Rob Bierregaard (L) and Iain MacLeod with Art, May 2012. Photograph by Chris Martin.
The Osprey (Pandion haliaetus) is one of the more familiar and charismatic birds of New England. Its large nests, conspicuous habits, fishing prowess, and tolerance of human activity have made it a favorite of birders and the general public alike.
Of course, Ospreys are only a New England bird for less than half the year. Their specialized food requirements—the only diurnal raptor in the world to feed exclusively on live fish—means that as cooler temperatures reach New England in September and October, Ospreys depart our shores before the freeze of winter locks its piscean diet under a shroud of ice.
Through banding studies, we knew that almost all of our New England Ospreys spend our winter months in South America. Or, I should say the recovery of dead banded Ospreys in places such as Brazil, Colombia, and Venezuela led us to conclude that is where our Ospreys go. (See Figure 1 for the wintering location of seven of the Ospreys we’ve tagged.) Hawk migration observers had also documented the southward push of Ospreys along the Eastern Seaboard each fall, including through Florida and Cuba, so we had a good idea of how the birds reached South America and when they migrated. It was only with the development of miniature GPS tracking units in the 1990s, however, that we had the opportunity to see in detail where these birds go, how they get there, and what hazards they face along the way.
Figure 1. Map of migration routes and wintering locations of seven Ospreys tagged in New Hampshire.
In 2011, the Squam Lakes Natural Science Center launched a new Osprey research and education project under my leadership and in partnership with Dr. Richard O. (Rob) Bierregaard. At that time, Rob was a Distinguished Visiting Research Professor in the Department of Biology at the University of North Carolina at Charlotte. He is now a Research Associate at the Academy of Natural Sciences of Drexel University in Philadelphia. Bierregaard had been studying Ospreys—starting on Martha’s Vineyard—since 1970, and in 2000 he began deploying lightweight satellite backpacks to track Ospreys.
Now after 17 years, and more than 100 birds tagged, this project has revealed migration differences among Ospreys and is helping to pin down where threats to Ospreys lie. For example, like human adolescents, juvenile Ospreys wander, loiter, and get lost. They even cross open oceans unnecessarily. Adults, in contrast, appear to be more sure of where they are headed and thus fly more direct migration routes. The tracking project also confirms that the mortality rate of juveniles is much higher than for adults; 70–80% of juveniles die in their first year, but the mortality rate for experienced adults is about 10% per year.
Accessing the nest via bucket truck, Tilton, New Hampshire, May 2012. Photograph by Iain MacLeod.
Since 2011, we have outfitted sixteen Ospreys in New Hampshire with GPS satellite transmitters known as Platform Transmitter Terminals (PTTs) made by Microwave Telemetry Inc. Each PTT weighs 30 grams and has a small photovoltaic cell on the upper surface so that the battery is charged by the sun. Our tagged birds have included six adult males and ten recently fledged juveniles (see Table 1). Here are some of their stories.
One of our tagging sites is a nest on a disused 40-foot electric pole that is located in the wood chip yard of a biomass power plant on the edge of the Pemigewasset River in Bridgewater, New Hampshire. To put a PTT on an Osprey, you first have to catch it. We use a trap known as a noose carpet that consists of a four-foot square piece of heavy gauge wire mesh covered in hundreds of monofilament fishing line slip knots that we call nooses. We tether the trap to the nest so that it covers a clutch of dummy eggs, while we keep the real eggs warm in an insulated box. The idea is that the target Osprey will try to incubate the dummy eggs and become trapped by its toes. We choose only nests that are easily and quickly accessible so we can quickly extract the trapped bird without harm. At the Bridgewater nest, we had the help of a large hydraulic lift operated by Arthur, one of the power plant employees. It was a perfect nest for our project.
In 2011, we attempted to catch the adult male at this nest, but he didn’t cooperate and we failed to catch him. We did, however, trap and band his mate, though we did not outfit her with a PTT. We usually target the adult males for PTTs because we have major gaps in our knowledge about the foraging habits and territory sizes of male Ospreys. In the Osprey world, there is a clear demarcation of responsibility during nesting. The male does all the fishing for the family, while the female defends the nest and does 70-80% of the egg incubation and almost all of the chick brooding. So, if you want to find out where Ospreys fish and how far they travel from the nest, you have to track males.
Table 1. Data Overview of 16 Ospreys Tagged In New Hampshire.
After failing to catch the male at this nest in 2011, we were back for a second attempt in May 2012. The same pair was back and incubating three eggs. This time, we quickly caught the male and equipped him with his custom-fit hi-tech backpack. The Bridgewater male was christened Art after the power plant employee who had been so helpful to our work. Because education and public outreach are important aims of our project, we give each of our tagged birds a name. Our rationale is that online followers will be more invested in an Osprey named Art rather than ID #110967.
Figure 2. Art’s Foraging Range, April-September, 2013.
Art immediately started transmitting fascinating data. Each transmitter communicates with a network of orbiting satellites on an every-third-day schedule. The data upload has a GPS location for each PTT every hour from 7:00 am to 7:00 pm. Those times are programmed to adjust at different times of the year, but consistently give 13 hourly points per day. Being diurnal, Ospreys rarely move at night, so nighttime points are not worth recording. For each time point, we also get the height of the transmitter above sea level, what direction it is facing, and how fast it is moving.
Throughout the rest of the summer of 2012, I could see exactly where Art spent his time. I could see on what stretches of river or which ponds and lakes he fished and at what times. I could tell when he was interacting with intruder Ospreys, how he overlapped with his neighbors, and how often he perched near the nest or incubated. We could even tell how efficient a hunter he was. Quick trips between a fishing spot and the nest indicated successful hunts. The transmitters provided an amazing insight into the lives of these Ospreys.
Table 2. An analysis of Art’s foraging activity in summer 2013.
In 2012, Art and his mate successfully raised one chick that fledged in mid-August. Art left New Hampshire on September 11 and made an epic 4,900-mile migration to the Araguaia River in east central Brazil where he spent the winter. Art followed what we know to be the classic adult migration route along the Eastern Seaboard. He passed through Florida, over to Cuba, across to Haiti and the Dominican Republic, and then flew across the Caribbean Sea to Venezuela and finally south into Brazil. He reached his winter home on the Araguaia River on October 22.
The winter habits of an adult Osprey are very different from their time on the breeding grounds and Art demonstrated that well. Because Osprey pairs have no association outside the breeding season and take separate winter vacations, Art had no mate to feed, no nest to defend, and no chicks to rear. By all accounts the living was easy and relaxed. I probably oversimplify, but the basic daily routine seemed to be: roost on a favorite tree branch or stump, fly to the river, catch a fish, eat fish, sit in the sun along the river—no doubt preening—catch another fish in the afternoon, sit in the sun, roost, and repeat for five months. Throughout the winter of 2012–13, I checked in on Art’s virtual self on Google Earth every three days and confirmed his activity.
Rob Bierregaard with Artoo, May 2013. Photograph by Chris Martin.
Art left his winter home in Brazil on March 15, 2013. He reached the coast of Venezuela on March 26, crossed over to Haiti, and zipped through Cuba by March 31. He arrived back at his nest in New Hampshire on April 10 where he had a welcoming party. His same mate had arrived back from her winter vacation five days earlier, and I was there along with a crew from the local ABC TV affiliate and reporters from three newspapers. Art was a showman and arrived in spectacular fashion. He heralded his arrival with a high aerial display before plummeting to his nest and joining his mate. Though they hadn’t seen each other in six months, within 20 minutes they had rekindled their partnership and mated. Within 11 days of Art’s arrival, they were sitting on eggs. The pair hatched and successfully reared three chicks.
Once again we followed Art’s fishing routine throughout the summer of 2013 as he and his mate reared their chicks. Table 2 shows details of his foraging activities in 2013. Figure 2 depicts his territory and foraging range.
On August 12, 2013, Rob and I were back at Art’s nest. Our goal was to catch one of the recently fledged chicks and outfit it with a new PTT. We agreed that if we caught Art, we would remove his transmitter. We had learned more than enough about Art and there was no need for him to continue to carry the backpack for another long migration. Catching him was a long shot as he had obviously seen the trap before and would likely be wary.
We set up the trap on the nest with a fish as an enticement for the hungry chicks, who were perched on snags along the river. Art’s mate also sat watching us. She too had been caught before and was wary. As luck would have it, Art was off fishing on Little Squam Lake and had no clue we were at his nest. Within 20 minutes of us installing the trap, Art came over the hill with a big trout for breakfast. One of his chicks flew to the nest to be first in line. Art landed next to him and a second chick flew in to share the feast. All three were caught! Arthur hoisted Rob up to the nest on the lift and we soon had three Ospreys hooded and swaddled in custom-made fabric straitjackets—we call them Osprey cozies.
We quickly removed Art’s transmitter, thanked him for his amazing contribution to avian science, and released him. We put Art’s PTT on his son, who we named Artoo, and put a new PTT on his other son, who we named Bergen. Now we could follow Art’s sons and see how their migrations and habits compared to their father.
Art, who was recognizable by the silver band on his left leg, returned to his nest in April 2014 and once again raised three chicks with the same mate, who was recognizable by the silver band on her right leg. They were both back in 2015, when they again raised three chicks, and in 2016, when they raised two chicks. Tracking of other birds over multiple winters confirms that adult Ospreys return to the same winter home each year, so even though Art no longer carries a transmitter, I can be sure that he makes his 9,800 mile round-trip each year between his little stretch of the Araguaia River in Brazil and his nest in New Hampshire. Each spring, I’ve been delighted to welcome this old friend back to New Hampshire.
Artoo and Bergen were fascinating to follow. Artoo began his first migration on August 15, just three days after we tagged him. He headed for inland Pennsylvania where he found some rivers to his liking. His brother Bergen began his migration on August 21 and headed for the coast of Virginia and Maryland. After a month of separate wanderings, we were amazed when, on the evening of September 25, they both ended up on the Virginia coast and both flew through the night across the Georgia Bight. They were at times so close that they must have seen each other—what are the chances?
From then on, the brothers followed separate routes through Florida and into Cuba. On October 14, Bergen crossed the Caribbean Sea to Colombia where he spent time exploring several upland rivers along the north edge of the Andes. On October 20, Artoo left the Dominican Republic and crossed to Venezuela. He settled just north of the Orinoco River for the next couple of months. Bergen renewed his migration on October 28 and headed for the Amazon Basin in Brazil. By November 6, he had settled on the Rio Purus just to the south of the main trunk of the Amazon River and more than 4,000 miles from his natal nest. Interestingly, although he was more than 1,000 miles west of his father Art’s winter home, he and his father were on exactly the same latitude.
Figure 3. Map of migration routes of 16 Ospreys tagged in New Hampshire.
To our surprise, in January 2014, Artoo renewed his migration and headed south again. He ended up another 700 miles farther south, also on the Amazon and within 100 miles of his brother. On February 13, Bergen’s PTT stopped transmitting. We had no indication that Bergen was in trouble. He was in an area he knew well and all seemed normal, but we never heard from him again.
For the next month or so, Artoo wandered around the great Amazon Basin exploring the Rio Solimões—which is what the Brazilians call the upper reaches of the Amazon River—and the Rio Japura. He finally settled on a small lake next to the Rio Solimões on March 28. He would spend the next six months there. Young Ospreys do not return to the breeding grounds until they are nearly two years old, in their third calendar year, so Artoo had found the location for his “gap year.” He left this lake on October 5, 2014, and went for a wander again up the Solimões. My guess is that he was displaced by a returning adult Osprey who vacated the lake in spring to head north to breed and returned in early October to find an intruder. After a while, Artoo settled on the river close to “his” lake, where he remained until March 31, 2015, when the urge to return north kicked in. Artoo arrived back home in the Lakes Region of New Hampshire on July 24 after a long meandering journey north. He settled in northern Massachusetts for the remainder of the summer and headed south again on September 1. He reached southern Florida on September 17 and headed toward Cuba on the next day. Something dramatic must have happened during the night, because the next morning his signals indicated that he was floating on the sea off the east coast of Florida. We never heard from him again and will never know what happened. We knew that the early years of an Osprey are filled with peril, but losing Artoo was particularly tough.
The fates of other birds have also remained a mystery. Jill, a 2012 juvenile from a nest in Tilton, made it to Brazil but after just a day or two her signal stopped and we assume she died. Weber, a 2013 juvenile from a nest in Seabrook Harbor, arrived in Venezuela and flew into a remote ravine along a river. His transmitter continued to send signals from the same exact location for several weeks before going dead and we assumed Weber had perished. Interestingly, the signals started up again from the same location several months later indicating that the PTT was exposed to the sun again, causing the battery to charge and start transmitting. While compiling data for a table in this article, I noticed that data points from Weber’s PTT continued to trickle in over a five month period. We now believe that Weber was still alive at least until December 2014, and we have no reason now to believe he isn’t still alive. Tilton, a 2014 juvenile from the same nest as Jill, headed for Cape May, New Jersey, and settled there for several weeks before his PTT signal indicated that Tilton was down. A couple of ground searches revealed no sign of the bird or the transmitter. Juliet, a chick from the same nest in 2015, arrived in Venezuela. She settled along a river close to a major highway and her signal went dead within a few days.
Rob Bierregaard with Staddler. The PTT attached and he is calmed with the hood. May 2015. Photograph by Iain MacLeod.
The fates of other birds have not been so mysterious. Chip, Jill’s brother and nest mate in 2012, ended up landing on a large container ship off the coast of New York. He rode the ship east across the Atlantic for a couple days, then he landed on a second ship and finally on a third ship, all of which were headed east. After a week of hitching rides and getting farther and farther off course, he ditched in the ocean not far from the Azores. No doubt he was weak after a week without food. Bridget, one of Art’s daughters from 2014, wintered near Vero Beach in Florida. Her signal stopped moving near a road in January and we suspect she was hit by a car.
Mackenzie, an adult male from a nest in Stratford in northern New Hampshire, died on the shore of a pond in Berlin, New Hampshire, after successfully raising a chick. He was fattening up and getting ready to migrate when he stopped moving. I searched the area and found his remains. He had been preyed upon by a larger raptor, perhaps a Bald Eagle or a Goshawk.
Lizzie, one of Art’s daughters from 2015, was absolutely fascinating. She left the nest on August 13, one day after we tagged her. She flew south to Belcher Cove in Rhode Island and stopped moving. I assumed the worst, but when I zoomed in on her location on Google Earth I could see the telltale shadow of a tall Osprey nesting pole, so I assumed she was on that nest. A quick phone call to the active nest monitors in Rhode Island led us to Butch Lombardi. Butch had been checking on that nest all season and it had fledged two chicks. When Butch checked the nest now, however, he found that Lizzie had “force-adopted” herself at this nest and was being fed by the resident male. She aggressively fought off another youngster—presumably the rightful tenant of the nest—and claimed fish at this nest for several days. Although post-fledging youngsters have been recorded visiting neighboring nests and being fed, this behavior had never been confirmed to occur over such a long distance. In this case, the nests were 222 kilometers apart. Perhaps it is common for young Ospreys to mooch where they can as they disperse from their natal area. We are publishing a short paper in the Journal of Raptor Research to describe this incident.
Unfortunately, Lizzie’s story had a sad ending. Twelve days after arriving in Belcher Cove, she was found dead under a power line near her adopted nest.
Other birds have been more successful. Donovan, a breeding male from the nest in Tilton who was the father of Jill, Chip, Tilton, and Juliet, wintered on a small river just north of the Orinoco River in Venezuela. We tagged him in 2013 and followed him for three breeding seasons, three southbound migrations, three winters, and two northbound migrations. We learned about his foraging and saw some intriguing changes each year in his territory. Over the three summers, his foraging area became smaller and his fishing more concentrated. My guess is that he got more efficient and as he got to know the area better and could focus more on one favorite fishing spot. In November of 2015, after returning to his winter home for the third time, his signal went dead and we never heard from Donovan again. I held out hope that he might return in the spring with a dead transmitter, but he did not. His old mate did return, however, and she found a new mate immediately. They raised two more chicks at this successful nest.
Rob Bierregaard with Staddler. The hood is off and he is ready to be released, May 2015. Photograph by Iain MacLeod.
Another adult male named Gundersen, whom we tagged in May 2015, also died on his wintering ground in Venezuela in January 2016. His old mate quickly found a new male and raised two chicks in 2016. These adult mortalities do allow us to track how quickly lost mates are replaced—VERY quickly as it turns out. This rapid replacement of mates indicates that there is a healthy surplus of young birds looking for opportunities to claim a nest.
Two other adult males that we tagged in 2015 did survive the winter and returned to New Hampshire in 2016. Wausau, who nests on a huge pole in Groveton, New Hampshire, spent his winter near the Meta River in the Casanare region of Colombia. He arrived back at his nest a little late and found that his mate had taken a new male. I was at his nest on April 18 to see his arrival and, like Art in 2013, he put on a spectacular show indeed. A high skydance proclaimed his arrival, but now he also had to see off the interloper. Apparently, that didn’t take long, as an hour later he arrived at the nest and mated with the female. She greeted him by then demanding that he go get a fish. They commenced incubation shortly afterwards, but later in the season they failed. Wausau remained near the nest until he set off on his southern migration between 11:00 am and noon on September 4. He arrived back at his winter home in Colombia on October 5, 2016.
Staddler gives us the eye as we approach his nest, May 2015. Photograph by Iain MacLeod.
Staddler, a male we tagged at his nest in Seabrook Harbor in May 2015, spent the winter on the Rio Tefé next to the main trunk of the Amazon River in central Brazil. He obviously was in a prime spot as he spent 95% of his time in a three-quarter square kilometer area on the shore of the lake. He left his winter home on March 18 and reached his nest and his old mate on April 7. He and his mate raised two chicks. Staddler began his 2016 fall migration on September 5 and arrived back at the Rio Tefé on October 13.
Table 1 looks at the number of data points collected and the distances traveled between those points by the Ospreys we have tagged in New Hampshire. One thing that jumps out from this table is the difference in the duration of data gathering between adults and juveniles—an indication of the high mortality rate of juveniles in their first year. The six adults we have followed accounted for 33,563 GPS points. Two birds, Staddler and Wausau, are still active and their data point total has been accumulated through September 28, 2016 when I created the table. That’s an average of 5,592 GPS data points per adult bird. The combined travel distance between those points was 142,604 kilometers—an average of 23,764 km per bird. Donovan provided the greatest amount of data with 11,440 points and 54,375 km. The total for the 10 juveniles was 19,546 data points and 77,334 kilometers traveled, for an average of 1,955 points and 7,733 km per bird. Figure 3 shows the migration routes of all 16 of these Ospreys.
My colleague Rob Bierregaard has been tagging other Ospreys in different states including Virginia, Maryland, and Massachusetts. In 2016, he expanded our research to Newfoundland. In August, he tagged six Ospreys on the Avalon Peninsula—the most easterly breeding site for Ospreys in North America. It will be fascinating to see where these birds go. Rob suspects that some juveniles, reacting to their innate sense to fly south—and because they don’t know any better—might head due south from Newfoundland and end up flying as many as 3,200 km over water to the eastern Caribbean Islands. A few lucky ones may find Bermuda. This route would be a truly astonishing migration for a young Osprey.
All of the information in this article can be found on the website of the Squam Lakes Natural Science Center.
Interactive maps and blogs, as well as educational materials for schools, and links to all kinds of Osprey-related materials, are available. We also have a phone app—called Animal Tracker—that tracks all of our Ospreys, so you can follow these amazing migrations from your armchair.
Iain MacLeod is Executive Director of the Squam Lakes Natural Science Center in Holderness, New Hampshire and has been studying Ospreys for more than 35 years, first in his native Scotland and now in New Hampshire. He is on the Board of NorthEast Hawk Watch and is a former chairman of the Hawk Migration Association of North America. Iain also is a member of the New Hampshire Bird Records Editorial Team and New Hampshire Rare Birds Committee. He lives in Ashland, New Hampshire.