As autumn approaches, many bird species that breed in the northern United States and Canada begin their yearly journey south. White Memorial is contributing to the Hawk Migration Association of North America's yearly hawk count. Our hawk counting station is located near the observatory (a green, shed-sized building) on Sawmill Field. Volunteers who are interested in taking part are encouraged. Data sheets and raptor silhouette ID sheets are located hanging from a nail inside the cellar door on the side of the museum. If you choose to be a part of our hawk count, please bring binoculars, watch from near the observatory, and return the sheets to the cellar when you are finished. To see our data, check out our site data on hawkcount.org.
How hawks migrate
When migrating, birds of prey rely on thermals, or columns of rising hot air. They circle upwards, using the thermal for lift to save energy. Once they reach their desired elevation, they leave the thermal and soar southward, gradually losing elevation until they reach another thermal. Many raptors wait until the wind is coming from the north so that it pushes them south. Ideal days for migration are sunny and clear, with wind blowing from the north or northeast. On ideal days like that, spots where thermals form can get very busy, with many hawks circling upwards in the same thermal. This occurrence is called a kettle of hawks. Identifying and counting hawks in a kettle can be difficult, and it is recommended that individuals are only counted as they leave the kettle.
|A kettle of hawks, mostly broad-wings, from HMANA.org|
Many hawk species have experienced a steep drop in population since the advent of the pesticide DDT in the 1940s. DDT worked its way up the food chain through insectivorous birds and mammals, and fish when the chemical leached into streams. Since all of their prey species were full of DDT, the toxin bioaccumulated in the bodies of raptors. This caused them to lay eggs with shells so thin that the weight of the parent birds warming them would cause them to crumble before chicks could fully develop. Since DDT was banned in the 1970s, many species have made incredible comebacks, while others are still in trouble because of other factors like habitat loss. By keeping track of the number of raptors that pass through during migration every year, HMANA will notice fluctuations in the populations and be able to respond if need be.
Notable sightings so far this year
- Several crows attacked a Cooper's hawk as it tried to enter the thermal. Rather than making a speedy getaway as hawks usually do, this one fought back, showing off its incredible accipiter agility, dodging and diving at the crows.
- A pair of adult bald eagles kettled together
- A juvenile golden eagle entering the thermal shortly after a juvenile bald eagle made a mock attack at the bald eagle while passing it.