The 2016 breeding season is wrapping up, and the Caspian terns are on the move.  Some are busy prospecting for next year’s breeding sites in the north, while others are ready to enjoy the winter weather in southern California or Mexico.  This brief slideshow runs through maps which summarize the movements of each of the tagged terns during the 2015 and 2016 breeding seasons (01 April – 31 July).

We saw each of these birds return to the breeding grounds later in 2016 than in 2015, but we are not sure why that was the case.  It could be because raising young is energetically costly and, with the exception of A795, all of these terns were observed with nests during the 2015 breeding season.  A795 may not have attempted to nest, but she did travel extensively throughout the 2015 breeding season; another energetically costly activity.  As such, all of these birds may have needed a little more time this year to get in shape for the trip back north to the breeding grounds.

Also, notice that these birds used similar migration paths during each of their migration trips.  That isn’t always the case with Caspian terns in the Pacific Flyway.  Although migrating along the same route may have some obvious advantages, we have seen other tagged terns use different migration routes within and between years. These featured terns may be creatures of habit, but the ability of other Caspian terns to migrate along alternate routes demonstrates that they are capable of some behavioral plasticity when it comes to long distance travel.

This map was created using satellite location data from all of our tagged terns to show the areas used between 01 January and 31 March, 2016. The red areas indicate the places where the probability of finding an individual tagged tern is 50% and the orange encompasses the area where that probability is 90% (note: higher percentage areas also include the lower percentage areas contained within). Take a look at the previously posted animation to see how our featured terns fit into the overall distribution of the wintering grounds.


Content Contributors

Don Lyons – Assistant Professor (Senior Research) at Oregon State University.
Tim Lawes – Faculty Research Assistant at Oregon State University.