Blog #421 The Urge To Move
Osprey sitting calmly before being overcome with Zugunruhe, courtesy of Karel and Cindy Sedlacek.
One minute the birds are perched contently, and the next they take off on migration succumbing to Zugunruhe, a German word describing the intense “migratory restlessness period.” Zugunruhe hormones are powerful internal cues that signal seasonal migrations; it prompts the uncontrollable urge to move and travel thousands of miles, battling hungry predators, strong winds, food shortages, and stormy weather to get to the safety of their winter home in the tropics.
Autumn in the Eastern U.S. is a restless time of year for wildlife and especially birds. Reports of incredible endurance and distances traveled during migrations of monarch butterflies, elk, humpback whales, American eels, Atlantic salmon, menhaden, and striped bass. Birds are famous for their migration feats and global travels, notably shorebirds. Notable examples include the Bar-tailed Godwit, Red Knot, and Artic Tern, and long-distant raptors such as Broad-winged, Sharp-shinned, and Red-tailed Hawks, and the Osprey. As soon as Osprey fledglings learn to fly and capture food, they are considered juveniles and are ready to migrate to South America for the winter. Instead of traveling in family groups as do many species, Osprey travel alone. How do the young migrate on their own without prior knowledge of the route? How
A Salt Point juvenile readys for her departure, courtesy of Karel and Cindy Sedlacek.
Osprey juveniles know where to go and how to get there is one of the greatest migration mysteries.
In the time between fledging and migrating, the Ospreys must prepare for their migration. Adult females spend several weeks gaining back the weight that was lost during the nesting period, as mothers often subsist on leftovers. Ursula and most of the mature mothers begin their southern migrations once their young start learning to fish. Osprey expert Alan Poole suspects that Osprey mothers are probably hungry much of the time they are rearing their young, especially as the young get older and hungrier. Most mothers leave by mid-to-late- August and follow their traditional routes south to the Caribbean and South America.
Juvenile Ospreys build up their energy stores as they perfect their flight and hunting prior to leaving. Orpheus and the other fathers also put on weight as they continue bringing food to their nests until the youngsters migrate. According to Poole, the father’s role is to transform the fledgling Ospreys into independent juveniles. By mid-September, most Osprey young depart the nest. Juveniles may also explore the area for hundreds of miles before beginning migration, which sometimes puts them off course.
Each Osprey is flooded with Zugunruhe hormones urging them to take to the sky. Flying on a course that will reveal itself in time, the juveniles perform this momentous journey to an unknown place they have never been and do so without any help from other Ospreys. The Osprey family travel individually. yet may see each other at a fishing hole along the migration route or while following the same thermal en route.
GPS tracking studies show that first-time migrants tend to fly off course and have to course correct. Over the years, their routes become more uniform and more precisely hug the coastline. The map below of the 2016 fall migration of an Osprey named Wausau superimposed on paths of other Ospreys.
Fall migration route of Wausau (male, aqua) from NH to Colombia in 31 days.
The other colors represent signals from more Osprey, courtesy of Dr. Rob Bierregaard.
There are many theories as to how juvenile Ospreys navigate. They are likely guided by the sun and stars, the topography along the coastline of North America to the tip of Florida, as well as the natural air currents. They typically cross the Straits of Florida to Cuba before heading east to Haiti and the Dominican Republic, all using their keen eyesight. What must be a treacherous part of the trip, the juveniles fly 500 miles over open water to the northern shores of South America where they fan out and overwinter along the coastline or rainforest waterways as far south as Argentina—a 3,500–5,000-mile journey. After spending 18 months in South America, the young Ospreys migrate northward to the region of their birth to find a mate, a nest, and to raise a family of their own.
Danger abounds during first-time fall migrations. Birds can get hit by a car, tangled up in power lines, or shot at by subsistence aquaculture farmers in the Caribbean or South America. Ospreys are easily blown off course by storms and hurricanes and lost over the open ocean. Over 60% of young fail to successfully return north. The good news is that, statistically, those young Ospreys that do survive their first year have a good chance of surviving future migrations.
Eyes to the sky!
Candace
Candace E. Cornell
Friends of Salt Point, Lansing, NY
Cayuga Lake Osprey Network
Guest Photographer:
Cynthia Sedlacek, musician and Director of Data Administration and Reporting at Cornell University, is a surprising artistic talent. Cynthia’s affection and admiration for raptors are evident in her exciting photographs primarily of Ospreys nesting around Cayuga Lake and the red-tailed hawks of the Cornell Campus. Her photographs of local Ospreys are incomparable as she captures their essence, their jizz, and their inner bird. From the hard-to-see nestlings to the fast-flying adults, Cindy goes beyond the pale to catch all aspects of Osprey life in the Cayuga Basin. “My camera allows me to capture their beauty in many ways that the human eye can’t see,” she says, “like their spectacular wing positions and detailed feather patterns.” Cindy and her husband Karel are also avid nest monitors for the Cayuga Lake Osprey Network and video stream footage of the campus hawks.
EYES TO THE SKY!
WATCH!
READ!
On Osprey Time: Ospreys of the Finger Lakes
VISIT!
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.
•Help keep local waters clean, healthy, and safe.
•Recycle used fishing lines, twine, and nets, which can kill Osprey.
•Join the Cayuga Osprey Network and volunteer to help monitor Osprey nests: cec222@gmail.com.
Comments
Post a Comment