Morphometrics of the pink-footed shearwater ( Puffinus creatopus): influence of sex and breeding site

We present morphometric data for the pink-footed shearwater (Puffinus creatopus) from both Chilean breeding colonies on Isla Mocha and Juan Fernández: weight, total length, wing length, tail length, head length, three bill and three tarsus size measurements and length of middle toe. Significant differences were found for most measurements between males and females as well as between birds from the two different breeding localities. In general, males were bigger than females, and birds from Juan Fernández were bigger than those from Isla Mocha. Geographic differences most likely reflect some kind of ecomorphological adaptation. Some variables, especially the total length of head, seem to be useful for sex determination in the field.     

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.     

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 Adult Pale-Winged Starlings Using Morphometric and Discriminant Function Analysis

Accurate sexing of birds is vital for behavioral studies but can be a real problem in the field, especially for monomorphic species. Our goal here was to characterize the morphology of male and female monomorphic pale-winged starlings (Onychognathus nabouroup), a South African sturnid whose plumage is sexually monomorphic. Morphological measurements of genetically sexed animals indicated that males were statistically larger than females for five measurements: Mass, tail length, tarsus length and wing length. By using a Discriminant Function Analysis based on the measurements taken by one ringer, we were able to predict correctly the sex of 81.10% of the birds of data collected in the field and 77.9% of museum skins independently of year of capture and ringer. The model developed here should be useful for further field studies of this species.     

Cuckoo Hosts in Southern Africa

There is currently no reliable, affordable method of sexing Mauritius Fodies in their first non-breeding season. Ringed immature fodies from a released population on an offshore island were caught in April and May 2005 and sexed in later breeding seasons. Males had longer wing lengths and tarsi than females, with no overlap in wing length between sexes. Males in their first breeding season could usually be differentiated from older males by the paleness and completeness of their breeding plumage. Two adult females grew red feathers characteristic of breeding males in the winter of 2006. It is possible to sex Mauritius Fodies using wing length and separate immature males from adults using the darkness of the bill in the non-breeding season. It is not possible to separate unringed adult and immature females following the postjuvenile and postbreeding moults using current knowledge.     

Sexual size dimorphism and morphometric sexing in a North African population of Laughing Doves Spilopelia senegalensis

Like the majority of Columbiformes, the Laughing Dove Spilopelia senegalensis is sexually monomorphic in plumage, but seems to be slightly dimorphic in size. However, due to the lack of studies little is known about the sexual size dimorphism in this species. In this work, we used morphometric data on a sample of 61 Laughing Doves from southern Tunisia, and sexed using a DNA-based method, to assess size differences between males and females and to determine a discriminant function useful for sex identification. The results showed that wing length was the most dimorphic trait, which could be due to the effects of sexual selection. The best function for the discrimination between sexes included wing length and head length, which is comparable with findings on other dove species. This discriminant function accurately classified 89% of birds, providing a rapid and accurate tool for sex identification in the studied population. Further data from different populations are needed for firmer conclusions about the extent of sexual size dimorphism and the reliability of the morphometric sexing approach in this dove species.     

Establishing body-size indicators in a study of female spruce grouse Dendragapus canadensis

Seven measurements were taken from 72 adult and yearling spruce grouse Dendragapus canadensis hens collected over a 10-year period from north-eastern Ontario, Canada. A principal components analysis (PCA) indicated keel ridge length, keel total length, and femur length, these being the most representative measurements of general body size. Skeletal mass, caecal length, wing length, and foot length had lower character loadings on the first principal component axis (PC1), suggesting they are unreliable measurements of body size. Measurements taken from bones (i.e. keel, femur) were more representative of general body size than external morphometric measurements (e.g. wing and foot length) which ornithologists traditionally use to estimate body size. Pre-laying adults were the smallest individuals and pre-laying yearlings the largest in the population studied. A discriminant functions analysis (DFA) of the seven measurements, with separated body mass as an eighth variable, demonstrated distinct separation between pre-laying and post-laying groups of birds on the basis of separated body mass. Keel ridge length was further implicated as an effective variable in the discrimination of birds from different laying groups.     

Morphometric sex determination of Milky and Painted Storks in captivity

Logistic regression was applied to develop a morphometric sexing method of two closely related stork species that were previously sexed through amplification of the CHD gene. Tarsus length (TL) and bill length (BL) measurements were recorded from captive populations of adult Milky Stork (Mycteria cinerea) (n = 60) and Painted Stork (Mycteria leucocephala) (n = 58) at Zoo Negara Malaysia. Despite having monomorphic plumages, both stork species exhibited normal sexual size dimorphism in which males were significantly larger than females in the tested variables. Based on logistic regression analysis, BL correctly classified the sex of sampled individuals from Painted and Milky stork with an overall predicted accuracy of 94.8 and 90.0%, respectively. However, TL measurements generated a lower predicted accuracy level of 86.2% and a same accuracy level of 90% on the sex classification of individuals from Painted and Milky stork, respectively. By comparing the measurements of both species, only the average BL measurements of the Milky storks were significantly lower than that of Painted storks (t-test, P80.001). The logistic regression equation in this study may serve as a simple and more practical option for sexing Milky and Painted storks for their breeding and conservation programmes.     

Feral cat diet and impact on sooty terns at Juan de Nova Island, Mozambique Channel

Feral cat Felis catus predation on seabirds has been well documented; however, details regarding shifts in feral cat diet in relation to seabird availability, seabird predation rate and impact on seabird population dynamics are scarce. Here, we present data documenting a seasonal shift in feral cat diet at Juan de Nova Island, Mozambique Channel. We also quantify sooty tern Sterna fuscata predation by feral cats and examine the impact on sooty terns over both the short term (by removing individual cats from sub-colonies) and over the longer term by highlighting their influence on population growth rate ( λ ) using a deterministic matrix model. Cat diet shifted dramatically from insects, rats and mice outside the tern breeding season to primarily terns when terns were breeding. The predation rate of sooty terns at Juan de Nova was estimated at 5.94 terns cat⁻¹ day⁻¹, with a proportion of these (22%) being killed without being consumed ('surplus kills'). When only one cat was removed from each sub-colony, tern predation declined tenfold in the short term. From our matrix model, the annual growth rate for sooty terns was 1.01 in the absence of cat predation. It remained above one until a predation impact equivalent to approximately three times the estimated cat density (12.04 per km²) was incorporated. Our results demonstrate that cats preferentially predate and have an impact on breeding sooty terns at Juan de Nova, and that an increase in cat density could lead to negative effects on population growth, despite the large breeding tern population.     

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)     

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。     

Sex differences in body size and body condition in breeding Temminck’s Stints Calidris temminckii

There have been very few reports of body size measurements of live Temminck’s Stints, but earlier studies have shown sex differences in body mass and tarsus length. Here we use molecular techniques to determine the sex of Temminck’s Stints from a Norwegian breeding population. In total, we report measurements of body weight, wing length, tarsus length, bill length, skull length and keel length from 17 males and 30 females. We found significant sex differences in all of these variables, with the exception of tarsus length. The differences in skull length disappeared after the bill lengths had been subtracted from the measurements. A discriminant function analysis based on wing length and bill length correctly classified 86% of the cases (12/16 males, 25/27 females). Female Temminck’s Stints are known to regularly lay more than one clutch of eggs per season and could therefore be expected to be physiologically deprived of bodily energy stores. Nevertheless, we found females to be in better body condition than males.     

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.     

Sex‐specific patterns of fuelling and pre‐breeding body moult of Little Stints Calidris minuta in South Africa

The timing and duration of each stage of the life of a long‐distance migrant bird are constrained by time and resources. If the parental roles of males and females differ, the timing of other life stages, such as moult or pre‐migratory fuelling, may also differ between the sexes. Little is known about sexual differences for species with weak sexual dimorphism, but DNA‐sexing enables fresh insights. The Little Stint Calidris minuta is a monomorphic long‐distance migrant wader breeding in the Arctic tundra. Males compete for territories and perform elaborate aerial displays. Females produce two clutches a season. Each sex may be a bigamist and incubate one nest a season, each with a different partner. We expect that these differences in breeding behaviour entail different preparations for breeding by males and females, so we aimed to determine whether Little Stints showed any sex differences in their strategies for pre‐breeding moult and pre‐migratory fuelling at their non‐breeding grounds in South Africa. We used body moult records, wing length and body mass of 241 DNA‐sexed Little Stints that we caught and ringed between 27 January and 29 April in 2008–2018 at two neighbouring wetlands in North West Province, South Africa. For each individual we assessed the percentage of breeding plumage on its upperparts and took blood samples for DNA‐sexing. We calculated an adjusted Body Moult Index and an adjusted Wing Coverts Moult Index, then used the Underhill–Zucchini moult model to estimate the start dates and the rate of body moult in males and females. We estimated the changes in the sex ratio of the local population during their stay in South Africa, and also estimated the timing and rate of pre‐migratory fuelling and the potential flight ranges for males and females. The males started body moult on average on 7 February and the females on 12 February, but the sexes did not differ in their timing of wing covert moult, which started on average on 10 February. In January to mid‐February, males constituted c. 57% of the population, but their proportion declined afterwards, indicating an earlier departure than females. We estimated that both sexes began pre‐migratory fuelling on average on 15 March. The sexes did not differ in fuelling rate, but most females stayed at the non‐breeding site longer than the males, and thus accumulated more fuel and had longer potential flight ranges. These patterns of moult and fuelling suggest sex differences in preparations for breeding. We suggest that the males depart from South Africa earlier but with smaller fuel loads than the females to establish breeding territories before the females arrive. We conclude that for each sex the observed trade‐offs between fuelling and moult at the non‐breeding grounds are precursors to different migration strategies, which in turn are adaptations for their different roles in reproductive behaviour.     

Sexing greater flamingos by weight and linear measurements

The sex of 59 adult Greater Flamingos (Phoenicopterus ruber roseus L.) was determined by laparoscopic exam of the gonads. Concomitant body weight (kg) and linear measurements (mm) of the culmen (bill), tarsus, middle toe, and wing were taken and compared for males vs. females. Although an overlap between sexes existed in all measurements, males on average were larger than females. Student's t-test indicated significant sexual differences for all five measurements. Thus, weights and linear measurements—especially tarsus, middle toe, and wing length—appear to be a useful parameter in determining an individual's sex in lieu of laparoscopic, feather pulp, blood chromosome, or fecal steroid analysis.     

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...     

The discriminant power of biometrics for sex determination in European Bee-eaters Merops apiaster

ABSTRACT

Capsule A combination of several biometric measures enables the reliable sexing of the European Bee-eater Merops apiaster, a species with subtle sex differences in plumage and morphometry.

Aims To explore variation in biometrics and their suitability to discriminate sex in adult European Bee-eaters Merops apiaster.

Methods We sampled populations of a long-distance migratory species with low sexual size dimorphism, the European Bee-eater Merops apiaster, from colonies in western Iberia (Portugal) and Central Europe (Germany) to investigate body size variation and derive population-specific and general sex discriminant functions.

Results Overall, male Bee-eaters were larger than females while Bee-eaters from Germany and Portugal did not differ in size, except for primary length and tail length. The best single measurement to discriminate sex was wing length for Portuguese birds and tail tip length for German birds, as in the combined dataset. Multivariate discriminant functions of head-bill, wing and tail tip lengths provided the highest discriminant accuracy, discriminating sex for 91% of the birds from Portugal, 96% from Germany and 94% when using the combined dataset. Nonetheless, the discriminant accuracy remained high in the functions using only two variables for Portugal (head-bill and tail tip 91%, head-bill and wing 88%, wing and tail tip 88%), Germany (head-bill and tail tip 95%, wing and tail tip 97%) and in the combined dataset (head-bill and tail tip 92%, wing and tail tip 93%).

Conclusions Population specific discriminant functions allow sexing of European Bee-eaters by morphometry with high degree of accuracy at least for Iberia and Central European populations. Such discriminant functions can be used to assign the sex of adult Bee-eaters reliably and swiftly while the bird is still in the hand, highlighting the potential of these functions for rapidly sexing species with low degrees of sexual size and plumage dimorphism.     

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.     

Sexual Dimorphism in Sturnira lilium (Chiroptera,Phyllostomidae): Can Pregnancy and Pup Carrying Be Responsible for Differences in Wing Shape?

Competition is one of the most cited mechanisms to explain secondary sexual dimorphism in animals. Nonetheless, it has been proposed that sexual dimorphism in bat wings is also a result of adaptive pressures to compensate additional weight caused by fetus or pup carrying during the reproductive period of females. The main objective of this study is to verify the existence of sexual dimorphism in Sturnira lilium wings. We employed geometric morphometrics techniques using anatomical landmarks superimposition to obtain size (Centroid Size) and shape variables of wings, which were reduced by Linear Discriminant Analysis (LDA). We also employed classical morphometrics using wing length measurements to compare efficiency between these two morphometric approaches and make comparisons using wing area measurements. LDA indicated significant differences between wing shapes of males and females, with 91% (stepwise classification) and 80% (leave-one-out cross validation) of correct classification. However, the size variable obtained did not contribute to such classifications. We have observed larger areas in female wings, but we found no differences in wing length measurements and no allometric effects in wing length, shape and area measurements. Interestingly, our study has provided evidences of morphological differences where classical morphometrics have failed. LDA and area measurements analyses revealed that females have a different area distribution in distinct portions of the wing, with wider dactylopatagia and plagiopatagia, and wingtips more triangular than males. No differences in body length or relative wing length were observed between the sexes, but pregnant females have more body weight than non-pregnant females and males. Our findings suggest that sexual dimorphism in the wing shape of S. lilium is probably related to the increase in flight efficiency of females during reproductive period. It decreases wing loading in specific portions of the wing and reduces energy cost to maintain a faster and maneuverable flight.     

Decrease in body size of Danish goshawks during the twentieth century

Recent studies indicated that body size of various animals, including birds, changed during the twentieth century, and these changes were attributed to changes in food availability and climate. We used museum skins of goshawks (Accipiter gentilis) collected between 1854 and 1941 and between 1979 and 1998 in order to check whether body size of this species in Denmark changed during the study period. We compared three body measurements (wing, beak and tarsus length) and the first principal component (PC1) derived from these measurements of four groups of goshawks (adult and immature, females and males). We found that the wing length of goshawks collected after 1979 was significantly smaller in comparison with those collected before this year, and females were more affected than males. Immature birds (but not adults) collected after 1979 had significantly shorter beaks than those from the early period. Immature females collected after 1979 had shorter tarsi than those collected in the early period. There was a significant decrease in body size (as represented by PC1) from the early to late period, which was more pronounced among females and immature birds. In conclusion, body size of goshawks in Denmark decreased during the twentieth century.