Tuesday, December 2, 2008

Migration Revealed!!!

Since this past summer when myself and our volunteers banded almost 80% of the young (357 out of 454) that were produced we have gotten several recoveries of those bands. When a band is recovered, it is found on either a live or dead bird. So far we have had 5 bands recovered from this year's fledglings. Most of the time the bird is found found dead. In this case the bird was found dead and the USGS Bird Banding Lab was notified by the finder calling the phone # that was on the band (1-800-327-BAND).

This bird originated from a nest on a channel marker in West Wildwood and was banded by one of our volunteer banders, Hans Toft. Amazingly enough, this juvenile actually lost it's mom due to being entangled by monofilament. The adult was found dangling from the nest and had its legs bound by the line. Luckily a bulkheading crew that was passing by cut the bird free and got it to us so we could transport to our rehabilitator, Don Bonica of Toms River Avian Care. Tragically the adult did not survive, but we do know that the adult male was successful with raising its two young to fledge, and one of those young survived enough to make it to it's wintering area in South America.

The bird and band was recovered on 10/28 and was found near Tolima, Colombia in the town of Ibague. This recovery shows that this juvenile osprey traveled around 2,300 miles to its wintering area. Ospreys normally spend the next breeding season in that area then return to NJ the following year. So young that were produced this year will most likely return to NJ in late March, 2010.
However, not many young survive during the first year of life. A young osprey faces many difficult challenges and the mortality rate for most birds of prey including ospreys is around 80%. So of the 454 fledglings from NJ, only 91 may survive to return to breed in NJ in 2010. Not a very optimistic statistic.

While in their wintering areas ospreys face many perils that they do not see here in the U.S. In South America, many countries still have not banded DDT (however it isn't used as heavily as it was here in the 1960's) and other harmful chemicals which eventually runoff and make their way into the water table (where ospreys find food). Also, in many areas in the Southern Hemisphere there are large fish farms. These fish farms are bound to attract the attention of young ospreys and when they do, the farmers probably do not hesitate to shoot them! Other major causes of death are impacts with many man-made structures including buildings, power poles, and radio guide wires. Electrocution is another cause of death when an unsuspecting bird perches on a power pole.

I'll post more maps of where we have had other recoveries from this years young soon. If you'd like to see more detailed accounts of other fledglings from Delaware and Massachusetts, click here for a link to a satellite tracking project with UNCC.


Greg M said...

Very interesting stuff. I have a question, if there weren't the man-made perils that made life so difficult for birds of prey, what would a more realistic mortality rate be? I would guess it would still be fairly high, considering Natural Selection and all, but nowhere near 80%.

Ben said...

I'm not sure what the exact mortality rate would be, but yeah nowhere near 80%. Most causes of mortality are natural. Like the ability or inability to catch prey or the instinct to fly the right direction during migration....
With human interaction we can also help raise the odds of survival. Read one of my first posts about human intervention.

Anonymous said...

i would like to know what month ospreys leave Long Island to begin their migration.

Ben said...

Juvenile ospreys locally disperse before they leave for migration to their wintering areas. But usually migration begins in September along the East Coast and continues into October.