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1. The response of orangutans to a total solar eclipse event

   Prasetyo, D. (April 2021, Journal of Tropical Biodiversity)

   null (Ed.)

   A complete solar eclipse is a rare event, and we know very little about how other species, including our closest living relatives the primates, react to these events. We observed orangutans on the island of Borneo, Indonesia during a rare astronomical event of a total solar eclipse. Captive orangutans in Nyarumenteng rehabilitation center, Central Kalimantan were observed to document their reaction to this unexpected environmental event. Based on this study that was conducted in 2016, the dramatical behavior demonstrated in the time of the total solar eclipse, and the general response differed between before and after the event. During the total solar eclipse, flanged males tended to increase their social behavior compared to the unflanged males. These findings indicate that the total solar eclipse resulted in an environmental stressor for these captive orangutans. 

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2. Does total column ozone change during a solar eclipse?

   https://doi.org/10.5194/egusphere-2024-2659  

   Bernhard, Germar H; Janson, George T; Simpson, Scott; Cordero, Raúl R; Sepúlveda_Araya, Edgardo I; Jorquera, Jose; Rayas, Juan A; Lind, Randall N (September 2024, EGUsphere preprint repository of Copernicus Publications)

   Abstract. Several publications have reported that total column ozone (TCO) may oscillate with an amplitude of up to 10 Dobson Units during a solar eclipse while other researchers have not seen evidence that an eclipse leads to variations in TCO beyond the typical natural variability. Here, we try to resolve these contradictions by measuring short-term (seconds to minutes) variations in TCO using “global” (Sun and sky) and direct-Sun observations in the ultraviolet (UV) range with filter radiometers (GUVis-3511 and Microtops). Measurements were performed during three solar eclipses: the Great American Eclipse of 2024, which was observed in Mazatlán, Mexico, on 8 April 2024; a partial solar eclipse taking place in the United States on 14 October 2023 and observed at Fort Collins, Colorado (40.57° N, 105.10° W); and a total solar eclipse occurring in Antarctica on 4 December 2021 and observed at Union Glacier (79.76° S, 82.84° W). The upper limit of the amplitude of oscillations in TCO observed at Mazatlán, Fort Collins, and Antarctica were 0.7 %, 0.3 %, and 0.03 %, respectively. The variability at all sites was within that observed during times not affected by an eclipse. The larger variability at Mazatlán is likely due to cirrus clouds occurring throughout the day of the eclipse and the difficulty of separating changes in the ozone layer from cloud effects. These results support the conclusion that a solar eclipse does not lead to variations in TCO of more than ± 2 Dobson Units and likely much less, drawing into question reports of much larger oscillations. In addition to calculating TCO, we also present changes in the spectral irradiance and aerosol optical depth during eclipses and compare radiation levels observed during totality. The new results augment our understanding of the effect of a solar eclipse on the Earth's upper atmosphere. 

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3. Facial Widths in the Three Adult Morphs of Orangutans

   Harwell, Faye S; Albert, Zoe A; Knott, Cheryl D. (November 2021, Northeastern Evolutionary Primatologists)

   Orangutans challenge our dichotomous perception of phenotypic sex seeing as they have three sexuallymature adult morphs: females, unflanged males, and flanged males. In males, a significant increase in androgen levels is associated with numerous changes in physical characteristics and behavior that develop during the flanging process. While unflanged males lack these obvious secondary sexual characteristics, they still have higher testosterone levels compared to females. Here, we test whether captive unflanged males and females have similar facial ratios (facial width/bi-orbital distance), since flanges form from a facial compartment that contains androgen receptors and is present prior to flanging. When flanging, males deposit fat to these compartments. In the field, unflanged males can be hard to distinguish from female orangutans, without a clear view of the genitalia. Flanged males (3.9 ± 0.5, range=2.7-5.1, N=20) have significantly wider facial ratios compared to unflanged males (2.4 ± 0.3, range=2.1-3.0, N=9) and females (2.3 ± 0.3, range=1.9-2.7, N=22; F(2,48)= 98.18, p-value >0.0001), who are similar in their facial ratios. Interobserver reliability between measurements (N=74) of the bi-orbital distance (V=1171, p=0.3251), facial width (V=1711, p=0.04779), and facial ratio (V=496.5, p=0.2434) are low. While there are other morphological differences between them, unflanged males and females do not differ in their facial ratios. The lack of significant differences in facial ratios between unflanged males and females, despite the higher testosterone levels in unflanged males, is consistent with them having an alternative 'sneaker' male reproductive strategy that includes mimicking female size and appearance. 

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4. Does total column ozone change during a solar eclipse?

   https://doi.org/10.5194/acp-25-819-2025  

   Bernhard, Germar H; Janson, George T; Simpson, Scott; Cordero, Raúl R; Sepúlveda_Araya, Edgardo I; Jorquera, Jose; Rayas, Juan A; Lind, Randall N (January 2025, Atmospheric Chemistry and Physics)

   Kazadzis, Stelios (Ed.)

   Abstract. Several publications have reported that total column ozone (TCO) may oscillate with an amplitude of up to 10 DU (Dobson units) during a solar eclipse, whereas other researchers have not seen evidence that an eclipse leads to variations in TCO beyond the typical natural variability. Here, we try to resolve these contradictions by measuring short-term variations (of seconds to minutes) in TCO using “global” (Sun and sky) and direct-Sun observations in the ultraviolet (UV) range with filter radiometers (GUVis-3511 and Microtops II®). Measurements were performed during three solar eclipses: the “Great American Eclipse” of 2024, which was observed in Mazatlán, Mexico, on 8 April 2024; a partial solar eclipse that took place in the United States on 14 October 2023 and was observed at Fort Collins, Colorado (40.57° N, 105.10° W); and a total solar eclipse that occurred in Antarctica on 4 December 2021 and was observed at Union Glacier (79.76° S, 82.84° W). The upper limits of the amplitude of oscillations in TCO observed at Mazatlán, Fort Collins, and Antarctica were 0.4 %, 0.3 %, and 0.03 %, respectively. The variability at all sites was within that observed during times not affected by an eclipse. The slightly larger variability at Mazatlán is due to cirrus clouds occurring throughout the day of the eclipse and the difficulty of separating changes in the ozone layer from cloud effects. These results support the conclusion that a solar eclipse does not lead to variations in TCO of more than ± 1.2 DU and that these variations are likely much lower, drawing into question reports of much larger oscillations. In addition to calculating TCO, we also present changes in the spectral irradiance and aerosol optical depth during eclipses and compare radiation levels observed during totality. The new results augment our understanding of the effect of a solar eclipse on the Earth's upper atmosphere. 

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5. The development and maintenance of sex differences in dietary breadth and complexity in Bornean orangutans

   https://doi.org/10.1007/s00265-021-03014-3  

   Schuppli, Caroline; Atmoko, S. Suci; Vogel, Erin R.; van Schaik, Carel P.; van Noordwijk, Maria A. (May 2021, Behavioral Ecology and Sociobiology)

   null (Ed.)

   Abstract Orangutans show a pronounced sexual dimorphism, with flanged males (i.e., males with fully grown secondary sexual characteristics) reaching twice the size of adult females. Furthermore, adult orangutans show sex-specific dispersal and activity patterns. This study investigates sex differences in adult foraging behavior and sheds light on how these differences develop in immatures. We analyzed 11 years of feeding data on ten adult female, seven flanged male, and 14 immature Bornean orangutans ( Pongo pygmaeus wurmbii ) at Tuanan in Central Kalimantan, Indonesia. We found that the diets of the adult females were significantly broader and required more processing steps before ingestion than the diets of flanged males. We also found evidence for a similar difference in overall diet repertoire sizes. For the immatures, we found that whereas females reached 100% of their mothers’ diet spectrum size by the age of weaning, males reached only around 80%. From the age of 4 years on (i.e., years before being weaned) females had significantly broader daily diets than males. We found no difference in daily or overall diet processing intensity of immature males and females but found preliminary evidence that immature males included fewer items of their mother’s diet in their own diets that were processing-intensive. Overall, our results suggest that by eating a broader variety and more complex to process food items, female orangutans go to greater lengths to achieve a balanced diet than males do. These behavioral differences are not just apparent in adult foraging behavior but also reflected in immature development from an early age on. Significance Statement In many species, males and females have different nutritional needs and are thus expected to show sex-specific foraging behavior. Sex differences in several aspects of foraging behavior have been found in various species, but it remains largely unclear when and how those develop during ontogeny, which is especially relevant for long-lived altricial species that learn foraging skills over many years. In our study, we analyzed a cross-sectional and longitudinal data set containing more than 750,000 feeding events of adult and immature Bornean orangutans ( Pongo pygmaeus wurmbii ). We found that adult females had significantly broader and more complex diets than males. We also found that these differences started to develop during infancy, suggesting that immature orangutans prepare for their sex-specific foraging niches long before those become physiologically relevant while they are still in constant association with their mothers and before being frequently exposed to other role models. 

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