In this moment I am located in the forests of Småland, SE Sweden studying European Nightjars with the overall aim to learn about aspects of its migration and movement outside the breeding period. This will be done by using various kinds of miniaturized data loggers that register the movement of individual birds throughout the annual cycle. Up to current season this has been done by using geolocators that gives us a general picture of the movement in the non-breeding part of the annual cycle, describing areas used during migration and wintering. The geolocators will now be replaced with GPS-loggers that can be used to reveal spatial characteristics of the migration in more detail. Other birds will carry custom-made accelerometer loggers build in our technical lab. These loggers will hopefully reveal interesting details about the birds’ time allocation during migration.
Along with a local ringer I mainly trap territory holding males with mist net and a play-back. The data loggers lack a transmitter to minimize the weight, which means that we need to catch the bird again to retrieve the data. To improve our efficiency to re-trap the birds and to be able to include more females in the study we are currently evaluating the possibilities to catch nightjars in the vicinity of their nests. Except the fact that finding a nightjar’s nest in the forest is like finding a needle in a haystack, this alternative method has shown some promising results.
The European Nightjar is a medium-size crepuscular and nocturnal insectivorous bird that, when undisturbed, spends most of the day resting on a tree branch or on the ground. Being well camouflaged it is usually rarely seen and most birdwatchers associate it with the males´ “churring” sound which can be heard throughout the summer nights.
A trapped male (recognized by the large white spots on some of the longest flight feathers) is examined while he is demonstrating his huge gape.
This photo from a previous year illustrates the mounting of a data logger, here a geolocator. Most of the data logger will, when mounted, be covered by the nightjar’s feathers and only the stalk with the light sensor is visible. This will enable the geolocator to measure and log the daylight which later is used to estimate the bird’s location throughout the annual cycle.
A bird equipped with a GPS-logger. The tiny data-logger is mounted as a backpack on the bird and is here completely covered by the bird’s feathers (only the antenna is visible). Photo: Patrik Rhönnstad.