Investigating the influence of colony dynamics and diet change on recovery of the endangered roseate tern (Sterna dougallii) on Country Island, Nova Scotia

Master of Science (Biology) candidate: Ruby Schweighardt

8 December 2025

10:00 AM Atlantic

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Meeting ID: 260 681 789 738 06
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Thesis Committee:

Dr. Mark Mallory, Supervisor
Dr. Sarah Wong, Enviro Can. & Climate Change Can., External Examiner
Dr. Shawn Craik, Internal Examiner
Dr. Chris Shields, Chair of the defence

Abstract

Seabirds face a variety of anthropogenic threats and as a result are one of the most threatened group of birds. Roseate terns (Sterna dougallii) are one of these species, listed as endangered in both the US and Canada since the late 80s and 90s. In Canada, roseate terns have had a historically limited breeding distribution and were known to predominately breed on three islands in Nova Scotia. One of these sites is Country Island, located on the eastern shore of Nova Scotia and one of the most northern breeding locations for roseate terns. When researchers spent the first season on the island in 1996, they witnessed predation on roseate tern eggs and chicks which prompted the initiation of a predator control program in 1998. This predator control program was initially successful, increasing the number of breeding roseate terns, and the program was ongoing for 22 years. However, over time, the number of roseate terns breeding declined despite continued predator management. To determine what factors may be influencing roseate tern breeding effort and breeding success on Country Island, I investigated trends in colony dynamics and diet of three tern species nesting on the island (common terns S. hirundo, Arctic terns S. paradisaea, and roseate terns). I found that Arctic and common terns both responded positively to predator management through increased numbers of breeding pairs, but roseate tern numbers declined over the same period. All tern species, however, had limited fledging success in the years that predator management was no longer occurring. The diet of the tern chicks was predominantly as we predicted and consistent with previous literature, with roseate terns mainly specializing on sand lance (Ammodytes sp.) and a decrease in sand lance deliveries being observed in Arctic and common terns. These results suggest that while predator control does influence roseate tern breeding success, other factors such as preferred prey availability, are likely a driving factor to roseate tern recovery on Country Island.

About Ruby…

Ruby completed her BSc in Biology and Environmental Science at Trent University and came to Acadia to undertake her MSc in Biology with Dr. Mark Mallory in collaboration with Jen Rock at Environment and Climate Change Canada. Ruby led two field seasons of seabird monitoring on Country Island, Nova Scotia while collecting data for her MSc, where she fell in love with seabirds.

During her time at Acadia, Ruby co-authored her first paper on Nelson’s Sparrow predation in Northeastern Naturalist and co-authored a second paper with the Mallory lab on the use of camera technology in wildlife research in Environmental Reviews. During her time in the lab, she also went on an Arctic science expedition in Nunavut and Greenland and presented her work at multiple conferences.

In her spare time, Ruby loves to spend time outdoors birding, baking bread and treats or doing something crafty. She is currently a Field Biologist with Birds Canada working on the Ontario Breeding Bird Atlas and hopes to continue conducting bird research and contributing to wildlife conservation.