Adult Common Tern arriving at nest site and other member of the breeding pair beginning its greeting display.
Single adult Common Tern bringing fish. This bird was unmated and kept bringing in fish which it tried to give to an adult bird and then to chicks. The adults rejected the offer and then drove this bird off when it attempted to feed chicks belonging to other pairs.
This bird would fly around carrying a small perch and as the fish dried out somewhat, it would fly to the edge of the rock and dip it into the water. Eventually the bird would eat the fish itself and fly off to get another one.
Common Tern chicks several days old. All chicks disappeared from the colony within a few days of hatching and the adults deserted shortly after.
We have not been able to determine just what happened but Ring-billed Gulls and Herring Gulls were taking over the colony area. They could have been the culprits but there are other possibilities as well.
It is possible that a Great-horned Owl or Black-crowned Night Heron visited the colony at night as they are both known to be in the area and both have been known to decimate Common Tern colonies.
The colony is located on a popular fishing lake and many boats make large waves without even being near the colony. It is possible that some chicks could have been washed away from the rock when attempting to get a drink.
After working out a Common Tern Recovery Program with the Ministry of Natural Resources and the Muskoka Field Naturalists gravel was placed in low areas of the colony the next spring. After nesting started these A-frame shelters were placed in the area of each nest in the colony.
Newly hatched chicks begans using the A-frames for shelters at about 2 days of age. Thirty-five chicks survived and approximately twenty-five fledged and left the colony to migrate.
Although the first year of the Recovery Program seemed extremely successful there have been setbacks. The second year the gulls had encroached even more on the colony but some pairs nested on another island. About the same number of chicks fledged successfully as the year before.
The next year no Common Terns were able to nest in the original colony and all attempted to nest on the second low-lying rock island.
All nests were washed away during one storm early in the breeding season and no chicks hatched.
We have more ideas up our sleeves and hope to implement new precautions in the coming breeding season.
Below is the link to the follow-up article on Naturescapes.net