Florida scrub-jays move elsewhere when competition gets tough

This blog post is provided by Young Ha Suh and tells the #StoryBehindThePaper for the paper “Staging to join non-kin groups in a classical cooperative breeder, the Florida scrub-jay”, which was recently published in the Journal of Animal Ecology.
Young Ha Suh is a PhD Candidate in the Department of Ecology and Evolutionary Biology at Cornell University and is also a collaborator of the Archbold Biological Station where she participated in the long-term demography study on Florida scrub-jays for the past few years. Reed Bowman is Senior Research Biologist and director of the Avian Ecology Lab at Archbold Biological Station. Reed oversees all aspects of the Florida scrub-jay field research project. John W. Fitzpatrick is a professor in the Department of Ecology and Evolutionary Biology at Cornell University, and recently stepped down as director of the Cornell Lab of Ornithology. Fitz has been studying Florida scrub-jays for 50 years.

Group-living in animals has traditionally been explained by invoking kin selection – i.e., individuals helping other genetically related individuals to produce more offspring. Especially in environments having limited breeding space and strong competition for breeding vacancies, many social species exhibit delayed dispersal in which the offspring forgo independent reproduction and stay at home, helping rear younger siblings and thereby gaining some “indirect” genetic benefits. Increasing use and accessibility of genetic tools, however, show not all social groups are comprised of relatives – even in species like the Florida scrub-jay where kin-based group-living is the norm. This presents a mystery: why do some individuals shun the benefits of living at home in favor of joining other, non-kin groups?

Florida scrub-jays are habitat specialists dependent on oak-scrub patches for food (mainly arthropods and acorns) and cover. Breeding pairs defend territories year-round, often aided by their retained offspring. (Photo: Young Ha Suh)

Florida scrub-jays represent a so-called “classical” cooperative breeding system in which social groups consist of a breeding pair and their offspring that delay dispersal to stay at home as “helpers” for at least a year. Their distinct social system ignited a demography study more than 50 years ago that continues to this day at Archbold Biological Station in central Florida. To study the species’ life history, researchers – including coauthors Reed Bowman and John Fitzpatrick – have been monitoring the population through nest searches, territory mapping, and monthly censuses that provide insight on reproductive success, territory residency, and dispersal.

Recently, Young Ha Suh noticed that every year a few birds leave their home groups and become helpers elsewhere. Previously, such birds were called “adopted helpers” believed to occur when the home group disintegrates (often due to a death of one or both parents). But many of the cases we observed did not fit this category, as their home groups were intact. We decided to study our decades long data archives to find more instances of this intriguing strategy.

A Florida scrub-jay family in which the one-year-old son (right) was “staging” at a neighboring territory with another brother. Meanwhile, the third brother stayed at home with a three-year-old sister (middle). (Photo: Young Ha Suh)

In our recent paper in the Journal of Animal Ecology, we sought to determine why some young Florida scrub-jays join unrelated groups (termed “staging”) instead of helping kin at home. Utilizing data from 35 years of monthly censuses and nest monitoring, we were able to quantify the number of staging individuals and compare their survival and reproductive success to those that stayed at home. Our analyses showed that these unrelated group members joined groups with fewer competitors (thereby increasing access to breeding opportunities) than in their home group. Staging had sex-related outcomes, with females producing similar number of young regardless of their strategy, while males that joined unrelated groups produced fewer young than males that stayed at home. Sex-based differences in reproductive success between the dispersal strategies was likely driven by sex-based differences in territory acquisition, as males are able to inherit or bud off the natal territory whereas females must leave home in order to breed.

Male Florida scrub-jays form long-lasting bonds with their fathers; here, a grown son (left) is on sentinel duty with his father (right). Fathers sometimes help sons gain territories through “territorial budding” in which the son takes a small part of the home territory. (Photo: Young Ha Suh)

Our results show that animals can benefit by joining unrelated groups if this results in shorter “queues” to breeding positions compared to waiting at home. This research highlights how birds can respond plastically to social and environmental conditions. and offers a new perspective in our understanding of the evolution of non-kin-based social groups.

At Archbold Biological Station, we train Florida scrub-jays with peanut bits so they become habituated to the trap. Once captured, each bird gets a unique combination of color bands on their legs for individual identification. (Photo: Young Ha Suh)
Read the paper

Read the full paper here: Suh, Y.H., Bowman, R. and Fitzpatrick, J.W. (2022), Staging to join non-kin groups in a classical cooperative breeder, the Florida scrub-jay. J Anim Ecol. Accepted Author Manuscript. https://doi.org/10.1111/1365-2656.13669

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