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Table 1.

Eye dimension and optical sensitivity

Budgerigar (Melopsittacus undulatus)NBourke's parrot (Neopsephotus bourkii)N
Cone outer segment length (μm) 8.9±1.4 145 8.5±2.1 149 
Cone outer segment diameter (μm) 1.9±0.3 145 1.7±0.4 149 
Oil droplet diameter (μm) 2.6±0.3 145 2.5±0.4 149 
Rod outer segment length (μm) 13.3±1.8 92 18.5±2.2 137 
Rod outer segment diameter (μm) 3.4±0.5 92 2.8±0.4 137 
Cone to rod ratio 2.1:1 1401:667 1.2:1 1128:930 
Focal length (μm) 4000 5000 
Intensity threshold for colour vision (cd m–20.1 0.4 
Eye at colour vision threshold     
   Pupil size (μm) 2960 3760 
   f-number 1.35 n.a. 1.33 n.a. 
   Optical sensitivity of cones (μm2 sr) 0.27 (0.15) n.a. 0.25 (0.12) n.a. 
Eye at absolute threshold     
   Max. pupil size (μm) 3000 4000 
   Min. f-number 1.33 n.a. 1.25 n.a. 
   Optical sensitivity of rods (μm2 sr) 0.94 n.a. 0.93 n.a. 
Budgerigar (Melopsittacus undulatus)NBourke's parrot (Neopsephotus bourkii)N
Cone outer segment length (μm) 8.9±1.4 145 8.5±2.1 149 
Cone outer segment diameter (μm) 1.9±0.3 145 1.7±0.4 149 
Oil droplet diameter (μm) 2.6±0.3 145 2.5±0.4 149 
Rod outer segment length (μm) 13.3±1.8 92 18.5±2.2 137 
Rod outer segment diameter (μm) 3.4±0.5 92 2.8±0.4 137 
Cone to rod ratio 2.1:1 1401:667 1.2:1 1128:930 
Focal length (μm) 4000 5000 
Intensity threshold for colour vision (cd m–20.1 0.4 
Eye at colour vision threshold     
   Pupil size (μm) 2960 3760 
   f-number 1.35 n.a. 1.33 n.a. 
   Optical sensitivity of cones (μm2 sr) 0.27 (0.15) n.a. 0.25 (0.12) n.a. 
Eye at absolute threshold     
   Max. pupil size (μm) 3000 4000 
   Min. f-number 1.33 n.a. 1.25 n.a. 
   Optical sensitivity of rods (μm2 sr) 0.94 n.a. 0.93 n.a. 

Pupil sizes are entrance pupil diameters; N is sample size;photoreceptor dimensions are expressed as means ± s.d.; n.a., not applicable. The optical sensitivities of single cones (see Eqn 1) were calculated using the oil droplet diameters and the cone outer segment diameters (within brackets)

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