In seasonally breeding animals, costs and benefits of territorial
aggression should vary over time; however, little work thus far has
directly examined the scope and adaptive value of individual-level
plasticity in aggression across breeding stages. We explore these issues
using the tree swallow (Tachycineta bicolor), a bird species in which
females compete for limited nesting sites before producing a single brood.
We measured the aggressiveness of nearly 100 females within three
different stages: (1) shortly after territory-establishment, (2) during
early incubation, and (3) while caring for young chicks. We used k-means
clustering to categorize females into four distinct plasticity ‘types’
based on the timing, direction, and magnitude of their changes in
aggression between stages. We then tested whether plasticity type and
stage-specific aggression vary with key performance metrics. Two of the
four plasticity types became less aggressive across consecutive breeding
stages, consistent with population-level patterns, though these plasticity
types largely did not differ from one another in survival or reproductive
success. A third type was characterized by high levels of among-stage
plasticity; these females, had significantly lower body mass while
parenting, tended to hatch fewer eggs, and had the lowest observed
overwinter survival rates. A final type exhibited limited plasticity, with
moderate to low levels of aggression in all stages; this low plasticity -
low aggression phenotype was not associated with any negative effects to
performance. These results reveal substantial among-individual variation
in behavioral plasticity, which may reflect diverse solutions to
trade-offs between current reproduction and future survival.