Variation in survivorship throughout the annual cycle in first-year Canada jays

Background/Question/Methods

Natal dispersal is a complex ecological process and knowledge of natal dispersal patterns, mortality rates of juveniles, and the factors that influence survival are critical for understanding population dynamics and individual success. However, juveniles can be challenging to follow after they stop receiving parental care and especially when they leave their natal territory. We used radio-tracking to examine patterns of natal dispersal and quantify juvenile survival throughout the annual cycle in first-year Canada jays (Perisoreus canadensis) in Algonquin Provincial Park, Ontario. The Canada jay (Perisoreus canadensis) is a food-caching resident songbird that occupies the sub-alpine and boreal ecosystems of North America. Soon after juveniles become nutritionally independent, intra-brood dominance struggles lead to one juvenile (dominant juvenile) delaying dispersal after expelling its subordinate siblings (ejectees). During 2017-2021, we fitted nestling Canada jays with radio transmitters and monitored them throughout their first year of life. We used cumulative annual survival models and Cox proportional hazard models to estimate rates of annual survival and causes of mortality risk throughout multiple life stages. We examined the factors influencing dispersal distances and the probability of delayed dispersal using generalized linear-mixed modeling approach. To rank all models, we used an information-theoretic framework using AIC.

Results/Conclusions

We analyzed radio-tracking data from 95 nestlings over six years. Mean annual survival for first-year Canada jays was 0.28, with the change in survival estimates being greatest after fledging and before sibling expulsion. We also present evidence that dominant juveniles had higher rates of annual survival. Males and individuals that were in above-average body condition were more likely to become dominant juveniles. Males and individuals that were dominant juveniles dispersed significantly shorter distances, often moving to neighboring territories, compared to ejectees that travelled over several territories before settling. We provide evidence that being the dominant juvenile can lead to direct survival benefits, which could be associated with protection from predators, access to resources, or dispersing shorter distances. Our study also indicates that the stage after fledging before juveniles dispersal is what most limits first-year survival, potentially due to limited food and an influx of predators during that time.