DOI: 10.5061/dryad.12jm63z75
title: Parrots live in smaller groups on islands

description: Species living on islands are predictably different from their mainland
 counterparts in morphology and behaviour, but the source of these
 differences is still debated. Islands, in particular, are characterized by
 depauperate predator communities. Relaxed predation pressure might explain
 why living in groups, a common anti-predator adaptation in animals, is
 considered less likely on islands. However, the empirical evidence for
 this effect is scant and alternative explanations have been overlooked.
 For instance, smaller groups might be more common because island species
 are less studied, because more stable food supply associated with benign
 climate on islands favours territoriality or because population density is
 too low to allow the formation of larger groups. I examined the
 determinants of foraging group size in parrots, a large worldwide avian
 order with many island populations. Using a multivariable phylogenetic
 framework, I found that foraging group size was smaller on islands than on
 the continents controlling for ecological variables known to influence
 group size such as diet and body size. In addition, the island effect
 persisted after controlling for research effort, climate variables, and
 population density, suggesting that impoverished predator communities are
 an important driver of group size on islands.
description: I searched the literature for studies reporting foraging group
 size in parrots. I excluded extinct species or species extinct in the
 wild. As nearly all parrots are diurnal, I excluded nocturnal species
 because timing of activity can influence group size. To obtain the minimum
 and maximum group sizes for each species, I started with two general
 monographs on parrots and updated these values by carrying out searches
 from primary sources on Google Scholar combining each species name and the
 key words flock or group. I did not consider group sizes associated with
 flying or roosting groups when that distinction was made. I also did not
 consider group sizes coming from studies conducted in cities or with
 species outside their native range because of possible anthropogenic
 effects on group size. In addition to foraging group sizes, I determined
 whether the data for a particular study came from an island or the
 continent as some species of parrots are known to live on islands as well
 as the continent. Other traits were taken from the published
 literature. 
description: # Parrots live in smaller groups on islands 
 [https://doi.org/10.5061/dryad.12jm63z75](https://doi.org/10.5061/dryad.12jm63z75) ## Description of the data and file structure The data used in this study are available in xls format. The file contains information for each species used in the study along with the references used to glean the data. The geographic coordinates (longitude and latitude) are centroids for the breeding range of each species and as such do not provide the exact locations of species observations. Data for some variables were not available and this is shown with the label n/a. ### Files and variables #### File: appendix2.xlsx **Description:** Data used for each species ##### Variables * Species names (the name in the first column refers to names used in the current phylogeny. Alternative names are provided in the second column * Island living (yes or no) * Minimum, maximum, and geometric mean foraging group sizes (in log scale) are provided * Altitude range in m and mountain living (nm: lowlands and m: restricted to mountains) * Conservation status according to IUCN * Average body mass in log scale * Habitat type (1 = closed; 2 = semi-open; 3 = open) * Diet (three classes: omnivore, granivore and frugivore * Centroids for latitude and longitude for the breeding range * Range size (square km) * Population size estimate * Population density (number per square km) * Habitat use (% spent on the ground) * Research effort (number of sources with available information on flock sizes) * Weather variables (temperature range in Celsius and annual precipitation in mm) * References (sources with available information on flock sizes for that particular species excluding general texts) ## Code/software The file can be opened with Excel.