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Tree swallow vision: the science and the numbers

Tachycineta bicolor · order Passeriformes · Birds: all the numbers

Its sharpest vision resolves 10.05 cycles per degree, against 63.75 for people in this dataset.[6] Its eyes cover about 307° with 23.03° seen by both eyes.[9]

See it on your photoBack to How does the tree swallow see?
  • 10.05cycles per degree (sharpness)Measured
  • 307°field of viewEstimated

The tree swallow (Tachycineta bicolor) is a bird in the order Passeriformes. Its eyes belong to the vision type UV songbird, parrot and hummingbird: four cone types including a true ultraviolet cone, coloured oil droplets and fast motion vision. Measured in this species: sharpness, field of view 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 tree swallow sees: colour receptors

Tree swallow colour receptor peaks, 300 to 700 nmTree swallow: 4 receptor peaks at 367.5, 443, 502.5, 570 nm; you: 3 at 421.5, 532, 558.4 nm. ultraviolet300400500600700
Tree swallow: 367.5, 443, 502.5, 570 nmPeople: 421.5, 532, 558.4 nmWavelength in nanometres

What stands out

  • Its sharpest vision resolves 10.05 cycles per degree: the finest stripe pattern it can tell apart from grey.
  • Its eyes cover about 307° around the head, with 23.03° seen by both eyes at once.
  • 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 tree swallow (Tachycineta bicolor), catalogue-v1
DialValueEvidenceSourcesPeople
ColourColour receptors
4 receptor classes: 367.5 nm (UVS), 443 nm (SWS (blue)), 502.5 nm (MWS (green)), 570 nm (LWS (long))
receptor set of nearest measured relative Serinus canaria (same order Passeriformes)
Group default[1][2]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][3][4][5]
Ultraviolet
yes: at least one receptor peaks in the ultraviolet		Group default
SharpnessAcuity
10.05 cycles per degree
median of 1 anatomical-ganglion rows (method priority rule)
Measured[6]Acuity: 63.75 cycles per degree Measured[7][8]
Field of viewBinocular overlap
23.03°
median of 1 rows (eyes-at-rest rows preferred)
Measured[9]Binocular overlap: 122.5° Measured[10][11]
Total field of view: 200° Measured (not re-verified)[12]
Blind area behind the head: 160° Derived[12]
Eye placement: frontal Derived[10][11]
Total field of view
307°
rule: total = 360 - blind area
Derived[9]
Sharp zones (foveas)Number of foveas
2
median of 2 relatives in family Hirundinidae: Hirundo rustica, Delichon urbicum
Estimated[13]Number of foveas: 1 Measured[14]
Fovea type: fovea Measured[14]
Fovea type
central and temporal fovea		Estimated[13]
Night visionActivity pattern
diurnal
mode of 3 rows (of 3 rows): diurnal; not_nocturnal; photopic
Measured (not re-verified)[15][16][17]Activity pattern: diurnal Measured (not re-verified)[18][19][20][1][21][22][16][17]
Pupil shape: vertical Group default[23][24]
Reflective layer (tapetum): no Measured[25]
Rods vs cones: cone-dominated Derived[18][19][20][1][21][22][16][17]
Rods vs cones
cone-dominated
nocturnal -> rod-dominated; crepuscular / cathemeral / mixed -> mixed; diurnal -> cone-dominated
Derived[15][16][17]
Motion (flicker fusion)Flicker fusion frequency
100 Hz
median of 7 relatives in order Passeriformes: Passer domesticus, Taeniopygia guttata, Molothrus ater, Sturnus vulgaris, Cyanistes caeruleus, Ficedula albicollis
Group default[26][27][28][29]Flicker fusion frequency: 60 Hz Measured[27][28]

Other senses

  • magnetoreception: NOT RENDERED (no agreed visual percept) (Group default)

All birds side by side: Birds: every measurement. Method: how we know what animals see.

Sources

  1. Longcore 2023
  2. VPOD in-vivo (MSP / single-cell) lambda… 2025
  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. Tyrrell et al. 2017
  10. Heesy 2004
  11. Heffner et al. 1992
  12. Campbell & Green 1965
  13. Rodrigues et al. 2026
  14. Kopania et al. 2025
  15. Wilman et al. 2014
  16. Schmitz et al. 2011
  17. Moura et al. 2024
  18. Anderson et al. 2017
  19. Borges et al. 2018
  20. Wilman et al. 2014
  21. Maor et al. 2017
  22. Jones et al. 2009
  23. Banks et al. 2015
  24. Cervino et al. 2021
  25. Guareschi et al. 2025
  26. Boström et al. 2016
  27. Healy et al. 2013
  28. Inger et al. 2014
  29. 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.