Modelling migration in birds: competition’s role in maintaining individual variation

Authors: D. W. Kikuchi and K. Reinhold

Year: 2021

Publication: Proceedings of the Royal Society B

Publication Link:

Keywords: individual variation, seasonality, personality, risk-taking, competition

Abstract: Animals exhibit extensive intraspecific variation in behaviour. Causes of
such variation are less well understood. Here, we ask when competition
leads to the maintenance of multiple behavioural strategies.We model variability
using the timing of bird migration as an example. Birds often vary in
when they return from non-breeding grounds to establish breeding territories.
We assume that early-arriving birds (counting permanent residents
as ‘earliest’) select the best territories. But arriving before the optimal
(frequency-independent) breeding date incurs a fitness penalty. Using simulations,
we find stable sets of return dates. When year-round residency is
viable, the greatest between-individual variation occurs when a small proportion
of permanent residents is favoured, and the rest of the population
varies in their return times. However, when fitness losses due to yearround
residency exceed the benefits of breeding in the worst territory, all
individuals migrate, although their return dates often vary continuously.
In that case, individual variation is inversely related to fitness risks and positively
related to territory inequality. This result is applicable across many
systems: when there is more to gain through competition, or when its
risks are small, a diversity of individual strategies prevails. Additionally,
stability can depend upon the distribution of resources.

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