How does the squacco heron see?
The squacco heron (Ardeola ralloides) is a bird in the order Pelecaniformes. Its eyes belong to the vision type Panoramic grain-eater and wader.
Measured in this species: field of view 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 4 colour receptor classes; people have 3.
- Its sharpest vision resolves 12.18 cycles per degree: the finest stripe pattern it can tell apart from grey.
- Its eyes cover about 338° around the head, with 10° seen by both eyes at once.
- It stops seeing flicker at 88.5 Hz, against 60 Hz for people in this dataset, so fast motion looks about 1.5 times slower to it.[15][16]
- 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 4 receptor classes: 417.5 nm (VS/SWS (violet)), 452 nm (SWS (blue)), 501 nm (MWS (green)), 570 nm (LWS (long)) receptor set of nearest measured relative Anas platyrhynchos (same class Aves) | Group default | [1][2] |
| Sharpness | Acuity 12.18 cycles per degree allometry (Aves): log10(acuity_cpd) = intercept + slope * log10(eye_axial_length_mm); slope 0.9017, intercept 0.1397, R2 0.453, n 99 (fitted in this script; fitted range [4.36, 39.81] mm); eye_axial_length_mm 11.2 mm | Estimated | [3] |
| Field of view | Binocular overlap 10° median of 1 rows (eyes-at-rest rows preferred) | Measured | [4] |
| Total field of view 338° group default: median total field of vision type V10 within phylum Chordata in species-v1: Columba livia, Scolopax minor | Group default | [5][6] | |
| Sharp zones (foveas) | Number of foveas 1 median of 48 relatives in class Aves: Branta canadensis, Cardinalis cardinalis, Passerina cyanea, Zenaida macroura, Cyanocitta cristata, Junco hyemalis | Group default | [7][8][9] |
| Fovea type single central fovea (displaced dorso-temporally from retinal centre) | Group default | [7][8][9] | |
| Night vision | Activity pattern diurnal mode of 3 rows (of 3 rows): diurnal; not_nocturnal | Measured (not re-verified) | [10][11][12] |
| Rods vs cones cone-dominated nocturnal -> rod-dominated; crepuscular / cathemeral / mixed -> mixed; diurnal -> cone-dominated | Derived | [10][11][12] | |
| Motion (flicker fusion) | Flicker fusion frequency 88.5 Hz median of 17 relatives in class Aves: Bubo virginianus, Melopsittacus undulatus, Passer domesticus, Taeniopygia guttata, Columba livia, Calypte anna | Group default | [13][14][15][16][17] |
Related animals
- Black-crowned night-heron same vision type
- Cattle egret same vision type
- Rock pigeon same vision type
- Chicken same vision type
- Canada goose same vision type
- Common ostrich same vision type
More birds: all birds with measured vision data.
Sources
- Lind O, Mitkus M, Olsson P, Kelber A. 2014. Ultraviolet vision in birds: the importance of transparent eye media. Proc R Soc B 281:20132209. Table 1. doi.org/10.1098/rspb.2013.2209
- 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
- Ausprey I.J. & Ritland S. 2024. Eye morphology contributes to the ecology and evolution of the avian tree of life [Dataset]. Dryad. Digitised Table 7 of Ritland S. 1982, The allometry of the vertebrate eye, PhD dissertation, University of Chicago. Paper: Ausprey 2024 J Anim Ecol doi:10.1111/1365-2656.14141. doi.org/10.5061/dryad.3xsj3txq7
- Tyrrell LP, Fernandez-Juricic E 2017. Avian binocular vision: it's not just about what birds can see, it's also about what they can't. PLoS ONE 12(3): e0173235. S1 Table.. doi.org/10.1371/journal.pone.0173235
- species_v1:Martin & Young 1983
- species_v1:Martin 1994
- Moore BA, Tyrrell LP, Pita D, Bininda-Emonds ORP, Fernandez-Juricic E 2017. Does retinal configuration make the head and eyes of foveate birds move? Sci Rep 7: 38406. Appendix 1.. doi.org/10.1038/srep38406
- Potier S, Mitkus M, Bonadonna F, Duriez O, Isard P-F, Dulaurent T, Mentek M, Kelber A 2017. Eye size, fovea, and foraging ecology in accipitriform raptors. Brain Behav Evol 90: 232-242. Supplementary material (Tables S1, S2).. doi.org/10.1159/000479783
- Rodrigues T, Matter MM, Chiodini A, et al. 2026. Foveal vision in fast-flying birds hunting on the wing. bioRxiv 2026.06.05.730304. doi.org/10.64898/2026.06.05.730304
- Light conditions and the evolution of the visual system in birds (figshare dataset, SupplementaryDataset1). doi.org/10.6084/m9.figshare.22116371.v3
- Wilman H, Belmaker J, Simpson J, de la Rosa C, Rivadeneira MM, Jetz W. 2014. EltonTraits 1.0: species-level foraging attributes of the world's birds and mammals. Ecology 95:2027. BirdFuncDat.txt. doi.org/10.6084/m9.figshare.3559887.v1
- 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
- Boström JE, Dimitrova M, Canton C, Håstad O, Qvarnström A, Ödeen A. 2016. Ultra-rapid vision in birds. PLoS ONE 11(3): e0151099. S1 Table. doi.org/10.1371/journal.pone.0151099
- 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
- Lafitte A, Sordello R, Legrand M, Nicolas V, Obein G, Reyjol Y. 2022. A flashing light may not be that flashy: A systematic review on critical fusion frequencies. PLoS ONE 17(12): e0279718. S10 File (CFF database). doi.org/10.1371/journal.pone.0279718
Every value cites its sources (all sources). Data: catalogue-v1, built 2026-09-29. Accuracy notes: how accurate is this?