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Investigating social and environmental predictors of natal dispersal in a cooperative breeding bird

Citation

Suh, Young Ha et al. (2020), Investigating social and environmental predictors of natal dispersal in a cooperative breeding bird, Dryad, Dataset, https://doi.org/10.5061/dryad.stqjq2c0f

Abstract

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.

Methods

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.

Usage Notes

Data is formatted for a discrete time logistic regression.

Funding

National Science Foundation, Award: BSR-8705443, BSR-8996276, BSR-9021902, and DEB97-07622

U.S. Fish and Wildlife Service