Tuesday, March 2, 2010

Happening Now: Spring Migration!

An adult Osprey carries its catch. Photo by Steve Byland.

In early March adult ospreys are beginning their migration to their summer breeding grounds. In the Mid-Atlantic region past band recovery data has shown that 66% of banded nestlings (older than 3 years) returned to their breeding grounds in March as compared to 91% in April (Poole & Agler 1987). Osprey nestlings that were banded last year will remain on their breeding grounds until next summer. This year ospreys that were banded in 2008 will return to the the areas where they originated. In New Jersey, 448 young were produced in 2008. We can expect that less than half will have survived to return to breed in New Jersey. Studies have shown that osprey young that hatched earlier in the breeding season have a better chance of returning to breed. Early hatching dates had a 10.5% recovery rate (306 banded v. 32 recovered on breeding grounds) while late hatching dates had a 3.5% recovery rate (200 banded v. 7 recovered on breeding grounds)(Poole 1989). Not very good statistics, but these numbers are expected for most predators, especially birds of prey.

Osprey pair at a nest site in New Jersey. Photo by Ken Connelly.

Young adults (two year old ospreys) migrate slower than older individuals. Most do not breed their first season back where they originated. So, they can migrate more slowly or leave late in the breeding season. This first year many young adults return and "house-keep" or build nests but don't reproduce. This may help them establish pair bonds that will be strengthened the following year.
Ospreys follow the same migration routes as they do in fall. Ospreys are generally known to follow direct routes and travel in stages. From Northern South America (where large numbers of ospreys overwinter) many will fly north in Hispaniola and Cuba to the Florida panhandle north along the coast until they reach their breeding grounds.

Poole, A.F. 1989. OSPREYS: A natural and unnatural history. Cambridge University Press. New York, NY. Pg. 63. 
Poole, A.F. & Agler B. 1987. Recoveries of Osprey banded in the United States, 1914 - 1984. Journal of Wildlife Management, 51, 148-55.

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