Wednesday, April 02, 2008

Return of the Osprey

We first heard and then saw osprey March 27th, two days earlier than last year. Their distinctive and frequent high-pitched calls make them impossible to miss.

This species is recovering from low populations earlier in the 1970s and 80s. We did not observe them until 1991. In the subsequent year there were three - the parents and their single offspring who sometimes followed them and sometimes not.

These birds mate for life, and the father does all the hunting while nesting is underway.

Trees are the favored perches for osprey. They will wait for a likely meal to surface and then dive feet-first into the water very rapidly. Sometimes they hover like a kestrel waiting for the fish to surface. Once a fish is caught, they carry it in the most aerodynamic way possible - face first. Rarely if hungry they will catch small animals but well over 99% of their diet is fish.

Trees are also needed for nesting sites - and only large trees will do. They have been known to use cliffs and various man-made structures for nesting sites. As suitable sites can be rare with the lack of old forests, nesting platforms can be made that they find very useful! Some studies have found that these purpose-built designs actually increase the number of hatchlings, as they are more stable and require less nest building by the birds.

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