DOI: 10.5061/dryad.crjdfn3bz
title: Data from: Birds that breed exclusively on islands have smaller clutches

description: The ‘island syndrome’ refers to similarity in the biology of island
 organisms, but its generality is questionable, as the scope of species and
 traits examined are often limited. Here, I show that birds breeding
 exclusively on islands (breeding island endemics) evolved smaller
 clutches, using a dataset of 4,530 bird species. Using an inclusive
 definition of a breeding island endemic, which also encompasses migratory
 species and seabirds, I examine the evolution of clutch sizes in island
 breeding species using phylogenetic generalized linear models. Across
 disparate phylogenetic hypotheses, and after accounting for biological and
 geographical co-variables, I show that breeding island endemic landbirds
 (470 species) evolved smaller clutch sizes than continental breeding
 species (3,818 species). I show that the evolution of clutch size follows
 the expectations of the island syndrome, as among breeding island endemic
 landbirds there is a positive relationship between clutch size and
 breeding range area. Finally, I reinforce the view that the island
 syndrome is a general pattern in birds, spanning diverse phylogenetic and
 ecological groups, by showing that in a seabird-only dataset (242
 species), breeding island endemic seabirds show evolution of smaller
 clutch sizes. In a model of the full dataset of both landbirds and
 seabirds (4,530 species) there was no evidence of an interaction of being
 a seabird with breeding island endemicity, showing that seabirds and
 landbirds respond in the same way. This study, using more than 40% of all
 bird species, provides the first evidence of a general evolutionary
 response in a life history trait, clearly showing the island syndrome as a
 general evolutionary tendency associated with island environments.
description: # Data from: Birds that breed exclusively on islands have smaller clutches
 Related article published in *Ornithology* in 2024 by M. T. Jezierski.
 Data and code versioned 16th January 2024. README versioned 16th January
 2025. [jezierski.m.t@gmail.com](mailto:jezierski.m.t@gmail.com)
 [https://github.com/jezierskim/clutch](https://github.com/jezierskim/clutch) ## Repository contents: #### README file (this). * clutch_data_code.R (R script for data preparation; uses files: clutch_dataset.csv and dev_sp.csv) * clutch_dataset.csv (raw data for the above R script) * dev_sp.csv (family level data on precociality) * analysis_dataset.csv (final output of clutchdatacode.R; to be used with clutch_analysis_code.R) * clutch_analysis_code.R (R script for data analysis; uses the file seabirds.csv) * seabirds.csv (list of species identified as seabirds (see Methods)) #### In addition to files provided in the repository, clutch\_data\_code.R requires two extra files that cannot be provided due to copyrights. These are: * BirdLife International data ranges; freely available at [https://datazone.birdlife.org/species/requestdis](https://datazone.birdlife.org/species/requestdis) upon request. NB: the code in uses version 2020.1. NB: file needs to be named 'BOTW.gpkg' in the code. Natively, it is downloaded as BOTW.gdb (and can be used if the extension is supplanted in the code.) * Natural Earth data land file at 50 million resolution; freely available at [https://www.naturalearthdata.com/downloads/50m-physical-vectors/](https://www.naturalearthdata.com/downloads/50m-physical-vectors/). NB: file needs to ba named and located in directory: 'ne_50m_land/ne_50m_land.shp'. This is the native name. #### In addition to files provided in the repository, clutch\_analysis\_code.R needs an extra file that cannot be provided due to copyrights. These are: * 100 phylogenetic trees based on genetic data with Hackett backbone. These can be obtained in birdtree.org. The file should be named: 100_trees_Hackett_genetic.tre. ## Dataset contents and metadata. Below are the contents and metadata of original files provided in this repository. Metadata of external files (listed above) is provided by the providers. ### clutch\_dataset.csv Main dataset file containing the data needed for analysis. Columns and descriptions are: * order - taxonomic order according to Clements taxonomy 2019. * family - taxonomic family according to Clements taxonomy 2019. * ebird_name - binomial name according to Clements taxonomy 2019. * treelabels - binomial names as used in the phylogenetic trees from birdtree.org. * binomial - binomial names according to IUCN taxonomy 2020. * clumin - minimum clutch size, units: 1 egg. * clumax - maximum clutch size, units: 1 egg. * bodmin - minimum body mass, units: 1g. * bodmax - maximum body mass, units: 1g. * is - binomial term indicating island endemic; Y - yes; N - no. ### dev\_sp.csv Dataset on development mode in bird families. Columns and descriptions are: * family - taxonomic family according to Clements taxonomy 2019; synonymous with family in clutch_dataset.csv. * mode - binomial term indicating developmental mode; two states: altricial OR precocial. ### analysis\_dataset.csv Analysis ready dataset produced by code file clutch_data_code.R. Columns and descriptions are: * binomial - binomial names according to IUCN taxonomy 2020. * latitude - latitude centroid obtained in clutch_data_code.R from IUCN species ranges, units: degrees. * area - breeding range area obtained in clutch_data_code.R from IUCN species ranges, units: meters squared. * order - taxonomic order according to Clements taxonomy 2019. * family - taxonomic family according to Clements taxonomy 2019. * ebird_name - binomial name according to Clements taxonomy 2019. * treelabels - binomial names as used in the phylogenetic trees from birdtree.org. * binomial - binomial names according to IUCN taxonomy 2020. * clumin - minimum clutch size, units: 1 egg. * clumax - maximum clutch size, units: 1 egg. * bodmin - minimum body mass, units: grams. * bodmax - maximum body mass, units: grams. * is - binomial term indicating island endemic; Y - yes; N - no. * migratory - binomial term indicating whether the species is migratory or not; migratory - yes, NA - no. * mode - binomial term indicating developmental mode from dev_sp; two states: altricial OR precocial. * clu_geom - geometric mean clutch size calculated in clutch_data_code.R. * mass_geom - geometric mean body mass calculated in clutch_data_code.R. ### seabirds.csv Dataset containing data on marine habitat use of birds identified as seabirds (see Methods). Columns and descriptions are: * order - taxonomic order according to Clements taxonomy 2019. * family - taxonomic family according to Clements taxonomy 2019. * name - common name according to Clements taxonomy 2019. * genus - taxonomic genus according to Clements taxonomy 2019. * species - taxonomic specific epithet according to Clements taxonomy 2019. * sea - mode of marine habitat sea use; three states: coastal - uses water 'near' the coast; offshore - further away from the coast but along the continental shelf; pelagic - uses seas beyond the continental shelf.