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Eye morphology contributes to the ecology and evolution of the avian tree of life

Cite this dataset

Ausprey, Ian; Ritland, Stanley (2024). Eye morphology contributes to the ecology and evolution of the avian tree of life [Dataset]. Dryad.


The avian eye is the single most important external anatomical trait for interpreting light environments by birds and varies widely in size and shape across the avian tree of life. The attached dataset provides measurements on eye size taken from preserved museum specimens for roughly one third of the avian tree of life (N = 3,475 species). The original dataset was collected by Stanley Ritland and Alice Hutchinson and archived as appendices in Stanley Ritland’s Dissertation from the University of Chicago (1982): “The Allometry of the Vertebrate Eye”.


Figure_3_measurement_diagram.jpg: Screenshot of page 12 (Figure 3) of the original Dissertation that show the exact dimensions of the different eyes measurements.

Ritland_eyes_raw_final.csv: The complete Table 7 from the original Dissertation (pages 1415 – 1647). The only added fields relate to the updated taxonomy (Jetz Bird Tree).

Data Fields:

The columns that end in the word "LET" (e.g., AD_LET) indicate a qualification for the associated measurement. A = "based on measurements of two eyes", B/C/D/E = "estimate or measurement in question". Unfortunately, Ritland did not detail the difference between these four codes.

enter_order: Order of digitization and data entry.

species_jetz: Updated species taxonomy based on the Jetz Bird Tree (Jetz et al. 2012)

family_jetz: Updated family taxonomy based on the Jetz Bird Tree (Jetz et al. 2012)

tax_jetz: Taxonomic order for phylogenetic sorting based on the Jetz Bird Tree (Jetz et al. 2012).

obs: Initials of person who digitized and entered the data.

flag: Unknown species (unk) or extinct (ext).

page_ritland: Page number in the pdf for easy searching. Note that this is not the printed page number. This is the number that you enter in the pdf.

order/family/genus/species_ritland: Original taxonomy provided in the Dissertation. Note that spellings are not always exact due to illegible entries in the original Dissertation.

O: Code for museum collection (institution). See page 1356 for institution codes.

S: Sex and age of specimen. See page 1357 for codes.

OAL: Body length (mm) from tip of bill to tip of tail

HBL: Body length (mm) from tip of bill to base of tail

HW: Max head width (mm)

WING and BILL: Wing and bill length (mm)

CD1 and CD2: min and max corneal diameter (mm)

AD: optical axial diameter (mm)

TD1 and TD2: min and max transverse diameter (mm)

CT: ".....the average diameter of the cornea divided by the average transverse eye diameter multiplied by one hundred, which can be used as a relative indication of the brightness of the image." (pg 1358)

EYED: "......the deviation of the specimen from the overall bird eye diameter/body length allometry (in thousandths of a log unit)."

group: Terrestrial or aquatic species. See the associated manuscripts Ausprey, I. (2024). Journal of Animal Ecology for definition of aquatic.


The attached dataset includes all avian measurements from the Dissertation, corresponding to the entirety of Table 7 (pages 1415 – 1647). Digitization was led by I. Ausprey, S. Montgomery, and K. Perez, with financial support from the Katherine Ordway Chair in Ecosystem Conservation at the Florida Museum of Natural History, USA.

Users are asked to please consult the original Dissertation (available on ProQuest) for details on measuring methodology, specimen origins, caveats, and sources of data for other morphological traits provided in Table 7 (i.e., wing, bill, body mass). In particular, users must consider the columns “O” and “S” which can be used to screen for relevant biases, such as specimen age (embryo, juvenile, adult, etc.) and sex.

Table headings were preserved from the original Dissertation and definitions are define in the original Dissertation. The taxonomy was aligned to the Jetz Bird Tree (Jetz et al. 2012). Taxonomic columns are clearly indicated as pertaining to the original Ritland taxonomy or the Jetz taxonomy.

Please note that a portion of this dataset was previously published on Dryad as part of a different publication ( This included only diurnal terrestrial species. The dataset attached to this Dryad citation should be considered the final and complete version of the Ritland dataset related to birds.

The following details on the dataset are quoted directly from the original Dissertation:

Sample Coverage:

"Ocular dimensions (anterior-posterior diameter, minimum and maximum transverse diameters, and minimum and maximum cornea diameters and body-size measurements.....birds were covered in the greatest detail, with 4807 specimens, including virtually all families and subfamilies, about eighty percent of the 2035 genera, and about forty percent of the 9000 species." (pg. xiii)

Measurement Techniques:

"Preserved specimens were generally in the form of preserved whole animals. These specimens were primarily from museum collections......" (pg. 6)

"The preserved specimens were generally fixed in formaldehyde and stored in seventy to eighty percent alcohol. The older museum specimens were sometimes fixed directly in alcohol." (pg. 7)

"Eyes were removed from the specimens by slitting the skin on either side of the eye and cutting the muscles around the eye and the optic nerve with curved scissors. If the eye had collapsed or lost its pressure, it was reinflated with a syringe containing preservative. Measurements were made of the diameter of the optic axis and the maximum and minimum transverse (equatorial) diameters. Maximum and minimum corneal diameters were also measured in most cases. Measurements on the eye were made with a Craftsman vernier caliper calibrated to 0.05-mm increments." pg. 11

See figure of measurements on Figure 3 (pg. 12) or in the attached image copied from Figure 3.

"Various measurements were also made on the animal itself. Overall length was measured from the tip of the nose or bill to the tip of the tail........Wing length was measure as the maximum width of the head......Wing length was measured in birds and bats from the wrist to the tip of the wing as another estimate of body size and an indication of behavior. Bill length was measured in birds to subtract from the head-and-body measurement and as an indication of behavior.......Weight was measured in fresh specimens and some preserved specimens......Where body measurements were not available (if the specimen consisted of eyes or head only, if the wings were cut, or if particular measurements were missed or inaccurate), measurements were made on other museum specimens (typically skins) or taken from the literature." (pg 13)


Katherine Ordway Chair in Ecosystem Conservation