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Multiple within-year breeding bouts during early colony establishment of Great Cormorants Phalacrocorax carbo at an inland reservoir in Taiwan

Hung-Chun Yen, Wei-En Lin, Yu-Wun Deng, Wen-Loung Lin

Published on: 27 October 2026

Page: 782 - 787

DOI: 10.6165/tai.2026.71.782

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    Abstract

    Great Cormorants Phalacrocorax carbo have long been treated as winter visitors in Taiwan, with no established breeding population historically reported. Since 2021, individuals have remained year-round at Hushan Reservoir (Yunlin County, Taiwan). In 2023, we documented the first confirmed colonial breeding of the species in Taiwan. Using monthly boat-based surveys supplemented by drone verification (2023–2025), we quantified breeding phenology and productivity during the early stage of colony establishment. The colony showed multiple breeding bouts per year, increasing from two bouts in 2023 (April, September) to three in 2024 (February, May, October) and four in 2025 (February, May, August, November). Annual nest attempts increased from 6 in 2023 to 33 in 2025. Nest success to ≥4 weeks was 83.3% in 2023, 57.9% in 2024, and 100.0% in 2025, and the annual number of chicks reaching ≥4 weeks was 15, 27, and 83, respectively. Mixed-age pairs involving subadults were recorded across all years, and nest placement varied among bouts in relation to reservoir water-level conditions and available nesting substrates. These observations document increased breeding activity during the early establishment of an inland colony and suggest that reservoir systems may provide suitable conditions for Great Cormorant breeding in Taiwan.

    Keyword: Breeding phenology, colony establishment, Great Cormorant, Phalacrocorax carbo, reservoir, Taiwan

    Literature Cited

    Bregnballe, T. 2006 Age-related fledgling production in Great Cormorants Phalacrocorax carbo: constraints or selection? J. Avian Biol. 37(2): 149–157.
    DOI: 10.1111/j.0908-8857.2006.03088.xView Article Google Scholar

    Bregnballe, T., Carss, D.N. 2012 Sexing, ageing and measuring cormorants. In: Carss, D.N., Parz-Gollner, R., Trauttmansdorff, J. (eds.), The INTERCAFE field manual: research methods for cormorants, fishes, and the interactions between them. NERC Centre for Ecology & Hydrology, Edinburgh, UK, pp. 54–65.

    Buatip, S., Karntanut, W., Swennen, C. 2013 Nesting period and breeding success of the Little Egret Egretta garzetta in Pattani province, Thailand. Forktail 29: 120–123.

    Craik, C., Bregnballe, T. 2008 Late breeding by Great Cormorants Phalacrocorax carbo. Seabird 21: 93–97.
    DOI: 10.61350/sbj.21.93View Article Google Scholar

    Ding, T.-S., Juan, C.-S., Lin, R.-S., Tsai, Y.-J., Wu, J.-L., Wu, J., Yang, Y.-H. 2023 The 2023 TWBF checklist of the birds of Taiwan. Taiwan Wild Bird Federation, Taipei, Taiwan.

    Dragonetti, M., Giovacchini, P. 2009 Aspects of breeding biology of Cattle Egret Bubulcus ibis in a Grosseto province colony (Tuscany, central Italy). Avocetta 33: 199–204.

    Frederiksen, M., Lebreton, J.-D., Bregnballe, T. 2001 Conspecific reproductive success affects age of recruitment in a great cormorant colony. Proc. R. Soc. B 268(1475): 1519–1526.
    DOI: 10.1098/rspb.2001.1701View Article Google Scholar

    Fukuda, M. 2002 Breeding biology of the Great Cormorant Phalacrocorax carbo in Japan. Jpn. J. Ornithol. 51(2): 116–121. https://doi.org/10.3838/jjo.51.116

    Fukuda, M., Narusue, M., Kato, N. 2002 Changes in the distribution and abundance of Great Cormorants in Japan. Jpn. J. Ornithol. 51(1): 4–11.
    DOI: 10.3838/jjo.51.4View Article

    Grieco, F. 1994 Fledging rate in the Cormorant Phalacrocorax carbo at the colony of Val Campotto (Po Delta, N-E Italy). Avocetta 18: 57–61.

    Ishida, A., Matsuzawa, T., Kameda, K., Narusue, M. 2000 The population increase of the Great Cormorant Phalacrocorax carbo and its damaging effect on fisheries and trees in Japan: the present situation, the problems in each area and future measures. Strix 18: 1–28.

    Lin, W.-E., Yen, H.-C., Deng, Y.-W., Li, C.-H., Hsu, C.-H. 2025 Observations on the colonial breeding of the Great Cormorant (Phalacrocorax carbo) at Hushan Reservoir. Nat. Conserv. Q. 130: 66–75.

    Liordos, V., Goutner, V. 2008 Reproductive success of Great Cormorants Phalacrocorax carbo sinensis at two colonies in Greece. J. Nat. Hist. 42(5-8): 317–331.

    Maxwell, G.R., Kale, H.W. 1977 Breeding biology of five species of herons in coastal Florida. Auk 94(4): 689–700.
    DOI: 10.2307/4085265View Article Google Scholar

    Newson, S.E., Hughes, B., Hearn, R.D., Bregnballe, T. 2005 Breeding performance and timing of breeding of inland and coastal breeding cormorants in England and Wales. Bird Study 52(1): 10–17.
    DOI: 10.1080/00063650509461369View Article Google Scholar

    Prosper, J., Hafner, H. 1996 Breeding aspects of the colonial Ardeidae in the Albufera de Valencia, Spain: population changes, phenology and reproductive success of the three most abundant species. Colon. Waterbirds 19: 98–107.
    DOI: 10.2307/1521952View Article Google Scholar