How does the hippopotamus see?
The hippopotamus (Hippopotamus amphibius) is a mammal in the order Artiodactyla. Its eyes belong to the vision type Grazing ungulate panorama.
Measured in this species: foveas and night vision. 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 14.99 cycles per degree: the finest stripe pattern it can tell apart from grey.
- Its eyes cover about 350° around the head, with 45° seen by both eyes at once.
- It stops seeing flicker at 60 Hz, against 60 Hz for people in this dataset, so fast motion looks about the same.[15][16]
- Activity pattern: nocturnal.
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: 438 nm (VS/SWS (violet)), 554 nm (LWS (long)) receptor set of nearest measured relative Bos taurus (same order Artiodactyla) | Group default | [1][2] |
| Sharpness | Acuity 14.99 cycles per degree allometry (Mammalia): log10(acuity_cpd) = intercept + slope * log10(eye_axial_length_mm); slope 1.2182, intercept -0.6097, R2 0.45, n 72 (fitted in this script; fitted range [1.9, 48.147] mm); eye_axial_length_mm… | Estimated | [3] |
| Field of view | Binocular overlap 45° median of 4 relatives in order Artiodactyla: Ovis aries, Bos taurus, Capra hircus, Sus scrofa | Group default | [4][5] |
| Total field of view 350° group default: median total field of vision type V04 within phylum Chordata in species-v1: Equus caballus | Group default | [6] | |
| Sharp zones (foveas) | Number of foveas 0 fovea_present / area_centralis_type (retinal topography; count 1 = fovea present, 0 = none) | Measured | [7] |
| Fovea type area centralis, horizontal streak | Measured | [7] | |
| Night vision | Activity pattern nocturnal mode of 6 rows (of 7 rows): cathemeral; mixed (nocturnal/crepuscular, cathemeral, crepuscular or diurnal/crepuscular); nocturnal | Measured (not re-verified) | [8][9][10][11][12][13] |
| Rods vs cones rod-dominated nocturnal -> rod-dominated; crepuscular / cathemeral / mixed -> mixed; diurnal -> cone-dominated | Derived | [8][9][10][11][12][13] | |
| Motion (flicker fusion) | Flicker fusion frequency 60 Hz median of 2 relatives in order Artiodactyla: Ovis aries, Sus scrofa | Group default | [14] |
Related animals
- Cow same vision type
- Pig same vision type
- Sheep same vision type
- Goat same vision type
- Arabian camel same vision type
- Giraffe 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
- Müller B, Glösmann M, Peichl L, Knop GC, Hagemann C, Ammermüller J (2009) Bat eyes have ultraviolet-sensitive cone photoreceptors. PLoS ONE 4:e6390
- Vertebrate eye-size compilation in Thomas et al. 2020 Dryad deposit (Thomas_vertebrates.csv). Primary sources: Howland et al. 2004 (n=313); Schmitz & Wainwright 2011 (n=265); Schmitz et al. 2013 (n=237); Hall 2008 (n=116); Veilleux & Kirk 2014 (n=91); Hall & Heesy 2011 (n=88); Liu et al. 2012 (n=66); Werner & Seifan 2006 (n=62); Lisney & Collin 2007 (n=46). doi.org/10.5061/dryad.1zcrjdfq7
- 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
- Heffner RS, Heffner HE 1992. Visual factors in sound localization in mammals. J Comp Neurol 317:219, Table 1 (via Evo-M1 sensory merge). doi.org/10.1002/cne.903170302
- species_v1:Timney & Keil 1992
- 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
- Anderson SR, Wiens JJ. 2017. Out of the dark: 350 million years of conservatism and evolution in diel activity patterns in vertebrates. Evolution 71:1944-1959. Dryad doi:10.5061/dryad.fg700. doi.org/10.5061/dryad.fg700
- Banks MS, Sprague WW, Schmoll J, Parnell JAQ, Love GD. 2015. Science Advances 1:e1500391. doi.org/10.1126/sciadv.1500391
- 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
- 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
- Haarlem CS, Hynes C, Jackson AL, Mitchell KJ, O'Connell RG, Healy K. 2026. Pace of ecology drives the tempo of visual perception across the animal kingdom. Nature Ecology & Evolution (doi:10.1038/s41559-026-02994-7). Figshare dataset 10.6084/m9.figshare.30556475. doi.org/10.6084/m9.figshare.30556475
- 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?