Ecological and Morphological Correlates of Acuity in Birds

Birds use their visual systems for a variety of important tasks, such as foraging and predator detection, that require them to resolve an image. However, visual acuity (the ability to perceive spatial detail) varies by two orders of magnitude across birds. Prior studies indicate that eye size and aspects of a species’ ecology may drive variation in acuity, but these studies have been restricted to small numbers of species. We used a literature review to gather data on acuity measured either behaviorally or anatomically for 94 species from 38 families. We then examined how acuity varies in relation to (1) eye size, (2) habitat spatial complexity, (3) habitat light level, (4) diet composition, (5) prey mobility, and (6) foraging mode. A phylogenetically-controlled model including all of the above factors as predictors indicated that eye size, habitat spatial complexity, light level, and diet composition are significant predictors of acuity. Examining each ecological variable in turn revea..., We provide a brief description of methods here; refer to the published manuscript for more details.
Comparative database of acuity
We assembled a database of visual acuity in birds using published data; for each species, we recorded the highest reported acuity value. We then restricted the database to include only data measured using behavioral assays or anatomical methods (specifically the density of retinal ganglion cells, RGCs).
To determine whether it would be appropriate to combine acuity data derived from RGCs and behavioral assays for analyses, we performed two analyses. First, we compiled measures of acuity in 28 vertebrate species with camera eyes (the type of eye found in birds) in which acuity has been measured using both methods (Table S2). We found that behaviorally-derived and RGC-derived acuity measures from the same species are highly correlated (p<0.0001; Figure S1) in a phylogenetically-corrected model using a tree from timetree.org. However, this analysis included..., R, ## READ ME GUIDE TO SUPPLEMENTAL FILES

Caves, Fernandez-Juricic and Kelley. Ecological and Morphological Correlates of Acuity in Birds. Journal of Experimental Biology.

`Bird Acuity Analyses.R`:

* An R code file which runs all of the analyses and creates all of the figures in the manuscript and extended data. Originally created and run using R Version 4.0.3
* Several files are necessary to run the complete R file:

1. `Bird_Acuity_Data.csv`: this file contains data regarding acuity, eye size, body mass, and ecological categorizations in birds.
Columns are:
* Rowname: identical to Binomial_BirdTree, exists for purposes of assigning row names upon upload into R
* Taxonomic_Order: a numeric variable that can be used to sort species into taxonomic order as specified by the Birds of the World Database ()
* Order: Taxonomic Order
* Family: Taxonomic Family
* Binomial_BirdTree: Latin name used in the phylogenetic tree
* Binomial_IOC: The Latin na...