With the start of April an increasing number of African penguins incubating eggs and brooding chicks can be seen throughout the colony. However, in recent years the African penguin has undergone a rapid population decline, which shows no sign of reversing.
Research suggests that a reduction in food availability is the largest factor influencing this decline. Therefore being able to determine the areas through which birds move and where they spend extended periods of time at sea to find their prey, is essential to shed some light on the mechanisms that are driving the penguin population trend. Although we still know surprisingly little about what the penguins do and where they are going when foraging for food at sea. The reason for this however, is relatively easy to understand: once they are at sea, they are out of sight and therefore much of what has been known of these birds was based on observations made on land, while their life at sea had stayed a well-kept secret.
Advances in logger technology have made it possible to achieve a glimpse of this other side of a penguin’s life. Advances in microchip technology have led to various devices being fitted to penguins (and other seabirds) to monitor their at-sea behaviour. Generally these miniature loggers fall into two categories: transmitters that emit a signal to a satellite and data loggers that store information on an embedded microchip. The latter often contains a GPS unit that records the penguin’s position. If these are used in combination with a Temperature Depth Recorder or TDR (a unit containing a pressure & temperature sensor), detailed information can be gained on how deep they dive, how often and long they dive, in what ambient temperatures they find their prey. Ultimately these devices provide a three-dimensional view on the bird’s movement at sea.
It may seem like an easy task to track penguins, as data collection is conveniently carried out by small electronic devices that are deployed on the bird’s back. Fieldwork however, and the all too common experience of sitting for hours (sometimes days) at the nest site waiting for the bird to return after its foraging trip, suggest otherwise.
Once the logger has been deployed, it must then be retrieved in order to collect the data. Hence, the penguin has to be captured not only once, but twice. For that reason breeding birds are a perfect target: you know where to find them (at the nest) and you know where they will return after foraging (to their nest)….in theory. However, if the bird fails to return or the logger falls off before the bird returns, all data are lost along with the logger.
Deploying a GPS logger.
This year Dr Antje Steinfurth is training MSc student Jennifer Grigg and Birdlife intern Mmatjie Mashaoto carry out logger deployments throughout the breeding season. To see how the loggers are deployed on each penguin, see the methods section of the site.
Programming one of the GPS loggers prior to deployment.
The first day of deployments got off to a sticky start, with the bakkie used for travelling between deployment nests getting stuck in the sand and Antje being attacked by a vicious branch, but ended with the first logger of the season being successfully deployed! During the ten days in April that Antje was training on the island 11 GPS loggers were deployed and retrieved successfully.
Some examples of African penguin foraging tracks, shown plotted in Google Earth.
To be continued……