{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"16143bea7b8084cc223709c810ba94b99180013f62797612911767ee63517ab6","created":"2026-10-03T07:17:57Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"f1a043c22018baba47a003a621ff39356581773abc4a3258b25074cc7dd4abaa","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"bio.collective-behavior.interaction-rules","kind":"well-posed","literature_status":"partially-resolved","n":"1","parents":[],"plain":"A bird could respond to all neighbors within a fixed distance, or to a fixed number of nearest neighbors whatever their distance. Field data favor the second for starlings, but why the number is about seven, and whether this holds across species, is open.","posed_since":"2008","precise":"Infer from 3D trajectory data the interaction kernel of birds, fish and insects: metric (range $r_c$), topological ($n_c$ nearest neighbors; $n_c \\sim 6\\ \\mathrm{to}\\ 7$ in starlings, Ballerini and co-workers, 2008) or visual-field based, using maximum-entropy or force-inference methods with model selection. Determine $n_c$ across species and the mechanism (perceptual limits, group-cohesion optimization) that sets it.","problem_ref":null,"references":"","settled_by":"Model selection on large trajectory data sets from several species showing which kernel fits and the measured $n_c$ or $r_c$ with uncertainties.","status_note":"","title":"Topological or metric interactions in animal 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