Ospreys’ return are a spring thing

Nature center highlights bird’s history in region

New London — Spring may be just around the corner, but for many the season got a jump start Sunday with a presentation on one of New England’s favorite birds: ospreys.

More than 60 people gathered in Bill Hall at Connecticut College to learn more about Connecticut’s “harbinger of spring” with a presentation by renowned osprey researcher and Drexel University research associate Dr. Rob Bierregaard.

Ospreys generally return from their southern migration around Saint Patrick’s Day and are often accompanied by the arrival of spring.

The presentation, hosted by the Denison Pequotsepos Nature Center in Mystic, drew an enthusiastic crowd from as far as West Hartford, and highlighted the bird’s history in the region, as well as Bierregaard’s extensive tracking research of their migration patterns.

The presentation began with Bierregaard offering a brief review of ospreys from the evolutionary traits that have made them excellent fish catchers to the species’ transition away from nesting in trees.

“Once upon a time ospreys used to nest in trees, nowadays when they nest in trees it’s almost a big story because now they nest everywhere,” Bierregaard joked, sharing photos of osprey nests in ship masts, statues, chimneys and movie marquees.

Threatened by DDT

Bierregaard also spent time discussing the telltale signs to distinguish between juvenile and adult ospreys — juveniles have gold speckled eyes whereas adults have yellow eyes and no speckles — as well the survival challenges the birds once faced due to DDT pesticides which caused the birds to lay eggs with thinner shells.

When DDT hit the Connecticut River area, the region saw its osprey population plummet from about 200 pairs in 1950 to about 25 pairs nearly 20 years later.

However, since DDT was banned in 1972 and communities widely began putting nesting poles up, the osprey population has grown dramatically with the birds nesting or trying to nest in all the states in the continental U.S.

But Bierregaard’s focus has been studying osprey populations, which he’s done in southern New England since 1971. Starting in 2000 though, he and his colleagues began a series of studies tagging and tracking ospreys using satellite telemetry, which involves attaching a small transmitter to the osprey’s back. This led to Ospreytrax, a website of data and interactive maps where people can observe osprey migration.

Bierregaard explained that ospreys, which migrate south as far as South America, navigate using some information they gather from the earth’s magnetic field, rather than learning migratory routes from their elders. He added that although it’s a learning process for the birds, the simplest theory is that the bird’s instinct tells them to go south and stay over land if possible.

Bierregaard — who’s tagged 108 ospreys from South Carolina to Newfoundland — also shared his insights on nesting posts and the tagging process and how male and female ospreys migrate seperately.

“Male and female ospreys have separate vacations and some suggest that’s why they mate for life,” he joked.