Caspian Tern

Caspian Tern - Showing Underwing Black Patch  [Internet Photo]

The Caspian Tern (Hydropogne caspia) is a rare spring migrant and a casual late summer and fall visitor to New Brunswick.  It is our largest tern, the largest tern in the world, in fact.  It is 33-36 cm long (13-14 inches) and weighs 782 g (28 oz).  One time in 1996 a neighbour called me about an unusual bird under her feeder.  When I arrived I was astounded to see a Caspian Tern lying on the ground.  I picked it up because it obviously had something wrong with it.  Examination revealed it normal physically.  My diagnosis was extreme exhaustion and hypothermia.  It was an exhausted spring migrant which had to put down in an unusual place.  What amazed me was the weight and size of this bird.  The Caspian Tern is a big bird!  It is about the size of a Ring-billed Gull but much more robust.

The Caspian Tern ranges sporadically worldwide.  In North America there are colonies in central Canada, around the Great Lakes, in Newfoundland and Labrador, and in the northwestern US states.  The North American population winters from northern California and North Carolina southward.  I have seen many in South Carolina and Florida.  They are found in Europe around the Baltic and Black Seas and also in Asia, Africa, Australia and New Zealand.  They are expanding their range northward presumably due to global warming.  In 2016 a nest was found in Cape Krusenstern National Monument in northwestern Alaska, 1600 km/1000 miles further north than previous records.  The global population is stable but the Baltic Sea population is declining and of concern.  

Caspian Tern Adult  [Marbeth Wilson Photo]

The Caspian Tern has a powerful flight with shallow wing beats.  This is very noticeable in comparing the Caspian Tern to the Royal Tern.  The Caspian Tern is distinctive and easy to distinguish from other terns.  The large size, heavy body, stout red bill and black cap are distinguishing characteristics.  The blood red bill (I have seen some that are more orangish but not as light as the Royal Tern bill) has a small black ring around the tip.  The black cap is sometimes crested. Winter adults and juveniles have white streaks in their black caps.  The tail is forked but less forked than other terns.  The upper wings and back are pale gray.  The underwings distinguish this species from the Royal Tern.  In the Caspian Tern the underwing is whitish with a large black patch at the wing tips.  The underwing of the Royal Tern is mostly whitish.  Caspian Terns do not have white foreheads like Royal Terns sometimes do. 

Caspian Terns nest in scrapes soon after arriving on the nesting grounds (late May or early June).  The scrapes are lined with egg shells and grass.  One to five brownish pink eggs are incubated for 20 to 28 days.  The young fledge after 37 days.  That is a long time to feed the young.  Some juveniles stay with the adults for many months thereafter.  This species eats mainly fish but also crayfish, and insects.  They will steal food from other birds.  They feed by plunge-diving or by catching fish at the surface as they fly low over the water. 

The Caspian Terns we see in New Brunswick in spring are rare spring migrants.  There was one at Mactaquac Dam on 30 April 2000.  The one I picked up at Douglas in 1996 was in May.  Most of our sightings are in August and September along the southern part of our east coast or along the Bay of Fundy.    There have been 1 to 3 Caspian Terns at Petit Cap for the last week.  I saw one there on August 27.  Occasionally one will migrate along the St. John River.  One was seen last week on 29 August 2020 at Fredericton.

Caspian Tern Adult on Favourite Habitat

So what happened to the individual I found under the bird feeder?  I picked it up and spent some time warming it.  After it got warmed and more active I took it to the river and released it.  It flew high in the sky and headed north.  Caspian Terns are known to be aggressive especially around their colonies.  They will pursue and attack predators including humans.  I did not know this when I rescued the bird in question. (It wouldn't have mattered).  Fortunately it was too stressed to worry about me.  I hope it went on to Labrador to breed successfully.