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Night-Time Colony Attendance Was 98% at Most Common Tern Colonies but Near Zero at One Marine Site

Two marked Common Terns standing on a monitoring platform above water
Research · Behaviour

Breeding common terns (Sterna hirundo) stayed at their colonies through the night at very high rates in most populations studied, but one marine colony showed an almost complete nocturnal absence. The Croatian GPS-tracking study was published online on 26 March 2026.

The researchers compared night-time movements at several freshwater and marine colonies. Across most colonies, terns were present at the breeding site for about 98% of the night. At one marine colony, however, night-time attendance was below 0.02%.

Predation was the leading explanation for the deserted colony

The authors consider nocturnal predation the most likely explanation for the near-total night-time desertion at the marine colony. Previous observations at the site included low breeding success in some years and the presence of an eagle owl in a nearby quarry.

Birds from this colony were also recorded flying slowly over the sea at night. The researchers interpret these movements as probable nocturnal foraging, showing that common terns can use the hours of darkness more actively than their mainly daytime feeding habits might suggest.

Some adults visited other colonies during the night

Both males and females made nocturnal trips to other common tern colonies beyond their normal foraging range. The study interprets these visits as prospecting — movements in which breeding adults gather information about alternative nesting locations.

This behaviour can be particularly relevant in unstable breeding environments where colonies shift between sites from year to year.

Sources and image credit

  1. Kralj, J., Taylor, L., Jurinović, L., Ječmenica, B., Meštrović, L., Barišić, S., Ćiković, D., & Tutiš, V. (2026). Nocturnal behaviour of breeding Common terns. Ethology Ecology & Evolution, 1–9. https://doi.org/10.1080/03949370.2026.2630798Primary peer-reviewed article published online 26 March 2026. GPS telemetry from three Croatian Common Tern colonies found about 98% night-time colony attendance at most sites but less than 0.02% at one marine colony, probably because of nocturnal predation; probable nocturnal foraging and prospecting visits were also documented.

Image: Peter H. Becker / Wikimedia Commons — marked Common Terns on a monitoring platform; representative research image, not birds from the 2026 Croatian GPS study · CC BY-SA 3.0 · Source

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