Sex determination of Antarctic Petrels Thalassoica antarctica by discriminant analysis of morphometric characters

We present data on sexual dimorphism in some morphological measurements (wing length, head length, bill depth and bill length) in the Antarctic Petrel Thalassoica antarctica. Males were on average larger than females for all measurements. Sexual dimorphism was on average largest for bill depths whereas wing lengths discriminated least between the sexes. A discriminant function including bill depth, head length and wing length correctly sexed 92% of the sample. Due to between-measurer variation it is recommended that morphometric measurements obtained by others on sexed birds are compared with ours before proceeding with the use of the discriminant function on unsexed individuals.Publication No. 116 of the Norwegian Antarctic Research Expeditions (1991/92)     

ON THE SOUTH AFRICAN RACE OF THE LITTLE SPOTTED WOODPECKER

Discriminant analysis functions have previously been determined for sexing Mediterranean Yellow-legged Gulls Larus michahellis michahellis from the western Mediterranean basin. However, data from eastern Mediterranean populations are lacking. In this work, we used morphometric data from a sample of 81 Mediterranean Yellow-legged Gulls (39 males and 42 females) breeding in the Gulf of Gabès in south-eastern Tunisia to (1) determine a discriminant function useful for sex discrimination, and (2) assess the accuracy of previously published functions in sexing Mediterranean Yellow-legged Gulls from our study area. Our results showed marked sexual differences in all morphological measurements, with males being significantly larger than females. The best discriminant function included head length, bill depth and wing length, and accurately classified 93% of sampled birds. We also found that Mediterranean Yellow-legged Gulls from the Gulf of Gabès could accurately be sexed using discriminant functions determined for another North African population, but not with a function determined for a South European population, although distances between sites are almost the same.     

Sexing terns using biometrics: the advantage of within-pair comparisons

Capsule Within-pair comparisons substantially improve the accuracy of sexing from biometrics for two congeneric species of seabird with monomorphic plumage and soft-tissue colouration.

Aims To examine the extent to which statistical limitations of sexing birds from biometrics using sample-level analysis could be overcome by sexing Common and Arctic Terns (Sterna hirundo and S. paradisaea) using measurements obtained from breeding pairs.

Methods Incubating adults were caught at the nest using walk-in traps and wing, tarsus, head-plus-bill, tail length, tail fork, and body mass measured. Each bird was individually colour-ringed and dyed with picric acid, enabling subsequent sexing by behavioural observations of copulation and courtship feeding. Birds were sexed using biometrics and the proportion of birds sexed correctly this way at the sample level was compared with the accuracy achieved if, within a pair, the larger bird was classified as male.

Results Head-plus-bill length was the single most accurate measurement for sexing individuals of both species, and correctly classified 72% of Arctic Terns and 73% of Common Terns. Combinations of measurements derived from discriminant analysis achieved slightly higher accuracy (73% and 78% respectively). Within-pair comparisons were more accurate than sample-level analysis for both single measurements and discriminant functions, and were able to sex 84% of Arctic Terns and 86% of Common Terns correctly.

Conclusion Comparing birds within pairs improves accuracy and can eliminate the need to calculate cut points or discriminant functions from a sample of birds of known sex for each particular study. We strongly advocate such comparisons wherever possible to increase accuracy and simplify computational procedures for predicting sex, thus reducing associated sources of error.     

发冠卷尾性别判定的初步研究

摘要：发冠卷尾（Dicrurus hottentottus）由于被认为是雌雄同态而在野外难以鉴别性别。我们研究了河南董寨国家级自然保护区79只已用分子生物学方法鉴定出性别的发冠卷尾（D.h.brevirostris）在形态量度上的性别差异,并据此构建了判别式方程,用于鉴定其性别。所考察的体征包括体重、喙长、喙粗、头喙长...     

Morphometric sex determination of young Ospreys Pandion haliaetus using discriminant analysis

Capsule Discriminant functions based on morphometric variables provide a reliable method for sex identification of free‐living and hacked young Ospreys.

Aims To describe an easy, accurate and low‐cost method for sex determination of fully grown nestling and fledgling Ospreys Pandion haliaetus based on morphometric measurements.

Methods Four different measurements were taken in 114 birds (40–73 days old) and a DNA analysis, using PCR amplification, was carried out for sex identification. A forward stepwise discriminant analysis was performed to build the best explanatory discriminant models, which were subsequently validated using statistics and external samples.

Results Our best discriminant function retained forearm and tarsus as the best predictor variables and classified 95.1% of the sample correctly, supported also by external cross‐validations with both hacked and free‐living birds. Moreover, a discriminant function with only forearm as predictor showed a similar high correct classification power (93.4%).

Conclusions These discriminant functions can be used as a reliable and immediate method for sex determination of young Ospreys since they showed high discriminant accuracy, close to that of molecular procedures, and were supported by external cross‐validations, both for free‐living and hacked birds. Thus, these morphometric measurements should be considered as standard tools for future scientific studies and management of Osprey populations     

Sex determination in the Lesser Flamingo (Phoenicopterus minor) using morphological measurements

Morphological measurements and blood samples were taken from 154 Lesser Flamingos Phoenicopterus minor, including adults (>3 years old), immature sub-adults (2–3 years old) and first-year juvenile birds of both sexes, captured at Lake Bogoria, Kenya (0°11'–20' N, 036°06' E) during 2001 and 2002. PCR amplification of the CHD-Z and CHD-W genes using DNA extracted from the blood samples was used to determine the sex of each bird. There were significant differences in mass and tarsus length among the three age groups, indicating that Lesser Flamingos continue to grow in skeletal size and mass between fledging and the attainment of adult plumage at 3–4 years of age. On average, males were significantly larger than females in all age groups, although there was substantial overlap between the sexes in all morphological measurements. The element with the least amount of overlap was head-and-bill length. Discriminant functions utilising head-and-bill length that correctly predict the sex of juvenile and immature birds with approximately 93% accuracy are presented. By adding total tarsus length, the sex of wild adult Lesser Flamingos is correctly predicted with approximately 98% accuracy. The same discriminant function developed for wild adult birds predicted the sex of 19 captive adult Lesser Flamingos of known sex with 100% accuracy.     

A new method for sexing Oriental White Storks

ABSTRACT.   For species where males and females are monomorphic, or nearly so, determining the sex of individual birds generally requires either capturing birds or collecting samples, such as feathers, for DNA analysis. We developed a new method, involving the use of photographs, to determine the sex of endangered Oriental White Storks ( Ciconia boyciana ). Using photographs, we analyzed the lateral features of the heads of 25 captive storks of known sex (12 males and 13 females) and found differences between males and females in the distance from the bill tip to the nape and the distance from the bill tip to the commissural point. These differences were used to generate a discriminant function that was then tested on 22 captive storks at Hyogo Homeland Park (Toyooka, Japan), and we correctly determined the sex of 18 individuals (82%). In addition, the sex of two wild storks was correctly assigned. Our results suggest that good-quality photographs can be useful for determining the sex of both captive and wild Oriental White Storks and, further, that similar methods may prove useful for determining sex in other species of birds.     

Sexual dimorphism,moult and body condition of seabirds killed by longline vessels around the Prince Edward Islands, 1996–97

Ryan, P.G. 1999. Sexual dimorphism, moult and body condition of seabirds killed by longline vessels around the Prince Edward Islands, 1996–97. Ostrich 70 (3&4): 187–192.

A total of 393 seabirds from nine species killed by longline fishing in South African waters around the Prince Edward Islands during summer 1996–97 were sexed, measured, and their body fat levels and primary moults scored. Males of Whitechinned Petrels Procellaria aequinoctialis and Greyheaded and (Indian Ocean) Yellownosed Mollymawks Thalassarche chrysostoma and T. [chlororhynchosj bassi averaged 1–9% larger than females. Measures of bill depth were the most dimorphic characters in all three species. I recommend that if only a single measure is taken to estimate sex of adults, bill depth at the base be the standard measure for petrels, and bill depth at the nail be the standard measure for mollymawks. Discriminant functions are described for predicting the sex of unknown individuals; the proportion of misclassified birds ranged from 2–10%. With the exception of giant petrels Macronectes spp., only two young birds were actively moulting their primary flight feathers. Analysis of wear patterns among adult Greyheaded Mollymawk primaries conforms with studies of moult in this species at South Georgia. Fat scores did not differ between sexes. They tended to decrease during the breeding season, but trends were masked by great inter-individual variation. There was no significant relationship between fat scores and the presence of ingested plastics. Plastic debris was found in the stomachs of 90 birds from five species. Incidence in Whitechinned Petrel stomachs (37%) was less than that reported from birds collected off South Africa in the early 1980s (57%), but this is probably due to the predominance of breeding adults. The frequency and size of plastic loads decreased through the breeding season, which is consistent with the hypothesis that inter-generational transfer is important in the dynamics of ingested debris.     

Morphological sexing of passerines: not valid over larger geographical scales

Sex determination of birds is important for many ecological studies but is often difficult in species with monomorphic plumage. Morphology often provides a possibility for sex determination, but the characters need to be verified. We tested whether five passerine species can be sexed according to standard morphological measurements applying a forward logistic regression with sex determined by molecular analysis as the dependent variable. Furthermore, we tested whether the results can be used on a larger geographic scale by applying morphological sexing methods gained by similar studies from other regions to our data set. Of the five species of this study only Garden Warblers Sylvia borin could not be sexed morphologically. In the Robin Erithacus rubecula, 87.2% of all individuals were sexed correctly. For Reed Warblers Acrocephalus scirpaceus, Willow Warblers Phylloscopus trochilus and Reed Buntings Emberiza schoeniclus, the respective values were 77.6, 89.4 and 86.4%. When the logistic regression functions from similar studies on Robins and Reed Buntings in Denmark and Scotland were applied to the birds from south-western Germany, they performed less well compared to the original dataset of these studies and compared to the logistic regression function of our own study. The same was the case for Willow Warblers when a wing length criterion used in Great Britain was applied to the birds of our study. These discrepancies may have several explanations: (1) the models are optimised for the dataset from which they were extracted, (2) inter-ringer variation in measurements, (3) the use of different age cohorts, (4) different morphology due to different habitat availability around the study site, or, most likely, (5) different morphology due to different migratory behaviour. We recommend that morphological sex differentiation methods similar to this study (1) be only used population specific, (2) only with one age cohort and (3) to adjust the extracted equations from time to time.     

Sexual dimorphism and sex determination in Black-necked Grebes Podiceps nigricollis: on the need to account for geographical variation in morphology and sex ratio

Capsule: The sex of Black-necked Grebes Podiceps nigricollis in Spain can be determined successfully using a locally derived discriminant function analysis (DFA) but a function derived from a North American population was not successful.

Aims: To determine the extent of sexual size dimorphism in the Black-necked Grebe and develop discriminant functions based on morphometric data. We also assessed the accuracy of visual sexing by fieldworkers with different levels of experience and compared the discriminant function for European birds with one for North American birds, in order to determine the geographical specificity of the function.

Methods: We used a data set of 370 Black-necked Grebes from a European population throughout the non-breeding seasons of 2008–11 in the Odiel saltmarshes (Spain), as well as published data from North America, to compare the accuracy of DFAs developed for European and North American populations when applied to the same population.

Results: Males were significantly larger than females for all body measurements. The DFA with the highest success rate included one single linear dimension (head-bill length), showing an efficiency of 88.5% in the same sample used to build the function and up to 91.5% in independent samples of birds. The more experienced ringer showed higher accuracy in visual sexing than the less experienced one (84 vs. 70%), although self-consistency in sex assignment of a given individual was similar. The function developed for European birds performed poorly for American birds (79.1% sexed correctly) and vice versa (18.4% sexed correctly).

Conclusion: Morphological and sex ratio differences between European and American subspecies both contribute to the discrepancy in the success rate. This illustrates the need for caution when applying discriminant functions developed in one bird population to individuals elsewhere.     

Sexing Cape Vulture Gyps coprotheres based on head morphometrics

The Cape Vulture Gyps coprotheres is considered sexually monomorphic in the literature, but visual differences in head shape between the sexes have been observed. Furthermore, head morphometrics of other Gyps species show statistically significant variation between the sexes. We show that head morphometrics can be used to determine the sex of Cape Vultures. Males generally have wider and shorter heads, and larger bill depths than females. Discriminant function analysis with data from 63 individuals identified the three most predictive variables in sex determination to be head width, head length and bill depth. We also provide an equation that can be used in conjunction with head measurements as a method to determine the sex of Cape Vultures in the field with an overall accuracy of 84% (92% accuracy for females and 72% for males).     

MORPHOMETRICS AND SEXING OF THE AFRICAN BLACK OYSTERCATCHER

Summary

Hockey, P. A. R. 1981. Morphometries and sexing of the African Black Oystercatcher. Ostrich 52: 244–247.

109 African Black Oystercatchers Haematopus moquini were caught, measured and sexed by cloacal examination during the 1979/1980 breeding season. Six standard taxonomic variables were measured. Females were larger than males in all dimensions considered. The most dimorphic characters were mass and exposed culmen length. The data were subjected to stepwise discriminant analysis and a linear function was derived which allowed birds of unknown sex to be sexed. The function is D = ?0,391x₁ ?0,016 x₂ +0,218 x₃ +0,714 x₄ +15,946 where x₁ = exposed culmen length (mm), x₂ = body mass (g), x₃ = length of tarsometatarsus (mm) and x₄ = culmen depth at the gonys. Values of D from the above equation less than zero indicate a female while those greater than zero indicate a male. The greater the divergence of D from zero, the higher the probability of correctly sexing an unknown individual: once D> ± 1,2, p>0,99.     

Geographical variation, sex and age in Great Bittern Botaurus stellaris using coloration and morphometrics

Biometrics, plumage and bare-part colour of 87 Great Bitterns Botaurus stellaris from the UK, France, Italy, Poland and Belarus, of known sex (sexed by behaviour, DNA or dissection), were analysed to provide reliable sexing and ageing criteria for this little-known species, and to investigate geographical variation in biometrics. Four parameters were analysed: bill length, tarsus, wing length and body weight. We found little (though significant) geographical variation across Europe, but this was not clinal and we cannot exclude variation in measurement technique among observers. Males were significantly larger than females for all biometric parameters: a discriminant function based on these parameters was able to sex correctly all individuals. Body weight varied with season, especially for males. During the breeding period, lore colour was also a reliable sex-criterion. Ageing proved more difficult and required a combination of iris colour (which darkens with age) and flight-feather moult. From this, the largest sample size of known-age Great Bitterns, we conclude that most previously published criteria for age determination of this species were wrong.     

基于形态特征判定五种鹬类性别的可靠性

快速准确地鉴定两性同型鸟类个体性别在鸟类生态学研究中具有重要意义。本文选择2008年春季迁徙期在崇明东滩停歇的大滨鹬(Calidris tenuirostris)、红腹滨鹬(C.canutus)、红颈滨鹬(C.ruficollis)、尖尾滨鹬(C.acuminata)及翘嘴鹬(Xenus cinereus)5种两性同型的鹬类,用分子生物学方法进行性别鉴定,并基于个体的形态特征(体重、翅长、喙长、头喙长及跗跖长)采用判别分析方法对性别进行判定。结果表明,尖尾滨鹬雄性各形态特征均显著大于雌性,其他4种鹬类则相反。5种鹬类形态特征的性别差异指数在0.5%~25.3%之间,重叠度在29.4%~98.6%之间。5种鹬类判别分析判定性别的准确率在(0.69±0.06)~(0.96±0.01)之间,其中,尖尾滨鹬判别准确率(0.96)最高,翘嘴鹬判别准确率(0.69)最低。形态特征在两性间的差异程度影响性别的判别准确率。另外,两性性比对性别判别的准确率也有影响:性比偏雄性鸟类的雄性判别准确率高于雌性,而性比偏雌性鸟类的雌性判别准确率高于雄性。采用判别分析估测的性比与分子生物学鉴定结果相似,表明判别分析在判定种群的性比方面具有较高的可靠性。     

Sex identification in King Penguins Aptenodytes patagonicus through morphological and acoustic cues

In the context of sexual selection, animals have developed a variety of cues conveying information about the sex of an individual to conspecifics. In many colonial seabird species, where females and males are monomorphic and do not show obvious differences in external morphology, acoustic cues are an important signal for individual and sex recognition. Here, we study the vocal and morphological sex dimorphism in the King Penguin Aptenodytes patagonicus, a colonial, monomorphic seabird for which our knowledge about the role of vocalizations and morphology in mate choice is very limited. Data were collected at Possession Island, Crozet Archipelago, in a breeding colony consisting of about 16 000 breeding pairs. Using measurements of six morphological features and analysing acoustic parameters of call recordings of adult individuals, we show that King Penguins can be sexed based on a single morphological measurement of the beak with an accuracy of 79%. We found a sex‐specific syntax in adult King Penguin calls that provided a 100% accurate method to distinguish between the sexes in our study population. To confirm the method at the species level, we analysed calls recorded from King Penguin adults in Kerguelen Island, 1300 km away from our study population and found the same accuracy of the sex‐specific syntax. This sex‐specific syllable arrangement is rare in non‐passerines and is a first step in understanding the mate choice process in this species. Furthermore, it offers a cost‐effective, non‐invasive technique for researchers to sex King Penguins in the field.     

An approach to sexing young Great Bustards Otis tarda using discriminant analysis and molecular techniques

Adult Great Bustards Otis tarda are sexually dimorphic, males weighing more than twice as much as females. However, there is no practical way to distinguish sex in chicks by their morphology. In this paper we describe a discriminant function, Tail Length/Weight, which correctly sexed 98.2% of 165 Great Bustard chicks at two study areas in Spain, the Wildlife Reserve of Lagunas de Villafáfila and the province of Madrid. The value for Tail Length/Weight separating the sexes was 0.099: Tail Length/Weight for males < 0.099 < Tail Length/Weight for females. We also show that the recently described PCR-based sex determination technique using genomic DNA is valid for the Great Bustard. Both approaches should be useful for sexing young Great Bustards in captive breeding programmes and studies on wild populations.     

An assessment of sex using the skull of black South Africans by discriminant function analysis

The derivation of discriminant function equations for skeletal elements of South African populations continues to be an area of interest to both forensic anthropologists and skeletal biologists alike. The skull of black South Africans has previously been subjected to discriminant function analysis, using four measurements and two indices; however, no equations were derived to address the issue of sex determination. Recently Franklin, Freedman and Milne [2005. Sexual dimorphism and discriminant function sexing in indigenous South African crania. HOMO J. Comp. Hum. Biol. 55, 213-228] used the crania of black South Africans, in a three-dimensional approach, with eight linear measurements to investigate sex determination. This study, although valuable, requires the use of highly technical and expensive morphometric equipment that renders it less feasible in South Africa. In response to this, our study uses traditional anthropometric measurements and equipment to address the question of sex determination from the crania and mandible of blacks. One hundred and twenty non-pathological skulls were randomly selected from the Raymond Dart Collection of Human Skeletons, equally distributed by sex and belonging to individuals whose age at death ranges between 25 and 70 years. Fourteen cranial and six mandibular measurements were subjected to discriminant function analyses and discriminant function equations were derived for sex determination. Average accuracies ranged between 80% and 85% and were on par with that obtained in previous studies. Our study shows that traditional methods provide average accuracies that are comparable to those obtained using more complex techniques.     

Sexing Wrens Troglodytes troglodytes indigenus using morphological measurements and discriminant analysis

Within the breeding population of a deciduous woodland, male Wrens averaged slightly larger than females in wing length, foot length, head plus bill length and body mass. First-year and older birds were similar for three of these morphometric variables, but the first-year group were shorter-winged than the older birds (by 3%). Despite this, wing length still proved to be a useful discriminator of sex when the data were pooled for all ages (74% of males exceeding the maximum female value of 49.8 mm). A discriminant function utilizing wing length and head plus bill length correctly sexed 96% of individuals in the sample from which it was derived (n = 49 males, 36 females). This function was converted into a predictive equation for the probability of an unknown case being male, and a plot of wing length against head plus bill length along with probability contours which enabled the sexing of unknown cases without the need for calculations. Measurements of the morphological variables investigated were found to be highly repeatable for a single worker, with the exception of body mass which differed substantially between the sexes but which was only moderately repeatable. The methods provided should prove valuable for sexing British mainland Troglodytes troglodytes indigenus, and probably also Western European T. t. troglodytes, but should not be applied to the larger, offshore island races.     

Bill length: a reliable method for sexing Purple Sandpipers

ABSTRACT.   Purple Sandpipers ( Calidris maritima ) are sexually dimorphic, with females larger than males. We tested the reliability of using bill length to sex individuals and estimate the sex ratio at a stopover site in Iceland in May 2003 and 2005. Feather samples from 65 of 324 captured birds were used for molecular sexing, and generalized linear models (GLMs) were used to discriminate the sexes from body measurements of the molecularly sexed birds. About 3% of the 324 individuals were misclassified by the Harding-Cassie method, and the proportion of males was 0.657 compared to 0.656 according to the best GLM. Our results showed that the reliability of determining the sex and sex ratio of Purple Sandpipers using a Harding-Cassie plot of bill length measurements was high, but that reliability was improved by including other variables in a GLM. The estimate of an uneven sex ratio in the population we studied was not due to a systematic error, and supports the conclusion of earlier studies that Purple Sandpipers exhibit an uneven sex ratio in favor of males.     

Using interpubic distance for sexing manakins in the field

ABSTRACT Field methods for determining the sex of birds are often limited due to morphometric overlap between sexes, intermediate plumages, seasonality, and reliance on subjective age classification. Interpubic distance, characterized in birds as the distance between the distal ends of the pubic bones, has not been formally tested as a method for determining the sex of birds, despite references among parrot breeders and the frequent use of analogous measurements in mammals. We developed a harmless and easily performed field method for measuring interpubic distance in studies involving bird capture, and compared the interpubic distances of known sex White‐ruffed Manakins (Corapipo altera), Orange‐collared Manakins (Manacus aurantiacus), and Blue‐crowned Manakins (Lepidothrix coronata) to evaluate the possible use of this measurement to determine sex. Using interpubic distance ranges based on 85% confidence intervals where overlap existed between sexes, the sex of 92.8–100% of all manakins in our study was accurately determined with no misclassification. Interpubic distance performed better than plumage‐based methods that sexed 74.0% of all individuals and misclassified 1.5%. Using linear discriminant analysis, we developed classification equations that allowed us to accurately determine the sex of all individuals with 100% accuracy using mass and interpubic distance. Additionally, we compared the interpubic distances of female White‐ruffed Manakins to evaluate the potential to determine age and reproductive status. Despite an apparent relationship between interpubic distance, age and reproductive status, we concluded that interpubic distance has limited use for determining age and reproductive status due to extensive overlap (31.6–100%), but shows potential in other applications. Based on these results, we endorse the use of interpubic distance to determine the sex of manakins. We encourage further study to develop additional classification equations using different morphometric measurements and to test the efficacy of interpubic distance to determine sex in other bird species.