差异不显著，其余 5 项指标均显著大于雌性。此外，身体大小指标的两性差异不随季节显著变化，但两性的跗跖长在秋季均显著短于冬季和繁殖季，尾长在繁殖季均显著长于秋季和冬季。上述结果表明，大山雀身体大小的性二态及其季节性差异与欧亚大山雀并不完全相似。无论其身体大小存在性二态和季节变化的原因，还是其与欧亚大山雀在身体大小性二态模式上的差别，都有待今后进一步的研究。     

Exploiting uncertain ecological fieldwork data with multi-event capture-recapture modelling: an example with bird sex assignment

1.?Sex plays a crucial role in evolutionary life histories. However, the inclusion of sex in demographic analysis may be a challenge in fieldwork, particularly in monomorphic species. Although behavioural data may help us to sex individuals in the field, this kind of data is unlikely to be error free and is usually discarded. 2.?Here we propose a multi-event capture-recapture model that enables us to exploit uncertain field observations regarding the sex of individuals based on behavioural or morphological criteria. The multi-event capture-recapture model allows us to account for sex uncertainty not restricting our ability to estimate the parameters of interest. In this case, by adding the confirmed sex of just a few individuals, we greatly improve the efficiency of the optimization algorithm. 3.?Using such an approach, we analysed sex differences in demographic parameters (e.g. survival, transience and sex ratio) in a population of Audouin's gulls using observations from long-term fieldwork monitoring (1988-2007). We also assessed the probability of ascertaining sex over time and the probability of error for each field-sexing criterion. 4.?We detected no strong effect of sex on either survival or transience probabilities, and both sexes showed a decreasing trend in survival over time and transience probability after recruitment increased with age and over time. The probability of ascertaining sex over time depended on observers' experience. Strikingly, courtship feeding (but not copulation) emerged as the most reliable clue for sexing individuals, which would suggest that Audouin's gulls engage in same-sex sexual behaviour such as same-sex mounting. 5.?The present modelling emerged as a reliable method for estimating demographic parameters and state transition parameters in ecological studies in which field observations of sex or other individual states are assigned erroneously and uncertainly. This approach could also be useful for applied ecologists for assessing the reliability of their criteria for assigning sex or other individual covariates in the field, thereby permitting them to optimizing their field ecological protocols.     

Variable colour patterns indicate multidimensional,intraspecific trait variation and ecological generalization in moths

Animal colour patterns long have provided information about key processes that drive the ecological and evolutionary dynamics of biological diversity. Theory and empirical evidence indicate that variation in colour patterns and other traits among individuals generally improves the performance of populations and species, for example by reducing predation risk, increasing establishment success, improving resilience to environmental change, and decreasing risk of extinction. However, little is known about whether and how variation in colour pattern among species is associated with variation in other phenotypic dimensions. To address this issue, we analysed associations of colour pattern with morphological, behavioural and life-history traits on the basis of data for nearly 400 species of noctuid moths. We found that moths with more variable colour patterns had longer flight activity periods, more diverse habitats and a greater number of host plant species than species with less variable colour patterns. Variable coloration in adult noctuid moths therefore can be considered as indicative of broader niches and generalist diets. Colour pattern variability was not significantly associated with overwintering stage or body size (wing span), and it was independent of whether the colour pattern of the larvae was non-variable, variable or highly variable. Colour pattern variation during the larval stage tended to increase as the duration of the flight activity period increased, but was independent of the length of the larval period, diet breadth and habitat use. The realization that information on colour pattern variation in adult moths, and possibly other organisms, offers a proxy for niche breadth and dietary generalization can inform management and conservation biology.     

Population genetics, phylogeography and speciation of Cystodytes (Ascidiacea) in the western Mediterranean Sea

Several morphotypes that so far have been attributed to the allegedly cosmopolitan ascidian Cystodytes dellechiajei occur in the Mediterranean Sea. Colour variation is the difference most frequently reported. In this study, we addressed the genetic structure of this ascidian in relation to geographical location and colour morph. Partial sequences of the gene cytochrome  c oxidase subunit 1 (COI) were obtained from seven populations of the western Mediterranean, encompassing eight colour varieties. All population genetic analyses (exact test, pairwise F _ST, hierarchical analysis of molecular variance, multidimensional scaling, nested clade analysis) indicated clearly that differences between colour morphs are large enough to obscure any geographical differentiation when colours are combined within localities. When variance due to colour divergence was removed, however, a significant geographical variability between localities remained. The genetic divergence between the colour morphs analysed was significant in comparisons of the brown and purple forms with the others, but not among the green, blue, and white morphs. Phylogeographic analyses suggest that population fragmentation and range expansions have shaped the present-day distribution of the haplotypes. Taken together with existing chemotype information, our results indicate that several species are present in the area, and that a thorough revision of the genus is necessary.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 203–214.     

Growth stages and ageing criteria of Arabian Mountain gazelles (Gazella gazella Pallas, 1766: Antilopinae,Bovidae)

This research project was designed to be of both academic and practical value in the conservation of Mountain gazelle and represents an attempt to provide data for sex and age classification of this endangered species hitherto unpublished. Growth data and ageing criteria of 177 individuals of known age, obtained from a captive population, kept under uniform conditions at King Khalid Wildlife Research Centre in Saudi Arabia, were examined. Measurements of horn length, shoulder height, living body weight, neck circumference and forehead-horn length ratio were established and a field classification for ageing female and male Mountain gazelles was suggested.     

Effect of age,haemosporidian infection and body condition on pair composition and reproductive success in Great Tits Parus major

Several factors shape lifetime reproductive success, including genetic background, body condition, environmental conditions and ecological interactions such as parasitism. Adults often show higher reproductive success than their young conspecifics, especially in long-lived bird species, and this may be explained by the cumulative effects of an increase in reproductive experience and the selection of high-quality individuals from one year to the next. To test whether this pattern also exists in short-lived bird species, we used 13 years of monitoring data from two Great Tit Parus major populations. The effects of male and female age on several reproductive parameters were analysed in 419 pairs of Great Tits, while accounting for body condition and infection by haemosporidian parasites. Reproductive success was mainly affected by the age-class of males. Pairs containing a sub-adult male fledged one-third fewer chicks than pairs containing an adult male. The difference was not caused by variation in male fertility but could have been caused by better parental care provided by adult birds. In addition to lower reproductive success, first-year males also had reduced access to mating compared with adult males, suggesting an avoidance of sub-adult males by females. Nestling body condition was positively correlated with parental body condition, and the body condition of male and female members of breeding pairs was positively correlated. Finally, the number of fledged chicks was mainly affected by the infection status of males. These results temper our previously published results showing an effect of infection on Great Tit reproduction regardless of their sex. In our previous study, and as in most cases, the status of the partner was not taken into account and we show here that this is essential because it can lead to a biased interpretation of the results.     

Clinical pathology and morphometrics of African fish eagles in Uganda

Packed cell volumes (PCVs) and plasma chemistry parameters were measured in 15 adult and 18 nestling African fish eagles (Haliaeetus vocifer) sampled from June 2002 through January 2003 in Uganda. Morphologic measurements were obtained from 15 adult eagles. All eagles were examined for blood parasites and sexed by examination of DNA from red blood cells. Ten adults and eight nestlings were sampled from Lake Mburo and five adults and 10 nestlings were sampled from Lake Victoria near Entebbe, Uganda. Analysis of variance was conducted to assess the association between site, age, sex, and plasma chemistry parameters and the association between sex and morphologic characteristics. Plasma chemistry values for nestling and adult African fish eagles were similar to those reported for other captive and free-ranging eagle species. Packed cell volumes for nestling African fish eagles were markedly lower than values reported for nestlings of other eagle species, although the mean estimated age of nestlings sampled also was lower. A significant association (P < or =0.05) was found between PCV of nestling eagles and study site (lower at Lake Mburo) but no association was found between PCV and nestling body weight (P> or =0.05). An unidentified Plasmodium sp. was present in erythrocytes of three nestlings from Lake Mburo. No other blood parasites were seen. There was significant variation (P< or =0.05) in PCV, calcium, phosphorous, potassium, cholesterol concentrations, and creatine kinase activity between adults and nestlings; all were lower in adults. Aspartate transaminase activity was higher in adults. Like other Haliaeetus sp., body weight, bill depth, culmen length, footpad length, and hallux length as well as bill depth measurements were significantly (P < or = 0.05) greater for females than males. The objective of the study was to provide baseline biologic and physiologic information that may prove useful in the management and study of captive and wild populations of African fish eagles.     

Age,sex and beauty: methodological dependence of age‐ and sex‐dichromatism in the great tit Parus major

Carotenoid‐based colour expression is frequently involved in sexual dichromatism, particularly in bird plumage, suggesting a role in sexual selection. Despite much work on expression of the carotenoid‐based ventral plumage coloration of the great tit (Parus major), which represents a popular model in evolution and ecology, a consensus on even the most basic demographic patterns of variation (e.g. age and sex differences) is lacking. This may reflect the use of variable methods for analysing colour variation, although what is not clear, either in this case or in general, is the extent to which these alternative methods are equally effective at describing age‐ and sex‐related dichromatism. Using data obtained over 4 years from a large sample of free‐ranging great tits, we examined how colour‐scoring methodology influences estimates of age‐ and sex‐related dichromatism. We compare: (1) principal components analysis‐derived scores; (2) tristimulus colour variables; (3) a visual model‐independent, carotenoid‐focussed colour score; and (4) two colour scoring methods based on avian visual models, examining how they assess colour variation with respect to age and sex to determine how methodology may influence results. We demonstrate clear age‐ and sex‐dependent expression of this colour trait, both in our own data and in meta‐analyses of results from great tit populations across Europe, and discuss the merits of the various colour scores, which yield very different estimates of the extent of age‐ and sex‐dependent dichromatism. We show variation is likely to be visible to conspecifics and propose a novel, visual model‐derived scoring system for describing variation in carotenoid‐based colour patches, where the perceived signal is divided into independent chromatic and achromatic components, in line with current understanding of visual perception. The present study highlights the impact of colour‐scoring methodology and shows that, as novel measures continue to be developed, researchers should consider carefully how they quantify colour expression. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 777–796.     

Unexpected patterns of genetic structuring among locations but not colour morphs in Acropora nasuta (Cnidaria; Scleractinia)

Symbiotic relationships have contributed greatly to the evolution and maintenance of biological diversity. On the Great Barrier Reef, species of obligate coral-dwelling fishes (genus Gobiodon) coexist by selectively recruiting to colonies of Acropora nasuta that differ in branch-tip colour. In this study, we investigate genetic variability among sympatric populations of two colour morphs of A. nasuta ('blue-tip' and 'brown-tip') living in symbiosis with two fish species, Gobiodon histrio and G. quinquestrigatus, respectively, to determine whether gobies are selecting between intraspecific colour polymorphisms or cryptic coral species. We also examine genetic differentiation among coral populations containing both these colour morphs that are separated by metres between local sites, tens of kilometres across the continental shelf and hundreds of kilometres along the Great Barrier Reef. We use three nuclear DNA loci, two of which we present here for the first time for Acropora. No significant genetic differentiation was detected between sympatric colour morphs at these three loci. Hence, symbiotic gobies are selecting among colour morphs of A. nasuta, rather than cryptic species. Significant genetic geographical structuring was observed among populations, independent of colour, at regional (i.e. latitudinal separation by < 500 km) and cross-shelf (< 50 km) scales, alongside relative homogeneity between local populations on within reef scales (< 5 km). This contrasts with the reported absence of large-scale genetic structuring in A. valida, which is a member of the same species group as A. nasuta. Apparent differences in biogeographical structuring between species within the A. nasuta group emphasize the need for comparative sampling across both spatial (i.e. within reefs, between reefs and between regions) and taxonomic scales (i.e. within and between closely related species).     

Weak link between dispersal and parasite community differentiation or immunogenetic divergence in two sympatric cichlid fishes

Geographical isolation, habitat variation and trophic specialization have contributed to a large extent to the astonishing diversity of cichlid fishes in the Great East African lakes. Because parasite communities often vary across space and environments, parasites can accompany and potentially enhance cichlid species diversification. However, host dispersal may reduce opportunities for parasite‐driven evolution by homogenizing parasite communities and allele frequencies of immunity genes. To test for the relationships between parasite community variation, host dispersal and parasite‐induced host evolution, we studied two sympatric cichlid species with contrasting dispersal capacities along the shores of southern Lake Tanganyika. Whereas the philopatric Tropheus moorii evolved into several genetically differentiated colour morphs, Simochromis diagramma is phenotypically rather uniform across its distribution range and shows only weak population structure. Populations of both species were infected with divergent parasite communities and harbour differentiated variant pools of an important set of immune genes, the major histocompatibility complex (MHC). The overall extent of geographical variation of parasites and MHC genes was similar between host species. This indicates that immunogenetic divergence among populations of Lake Tanganyika cichlids can occur even in species that are strongly dispersing. However, because this also includes species that are phenotypically uniform, parasite‐induced evolution may not represent a key factor underlying species diversification in this system.     

Variation of adult Great Tit Parus major body condition and blood parameters in relation to sex, age, year and season

In recent years, an increasing number of studies have focused on the ranges of variation of health related biochemical and haematological parameters in wildlife, but information is still scarce for enzymatic activities which can be extremely important in detecting potential responses to environmental change. In a Great Tit (Parus major) population, we describe the variation in relation to age, sex, season and year of: (1) morphological: body condition index, fat and muscle, (2) haematological: hematocrit, haemoglobin, white blood cell count and heterophil/lymphocyte ratio, and (3) biochemical parameters: plasma protein and activities of plasma cholinesterases (acetylcholinesterase and butyrylcholinesterase) activity and red blood cell glutathione peroxidase. Sex had significant effects on all morphological parameters except fat. Age significantly affected cholinesterase activities, H/L ratio and haemoglobin, and there was a significant interaction between sex and age affecting hematocrit. There were significant interactions of year and season affecting almost all parameters studied—body condition index, fat, protein, acetyl and butyrylcholinesterase activities, glutathione peroxidase activity and haemoglobin. This study indicates that these parameters are largely influenced by year and seasonal effects, besides the individual’s intrinsic variation. Therefore, when evaluating experimental or environmental change effects, appropriate controls should be used.     

Drivers of protogynous sex change differ across spatial scales

The influence of social demography on sex change schedules in protogynous reef fishes is well established, yet effects across spatial scales (in particular, the magnitude of natural variation relative to size-selective fishing effects) are poorly understood. Here, I examine variation in timing of sex change for exploited parrotfishes across a range of environmental, anthropogenic and geographical factors. Results were highly dependent on spatial scale. Fishing pressure was the most influential factor determining length at sex change at the within-island scale where a wide range of anthropogenic pressure existed. Sex transition occurred at smaller sizes where fishing pressure was high. Among islands, however, differences were overwhelmingly predicted by reefal-scale structural features, a pattern evident for all species examined. For the most abundant species, Chlorurus spilurus, length at sex change increased at higher overall densities and greater female-to-male sex ratios at all islands except where targeted by fishermen; here the trend was reversed. This implies differing selective pressures on adult individuals can significantly alter sex change dynamics, highlighting the importance of social structure, demography and the selective forces structuring populations. Considerable life-history responses to exploitation were observed, but results suggest potential fishing effects on demography may be obscured by natural variation at biogeographic scales.     

Ecological divergence among sympatric colour morphs in blood pythons, Python brongersmai

Blood pythons in northeastern Sumatra display a series of discrete colour morphs, even among hatchlings within a single clutch. The first step towards understanding the maintenance of this polymorphism is to test the null hypothesis that colour variation in this species has no major biological correlates. Data on >2,000 blood pythons killed for the commercial leather industry enabled us to test, and reject, this hypothesis. The four colour morphs differed significantly in most of the traits that we measured, including temporal and spatial abundances, sex ratios, age structures, mean adult body sizes, body shapes (tail length and body mass relative to snout-vent length), energy stores, numbers of gut parasites, prey types, feeding frequencies and clutch sizes. The causal basis for these associations remains unclear, but is likely to involve three processes: direct effects of colour, linkages between genes for colour and other traits, and correlated spatial heterogeneity in colour, morphology and ecology. The colour polymorphism may be maintained by frequency-dependent selection and genotype-specific habitat selection, because these sedentary ambush predators are under strong selection for effective camouflage to hide them from both predators and potential prey. In support of this hypothesis, similar colour polymorphisms have evolved independently in several other snake taxa that rely upon ambush predation. Received: 18 December 1997 / Accepted: 23 March 1998     

Genetic differentiation of starling (Sturnus vulgaris: Aves) populations in New Zealand and Great Britain

Several hundred starlings (Sturnus vulgaris) were introduced to New Zealand from Great Britain during1860–1880. Allozymic variation at 24 loci was analysed in winter populations sampled at six localities in each country. New Zealand samples had fewer alleles per locus but the same mean heterozygosity (3% per locus) and proportion of polymorphic loci as did British samples. Winter populations in Britain contain European migrants and were genetically homogeneous. Paradoxically, genetic distances among derived New Zealand populations, and between New Zealand and Great Britain were much greater, similar in magnitude to those observed among allopatric populations in other avian species. The geographical pattern of genetic variation in New Zealand suggests that reproductive isolation of populations and random drift have contributed to the development of population differentiation.