Animals & nature · 2025
Do larger fish shoals detect bird attacks more often and decide faster without more false alarms?
Yes—that was the pattern observed in wild fish shoals. Compared with smaller shoals, larger shoals detected bird attacks more often and took less time to decide, while their responses to similar but harmless flybys stayed constant. The study did not establish how this pattern arose.
Details
Information spreading through a group can help animals detect danger, but it could also spread false alarms. Researchers studied wild fish shoals that dived together to escape attacking birds. They compared collective responses to actual attacks and similar but harmless flybys across shoals of different sizes.
Larger shoals detected actual attacks more often, while their responses to harmless flybys—the false alarms in this study—stayed constant. Decision time also decreased as shoal size increased. In this setting, better attack detection did not come at the cost of more false alarms or slower decisions.
These observations link larger shoal size with this combined advantage, but they do not explain the mechanism. The finding concerns these wild fish responding to birds, not all animal groups or all kinds of decisions.
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