Jan-Åke Nilsson, Editor-in-chief

Partial migrants are characterised by part of the population migrating to more benign regions during winter whereas part of the population stays at the breeding grounds. My research interests deals with causes and consequences of these two strategies to spend the winter. Choice of strategy may have a genetic background in which case the two genotypes are retained in the population due to varying selection pressures. However, in many partial migrants, e.g. in my favourite study species the blue tit, choice of strategy seems to be state- or condition dependent. That means that each individual may switch between migrating and staying depending on for example sex, age or nutritional condition. However, the decisive factor(s) underlying the choice of strategy is poorly known in most partial migrants. Even less is known about the fitness consequences of the two strategies. In cases where the outcome of the two strategies are more or less equal, frequency-dependent selection may be predicted; in cases where one of the strategies is superior, the less successful strategy may be the result of the-best-of-a-bad-job strategy.
A consequence of switching between the two strategies, as do for example individuals of the blue tit, is that each individual will need adaptations for both migration and for spending the winter in harsh environments. In my view, interesting questions include:

If and how known adaptations for being sedentary at high latitudes (metabolic and body temperature regulation) and for migrating (fat deposition rates and navigational system) may be compromised in partial migrants? Here interesting comparisons can be made between closely related species which are either migratory or sedentary.
How the insulating capacity of the plumage and wing form might differ between individuals opting for one or the other winter strategy?