Migration strategies and annual space‐use in an Afro‐Palaearctic aerial insectivore – the European nightjar Caprimulgus europaeus

Obligate insectivorous birds breeding in high latitudes travel thousands of kilometres during annual movements to track the local seasonal peaks of food abundance in a continuously fluctuating resource landscape. Avian migrants use an array of strategies when conducting these movements depending on e.g. morphology, life history traits and environmental factors encountered en route. Here we used geolocators to derive data on the annual space‐use, temporal pattern and migratory strategies in an Afro‐Palaearctic aerial insectivorous bird species – the European nightjar Caprimulgus europaeus. More specifically, we aimed to test a set of hypothesises pertaining to the migration of a population of nightjars breeding in south‐eastern Sweden. We found that the birds wintered across the central and western parts of the southern tropical Africa almost entirely outside the currently described wintering range of the species. The nightjars performed a narrow loop migration across Sahara, with spring Sahel stopovers significantly to the west of autumn stops indicative to an adaptive response to winds during migration. To our surprise, the migration speed was faster in the autumn (119 km d^{? 1}) than in the spring (99 km d^{? 1}), possibly due to the prevailing wind regimes over the Sahara. The estimated flight fraction in both autumn (14%) and spring (12%) was almost exactly as the theoretically predicted 1:7 time relationship between flights and stopovers for small birds. The temporal patterns within the annual cycle indicate that individuals follow alternative spatiotemporal schedules that converge towards the breeding season. The positive relationship between the spatially and temporally distant winter departure and breeding arrival suggests that individuals´ temporal fine‐tuning to breeding may be constrained, leading to potential negative fitness consequences.