Ospreys from North America, Europe, and northern Asia migrate south in the fall (ospreys from North America go to Mexico, Central America, and South America; ospreys from Europe and northern Asia go to Africa, India and southeast Asia).
“Why don’t you just stay in the south, where it’s sunny and warm?” asked the Doctor
The reason is because places like the tropics are too limited in space for breeding. We need lots of space when raising a family, and northern breeding grounds offer more room, food, and nesting habitats than the wintering grounds in the south.
Birds migrate from areas of low or decreasing resources to areas of high or increasing resources. The primary resource being sought by ospreys is food. To survive they must migrate to a climate where the fish are more accessible.
The mechanisms initiating migratory behavior are not understood by humans. Migration can be triggered by a combination of changes in day length, lower temperatures, changes in food supplies, and/or genetic predisposition. We humans really do not know.
Osprey cover thousands of miles in their annual travels, often traveling the same course year after year with little deviation in the path followed. First year birds migrate unescorted to a winter home they have never before seen and return the following spring to the area in which they were born.
The secrets of their amazing navigational skills are also unknown. Osprey appear to navigate using a variety of techniques, including navigation by the stars, sensing changes in the earth’s magnetic field, and other techniques that we have discussed before.
Taking a journey of several thousand miles is a dangerous and arduous undertaking; one hundred miles a day, 200 over large bodies of water. It is an effort that tests both the birds’ physical and mental capabilities. The physical stress of the trip, lack of adequate food supplies along the way, bad weather, and increased exposure to predators all add to the hazards of the journey. It is really tough.
The fact are not pretty.
Estimated mortality among first year birds is 57%. This rate decreases to 18% annually after the first year.
First osprey nests are often robbed by raccoons, american crows, and the common raven.
Nestlings are vulnerable to predation by pine martens in Canada, and goshawks in the norther latitudes.
Nest collapses kill nestlings. Collisions with power lines, adverse weather (i.e., cold rains, high winds, etc.) can cause high mortality among nestlings and fledglings.
The eagle-owl is known to kill both adult and nestling ospreys in Europe.
In North America, great horned owls are known to take over nest sites and have been documented to prey on young and adults.
Bald eagles compete directly with osprey for food resources and will often harass ospreys forcing them to drop fish.
A few each year in Africa are eaten by crocodiles.
Here are some more pleasant facts:
On average, ospreys reach full maturity at 4.8 years of age.
Osprey been known to live 30 years when safe in captivity. The greatest number of recorded breeding seasons for a single bird is 23 (Canadian Wildlife Service 2000).
Based on banding data, one osprey in the wild was 26 years and 2 months at time of recapture.
Osprey often follow preferred pathways on their annual migrations. These pathways are often related to important stopover locations that provide food supplies critical to the birds’ survival. One of the Doctor’s goals is to locate some of our important stopover points so he can take steps to protect and save these key locations.
As always; Love, Harriett