DOI: 10.5061/dryad.z34tmpgt2
title: Predictable evolution toward larger brains and lower hand-wing indices in long-tailed birds

description: 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 is supported by the
 finding that long-tailed birds with equivalent brain size faced a
 higher extinction risk than both normal- and short-tailed birds. Our
 results suggest that the evolutionary trade-off between brain size and HWI
 has sustained long-tail evolution in birds, thus providing new insights
 into understanding natural selection and adaptive evolution.
description: # 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 were not collected. ##### Variables | 
 
 | 
 
 | 
 
 | | :----------------------- |
 :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :-------------- | | Variable | Description | units | | Tree\_Species | Species taxonomy according to BirdTree | 
 
 | | Synonymy\_species | Species taxonomy (Synonymy species) | 
 
 | | Species | Species taxonomy according to BirdLife international | 
 
 | | Order | Order-level taxonomy according to BirdLife international | 
 
 | | Family.name | Family-level taxonomy according to BirdLife
 international | 
 
 | | Sampling.longitude | Sampling longitude | decimal degrees | |
 Sampling.latitude | Sampling latitude | decimal degrees | | Reference |
 Full details of the source for bofy mass and brain mass | 
 
 | | Body.Mass.g | Body mass | grams | | Brain.Mass.g | Brain mass | grams
 | | RedlistCategory | Redlist Category | 
 
 | | Tailtype.2 | Tailtype grouped into two types | 
 
 | | Tailtype.3 | Tailtype grouped into three types | 
 
 | | PGLS | Relative brain mass | 
 
 | | WING | Wing length | mm | | TAIL | Tail length | mm | | HWI |
 Hand-Wing Index, 100\*DK/Lw, where DK is Kipp’s distance and Lw is wing
 length (i.e., Kipp’s distance corrected for wing size) | 
 
 | | Tail-to-Wing Ratio (TWR) | Ratio of tail length to wing length | 
 
 | | devo\_mode | Developmental mode grouped into altricial and precocial
 | 
 
 | | Habitat | 1 = Dense habitats. Species primarily lives in the lower or
 middle storey of forest, or in dense thickets, dense shrubland etc. 2 =
 Semi-open habitats. Species primarily lives in open shrubland, scattered
 bushes, parkland, low dry or deciduous forest, thorn forest. 3 = Open
 habitats. Species primarily lives in desert, grassland, open water, low
 shrubs, rocky habitats, seashores, cities. Also applies to species living
 mainly on top of forest canopy (i.e. mostly in the open) | 
 
 | | Migration-2 | 1 = Sedentary. 2 = Partially migratory, i.e. minority
 of population migrates long distances, or most of population undergoes
 short-distance migration, nomadic movements, distinct altitudinal
 migration, etc. 3 = Migratory, i.e. majority of population undertakes
 long-distance migration | 
 
 | | Latitude | The geometric centre of the species range (restricted to
 breeding and resident range), calculated using the calcCentroid function
 from the R package PBSmapping (Schnute et al., 2017). This function
 projects ranges into the Universal Transverse Mercator (UTM) projection,
 to accurately calculate centroids at high latitudes. To generate the
 breeding and resident range, we used the following settings: Presence: 1
 (Extant). Origin 1 & 2 (Native & Reintroduced). Seasonality 1
 & 2 (resident and breeding season) | 
 
 | | AnnualTemp | Yearly average temperature | °C | | ref.temp | Full
 details of the source for average temperature | 
 
 | 
 
 **2.Worksheet-sister_species** includes relative brain size and hand-wing
 index across 299 sister- species pairs. ##### Variables | 
 
 | 
 
 | 
 
 | | :------- |
 :----------------------------------------------------------------------------------------------------------------------------- | :----- | | Variable | Description | units | | Long | Long-tailed birds | 
 
 | | Short | Short-tailed birds | 
 
 | | PGLS | Relative brain mass | 
 
 | | HWI | Hand-Wing Index, 100\*DK/Lw, where DK is Kipp’s distance and Lw
 is wing length (i.e., Kipp’s distance corrected for wing size) | 
 
 | 
 
 **3.Worksheet-Length** includes body length, wing length, tail length and
 ratio of body length to tail length, as measured across 142 species in
 this study. ##### Variables | 
 
 | 
 
 | 
 
 | | :--------------- | :------------------------------------- | :----- |
 | Variable | Description | units | | Species | Species taxonomy according
 to BirdTree | 
 
 | | Body\_length(mm) | Body length | mm | | Winglength(mm) | Wing length
 | mm | | Taillength(mm) | Tail length | mm | | Tail/bodylength | Ratio of
 tail length to body length | 
 
 | | Tail/winglength | Ratio of tail length to wing length | 
 
 | 
 
 **4.Worksheet-Predictive_variables** provides a description of the
 predictive variables used in this study.