Monday, September 15, 2008

Fall migration kicks in...

You can't fault nature.

We've been counting raptors for almost a month now, and the numbers have been really, really low. I've been promising everyone that the peak of raptor migration, will be within a day or two of the equinox, because that's how it always goes, but I was getting worried.

We weren't seeing enough birds. In particular, the accipiters (the Cooper's Hawk and Sharp-shinned Hawk), which form the bulk of the equinox peak, were nowhere to be seen. The counts consisted mainly of the Turkey Vultures and Red-tailed Hawks which are ubiquitous around Hawk Hill. Had something gone wrong? Had this summer's forest fires disrupted the breeding season and delayed the migration?

Look at the accipiter numbers for last week:
  • Sun 8: 2 sharpies, no coops
  • Mon 9: no birds (fog)
  • Tue 10: no sharpies, 1 coop
  • Wed 12: 1 sharpie, 1 coop
  • Thu 11: 8 sharpies, 3 coops
  • Fri 12: 5 sharpies, 3 coops
Then came my day on the hill, Saturday. It was a slow start, foggy at first, and overcast for most of the day, but the birds started coming. We had 40 sharpies, 8 coops. We also got a juvenile Golden Eagle (at 10.30am even -- conventional wisdom has it that eagles are late risers, like the thermals they soar upon), and a couple of Broad-winged Hawks. (According to the books, you won't see a broadie west of Kansas, but the Marin Headlands are very effective at channeling the few we do have into a narrow stream.)
  • Sat 13: 40 sharpies, 8 coops
And in the last couple of days, the trend has accelerated:
  • Sun 14: 111 sharpies, 29 coops
  • Mon 15: 133 sharpies, 44 coops
Yes folks, it looks like we have a fall migration after all. As sure as clockwork, the changing day-length is telling those birds to head south. Check the counts over the next week or two, you should see the spectacle continue.

(Note that all statistics quoted are copyright of the GGRO and may not be reproduced without permission.)

1 comment:

Julian Hyde said...

Follow up... Yesterday was the equinox, and it was a MASSIVE day, particularly for accipiters.

Day Total Hawks: 694
Hours Counted: 6.00
Hawks/Hour: 115.67
Species Count: 14

271 sharpies!
109 coops!
10 broadies!

And to top it off, a ferruge and a couple of golden eagles.

Just goes to show, the birds know what day of the year it is, and all you need is some good weather.