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Some Great Cormorants Repeatedly Used Fishponds, Others Rivers or Lakes Across Seasons

Great cormorant swallowing a fish on the water
Research · Ecology

Great Cormorants (Phalacrocorax carbo sinensis) breeding at Lake Balaton in Hungary did not all forage in the same kinds of freshwater habitat. Some individuals repeatedly concentrated on fishponds, while others repeatedly used rivers or lakes, often to the near-exclusion of the other main habitat types. These differences persisted across seasons. The study was published on 21 July 2026 in Movement Ecology.

Individual identity mattered far more than age

The researchers fitted solar-powered GPS transmitters to 24 birds — five adults and 19 fledglings — between 2021 and 2023. They classified 20,678 GPS positions as likely foraging locations from the birds’ movement patterns, across six habitat types. Most of the variation reflected which individual bird was being tracked: differences among individuals accounted for 73.6% of the variation in seasonal habitat use, while age class accounted for only 1.2%. In practical terms, knowing which bird was being followed told far more about its habitat use than knowing whether it was an adult or a young bird. Use of rivers and fishponds was especially consistent from season to season, and the researchers also found stable patterns for lakes and regulated water bodies.

The authors interpret this as stable individual foraging tactics, rather than age-related changes or birds simply switching habitats opportunistically. The GPS data show where birds were likely to be foraging, however, not how much time they spent diving or how many fish they caught. The study therefore documents consistent differences in habitat use, not individual differences in actual fish consumption.

Not every cormorant used fishponds

This matters where cormorants and fisheries come into conflict. If only part of a population regularly uses managed fishponds, measures aimed at all cormorants may affect many birds that rarely visit those sites. The authors therefore argue that management focused on particular habitats — and, where possible, the individuals that repeatedly use them — may be more effective than treating the whole population as if every bird foraged in the same way.

Sources and image credit

  1. Preiszner, Szinai & Kovács (2026) — Consistent individual differences in foraging movement tactics drive habitat partitioning in an inland-breeding Great Cormorant populationPrimary open-access peer-reviewed study in Movement Ecology, published 21 July 2026. Twenty-four Great Cormorants at Lake Balaton were GPS-tracked in 2021–2023. Individual identity accounted for 73.6% of seasonal habitat-use variation, age class for 1.2%, and habitat use was repeatable across seasons for rivers, fishponds, regulated water bodies and lakes. The authors note that GPS speed classification identifies likely foraging locations but cannot measure dive effort or prey capture rate.

Image: Mildeep / Wikimedia Commons — Great Cormorant (Phalacrocorax carbo sinensis) swallowing a fish at Taudaha, Nepal, 28 February 2021. High-quality representative image of the study species while feeding; not a bird or location from the Lake Balaton study. · CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ · Source

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