Blog #457 Spying on Ospreys

 

Salt Point’s Ursula starts her autumn migration, courtesy of Cindy Sedlacek.

Little was known about Osprey migrations prior to the twenty-first century. People were baffled how the Ospreys vanished in the fall, only to return to their nests to breed in the spring. Satellite tracking with Doppler transmitters introduced in 1995 in Sweden have become smaller, lighter, and more powerful. These advances changed daily check-ins into real time tracking during the Osprey’s spring and fall migrations.

The original migratatory data came from simple identification marks. It is said that in 1595, King Henry IV’s prized Peregrine Falcon disappeared while hunting grassland bustards. Amazingly, the falcon’s body was retrieved from the Isle of Malta, 1,350 miles away. In another instance, a stork was found one spring in the Middle East with a Massai spear in it, showing the bird had spent time in Kenya or northern Tanzania.

History credits John James Audubon with being the first to mark birds to learn about migration. Audubon tied silk threads around the legs of Eastern Phoebes nesting at his Pennsylvania farm. This enabled him to recognize migrating birds the following spring and track them, showing which species returned to the same nest each year.  

Beginning in the 20th century, birds were systematically marked with metal bands (called rings in Europe) on their legs carrying unique, identifyable numbers. Recovery of banded birds showed where they had travelled after being banded and how long they lived.

Worldwide migration pathways of Ospreys, courtesy of Osprey Watch.

                             

Nearly 30,000 Ospreys were banded in North America during the pre-satellite transmitter days. Being a large and conspicuous bird, the recovery rate for banded Ospreys was high enough to develop an understanding of their migrations. Most                                               East Coast and Midwest Ospreys were shown to spend their winters in South America whereas western Ospreys traveled to Mexico and beyond. Females migratle south in mid-August after the young fledge. Once they have mastered fishing, juveniles follow a few weeks later with the adult males close behind.

In the spring, the adults return north while the juveniles spend an extra gap-year on the wintering grounds. This year is spent maturing and preparing for the arduous and risky life of an adult Osprey.

Band recoveries illustrated the path the northeastern Ospreys flew overland to Florida. From there, they avoid long water crossings by island hopping from the Florida Keys through Cuba to Hispaniola and then down to South America. Banding data indicated that many northeastern Ospreys winter in the Cauca and Magdalena valleys of Colombia, while others fan out over northern South America. Since adult females leave weeks before the rest of the family, they have time to winter as far south as Argentina.

Finding a banded bird usually entails randomly stumbling upon a bird carcass. Information gained from banded birds has biases that might affect models of Osprey migration: did the bird die en route or was it blown off course? From bands found in Bermuda, it is clear that Ospreys fly over the Atlantic en route to the Caribbean, but how common is this? Are the Ospreys all island-hopping, or do some cross the Caribbean to South America? The questions remained unanswered as it was unlikely to find a banded Osprey dead in the open water. Were the Ospreys wintering in northern Colombia or were the carcasses found there owing to the higher human population density? Similarly, was the sparse number of bands recoveries in the Amazon rainforest a result of a small Osprey population or the limited human population?

Finally, technologies developed in the late 20th century provided answers to many of these questions. The first radio collars were bulky, rendering them useable only on large animals such as moose, caribou, and elk. But soon silicon-based transmitters shrunk and became compatible with Ospreys. By the mid 1990s, satellite transmitters weighed only a few ounce and could send signals to orbiting satellites. Standard research practice is to avoid putting anything on a bird that is more than 3% of the bird’s body weight.

 

The first transmitters simply sent a basic radio signal to a satellite with data about the transmitter itself—its ID number, its movements, and engineering and maintenance information about whether the transmitter (and consequently the bird) was still moving.

The most recent technological advances arrived in 2001 with the development of GPS (Global Positioning Systems) transmitters and solar-charged batteries.These advances greatly increased the lifespan of the transmitters. At 3 ounces, these devices were still

The migration path of one Osprey from the Chesepeake to Brazil, Osprey Trax.

too heavy for Ospreys but they were quickly miniaturized to under 1 ounce, appropriate for even a small male Ospreys—weighing between 2.4 – 3.5 lbs. This size reduction enabled us to follow multiple migration cycles of the same individual. The one-ounce transmitters sufficed even on the smallest (male) Ospreys, and the females which are usually 20% larger than the males.

The miniature GPS devices, carried by the bird in a backpack, indicates precisely where the birds fish. The tiny GPS data transmitters also include the bird’s speed, direction, and altitude for each hourly location, to determine how local weather affects migration.

Antenna of GPS data transmitter protruding from bird, Center for Conservation Biology.

 

As mindboggling as the GPS satellite data is, it is still limited. For various technological reasons the one-ounce device can only communicate with the satellite at 12 hourly locations and it can miss an entire hunting session. If a bird headed away from its nest at 1:00 pm and came back at 2:00 pm, we would at least know that he had been out fishing, but we couldn’t tell where the bird had gone. Given a fully charged transmitter, we can now get locations every two minutes! Now our Ospreys have no place to fly and hide: researchers can monitor the Osprey’s every move, especially around the breeding grounds.

Tagged Ospreys could now fly anywhere and their locations were recorded. Researchers monitored the Osprey’s every move, especially around the breeding grounds. Eventually, the backpacks fall off leaving the birds unharmed. The data from these experiments are available on line for students and researchers to use.

Eyes to the sky!

Candace

Candace E. Cornell

Friends of Salt Point, Lansing, NY

Cayuga Lake Osprey Network cec222@gmail.com

 

EYES ON OSPREYS

WATCH!

Salt Point Osprey Nest Cam 2022-23

READ!

 On Osprey Time: Ospreys of the Finger Lakes

VISIT!

Cayuga Lake Osprey Trail Nests Driving Tour

Complete Cayuga Lake Osprey Trail

        HELP PROTECT OSPREYS:

•Stay 300 feet away from nests during the breeding season.

If the Osprey vocalizes, you are too close! BACK OFF IMMEDIATELY.

•Carry binoculars to view wildlife from afar.

•Recycle used fishing lines, twine, and nets, which can kill Osprey.

•Join the Cayuga Osprey Network: cec222@gmail.com.

•Help keep local waters clean, healthy, and safe. Pick up trash and do not litter. Trash stays in the ecosystem a long time before it disintegrates. Plastic just breaks down into smaller pieces.

Aluminum Can-------------------80 to 100 years

Plastic 6-pack Holder----------100 years

Orange or Banana Peel-------Up to 2 years

Plastic Film Container---------20 to 30 years

Plastic Bags----------------------10 to 20 years

Glass Bottles---------------------1,000,000 years

Plastic Coated Paper----------5 years

Nylon Fabric---------------------30 to 40 years

Leather----------------------------1 to 5 years

Wool Socks----------------------1 to 5 years

Tin Cans--------------------------50 years

    Source: NYSDEC