Banding birds, and the retrieval of these bands, has provided valuable information on the movement of birds. Today we also have the benefit of satellite telemetry, in which a bird carries a tracking device and its location is calculated via satellites that orbit the Earth. The following is just a sample of what this tracking technology has revealed about the migration of Ospreys.
There are significant differences in male and female timing of migration (females leave up to a month before males), distance traveled and overwintering locations. There is strong fidelity to overwintering sites as well as to migration flyways. Breeding pairs of Osprey do not migrate or overwinter together, and adults do not migrate with their offspring. Ospreys rarely migrate at night over land but inevitably migrate at night when undertaking longer (more than 12 hours) water crossings.
Subtle insights into migratory behavior can be gained by the findings of satellite telemetry, as well. Their first flight south by juvenile Ospreys is often largely over water. A majority of juveniles migrating over the Atlantic Ocean from Massachusetts to the Bahama Islands flew as many as 1,500 miles over a period of up to 58 hours. The fact that no adults or 2nd year birds took this route over water suggests that juvenile Ospreys learn the coastal migration route during their first trip north.
Overwintering habitat preferences have also been assessed. Of 79 Ospreys tracked by satellite, 30.4% overwintered on coasts, 50.6% overwintered on rivers, and 19% overwintered on lakes or reservoirs, with differences based on both sex and region of origin.
These few facts don’t begin to exhaust the information gathered from banding and satellite telemetry on Ospreys, much less many other species. They just serve to illustrate how modern tracking technology compliments and increases the information formerly gathered by firsthand observation and banding.
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Adult female Ospreys begin their fall migration in August, before their young are completely independent. After females leave, males continue to feed this year’s young and don’t reach the peak of their migration until the middle of September. Ospreys tend to migrate during the day, except when crossing over large bodies of water, which they do at night. Unfortunately, the nocturnal flights of northeastern Ospreys over the Caribbean (a 25-hour nonstop flight) on their way to their wintering grounds in South America often coincides with the hurricane season. As treacherous as this is, 80 percent of adult Ospreys survive migration, according to the National Wildlife Federation.
As opposed to humans, who use the entire bottom of their feet for support, birds stand and walk only on the ball of their foot and with their toes. When you look at a bird’s leg, what appears to be its knee, bending backward instead of forward as it does in humans, is actually its heel.
Most birds have four toes, arranged differently according to the life style of the bird. Songbirds, as well as most other birds, have three toes pointing forward and one pointing back. Most woodpeckers, being active climbers, have two toes pointing in each direction, which provides added clinging support. The outer toe (of the three forward toes) of ospreys and owls is reversible, so that they can have two toes in back should they need to get a better grasp on slippery fish or other prey. Some birds that do a lot of running, such as sanderlings and most plovers, have only the three forward toes. (Photo: Mourning Dove tracks)
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.