Friday, November 7, 2014

Common Tern photos

Common Tern
Common Tern. Off San Diego, California. September 21, 2014. Greg Gillson.
Here are some photos of Common Terns from September. The first 3 are of one of the birds we had offshore on a pelagic trip. This particular bird uncharacteristically flew around and followed the boat for several minutes, allowing close views and photos, albeit primarily from below and strongly backlit by the sun.

Common Tern
Common Tern. Off San Diego, California. September 21, 2014. Greg Gillson.
Common Terns and Arctic Terns are very similar and have a similar migration timing on the West Coast. Common Terns are "front heavy," with a longer bill and longer appearing neck. Arctic Terns, on the other hand, have a shorter bill and short-appearing neck, thus appearing more long-tailed. It is perhaps analogous to Cooper's and Sharp-shinned Hawk head projection shape (Cooper's Hawk = Common Tern, Sharp-shinned Hawk = Arctic Tern).

Generally speaking, Common Terns are found within 15 miles of shore and Arctic Terns more than 30. However, Common Terns are more expected in the Southern California Bight--an area of warm shallower water from Santa Barbara southeast past San Diego, and inside the outer islands. At Santa Barbara the coastline faces south. This particular water mass is isolated from the colder California Current that runs from the middle of Baja to Washington State.

Common Tern
Common Tern. Off San Diego, California. September 21, 2014. Greg Gillson.
The second bird is below. It was one of two flying around the Oceanside pier the end of September. The prominent dark carpal bar on the rather silvery upper wing indicates this bird is a juvenile. Juvenile Arctic Terns have a barely noticeable dark carpal bar.

Common Tern
Common Tern. Oceanside, California. September 28, 2014. Greg Gillson.