Partial migration & residency
To evaluate this question, we have to study the conditions and adaptations necessary to pursue a resident versus a migratory strategy. For birds, adverse environmental conditions during winter at high latitudes, e.g. low food availability, short days and high costs for thermoregulation have to be handled to maximise the probability to survive this season, whereas in fish seasonal differences in food availability versus predation risk among habitats may be important drivers of migration patterns.
In order to study what factors promote partial migration we use two model systems, partially migrating birds and fish. In birds, we are especially interested in behavioural and physiological adaptations to survive the long winter nights, including choice of roosting place, reduction of surface area by postural adjustments or roosting in groups and increased basal metabolic rate to promote the capacity for heat production. However, reduced body temperature is also connected with costs such as increased vulnerability to nocturnal predators, compromised immune defence and reduced maintenance effects of sleep. In fish, we study differences in personality (behavioural syndromes), morphology and within-lake habitat use in migrating versus resident individuals. Further, we evaluate the consequences of partial migration on lake ecosystem dynamics using a combination of monitoring data and modelling.