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Bolivian squirrel monkey vision: the science and the numbers

Saimiri sciureus · order Primates · Mammals: all the numbers

The bolivian squirrel monkey has 2 colour receptor classes (434 and 554 nm): mainly blues and yellows; reds and greens look alike.[1] Its sharpest vision resolves 40.5 cycles per degree, against 63.75 for people in this dataset.[5] Both eyes see the same 146° in front of it.[7]

See it on your photoBack to How does the bolivian squirrel monkey see?
  • 2colour receptor classesMeasured
  • 40.5cycles per degree (sharpness)Measured
  • 146°seen by both eyesMeasured

The bolivian squirrel monkey (Saimiri sciureus) is a mammal in the order Primates. Its eyes belong to the vision type Day dichromat mammal: two cone types (blue and yellow, so reds and greens merge), moderate sharpness and a horizontal band of sharp vision. Measured in this species: colour, sharpness, field of view, foveas and night vision. Measured core: measured values on at least 3 of the 6 dials.

This is a simulation built from published eye measurements, not what the animal experiences.

Method: How we know what animals see (the See Like Animals vision engine) · Sources · Last updated . Every value below carries its evidence level and sources; nothing is typed by hand.

What the bolivian squirrel monkey sees: colour receptors

Bolivian squirrel monkey colour receptor peaks, 300 to 700 nmBolivian squirrel monkey: 2 receptor peaks at 434, 554 nm; you: 3 at 421.5, 532, 558.4 nm. ultraviolet300400500600700
Bolivian squirrel monkey: 434, 554 nmPeople: 421.5, 532, 558.4 nmWavelength in nanometres

What stands out

  • It has two colour receptor classes (a dichromat): reds and greens fall on one axis, as in red-green colour blindness in people.
  • Its sharpest vision resolves 40.5 cycles per degree: the finest stripe pattern it can tell apart from grey.
  • Both eyes see the same 146° in front of it (binocular overlap), where depth is judged best.
  • Activity pattern: diurnal.

The six dials

Evidence levels: how the tiers work. "Measured" means a value measured in this species; "Estimated" values come from a close relative or an eye-size formula. The last column gives the values for people from the same catalogue.

Vision values for the bolivian squirrel monkey (Saimiri sciureus), catalogue-v1
DialValueEvidenceSourcesPeople
ColourColour receptors
2 receptor classes: 434 nm (VS/SWS (violet)), 554 nm (LWS (long))
measured in this species
Measured[1]Colour receptors: 3 receptor classes: 421.5 nm (VS/SWS (violet)), 532 nm (MWS (green)), 558.4 nm (LWS (long)) Measured (not re-verified)[1][2][3][4]
SharpnessAcuity
40.5 cycles per degree
median of 1 behavioural rows (method priority rule)
Measured[5]Acuity: 63.75 cycles per degree Measured[6][5]
Field of viewBinocular overlap
146°
median of 1 rows (eyes-at-rest rows preferred)
Measured[7]Binocular overlap: 122.5° Measured[7][8]
Total field of view: 200° Measured (not re-verified)[9]
Blind area behind the head: 160° Derived[9]
Eye placement: frontal Derived[7][8]
Total field of view
200°
median species-v1 total field of order Primates: Homo sapiens
Group default[9]
Sharp zones (foveas)Number of foveas
1
fovea_present / area_centralis_type (retinal topography; count 1 = fovea present, 0 = none)
Measured[10]Number of foveas: 1 Measured[10]
Fovea type: fovea Measured[10]
Fovea type
fovea		Measured[10]
Night visionActivity pattern
diurnal
mode of 8 rows (of 8 rows): diurnal; photopic
Measured (not re-verified)[11][12][1][13][14][15][16]Activity pattern: diurnal Measured (not re-verified)[17][11][12][1][13][14][15][16]
Pupil shape: vertical Group default[18][19]
Reflective layer (tapetum): no Measured[20]
Rods vs cones: cone-dominated Derived[17][11][12][1][13][14][15][16]
Rods vs cones
cone-dominated
nocturnal -> rod-dominated; crepuscular / cathemeral / mixed -> mixed; diurnal -> cone-dominated
Derived[11][12][1][13][14][15][16]
Motion (flicker fusion)Flicker fusion frequency
69 Hz
median of 3 relatives in order Primates: Macaca mulatta, Macaca nemestrina, Homo sapiens
Group default[21][22][23]Flicker fusion frequency: 60 Hz Measured[21][22]

All mammals side by side: Mammals: every measurement. Method: how we know what animals see.

Sources

  1. Longcore 2023
  2. Kirwan
  3. Müller et al. 2009
  4. Thermal Activation and Photoactivation of Visual… 2004
  5. Veilleux et al. 2014
  6. Kirk et al. 2004
  7. Heesy 2004
  8. Heffner et al. 1992
  9. Campbell & Green 1965
  10. Kopania et al. 2025
  11. Borges et al. 2018
  12. Wilman et al. 2014
  13. Maor et al. 2017
  14. Jones et al. 2009
  15. Schmitz et al. 2011
  16. Moura et al. 2024
  17. Anderson et al. 2017
  18. Banks et al. 2015
  19. Cervino et al. 2021
  20. Guareschi et al. 2025
  21. Healy et al. 2013
  22. Inger et al. 2014
  23. Lafitte et al. 2022

Every value cites its sources (all sources). Values were extracted from these works and converted (units, medians, derived values); changes are ours, and the listed sources do not endorse this site. Data: catalogue-v1, built 2026-09-29. Accuracy notes: how accurate is this? Method: how we know.