DOI: 10.5061/dryad.stqjq2c0f
title: Investigating social and environmental predictors of natal dispersal in a cooperative breeding bird

description: Natal dispersal is a crucial life history trait that affects both
 individual fitness and population structure, yet drivers of variation in
 dispersal probability and distance are difficult to study in wild
 populations. In cooperatively breeding species, individuals typically
 delay dispersal beyond their first breeding season and remain on the natal
 territory as nonbreeders, which prolongs social dynamics that can affect
 dispersal decisions. Using a 35-year data set covering almost 600
 dispersal events in the cooperatively breeding Florida scrub-jay
 (Aphelocoma coerulescens), we examined the environmental and social
 parameters that predict dispersal probability over time and distance. In
 both sexes, dispersal probability increased with age, which in turn was
 negatively correlated with dispersal distance. In males, individuals
 occupying low quality natal territories and living with a stepfather had
 an increased probability of dispersal. Older and more dominant males were
 more likely to inherit their natal territory. In females, which generally
 disperse earlier and farther than males, socially subordinate jays
 dispersed farther than dominant ones. Overall, jays that delayed dispersal
 the longest were more likely to attain breeding status near their natal
 territory, which was previously found to be associated with increased
 survival and lifetime fitness. Our results suggest that social dynamics
 and environmental factors on the natal territory affect delayed dispersal
 patterns differently for the two sexes in this cooperative breeder.
description: We study a color-banded
 population of Florida scrub-jays at Archbold Biological Station in central
 Florida (27.10°N, 81.21°W), where intensive monitoring across a large
 spatial scale has been ongoing for five decades. Throughout each breeding
 season, all nests were located and monitored until fledging or failure
 (Woolfenden and Fitzpatrick 1984). Data for this study include successful
 natal dispersal events for birds hatched between 1980 and 2014. We
 included only successful dispersers that acquired a breeding position for
 at least one breeding season and laid or sired at least one egg (Townsend
 et al. 2011). Towards the end of the breeding season, we conducted surveys
 of suitable habitat up to 40 km from our study site. Dispersal beyond 25
 km is exceedingly rare in this species (Coulon et al. 2010) so our
 off-site surveys enabled us to document a number of long-distance
 dispersal events beyond our study plot. Early in each breeding
 season, all territories were mapped by assigning boundaries wherever
 territorial disputes occurred between neighboring groups (Woolfenden and
 Fitzpatrick 1984). Maps were digitized using ArcGIS (ESRI, Redlands, CA,
 USA) and we assigned an annual estimate of habitat quality to each
 territory based on area of oak scrub habitat within each territory
 (Abrahamson et al. 1984; Supplementary material 1).
 To capture social
 dynamics in the natal territory, we assigned within-group dominance
 hierarchies for each sex first by age, with older birds being dominant to
 younger birds (Woolfenden and Fitzpatrick 1977), and within-brood
 dominance using relative body mass at 11 days post-hatching. We assumed
 that relative body mass as nestlings drives within-brood dominance because
 this relationship has been observed in other avian species (Safriel 1981,
 Nathan et al. 2001). In Florida scrub-jays, relative mass among
 brood-mates is mostly determined by hatching order and tends to remain
 consistent over time (Mumme et al. 2015). We designated social position
 using a categorical ranking system in which nonbreeders within the group
 were ranked as dominant if oldest or, in the absence of older nonbreeders,
 heaviest within the same brood. Nonbreeders other than the dominant
 individual were ranked as subordinate and nonbreeders without same sex
 nonbreeders were designated as singletons. We defined stepparents as
 breeders that replaced a biological parent and recorded their date of
 arrival or acquisition of breeder position.
description: Data is formatted for a discrete time logistic regression.