Published Date Written by David EastmanThe broad-winged hawks' late September migration is spectacular and welcomed by hawk watchers. These social birds proceed southerly by spiraling up on thermals. Wonderfully cool nights we look forward to are followed by sunny fall days to create these thermals, which attract swirling groups of these chunky little hawks.
The column of warm, rising air is ridden until the hawks glide down to the next. This saves them energy. Birds of prey migrate by soaring high on these warm air currents, which are generated between mountain peaks and over high hills. They commonly use certain peaks and ridges which create this every year, and so if you attend a presentation on hawk migration, you will find that naturalists know where to place you for observing such movements. Your birdwatching group will probably array themselves on a well-known ridgetop and await the birds of prey gliding down in a straight line, until the hawks can pick up the next thermal (hopefully over your presence), then climb up and move a few miles away.
The broad-wings gather in groups, called "kettles" and these may string out in long lines between the thermals, but sometimes the flocks of thousands of these birds can even be too high to be seen by the naked eye. This particular little hawk soars to very great heights with widely extended, almost motionless wings. You will notice lots of telescopes and binoculars around on a hawk watching day, with eyes constantly looking to the north. Spectacular days usually occur around 15th of the month of September in New Hampshire. Here are notes written by Phil Brown in the ASNH newsletter last fall:
"The broad-winged hawk migration last year on September 17 and 18 will go down in NH's bird migration history as a record-setting event. Saturday's record count of 3,643 birds over Pack Monadnock, including a single-hour when 2,654 broad-wingeds circled high above in large 'kettles' (one of which contained 1,270 birds!), was only eclipsed the following day by its own tally of 5,208 birds on September 18. These numbers pushed Pack Monadnock Observatory's total raptor count over 11,000 by the end of the weekend – the highest number in the Observatory's seven-year history.
"On the same day, as the crowds were building for the hawk release event at Carter Hill, it was obvious that even Pack's daily raptor total was going to fall. By day's end, a dedicated team of volunteers tallied an observatory record for raptor migration in a single day with 7,300 birds, all but 88 of these broad-winged hawks. This compares to the 4,300+ total of all raptors seen here during the 2010 season! The numbers were truly staggering, and nobody had predicted such a huge push of broad-wingeds."
Not to be overlooked were record-high counts of migrating bald eagles (14) and ospreys (20) also moving over the Carter Hill Observatory on September 18th. A showing of "Flight of the Broad-winged" at the Red River Theater in Concord was an appropriately timed to wrap up the weekend, which must have been an enjoyable treat for the participants.
Phil pondered that there were several possible explanations for the huge numbers found that particular weekend. One is that the past summer's conditions of 2010 were obviously right for broad-winged's reproductive success and survival of its young. But, a great number of these small buteos, unfortunately, don't return to their breeding grounds because of high mortality rates during their first year, so we may not see such a large population the following season.
Another, more important factor for that great weekend's flight may simply be more related to luck. Because of weather patterns including favorable winds that concentrated birds, sky conditions--just enough cloud cover, not too blue a sky, so that hawks would be hard to detect by their human watchers-- created a 'perfect storm' of conditions for this flight. Thus, a larger percentage of the species' population (which is estimated at over one million worldwide) was observed in that particular New Hampshire airspace.
The Hawk Migration Association of North America (HMANA), which houses migration data from both Pack Monadnock and Carter Hill Observatories, is a partnering with the Raptor Population Index Project (RPI) to determine raptor trends across the continent. For more information, you might visit the RPI website at www.rpi-project.org.
After some research, it appears that the numbers tallied from Carter Hill on that Sunday fall just short of the single-day NH record of 7,688 Broad-wings seen from Blue Job Mountain in Farmington on Sept 19, 1999. But still, not a bad weekend to share with an estimated 1,000 plus visitors between both observatories.
After concluding their long southern flight of 4,000 miles, the broad-winged hawk winters from southern Mexico southward to Central and South America and into the Caribbean, but some do winter in southern Florida.