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Thread subject: Broad-front Migration.
||09/10/05 12:40 pm
||Looks like this question is too difficult, or people aren't checking in much these days.
Here are a couple of answers......
1) to reduce competition. These are big birds and need lots of space, except of course at breeding, nesting time.
and secondly, IT IS ALL about FISH,
2 ) Ospreys need to make use of unexploited rich fishing waters.. Ospreys are dependent on a high degree of success at all places that they stop off during migration. It is suggested in my migration book that when there are too many ospreys fishing in the one spot that competition might well create a problem. It is felt that the ospreys gain much by spreading out on a Broad-front MIGRATION so as to be the lone osprey at a good fishing site.
There must be some genetic programing too in the genes for the young juvenile ospreys to instinctively do this, for what baby wants to break all ties with its family, which is just what young ospreys do. Interestingly, in Sweden, where there are over 2000 nesting pairs, the young disperse in every direction possible and often head north for a while before they instinctively go south though the Mediterranean, Malta, Morocco and across the Sahara to West Africa. Some even head east through Ukraine. Georgia, and regions of the River Volga. These birds generally end up around the Persian Gulf and the Southern Caspian seas.
With no adults to show then the way it is just unbelievable that the few that do survive do as well as they do..... This is really SURVIVAL of the fittest
How do they DO THAT...IT IS TRULY AMAZING. !
||09/10/05 02:59 pm
||I've read that migrant ospreys tend to avoid wintering in areas where nonmigrant populations breed -- maybe that's part of the reason why, because of the food competition.
I've also found it interesting that females often settle south of the migratory males. I guess it's because they are bigger and can probably fly farther south for the winter.
||09/10/05 03:23 pm
||I have read that male birds do not migrate as far south as females because they want to get back first in the spring and claim the best territory. I dont know if this applies to ospreys though.
||09/10/05 04:11 pm
||It probably does. That certainly makes sense. :-)
||09/10/05 04:35 pm
||Good thoughts everybody, interestingly though in the Birder's handbook, on who goes where on migration, I am sure I read that females possibly stay more north at times relative to their size, being bigger and sometimes the more dominant of the pair. That way they were better at coping with more inclement weather that persist farther north.
Ahhhhhh so much to read and to study. The debate rages on. I personally think since the female leaves so much earlier than her mate that she is likely to migrate farther south but who knows! Guess the juveniles have to head even father south as they are low in the pecking order, but again they may tire and stay just where the fishing is good!
||09/10/05 05:49 pm
||I think this is what I was remembering from the Raptor Research Foundaton:
MARK MARTELL and MATTHEW SOLENSKY, The Raptor Center at the University of Minnesota- 1999
Using satellite monitored radio telemetry, we determined the wintering areas of Ospreys (Pandion haliaetus) breeding on study areas in Oregon, Minnesota, New York, and New Jersey. We determined that Ospreys arrived on their wintering grounds between 30 August and 5 November. Females arrived slightly ahead of males, with New York and New Jersey birds arriving slightly before Ospreys from Minnesota or Oregon. Wintering sites were located in nine countries, from Mexico to Brazil. Midwest birds were the most widely distributed, being found in eight countries. West Coast birds were most restricted; 9 wintered in Mexico and 1 in El Salvador. Females tended to winter further south than males from the same region. Once on a wintering area birds remained until departing in spring for the nesting grounds. The time individuals spent on their wintering areas ranged from 138 ΓΆ€“ 193. Departure from the wintering areas occurred from the end of February to the beginning of April. Individuals returned to the same wintering areas in subsequent years.