European ospreys from Scotland to Finland overwinter in north Africa, and Asia north of the Himalayas but not all ospreys abandon their fans so heartlessly. The subspecies that lives in the Bahamas, Cuba, southeast Mexico and Belize does not migrate. The Australian and southwest Pacific subspecies remains year round. But here, we observe the annual unfaithfulness of this beloved bird.
I must wait until March to hear their cry floating high on the wind telling me of their return to the nest by Caspar Cemetery. Then again, I will witness their "sky dance", an elaborate aerial display performed by males during courtship and early incubation. He carries a fish or nest material, utters his screeching call amid short, undulating flights, separated by periods of hovering that look to me as if he briefly climbs aerial stairs.
The male typically consumes one part of the fish before he delivers it to the female. They start at the head and work back to the tail. Most predators are lucky to have 20% of their attempts successful, but researchers report osprey dives-to-fish-captured rates from 24% to 74%. Clear, plant-free water, plentiful fish, and calm weather contribute to osprey successes.
These piscivorous birds are not without their own enemies. Great Horned Owls, Golden Eagles and raccoons have black marks on their reports and those Scottish birds that understandably abandon the wintry Highlands for the warmth of fishing along the Nile must beware of crocodiles as they bask in Tutankhamen's sun.
Fifty-five years ago, Scotland hosted no ospreys. Recolonization led to a population of 1600 breeding pairs in 2003. Success breeds success and now two areas of England support active nest sites.
Birds provide pointers to environmental changes. One indicator of global warming is the shorter migration of European ospreys. Some now stop in Spain and Portugal thus avoiding the crocodile's teeth. Recent technological developments have allowed for precise tracking of migratory birds, especially those large enough to carry GPS transmitters thousands of miles. As a result, researchers discovered that fledgling osprey remain in South America for eighteen months. On their return, they head for their natal grounds.
How do ospreys learn all these things? Their migratory instincts must be hard-wired and may be simple – head south. How does an adult osprey teach a fledgling to fish? I find no scientific conclusions on this subject, but there are scattered observations of an anecdotal nature. Parents gradually stop bringing food home but rest on a nearby perch eating and taunting the young. The fledgling stands at the nest, flapping its six-foot wingspan and jumping up and down with typical teenage angst. A gust of wind and it free falls into its first flight.
One Florida observer witnessed an adult dropping a fish over the sea and a youngster diving to retrieve it. A single observation does not support a complete explanation. Perhaps, ospreys learn by watching their parents. Judging by all the calls around the Caspar cemetery nest at fledging time, I think parents teach their young by example even if they do leave them to find their own way to Argentina.
True, when the ospreys depart, other birds migrate along the coast. David Jensen, president of MCAS, tells me his spirits rise with the advent of loons. Soon the magnificent Tundra Swans will coast onto the Stornetta Ranch. The seasons change and with them the birds and yet, part of me waits for March when I first hear that high mewing call that signals the return of the osprey. I shall look up and smile, my thoughts soaring with them again.