MORPHOLOGY: BIRDS
Vanstreels R. E. T., Adornes A. C., Ruoppolo V., Canabarro P. L., Silva-Filho R. P., Catāo-Dias J. L. (2011): Gender determination from morphometrics in migrating Magellanic Penguins Spheniscus magellanicus. Marine Ornithology 39: 215-220.
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Magellanic Penguins Spheniscus magellanicus are sexually dimorphic while breeding, but in winter the difference is not always sufficiently evident for visual determination of gender. We examined published discriminant functions and produced additional discriminant functions using morphometric data from 408 beachcast Magellanic Penguins from the Centro de Recuperação de Animais Marinhos on the most southerly point of the Brazilian coast (31°15’38″S to 33°45’03″S), for which gender was determined by post mortem examination or polymerase chain reaction. The discriminant functions correctly determined the gender of 70–90% of these penguins. However, an important gender-associated bias was detected, as previously published discriminant functions developed for animals in breeding colonies were systematically misclassifying males as females. A method is proposed to adjust the functions and correct this gender bias. While other methods may be more accurate, gender determination from morphometric data still offers reasonably reliable results and is an accessible, rapid, inexpensive and non-invasive method for determining the gender of Magellanic Penguins.
Maphalala M. I., Monadjem A. (2017): White-backed Vulture Gyps africanus parental care and chick growth rates assessed by camera traps and morphometric measurements. Ostrich 88: 123-129.
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Persistent vulture declines across Africa are a cause for concern as the number of species threatened with extinction increases. The White-backed Vulture Gyps africanus was, until recently, considered abundant but has been declining rapidly in recent years due to various threats including decreasing food availability. We used camera traps to investigate nest attendance and food provision at the nests of White-backed Vultures in north-eastern Swaziland. Chick age influenced brooding behaviour of the parents, with a reduction in brooding time as the chick aged. Mean food provision rate by parents to the nestling was 0.7 bouts d−1, which was mostly delivered between 09:00 and 15:00. Contrary to expectations, provisioning rates did not increase with age of the chick despite both adults delivering food. The growth of chicks showed a curvilinear relationship with age for the first 100 d with the tarsus and bill reaching maximum length after 80 d. We recommend further research into the availability of food for breeding vultures in order to understand the emerging threat of declining food availability in Africa.
Mahendiran M., Parthiban M., Azeez P. A., Nagarajan R. (2018): In situ measurements of animal morphological features: A non‐invasive method. Methods in Ecology and Evolution 9: 613-623.
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Measurements of morphological features are important for ecological studies, especially on free-ranging wild animal species. Conventionally, specimens either dead or in captivity are used for morphometric studies, which is difficult in the case of wild species for several reasons. Capturing would be even futile when research questions are relating to issues such as prey size selection or estimation of intake rate under field conditions, where in situ morphometric measurements are inevitable. Remotely estimating morphometric features via, avian bill and head lengths are always laden with wide variances. Hence, we developed this technique for in situ measurements of animal morphology through digital photographs. This non-invasive novel method for in situ estimation of individuals’ morphometric measurements uses digital photographs’ metadata. We extracted the metadata (field of view, focal length, subject-distance, etc.,) in exchangeable image file format from digital images using freely available software, and the unknown sizes were estimated from each image. Cardboard (fish) models were, at first, used to estimate the accuracy of measurements comparing actual and estimated values, and the same protocol was repeated on museum specimens (bird). Finally, we checked the repeatability of this method under field conditions using free-ranging Chickens (Gallus gallus domesticus). The results under different conditions were subjected to rigorous statistical testing. Upon comparing the actual with estimated values, obtained from three distinct types of objects (1. Cardboard model, 2. Museum specimens and 3. Live birds under field conditions), variations were found non-significant affirming the assumption that actual value (Y) = estimated value (X) with inconsequential variance of the Y from X. Moreover, both the relative and absolute errors between the actual and estimated values were so low, indicating that this method yielded neither overestimation nor underestimation. The advantage of this non-invasive method is that it could generate reasonably accurate morphometric measurements at a relatively low cost for routine morphometric works in field conditions. We envisage significant utility of this non-invasive technique in different fields of science such as biology, morphology, ecology, evolution, wildlife, conservation science, agriculture, forensics and engineering design.
Williams H. M., Wilcox S. B., Patterson A. J. (2020): Photography as a tool for avian morphometric measurements. Journal of Ornithology 161: 333-339.
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Accurate morphometric measurements of birds are frequently needed in studies to provide an index of body size. However, obtaining these measurements in the field can be challenging and inter-observer repeatability of taking these measurements using calipers has been questioned in the literature. Here we present a method for measuring tarsus length and bill length, width and depth using digital photography with open source software (ImageJ), and we compare the repeatability and handling time of the digital measurements with those traditionally made using calipers. The digital method was more or equally repeatable than manual measurements of bill and tarsus and its repeatability was independent of measurement length, making it especially suited to making shorter measurements. While digital and manual measures were highly correlated for all body measures, the digital method produced slightly higher measurements in all cases meaning digital and manual measurements may not be directly comparable. Morphometric measurements made from digital photographs were possible with a significantly shorter bird handling time, can be completed by less experienced fieldworkers, and create a permanent record that can be later verified, making them a useful alternative to traditional manual measurements of unfeathered skeletal body parts which can be clearly visualized in photographs.
Malo J. E., Mata C. (2021): Web databases of feather photographs are useful tools for avian morphometry studies. Ecology and Evolution 11: 7677-7684.
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Wing area, wing loading, and aspect ratio are key variables for studies of avian comparative ecology, despite the complexity of measuring wing characteristics in living and museum specimens. The systematic databases of feather photographs available on the Internet may offer an alternative way of obtaining such morphometric data. Here, we evaluate whether measurements of scanned feathers from web photograph databases may offer reliable estimates of avian morphometry. Published data on wing area were obtained for 317 bird species and feather measurements from web photograph databases for 225 of them. A variable termed “lift generation area,” a proxy for wing area, was calculated for each species on the basis of the mean length of the five distal secondary feathers and wingspan data from literature. The fit between this proposed variable and data extracted from the literature was examined by correlation, employing linear regression to explore the lack of fit among species. “Lift generation area” proved to be highly informative as a proxy for wing area for the study species as a whole (R2 > .98). Discrepancies observed between species were strongly negatively associated with the size of the original sample used to calculate wing area (p = .001) and, to a lesser extent, with bird size (p = .023), but not with aspect ratio. It was also found that the mean value of the mismatch between “lift generation area” and wing area (13.1%) among the study species as a whole was of similar magnitude to that found between sources of bibliographic wing area data for the 64 species for which two published estimates of this variable were available (15.3%). We conclude that measurements made from feather photograph databases are reliable for use in studies of avian comparative ecology, enabling the inclusion of biomechanical parameters of many more species than featured at present.
Forys E. A., Naundorff C., Kennedy K. M., Paddock P. T. (2022): Use of morphometric measurements of photographs of a sexually dimorphic bird to determine sex. Waterbirds 44: 324-329.
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This study investigated if morphological measurements made from digital photographs of banded adult Black Skimmers (Rynchops niger), using alphanumeric field readable leg bands as a scale reference, can be used to determine their sex. Black Skimmers are known for their extreme sexual dimorophism and make an excellent study subject. Measurements made in the field using calipers to determine length of the exposed culmen of skimmer chicks were significantly correlated to measurements made by three technicians using open-source software (ImageJ) measuring the culmen from photographs, with little variability among technicians. To determine sex, ImageJ was used to measure the culmen, bill depth at base, lower mandible and head + culmen lengths from photographs of 24 known sex adult skimmers (11 female, 13 male). Males were significantly larger than females for all four measurements and a stepwise Discriminant Function Analysis (DFA) using all 4 measurements retained exposed culmen and bill depth as the best predictor variables. This model correctly classified 100% of known sex males and females. Using the DFA equation, 40 additional banded skimmers were classified, and it was determined that 46 of the banded skimmers that were photographed as adults were male and 18 were female. Using a field readable band as a reference scale for other measurements may prove useful for research on other sexually dimorphic species that are banded and later photographed in the wild.
Mahendiran M., Parthiban M., Azeez P. A. (2022): Signals of local bioclimate-driven ecomorphological changes in wild birds. Scientific Reports 12: 15815.
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Across disciplines—biological, ecological, evolutionary, or environmental—researchers increasingly recognize the importance and the need for cost-effective, non-invasive techniques for in-situ morphological measurements of organisms in diverse research contexts. By applying a non-invasive technique using digital images taken under field conditions, we successfully measured the body sizes of wild Painted Storks (Mycteria leucocephala) in two different biogeographic regions of India, spatially separated by 20° of latitude. We have used the wild Painted Storks as model species for measuring their morphometrics using a non-invasive technique that could easily be applied to similar species, rare, endemic, colonial, aquatic, and even those with cultural taboos. Our results satisfactorily classify and predict the sexes of the species and their biogeographic origin based on independent morphological variables using Machine Learning algorithms. The BayesNet yielded the correct classification instances (Receiver Operating Characteristic (ROC) = 0.985), outperforming all the other tested classifying algorithms. A strong relationship was observed between the local bioclimatic conditions and the morphological variations in wild Painted Storks reflecting clear eco-geographic patterns. Without this non-invasive technique, it would be almost impossible to collect morphological measurements at a large scale from live birds under field conditions. Our study is a testimony to the effectual use of the non-invasive digital method for in-situ measurements from free-living wild species in the field, assuming significance, especially from climate change perspectives, biology, ecology, and conservation.
Estellés-Domingo I., López-López P. (2023): Non-invasive sex determination of nestlings and adult Bonelli’s eagles using morphometrics. Animals 13: 1201.
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Biometric analysis allows the sexing of most vertebrates, particularly birds. Birds of prey, and, especially, the Bonelli’s eagle (Aquila fasciata), show reverse sexual dimorphism (i.e., females are usually larger than males). In contrast to blood sampling, the use of morphometrics allows sex determination using a non-invasive method, and, therefore, it facilitates fieldwork. By means of a linear discriminant analysis of biometric variables, we obtained different equations that allow the sexing of nestlings and adult Bonelli’s eagles. We sampled 137 Bonelli’s eagles, 82 nestlings and 55 adults in eastern Spain during the period 2015–2022. The sexes obtained after linear discriminant analysis were compared with their molecular sexing. The validation procedure of the linear discriminant equations facilitated the reduction of the number of variables used and, consequently, optimised working time and sexing accuracy. After validation, some equations showed a 100% sexing efficiency for Bonelli’s eagles, particularly for adults. Our results showed that the variables with smaller overlap between the sexes were the lateral tarsus length and dorso-ventral tarsus length, particularly in nestlings. The rest of the variables showed some overlap between the sexes in both age classes. The results we obtained enable the sexing of juvenile and adult Bonelli’s eagles in the field using just these two measurements. Hence, this is an easy, accurate, quick and non-invasive method with multiple applications, including in studies on population dynamics, survival analysis or extinction risk assessments, which, ultimately, could contribute to the improvement of the conservation status of this endangered species.