Notes on the behaviour of Caspian Terns on Lake Opinicon

Posted by: Mark Andrew Conboy

There are several species of water birds that do not breed at QUBS but visit us during and after the breeding season. These species include Double-crested Cormorant (Phalacrocorax auritus), Black-crowned Night-Heron (Nycticorax nycticorax), Ring-billed Gull

An adult Caspian Tern with a juvenile on the right and a Ring-billed Gull on the left. Caspian Terns typically usurp the highest perches on loafing sites such as Bird Rock on Lake Opinicon. Photo: Philina English. Click on picture to see a larger version.

(Larus delawarensis), Herring Gull (L. smithsonianus), Common Tern (Sterna hirundo) and Caspian Tern (S. caspia). All breed colonially, mainly on island in Lake Ontario and the St. Lawrence River and in many cases colonies are over 50 km from QUBS. Although a fair amount of information is available on the breeding activates of these species in the Kingston region we have virtually no information on their behaviour or ecology when they visit Lake Opinicon and other inland waters. Here I present some brief notes on Caspian Terns from August 2010. More observations of this and other species will help us understand the natural history of visiting water birds at QUBS.

Time of year: Caspian terns visit QUBS from mid August to mid September.

Abundance and occurrence: Up to 12 have been seen foraging over Lake Opinicon or lofting on small rocky islands, particularly Bird Rock off Joe’s Point. In addition to Lake Opinicon, small numbers of Caspian Terns have been recorded at other lakes in the region during the same time period: Newboro, Indian, Big Rideau and Loughborough.

Age classes: In general, adult birds seem to outnumber juveniles (young of the year) about three to one.

Care of young: Juveniles closely accompany foraging adults or wait on loafing rocks to be fed; in both cases they frequently beg.

Foraging: I recorded 9 foraging attempts by one adult around Bird Rock in the course of 30 min. Eight of those foraging attempts (near vertical plunge dives) were successful. On four of those successful hunts, the adult fed a begging juvenile. All prey items were fish but the species could not be identified.

Interspecific interactions: Caspian Terns commonly loaf on Bird Rock with Herring Gulls and Ring-billed Gulls. They frequently displace both gulls from the highest points on the rock.

Roosting: No sign of overnight roosting of terns or gulls was found with repeated evening checks of Bird Rock off Joe’s Point. Terns and gulls may roost on nearby fields.

The reasons why some water birds come inland from Lake Ontario and the St. Lawrence River to forage in smaller lakes while others remain on the larger water bodies is unclear. At least some Caspian Terns find it worth while to bring their young to Lake Opinicon. Is there an advantage for doing so? Do the same birds bring their young every year? How do birds that frequent inland water ways differ from birds that remain on big water? Further research into the behaviour and ecology of these visiting water bird species could be very interesting.