Abstract
In a warming climate, migratory animals are under strong pressure to adjust their annual cycles. To ensure survival of their offspring, animals need to start breeding earlier to stay in synchrony with an earlier emergence of food in their breeding grounds. This requires earlier arrival, and as migrations take relatively little time, the most effective way to achieve this is via earlier departure from their wintering areas. However, earlier departures have rarely been shown in migrants, which poses the question what constrains an earlier departure. Dates of departure are often considered inflexible and driven by photoperiodic migration programmes. Such strict genetic programming of schedules would imply relatively slow change through natural selection. If, however, adjustment of departure timing of migrants occurs through individual flexibility, i.e. the capacity to adjust timing throughout an individual’s life, the change will be rapid. However, even under the scenario of flexibility, advances in departure timing may still be constrained by the need for fuelling body stores, and therefore the flexibility in the start and dynamics of fuelling. In the proposed project I aim to uncover the degree of flexibility of individuals to advance the timing of fuel deposition and departure. I propose to study flexibility in a shorebird model system, the Red Knot Calidris canutus. I will experimentally manipulate fuelling rates and photoperiod in captivity to uncover (1) whether earlier spring migration departure is constrained by migration programmes or time needed for fuelling, by recording captive behaviour and tracked departures of released manipulated individuals from wintering sites with state-of-the-art transmitters; and (2) whether individuals can advance the start of fuelling, by following individuals for multiple years in manipulated conditions while measuring advances in the annual cycle. This will deliver essential knowledge to tune conservation efforts to the abilities of migrants to cope with climate warming.
Netherlands