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Common terns on Oneida Lake

Paul Curtis, Martin Feehan, Emily Case (Funded by NYS DEC)

The long-term studies on the colonial waterbirds on Oneida Lake, initiated in the 1970s, continued during 2019. Investigators Paul Curtis and Martin Feehan worked with intern Emily Case from Penn State University to monitor the nesting activity of Common Terns. Breeding success for Common Terns at Oneida Lake was very poor during the 2019 field season, with only one tern chick likely fledged from Little Island. The peak nest count on Little Island was 417 nests on July 8, and on Willard Island was 35 nests on July 10. A single Common Tern nest was discovered on Grassy Island on June 18 but was later found abandoned. One hundred nineteen chicks were banded and 15 of these were later recovered dead. However, actual survival of tern chicks was much lower due to frequent occurrences of nighttime predation on Little Island from Night Herons and Great Blue Herons, which detrimentally affected the survival rates of Common Tern chicks in 2019. This nesting season definitely was challenging for the terns. Early season flooding at the beginning of June caused a large portion of the first nests to be washed away. On 17 June, approximately 80 non-viable tern eggs were found washed to the center of Little Island. These eggs were eventually removed to prevent them from decaying, and allowed more space for possible re-nesting attempts. In mid-July, approximately 20 to 30 eggs were also found that contained tough shell membranes that made it difficult for pipping chicks to hatch. The cost of having multiple laying attempts may have had physiological effects on the parents, and could have resulted in shell abnormalities, as egg shell quality decreases with the more eggs that are laid. While the Common Terns were able to comeback from the early season storms to reach above-average nest counts, predation appeared to have a high impact on the survival of many of the chicks, as only one tern chick was ever verified as having fledged. 

On both Little and Wantry Islands, we installed a gull-exclusion wire grids on 6 May 2019.  During 30 May through 1 July, we removed a total of 11 Ring-billed Gulls and Herring Gull nests from under the grid wires on Little and Wantry Islands, preserving the nesting space only for Common Terns. No tern nesting attempts were initiated on Wantry Island even though we used tern decoys for social attraction. On Little Island, a total of 16 banded adult terns was recaptured at their nests, ranging in age from 2-15 years (mode = 6 years). One foreign-banded tern was caught. Studies of nocturnal behavior of incubating Common Tern pairs occurred again on both Little Island (Oneida Lake), and Gull Island (Presqu’ile Provincial Park, ON), to examine sleep behaviors given different island sizes and predation rates. Infrared-triggered trail cameras were attached to metal stakes pounded into the rocky island substrate. These were used to monitor sleep behavior of temporarily marked tern pairs during the incubation period.  Pictures were taken at one-minute intervals for 48 hours to monitor mate presence and changeover frequency. These data were then used to investigate within-pair dynamics of sleep ecology. In total, 17 nests from Little Island were included in this study. Preliminary analyses are underway and results will be presented at a scientific meeting in 2020.