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Northern tree shrew vision: the science and the numbers

Tupaia belangeri · order Scandentia · Mammals: all the numbers

The northern tree shrew has 2 colour receptor classes (444 and 556 nm): mainly blues and yellows; reds and greens look alike.[1] Its sharpest vision resolves 2.1 cycles per degree, against 63.75 for people in this dataset.[6][7] The northern tree shrew stops seeing flicker at 60 Hz, against 60 Hz for people.[24]

See it on your photoBack to How does the northern tree shrew see?
  • 2colour receptor classesMeasured*
  • 2.1cycles per degree (sharpness)Measured
  • 60hertz flicker fusion (motion)Measured

The northern tree shrew (Tupaia belangeri) is a mammal in the order Scandentia. 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, night vision and motion (flicker fusion). 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 northern tree shrew sees: colour receptors

Northern tree shrew colour receptor peaks, 300 to 700 nmNorthern tree shrew: 2 receptor peaks at 444, 556 nm; you: 3 at 421.5, 532, 558.4 nm. ultraviolet300400500600700
Northern tree shrew: 444, 556 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 2.1 cycles per degree: the finest stripe pattern it can tell apart from grey.
  • It stops seeing flicker at 60 Hz, against 60 Hz for people in this dataset, so fast motion looks about the same.[25][24]
  • 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 northern tree shrew (Tupaia belangeri), catalogue-v1
DialValueEvidenceSourcesPeople
ColourColour receptors
2 receptor classes: 444 nm (SWS (blue)), 556 nm (LWS (long))
species-v1.csv value measured in this species (not in tidy tables)
Measured (not re-verified)[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)[2][3][4][5]
SharpnessAcuity
2.1 cycles per degree
median of 2 behavioural rows (method priority rule)
Measured[6][7]Acuity: 63.75 cycles per degree Measured[7][8]
Field of viewBinocular overlap
60°
median of 1 relatives in genus Tupaia: Tupaia glis
Estimated[9]Binocular overlap: 122.5° Measured[9][10]
Total field of view: 200° Measured (not re-verified)[11]
Blind area behind the head: 160° Derived[11]
Eye placement: frontal Derived[9][10]
Total field of view
250°
group default: median total field of vision type the "Day dichromat mammal" type within phylum Chordata in species-v1: Canis familiaris
Group default[12]
Sharp zones (foveas)Number of foveas
0
median of 1 relatives in genus Tupaia: Tupaia glis
Estimated[13]Number of foveas: 1 Measured[13]
Fovea type: fovea Measured[13]
Fovea type
area centralis, horizontal streak		Estimated[13]
Night visionActivity pattern
diurnal
mode of 4 rows (of 4 rows): diurnal
Measured (not re-verified)[14][15][16][8]Activity pattern: diurnal Measured (not re-verified)[17][18][14][2][15][19][20][16]
Pupil shape: vertical Group default[21][22]
Reflective layer (tapetum): no Measured[23]
Rods vs cones: cone-dominated Derived[17][18][14][2][15][19][20][16]
Rods vs cones
cone-dominated
nocturnal -> rod-dominated; crepuscular / cathemeral / mixed -> mixed; diurnal -> cone-dominated
Derived[14][15][16][8]
Motion (flicker fusion)Flicker fusion frequency
60 Hz
median of 1 bright-light rows (behavioural/whole-eye ERG rows; all rows: [60.0])
Measured[24]Flicker fusion frequency: 60 Hz Measured[25][24]

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

Sources

  1. Jacobs & Neitz 1986
  2. Longcore 2023
  3. Kirwan
  4. Müller et al. 2009
  5. Thermal Activation and Photoactivation of Visual… 2004
  6. Caves et al. 2024
  7. Kirk et al. 2004
  8. Veilleux et al. 2014
  9. Heesy 2004
  10. Heffner et al. 1992
  11. Campbell & Green 1965
  12. Miller & Murphy 1995
  13. Kopania et al. 2025
  14. Wilman et al. 2014
  15. Maor et al. 2017
  16. Moura et al. 2024
  17. Anderson et al. 2017
  18. Borges et al. 2018
  19. Jones et al. 2009
  20. Schmitz et al. 2011
  21. Banks et al. 2015
  22. Cervino et al. 2021
  23. Guareschi et al. 2025
  24. Inger et al. 2014
  25. Healy et al. 2013

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.