How does the American red squirrel see?
The American red squirrel (Tamiasciurus hudsonicus) is a mammal in the order Rodentia. Its eyes belong to the vision type Small prey mammal (UV).
Measured in this species: night vision and motion (flicker fusion). One measured dial: a value other than colour or sharpness is measured in this species; colour and sharpness are not measured here. Every value below carries its evidence level and sources; nothing is typed by hand.
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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 3.9 cycles per degree: the finest stripe pattern it can tell apart from grey.
- Both eyes see the same 60° in front of it (binocular overlap), where depth is judged best.
- It stops seeing flicker at 62.5 Hz, against 60 Hz for people in this dataset, so fast motion looks about the same.[12][13]
- 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.
| Dial | Value | Evidence | Sources |
|---|---|---|---|
| Colour | Colour receptors 2 receptor classes: 444 nm (SWS (blue)), 543 nm (LWS (long)) receptor set of nearest measured relative Sciurus carolinensis (same family Sciuridae) | Estimated | [1] |
| Sharpness | Acuity 3.9 cycles per degree median of 5 relatives in family Sciuridae: Sciurus carolinensis, Sciurus niger, Otospermophilus beecheyi, Sciurus griseus, Ictidomys tridecemlineatus | Estimated | [2][3][4] |
| Field of view | Binocular overlap 60° median of 1 relatives in family Sciuridae: Sciurus carolinensis | Estimated | [5] |
| Sharp zones (foveas) | Number of foveas 0 median of 2 relatives in family Sciuridae: Ictidomys tridecemlineatus, Otospermophilus beecheyi | Estimated | [6] |
| Fovea type horizontal streak | Estimated | [6] | |
| Night vision | Activity pattern diurnal mode of 6 rows (of 6 rows): diurnal; photopic | Measured (not re-verified) | [7][8][9][10][11] |
| Rods vs cones cone-dominated nocturnal -> rod-dominated; crepuscular / cathemeral / mixed -> mixed; diurnal -> cone-dominated | Derived | [7][8][9][10][11] | |
| Motion (flicker fusion) | Flicker fusion frequency 62.5 Hz median of 2 bright-light rows (behavioural/whole-eye ERG rows; all rows: [60.0, 65.0]) | Measured | [12][13] |
Related animals
- Brown rat same vision type
- House mouse same vision type
- Mongolian jird same vision type
- Syrian hamster same vision type
- Daurian ground squirrel same vision type
- Degu same vision type
More mammals: all mammals with measured vision data.
Sources
- Longcore T. 2023. A compendium of photopigment peak sensitivities and visual spectral response curves of terrestrial wildlife to guide design of outdoor nighttime lighting. Basic Appl Ecol 73:40-50. doi:10.1016/j.baae.2023.09.002. doi.org/10.5281/zenodo.8432720
- Borges R, Johnson WE, O'Brien SJ, Gomes C, Heesy CP, Antunes A (2018) Adaptive genomic evolution of opsins reveals that early mammals flourished in nocturnal environments. BMC Genomics 19:121
- Kirk EC, Kay RF 2004. The evolution of high visual acuity in the Anthropoidea. In Anthropoid Origins, Table 1 (behavioural acuity). doi.org/10.1007/978-1-4419-8873-7_20
- Veilleux CC, Kirk EC 2014. Visual acuity in mammals. Brain Behav Evol 83:43, Supplementary Table 1 (cleaned CSV in Evo-M1-Trait-Data). doi.org/10.1159/000357830
- Heesy CP 2004. On the relationship between orbit orientation and binocular visual field overlap in mammals. Anat Rec 281A:1104, Table 1. doi.org/10.1002/ar.a.20116
- Kopania EEK, Clark NL. 2025. Mammalian retinal specializations for high acuity vision evolve in response to both foraging strategies and morphological constraints. Evolution Letters 9: qrae072. Supplementary Tables S1-S2.. doi.org/10.1093/evlett/qrae072
- Wilman et al. 2014 EltonTraits 1.0, MamFuncDat.txt. doi.org/10.6084/m9.figshare.3559887.v1
- Maor R, Dayan T, Ferguson-Gow H, Jones KE. 2017. Temporal niche expansion in mammals from a nocturnal ancestor after dinosaur extinction. Nature Ecology & Evolution 1:1889-1895. Supplementary Table 1. doi.org/10.1038/s41559-017-0366-5
- Jones KE et al. 2009. PanTHERIA: a species-level database of life history, ecology, and geography of extant and recently extinct mammals. Ecology 90:2648. Ecological Archives E090-184. doi.org/10.1890/08-1494.1
- Schmitz L, Motani R. 2011. Science 332:705-708, SOM. doi.org/10.1126/science.1200043
- Moura et al. 2024. A phylogeny-informed characterisation of global tetrapod traits addresses data gaps and biases. PLoS Biol 22:e3002658. TetrapodTraits v3.0.1.. doi.org/10.5281/zenodo.22536349
- Healy K, McNally L, Ruxton GD, Cooper N, Jackson AL. 2013. Metabolic rate and body size are linked with perception of temporal information. Animal Behaviour 86:685-696. Table 1. doi.org/10.1016/j.anbehav.2013.06.018
- Inger R, Bennie J, Davies TW, Gaston KJ. 2014. Potential biological and ecological effects of flickering artificial light. PLoS ONE 9(5): e98631. Table 3. doi.org/10.1371/journal.pone.0098631
Every value cites its sources (all sources). Data: catalogue-v1, built 2026-09-29. Accuracy notes: how accurate is this?