Predictable evolution toward larger brains and lower hand-wing indices in long-tailed birds

The elongated tail increases body drag and alters aerodynamic efficiency, resulting in a decrease in flight performance that is closely associated with the hand-wing index (HWI). Enlarged brains provide cognitive benefits including tool-use behaviors, learning, and decision-making, that increase individual fitness. By enhancing individual fitness, they ultimately contribute to a reduced risk of species extinction. Therefore, predictable evolution towards larger brains and lower HWIs may be expected for antipredation in long-tailed birds. Here, we assembled brain and HWI data for 2473 bird species, including new brain measurements for 103 species, to test this hypothesis. We found that long-tailed birds had larger relative brain sizes and smaller HWIs than their normal-tailed counterparts, indicating that high cognitive capacity resulting from an enlarged brain probably offsets the negative effects of weak flight capacity, especially a higher predation risk. This..., , # Predictable evolution toward larger brains and lower hand-wing indices in long-tailed birds

Dataset DOI: [10.5061/dryad.z34tmpgt2](10.5061/dryad.z34tmpgt2)

## Description of the data and file structure

Dataset 1 includes body mass, hand-wing index, development mode, annual temperature, migration, habitat, latitude etc. across 2473 bird species and 299 sister- species pairs.

### Files and variables

#### File: Dataset_1.xlsx

**Description:** Dataset 1 includes body mass, hand-wing index, development mode, annual temperature, migration, habitat, latitude etc. across 2473 bird species and 299 sister- species pairs. The dataset comprises four worksheets. 'n/a' represents \"not available\", indicating that the data were not collected. The details are presented as follows:

**1.Worksheet-data** includes body mass, hand-wing index, development mode, annual temperature, migration, habitat, latitude etc. across 2473 bird species. 'n/a' represents \"not available\", indicating that the data we...,