More than four decades of close monitoring by Queen’s University researchers is showing that local tree swallow populations are in sharp decline, and they believe it could be partially due to climate change.

Since 1974, the Queen’s University Biological Station has kept track of an average of 168 nesting boxes every year on rural properties north of Kingston. In the past 45 years, researchers have measured 5,506 nests and banded 18,366 nestlings and 6,355 adult birds.

A handful of people attended a public talk at the Lennox and Addington County Museum and Archives in Napanee to hear a researcher talk about the data the biological station has gathered, how it does it, what the research is showing, and what citizens can do to promote tree swallow survival.

“This is a massive database, and this database has resulted in several important publications, 63 up to date, but ongoing,” Ivana Schoepf, research co-ordinator with the biological station, told those in attendance. “There is always more research coming out from this project.”

Schoepf said the data is helping researchers understand how the population has changed over time and is showing declining numbers, which biological station researchers initially believed could be due to predation.

However, after installing snake guards on nesting box posts — which were mostly effective — the population decline continues.

“It’s not just predation. There is something else going on. The negative trend continues,” Schoepf said.

A team from Queen’s is looking at long-term population trends in the tree swallow population.

“It was doing well until mid-1990s, but from then started to decline. This decline is ongoing,” Schoepf said.

Schoepf said the data is telling a “sad story” not only for tree swallows but for other aerial insectivore species.

Data from the State of Canada’s Birds 2019 report shows that aerial insectivore populations — such as barn swallows, purple martins, flycatchers and others — are down 59 per cent since 1970.

“They are all dramatically declining across North America,” she said.

“Some of the reasons have to do with the demise of their food source. As you’ve probably heard, there is a global decline in insect species as well, particularly pollinators like bees and wasps. Tree swallows feed on these insects.”

While insect decline could be due to agricultural practices such as pesticide use, a study has shown that tree swallows have not been directly affected by the development of agriculture.

Schoepf said that while disease, parasites and declining food sources are potential causes for population decline, researchers are suspecting climate change as the main culprit.

“Tree swallows, as all aerial insectivores, rely on insects to feed their babies,” Schoepf said. “The parents can go without feeding for a couple of days, but nestlings cannot. When you have a spell of unpredictable weather, particularly rain, they are not able to feed the babies, because when it rains there are no insects flying, and they cannot catch anything.”

Queen’s is participating with 20 other research institutes across the U.S. and Canada to figure out whether climate change and decreased insect abundance are the causes of the population’s decline.

Schoepf said there are a few things people can do to assist local tree swallows.

“If you want to have tree swallows on your property and you want to help them, the best is to place a nest box somewhere facing an open habitat,” she said. “The other thing is that if you want to help them out, you should not cut the grass during the breeding season. This is when the insects are reproducing, and they thrive on the foliage. Normally we do all our mowing at the end of the breeding season, once they’ve left. That’s in September or October. The grass allows the insects to thrive and the birds to feed.”

Having data on a single species that spans more than four decades is helpful, and a little unusual, Schoepf said.

“This population in particular is important because it’s such a long-running experimental study of the population in the wild. We have such long-term data that we have accrued over the years. This has allowed us to not just look at a population as it is now, but also how it was in the past, and to make predictions for the population’s trajectory in the future. This allows us to realize there is a problem, identify a problem, and perhaps try to understand what is causing it, to prevent further decline.”

Research is important in general, Schoepf said.

“It helps us better understand our place in the world, and also makes us understand how we are affecting the world around us, not just in a negative manner, but sometimes also in a positive manner,” she said. “There are a lot of successful conservation stories. Research gives us the raw data from which we can provide good recommendations to implement successful conservation projects.”

Learn more about the Queen’s University Biological Station at www.qubs.ca.

mbalogh@postmedia.com