Is the Asian Openbill Migratory? Population Status and Habitat Use in Eastern Nepal

Abstract

The Asian Openbill (Anastomus oscitans) is a colonial waterbird found across South and Southeast Asia. Despite its overall stable population status globally, it faces vulnerability in Nepal, mainly due to unplanned urbanization across farmlands, agrochemicals, and wetland encroachment. We assessed the population status through direct counts and analyzed habitat use using generalized linear mixed modeling across five districts of eastern Nepal (2020–2022). We found that the Asian Openbill predominantly roosted near waterbodies and frequently utilized farmland habitats. The population count of the species was significantly higher during the breeding season compared to nonbreeding season. Farmland and wetland areas had positive influence on the species' habitat use. Our findings suggest that the Asian Openbill migrates seasonally, likely from northern India, with large numbers arriving in eastern Nepal to breed, while a few remain resident year-round. These findings underscore the need for effective management of farmland and wetland landscapes for their conservation.

Keywords

farmland / migratory species / stork / telemetry tagging / urbanization / wetland

References

[1] Abidin, K., F. S. Mohd-Taib, and S. Md-Nor. 2017. “Distribution and Habitat Selection of the Asian Openbill (Anastomus oscitans) in Peninsular Malaysia.” Malayan Nature Journal 69: 169–181.

[2] Adhikari, J. N., B. P. Bhattarai, and D. N. Dhakal. 2018. “Conservation Value of Beeshhazari Lake: An Insight Into Diversity and Abundance of Wetland Birds.” Our Nature 16: 17–26.

[3] Amzah, B., R. Ramli, and N. Mamat. 2025. “Distribution Pattern and Abundance Dynamics of Asian Openbill (Anastomus oscitans) in Rice Field Throughout Peninsular Malaysia.” Turkish Journal of Zoology 49: 172–190.

[4] Baral, H. S. 2008. “Birds of Jagdishpur Reservoir, Nepal.” Forktail 24: 115–119.

[5] Bates, D., M. Mächler, B. Bolker, and S. Walker. 2015. “Fitting Linear Mixed-Effects Models Using lme4.” Journal of Statistical Software 67: 1–48.

[6] Bhattarai, B. 2012. “Distribution and Diversity of Storks in the Adjoining Areas of Chitwan National Park, Nepal.” In Himalayan Biodiversity in the Changing World, edited by P. Kindlmann, 97–114. Springer.

[7] Bhattarai, K., A. P. Adhikari, and S. P. Gautam. 2023. “State of Urbanization in Nepal: The Official Definition and Reality.” Environmental Challenges 13: 100776.

[8] Bibby, C. J., N. D. Burgess, D. A. Hill, and S. Mustoe. 2000. Bird Census Techniques. 2nd ed. Academic Press.

[9] BirdLife International. 2023. “Species Factsheet: Anastomus oscitans.” http://datazone.birdlife.org/species/factsheet/asian-openbill-anastomus-oscitans.

[10] Cheng, C., J. Liu, and Z. Ma. 2022. “Effects of Aquaculture on the Maintenance of Waterbird Populations.” Conservation Biology 36: e13913.

[11] Datta, T., and B. C. Pal. 1995. “Polygyny in the Asian Openbill (Anastomus oscitans).” Auk 112: 257–260.

[12] Department of Forest Research and Survey. 2014. Terai Forests of Nepal. Forest Research and Training Center.

[13] Djerboua, S., S. Djerdali, J. Guerrero-Casado, A. S. Bachir, and A. Guendouz. 2022. “Water Birds as Indicators of Ecological Conditions in a Ramsar Wetland (Sebkhet Bazer, East of Algeria).” Agricultural Science Digest 42: 341–350.

[14] Garg, A. 2016. “Nest–Plant Correlation and Predator Preclusion in Asian Openbill Storks (Anastomus oscitans): A Case Study From Nawabgunj Bird Sanctuary, India.” Indian Forester 142: 179–186.

[15] Green, A. J., and J. Elmberg. 2014. “Ecosystem Services Provided by Waterbirds.” Biological Reviews 89: 105–122.

[16] Grimmett, R., C. Inskipp, T. Inskipp, and H. S. Baral. 2016. Birds of Nepal. Helm Field Guide.

[17] Hahn, S., S. Bauer, and M. Klaassen. 2008. “Quantification of Allochthonous Nutrient Input Into Freshwater Bodies by Herbivorous Waterbirds.” Freshwater Biology 53: 181–193.

[18] Hara, Y., K. Yamaji, S. Yokota, D. Thaitakoo, and Y. Sampei. 2018. “Dynamic Wetland Mosaic Environments and Asian Openbill Habitat Creation in Peri-Urban Bangkok.” Urban Ecosystems 21: 305–322.

[19] Huxley, J. 1962. “The Openbill Stork Anastomus oscitans.” Ibis 104: 112.

[20] Inskipp, C., H. Baral, S. Phuyal, et al. 2016. The Status of Nepal's Birds: The National Red List Series. Zoological Society.

[21] Jiang, A. 2010. “A New Distribution Site of the Asian Open-Billed Stork (Anastomus oscitans) in Southwestern China.” Chinese Birds 1: 259–260.

[22] Kahl, M. P. 1971. “Food and Feeding Behavior of Openbill Storks.” Journal für Ornithologie 112: 21–35.

[23] Karra, K., C. Kontgis, Z. Statman-Weil, J. C. Mazzariello, M. Mathis, and S. P. Brumby. 2021. “Global Land Use/Land Cover With Sentinel 2 and Deep Learning.” In 2021 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Belgium, 4704–4707.

[24] Katuwal, H. B., S. Koirala, H. P. Sharma, and R.-C. Quan. 2025. “The Agricultural Landscapes of Nepal Have High Potential for Bird Conservation: An Analysis of Research, Threats and Policy Gaps.” Biological Conservation 308: 111251.

[25] Katuwal, H. B., J. Rai, K. Tomlinson, et al. 2022. “Seasonal Variation and Crop Diversity Shape the Composition of Bird Communities in Agricultural Landscapes in Nepal.” Agriculture, Ecosystems & Environment 333: 107973.

[26] Katuwal, H. B., K. S. G. Sundar, M. Zhang, et al. 2022. “Factors Affecting the Breeding Ecology of the Globally Threatened Lesser Adjutant Leptoptilos javanicus in Agricultural Landscapes of Nepal.” Avian Conservation and Ecology 17: 15.

[27] Khadka, B. B. 2006. “Nesting Colony of Asian Openbill Anastomus oscitans in Royal Chitwan National Park.” Danphe 15: 1–3.

[28] Khan, M. A., M. M. H. Khan, R. Ahmed, et al. 2000. Red Book of Threatened Birds of Bangladesh. IUCN- The World Conservation Union.

[29] Kittur, S., and K. G. Sundar. 2020. “Density, Flock Size and Habitat Preference of Woolly-Necked Storks Ciconia episcopus in Agricultural Landscapes of South Asia.” SIS Conservation 2: 71–79.

[30] Koju, R., B. Maharjan, K. R. Gosai, S. Kittur, and K. S. G. Sundar. 2019. “Ciconiiformes Nesting on Trees in Cereal-Dominated Farmlands: Importance of Scattered Trees for Heronries in Lowland Nepal.” Waterbirds 42: 355–453.

[31] Lei, Y., and Q. Liu. 2021. “Tolerance Niche Expansion and Potential Distribution Prediction During Asian Openbill Bird Range Expansion.” Ecology and Evolution 11: 5562–5574.

[32] Li, J., Y. Zhang, L. Zhao, W. Deng, F. Qian, and K. Ma. 2021. “Scale and Landscape Features Matter for Understanding Waterbird Habitat Selection.” Remote Sensing 13: 4397.

[33] Limbu, K., B. Subba, and B. K. Rai. 2013. “Nutritional Status of Three Species of Molluscs in Nepal.” In Perspectives in Animal Ecology and Reproduction, edited by V. K. Gupta, A. K. Verma, and G. D. Singh, 232–239. Daya Publishing House.

[34] Liu, Q., P. Buzzard, and X. Luo. 2015. “Rapid Range Expansion of Asian Openbill Anastomus oscitans in China.” Forktail 31: 118–120.

[35] Low, B. W., K. Lim, F. Yap, T. Lee, K. Lim, and D. L. Yong. 2013. “First Record of The Asian Openbill, Anastomus oscitans (Aves: Ciconiidae) in Singapore.” Nature in Singapore 6: 25–29.

[36] Lüdecke, D. 2018. “ggeffects: Tidy Data Frames of Marginal Effects From Regression Models.” Journal of Open Source Software 3: 772.

[37] Mandal, M. 2024. “Breeding Colony Contraction of Asian Openbill Stork (Anastomus oscitans): An Eco-Spatial Monitoring From Keleghai River Bank, India.” Environmental Monitoring and Assessment 196: 317.

[38] Mariyappan, M., M. Rajendran, S. Velu, et al. 2023. “Ecological Role and Ecosystem Services of Birds: A Review.” International Journal of Environment and Climate Change 13: 76–87.

[39] Mohapatra, R. K., B. Panda, M. Panda, et al. 2019. “Colonial Nesting of Asian Openbill Storks (Anastomus oscitans) in Nandankanan Wildlife Sanctuary, Odisha.” International Journal of Avian & Wildlife Biology 4: 14–17.

[40] Nepal, K., and I. Thapa. 2020. “Bird Conservation Nepal Water Bird Count 2017 in Wetlands of Nepal.” Danphe 27: 2–9.

[41] Paradis, E., and K. Schliep. 2019. “Ape 5.0: An Environment for Modern Phylogenetics and Evolutionary Analyses in R.” Bioinformatics 35: 526–528.

[42] Pöysä, H., J. Elmberg, G. Gunnarsson, S. Holopainen, P. Nummi, and K. Sjöberg. 2017. “Habitat Change and Population Decline in Breeding Wigeon Anas penelope.” In 33rd IUGB Congress and 14th Perdix Congress Montpellier.

[43] Pramanik, A. K., K. B. Santra, and C. K. Manna. 2014. “Seasonal Abundance and Factors Influencing the Population of Asian Openbilled Stork (Anastomus oscitans) in The Raiganj Wildlife Sanctuary, West Bengal, India.” Asian Journal of Conservation Biology 3: 28–37.

[44] Pramanik, A. K., K. B. Santra, and C. K. Manna. 2016. “Some Observations on Breeding Behaviour of The Asian Open-Billed Stork (Anastomus oscitans) in the Raiganj Wildlife Sanctuary, West Bengal, India.” International Research Journal of Environmental Sciences 5: 10–21.

[45] R Core Team. 2023. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna.

[46] Rahman, F., and A. Ismail. 2018. “Waterbirds: An Important Bio-Indicator of Ecosystem.” Pertanika Journal of Scholarly Research Reviews 4: 81–90.

[47] Ratanakorn, P., S. Suwanpakdee, W. Wiriyarat, et al. 2018. “Satellite Telemetry Tracks Flyways of Asian Openbill Storks in Relation to H5N1 Avian Influenza Spread and Ecological Change.” BMC Veterinary Research 14: 349.

[48] Rimal, B., H. Keshtkar, R. Sharma, N. Stork, S. Rijal, and R. Kunwar. 2019. “Simulating Urban Expansion in a Rapidly Changing Landscape in Eastern Tarai, Nepal.” Environmental Monitoring and Assessment 191: 255.

[49] Robson, C. 2000. A Field Guide to the Birds of South-East Asia. New Holland Publishers Ltd.

[50] Saunders, S. P., W. Piper, M. T. Farr, et al. 2021. “Interrelated Impacts of Climate and Land-Use Change on a Widespread Waterbird.” Journal of Animal Ecology 90: 1165–1176.

[51] Sharma, H. P., H. B. Katuwal, S. Regmi, et al. 2024. “Population and Conservation Threats to the Vulnerable Sarus Crane Grus antigone in Nepal.” Ecology and Evolution 14: e10929.

[52] SoIB. 2024, “State of India's Birds Factsheet: Asian Openbill Anastomus oscitans (India).” https://stateofindiasbirds.in/species/asiope1/.

[53] Sundar, K. S. G., R. Koju, B. Maharjan, B. G. Marcot, S. Kittur, and K. R. Gosai. 2019. “First Assessment of Factors Affecting the Breeding Success of Two Stork Species in Lowland Nepal Using Bayesian Network Models.” Wildfowl 69: 45–69.

[54] Sundar, K. S. G., B. Maharjan, R. Koju, S. Kittur, and K. R. Gosai. 2016. “Factors Affecting Provisioning Times of Two Stork Species in Lowland Nepal.” Waterbirds 39: 365–374.

[55] Tamang, G., H. B. Katuwal, A. Subba, and N. B. Singh. 2024a. “Breeding Ecology of the Asian Openbill in Eastern Nepal: Larger Trees Support Higher Fledgling Success.” Ecology and Evolution 14: e11504.

[56] Tamang, G., H. B. Katuwal, A. Subba, and N. B. Singh. 2024b. “Nutritional Dynamics in Early Development of Asian Openbill: A Study of Hatchling and Nestling Feeding Patterns.” Ecological Frontiers 44: 726–732.

[57] Tolohah, A. A., F. N. Arazmi, S. Md. Nor, and M. S. Mansor. 2023. “Spatial Distribution of Malaysian Storks Determined Based on Citizen Science (eBird) Data.” Pertanika Journal of Science and Technology 31: 2329–2338.

RIGHTS & PERMISSIONS

2025 The Author(s). Wildlife Letters published by Northeast Forestry University and John Wiley & Sons Australia, Ltd.