When do Ospreys first breed?
Surprisingly, Ospreys rarely nest successfully until they are at least three years old. For reasons poorly understood, when all the adult Ospreys are heading north to breed each spring, young Ospreys, who made their first fall migration the year before, stay put, spending a “gap year” on their wintering grounds. They return only in their second calendar year, arriving on the breeding grounds when they’re about two years old.
My work with satellite telemetry has given us some insight into this process. Adult Ospreys start heading north in February or early March. They need to get back to reclaim their territories and begin the breeding process. They are driven. Their trips north are more direct and they travel faster than they did in the fall. Young Ospreys are sort of like human teenagers. They’re slow to get moving, sometimes not leaving the wintering grounds until April or May, when breeding birds are already on eggs. And they dawdle. When they do arrive, it is almost always too late to breed.
During their first or second trip home, young Ospreys may find another young bird and begin building a nest. With most of the prime real estate spoken for, these young pairs, which we refer to as housekeepers, often wind up trying to nest in all the wrong places—on chimneys or live power lines.
These relationships seem rather ephemeral. Whether it is because one or both of the newly formed pair don’t return from their next migration, or because no real bond to either the other Osprey or the chosen nest site was formed when the pairing proved unfruitful, we don’t know. But it is not surprising when doing a spring nest inventory to find that a housekeeping pair did not return.
Another insight gained from my satellite tracking studies is that Ospreys in search of a nest site will prospect in late summer. I first saw this with a male on Long Island’s North Fork. We trapped him rather accidentally while trying to catch a male at an established nest. “North Fork Bob” was passing by and wound up caught in our trap and wearing one of our transmitters. As we followed his movements, we realized he did not have a nest. Late in the summer, he began spending a lot of time at a marsh fairly near where we had trapped him. The next spring, he returned to that same spot. Carefully looking at the satellite images of the marsh, I could tell that there was an Osprey platform there. So Bob had found the platform that first August and returned in the spring in hopes of establishing a territory there. As it happened the resident pair arrived and reclaimed their territory. Later that summer, we saw Bob again focus his time at a spot just down the shore. The next spring he returned there, attracted a mate and settled down.
Osprey nest east of Driving Range. Photo by John Wilton.