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August 23, 2011: Migration Underway

August 23, 2011: Migration Underway

Credit: Bob Sallinger

by Bob Sallinger

kgw.com

Posted on August 23, 2011 at 6:05 AM

Updated Wednesday, Oct 30 at 4:04 AM

I went looking for the raptor cam red-tails on Sunday afternoon and failed to find them for the first time this season. They may well have been around and I just missed them. However they may also have  moved away from the nest site. The young are no longer dependent on the parents and there is no reason for any of them to stick close tot the nest any longer.

Even as Portland experiences its first 90 degree days of summer, migration is already underway. Some early migrants such as osprey which nest all along our river ways are already beginning to leave for wintering grounds in Central America. Shorebirds are also already on their way south from breeding grounds in the sub-Arctic. In September migration will rally heat---it is a great time to keep your eyes open for birds. Migrating hawks will be easily visible perched on telephone and power poles along our highways. High spots such as Mt Tabor and Powell Butte are great places to see migrating songbirds. The Chapman School in NW Portland plays host to one of the most amazing migration spectacles you can see every year in September. Each  night tens of thousands of Vaux swifts roost (spend the night)  in the Chapman School chimney before resuming their flight southward. Historically they used hollowed out old growth trees for these roosts, but as old growth has disappeared they have substituted chimneys.As noted in the prior email, many of our local breeding red-tails do not migrate. The climate is mild enough that some choose to simply pass the winter in the local area.

Vaux Swifts at Chapman School by Dick Forbes

People watching swifts at Chapman School by Bob Sallinger

The first year of life is very tough for birds and many birds do not survive the challenges of their first migration and winter. Studies put red-tail mortality during the first year of life between 62%-73%. mortality rates for many other bird of prey species are similar. Regardless of whether our young red-tails from the raptor cam nest migrate or not, they will be roaming about through unfamiliar territories and fending entirely for themselves as the weather turns cold and rainy. If they make it through this first winter, mortality rates begin to drop substantially. Brown and Amadon have placed second year mortality rates at 40.9% (meaning that 40.9% of red-tails who survive their first year will suffer mortality on their second year, third year rates at 36.3%, fourth year at 34.5% and fifth year at 13.0%. Even so, you can see that it is a hard road that these birds have to travel!

 

 

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