Study
Lasting recognition of threatening people by wild American crows
Marzluff, John M.; Walls, Jeff; Cornell, Heather N.; Withey, John C.; Craig, David P.
Animal Behaviour, 2010
Researchers wore a distinctive rubber mask while trapping and banding wild American crows at several sites. Afterwards, volunteers walked fixed routes wearing either that "dangerous" mask or a different, neutral mask, and recorded how the birds responded. The masks were swapped between people so that the face, rather than the person wearing it, was the thing being tested.
- Studied in
- Corvus brachyrhynchos
- Sample size
- 7 study sites, with hundreds of crow encounters recordedWild, unmanipulated populations at each site.
Crows scolded and mobbed the dangerous mask far more than the neutral one, and did so months and then years after the original trapping. The response spread to birds that had never been captured themselves, and to sites the mask had not been used at.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
American crows recognise and remember individual human faces associated with threat, and that knowledge spreads horizontally and vertically through the population.
How NatureHQ reads it
This is the strongest single piece of evidence that a wild bird treats a human face as an identity rather than as a generic shape. The mask design is what makes it convincing: because different people wore the same face, the birds could not have been responding to gait, height or clothing. What it does not show is that crows read faces the way people do, or that a crow could pick a face out of a line-up in the absence of a threatening context.
- Masks are exaggerated and static; they are not a perfect stand-in for a real human face.
- The response measured is alarm behaviour, which tells us the birds discriminated but not what feature they used.
- Site-level effects and the spread of the response make it hard to separate individual memory from social learning.
The caveman mask experiment
Can a wild crow tell one human face from another, and remember which one is dangerous?
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Elsevier journalsPublished in an Elsevier journal.
doi.org/10.1016/j.anbehav.2009.12.022
This reference was resolved automatically against Crossref and OpenAlex on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-09.