Blog # 424 Winter Ecology and Marathon Migrators

“HELLO AGAIN, IT’S ME! LOOKING FOR MY NEST.” A female Osprey returning on migration and holding with her wings in the typical “M” shape, courtesy of Andy Morffew.

All over Central and South America and the Caribbean, North American Ospreys (Pandion haliaetus) are preparing for their northward marathon spring migrations to their breeding grounds thousands of miles away. A host of environmental cues, such as changes in day length, higher ambient temperatures, changes in the food supplies, and genetic predisposition may all trigger the overwhelming urge to migrate but that story is still being written. For now, our North American Ospreys have a few more days left in their winter vacations. 

For years people wondered what Ospreys did when they disappeared for the winter. Identification bands on a dead Osprey’s leg revealed the bird’s birth records but did not describe its activities. What is known about the winter ecology of Ospreys comes from information received from the satellite tracking devices worn in bird-sized backpacks. In 2000, Rob Bierregaard started tagging Ospreys with GPS satellite transmitters to follow their migrations to and from South America and track their behavior in the winter. Researchers using similar techniques to Bierregaard’s added to the data and soon had a basic picture the Osprey’s winter habitat, their daily movements, and other activity patterns. You can even tell when the Osprey is fishing and going back and forth to its perch.

Osprey with a GPS antenna and backpack, courtesy of Rob Bierregaard.

Year after year, adult Ospreys migrated in the fall to their traditional wintering roosts showing a strong fidelity for these exact locations. In a 2015 South American study lead by Washburn, Ospreys showed a preference for spending the winter on river systems (50.6%) compared to staying at lakes (19.0%), or coastal areas (30.4%). They also detected variations in schedules between the sexes. Males need to reclaim their nests in the spring as soon as possible and stayed on their wintering grounds for an average of five weeks days while females stayed for about seven weeks.

 

Juvenile Ospreys in their gap year may move about looking for their preferred wintering habitat but once they find their ideal spot, they remain loyal to it. Satellite telemetry suggests that wintering adults move infrequently, limiting their movements to nearby feeding grounds. Washburn described the wintering adult North American Ospreys are almost sedentary, demonstrating a pattern of limited daily movements and high fidelity to a few select roosts. Many wintering Ospreys expend little energy fishing by hunting from perches instead of performing the high aerial dives we often see in the Finger Lakes. This strategy maximizes energy conservation in preparation for the breeding period to come and might reduce their mortality. Osprey, flying north from their South American wintering zones (see map below), make a 400-700 mile crossings across the Gulf of Venezuela before resting briefly in Haiti, Jamaica, or Cuba. This exhaustive 25 to 40 hour flight is made treacherous by taking a risky route at night over the Caribbean. The birds travel as much as 5,000 miles from the Amazon basin to the Florida Keys, and up the Atlantic Coast before they end up at their breeding sites, which can be in northern Canada. This incredible winged migration takes an individual Osprey two-three weeks to complete from start to finish. 

Sample routes of Osprey on spring migration returning to the northeast, courtesy of Rob Bierregaard.

Spring migrations are short and fast-paced compared to fall migrations as there’s great competition for prime nesting sites. Timing is everything if you want to acquire a healthy mate and a first-rate nesting site.  

Many Ospreys mate for life, although their primary allegiance is to their nest. If their established mate dies or disappears during spring migration the mate’s loyalty weakens prompting it to accept the advances of joins the colony. Last year at Salt Point, Ophelia did not arrive promptly as she usually does. After five days a female floater tested the strength of Orpheus’ pair bond and found he was willing to mate. The nest’s new female, Ursula, moved in the nest and the pair began bonding and mating. Ophelia unexpectedly at the nest after a week and was perturbed that her place on the nest had been usurped. Orpheus welcomed them both to the nest, perhaps hoping he could convince them both to nest. However, the gals started fighting, most probably over nesting rights with Orpheus. Eventually, Ophelia gave up, sat on a nearby perch for a few days before leaving the area.

Migrating Osprey grabbing a bite to eat en route home, courtesy of Andy Morffew.

Along migration, Ospreys have many dangerous issues to deal with. One major hazard is weather, especially when crossing large bodies of water. The birds can be blown off course by a severe thunderstorm or windstorm. This event will drain limited fat reserves (fuel) and put an Osprey at risk of being too weak to continue. Ospreys cannot land on the water to rest like a gull. If an Osprey becomes exhausted while flying over the open water, it will drown. According to Osprey researcher Rob Bierregaard, one weary Osprey found refuge on a boat that took it to Portugal. 

The adult males tend to arrive at their nest first followed in a few hours to a few days by their mates. Soon unmated intruders or floaters appear looking for nest vacancies Lastly, the 2–3-year-old young arrive after spending a gap year in the tropic. It is time for them to start looking for nest sites and mates although the young often take a third year to find nests and mates.

Eyes to the sky!

Candace 

Candace E. Cornell 

Cayuga Lake Osprey Network

Friends of Salt Point 

Lansing, NY 

cec222@gmail.com 

EYES ON OSPREYS

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Coming Soon! Salt Point Osprey Nest Cam 2023

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On Osprey Time: Ospreys of the Finger Lakes

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