We are excited to report on the 2025 field season for Common Terns at Presqu’ile Provincial Park, detailing the management and monitoring undertaken collaboratively by park staff and ourselves. We thank the Friends for their continued support of this important work. The unprecedented success of Common Terns at Presqu’ile is in large part due to this continued effort and adapting management approaches to meet prevailing challenges.

The 2025 Common Tern breeding season broke many records, including seeing the largest colony at Presqu’ile since the 1970s and producing the most fledglings to leave the islands in over 50 years! Additionally, it was the first year in which Highly Pathogenic Avian Influenza was recorded for Common Terns in the Great Lakes, with those records being at Presqu’ile. Through our work, we managed to turn a potential tragedy into the most successful breeding season on record.

Once again, we utilized the predator exclusion grids we developed at Presqu’ile to protect breeding Common Terns from competition with other colonial birds and a range of nest predators. Prior to the breeding season, we secured breeding space using parallel polywires which were subsequently removed when the terns arrived and then replaced just prior to chicks hatching. We added two extra features to these grids in 2025: LED lighting to deter nocturnal predators and integrated chick shelters to provide extra protection for tern chicks.

This year, the Common Tern colony grew to 313 nests, the largest since we began work at Presqu’ile in 2008 and larger than any other record since the 1970s. Through our continued demographic research, we discovered that much of the growth in 2025 was caused by recruitment of adult terns that had been raised as chicks within the exclusion grids in previous years. Thus, continued successful management will maintain this growth into the future. This will ensure the persistence of Common Terns at Presqu’ile and contribute vitally to bolstering  declining regional populations (the most recent census in Canada indicated a drastic 43% decline over the last decade).

At the end of May, cases of Highly Pathogenic Avian Influenza (HPAI) were confirmed among both Caspian Terns and Common Terns at Presqu’ile Provincial Park. Since previous outbreaks of this virus in European colonies of Common Terns have led to over 60% mortality, we immediately implemented protocols to protect the Presqu’ile colony from HPAI to the greatest extent possible while simultaneously protecting nests and chicks from possible predators. One of the most important of these protocols was the daily removal of any dead terns from the colony. This prevented the spread of HPAI at the colony to adults and chicks and thus most infections likely occurred during interspecies interactions at roost sites. Overall, only 37 adult Common Terns (6% of breeders) were found dead at the park in postures consistent with avian influenza. Although this is more than usual breeding mortality, it is much less than that recorded at other colonies or for other species.

We are confident that our management approaches averted potential disaster for Common Terns at Presqu’ile in 2025. As a result, more than 500 Common Tern chicks fledged from Presqu’ile, comprising almost 30% of all chicks fledged at the park since 2008 and making 2025 the most prolific breeding year since the early 1970s.

In 2025, Friends’ funds contributed towards travel costs, expenses and equipment associated with the work described above. We are grateful for the continued support from the Friends of Presqu’ile. This has been an important factor in allowing this work to continue and to achieve the successes described, putting Presqu’ile’s Common Tern colony on the road to restoration. The Friends play a pivotal role in conservation activities at the park and we are privileged to be able to report on the success of the Common Tern research program.

Sincerely,

Jennifer M. Arnold, Ph.D.             .

Professor of Biology, Penn State University

Stephen A. Oswald, Ph.D

Faculty in Biology, Penn State University