Eyes watching skies Sept. 17, when Mass Audubon Hawk Watch returns to Wachusett Mountain – Worcester Telegram

PRINCETON — Looking up and seeing a hawk’s distinctive shape against the sky will elicit an instinctive pause, maybe a smile. Except for mating, raptors are well known to be solitary and as a rule, these birds of a feather do not flock together.
That all changes for two weeks in September. Between Sept. 12-24, thousands of raptors will be traveling through the state past Wachusett Mountain, a hawk highway as they fly south for the winter, congregating in numbers not seen at any other time of the year. 
More:Great migration is happening now — here are some tips to see the birds fly south
That two-week period is traditionally when the weather conditions are just right to create the thermals, rising currents of warm air, that the hawks ride in order to conserve energy, said Paul Roberts, founder of the Eastern Massachusetts Hawk Watch (EMHW). 
“When you get those conditions, you have the perfect weather to migrate,” Roberts said. “They use everything nature gives them, they rely on that good weather, for that there is only the month of September.”
The typically clearer skies combined with cooler temperatures allows the sun to warm the air, causing it to rise and creating the thermals. 
In a collaboration between Broad Meadow Brook and Wachusett Meadow, Mass Audubon will conduct a Hawk Watch event, 10-11:30 a.m. Sept. 17 at Wachusett Mountain State Reservation, 345 Mountain Road, Princeton.
Tickets can be purchased on the Mass Audubon website.
“It’s an amazing natural phenomenon,” said Martha Gach, conservation coordinator at Broad Meadow Brook, and who will be leading the event. In the winter, she said, food is too scarce to support the full raptor population, prompting the mass exodus. 
It’s possible to see as many as a dozen species in one day, Roberts said. The majority of the birds are following a southwestern route that takes them from the New Hampshire coast through Massachusetts to New Jersey and Pennsylvania then Texas, Roberts said, even if not all species are making the full trip. 
According to Roberts, “the star of September in Massachusetts is the broad-winged hawk,” which is the most abundant diurnal raptor and travels the longest distance in the largest groups.
A medium-sized hawk common to Massachusetts, the broad-wing hunts small mammals, amphibians, reptiles and birds, its name coming from its in-flight profile. Not typically being a long-distance flier, the thermals during September are particularly vital for this species. 
“It’s possible to go out on a good day and see a thousand,” he said, with one of the largest numbers recorded by the EMHW being 20,000 in a day. “Sometimes 85% of all the broad-wing hawks we see in a fall season may pass in one day,” he said.
One year at Wachusett, Roberts said he saw over 10,000 broad-wings within three hours.
Founded in 1976, the EMHW is an all-volunteer organization whose stated goal is to “promote the study, conservation and preservation of hawks locally and on a continental scale by monitoring migration in Massachusetts,” Roberts said.
The group gathers data for further research of the local raptor species by observing the migrations starting in August.
“We try to cover as much as we can until November,” Roberts said. During those two weeks in September, different groups set up at various points throughout the region, including Wachusett Mountain. 
Roberts will be teaching an online class, “Identifying Hawks In-Flight,” 7-8:30 p.m. Sept. 8, with registration also available on the Mass Audubon website
Mass Audubon’s Hawk Watch is not affiliated with the EMHW’s data collection, said Gach, instead running “programs to inspire people to pay attention to this amazing natural phenomenon that happens on a regular basis — just a really amazing opportunity to get connected to nature and these things that are bigger than we are.” 
Gach has been conducting the program for 10 years. She said one of her favorite things is seeing the interaction between different species of raptors brought into contact by the migration.
“Birds will literally dog fight in the air,” Gach said, “interactions between two very different kinds of birds that you would never see together normally.”
The exact reasons for this are not always clear. Predation between species likely plays a part, especially with the presence of apex predators such as the red-tailed hawk and even bald eagle, but is most often attributed to a large number of usually solitary animals being in close proximity.
“They just kind of get into it,” she said, “they don’t share space very well.”
Despite almost 50 years of hawk watching, as with many things, Roberts will never forget his first. When hiking at Mount Tom in Holyoke, Roberts and his wife witnessed a flight of over 1,000 broad-wings.
“I had never seen anything like that before in my life,” he said. “(It was) a life-changing experience.” 
Everyone present was silent as the birds flew overhead, Roberts said, before breaking into spontaneous applause. From that point on, Roberts, already an avid birder, said he fell under the hawk’s spell.
“To me it’s one of the most spectacular things people can see,” he said.