Sept. 14 was the best hawk watch day in Acadia National Park so far this year.

Who could have seen that coming? Everybody.

Most hawks migrate in autumn, and they know what days are best for travel. So do you. Starting in mid-September, when a forecast calls for a day to start with a northwest breeze, expect a good flight. That’s a hawk-friendly tailwind.

Hawks will migrate under various conditions, but they get stymied by obstacles such as Frenchman’s Bay. Since they can’t stop and rest over water, they’re reluctant to cross without a beneficial breeze. Cape May, New Jersey, is one of the most famous hawk watch sites in America because raptors get bottlenecked upon reaching Delaware Bay. Epic flights occur when conditions turn favorable.

The weather through the first two weeks of September was lousy, not hawk-friendly at all. Certainly, the hawks were paying as much attention as I was. The forecast suggested Monday, Sept. 13 would be good and Tuesday, Sept. 14 would be better. So, I went up both days, and joined the throng of spotters, counters, rangers and curious visitors atop Cadillac Mountain for the two best days of the year so far. On that Monday, 165 hawks passed the summit. The next day, 492 hawks astonished the counters.

Visitors were surprised to find that spotters could identify specific hawk species 5 miles away.  How were they doing it?

Put away the guidebook. It’s not going to help much. When you open a field guide, you see pictures of every hawk, as if each was equally likely. They’re not. A few hawks are much more common than all the others, depending on the location of the hawk watch. As of last Friday, 324 broad-winged hawks had passed Cadillac, but not a single red-shouldered hawk. There were 272 sharp-shinned hawks tallied, but only six Cooper’s hawks and two northern goshawks.  

Just a handful of species are likely, and it’s not that hard to tell them apart, even at a great distance. That’s because they act differently. In short, you are what you eat. Most Maine raptors fall into three families, and each family has a particular flying pattern depending on its favorite prey.

Falcons are the smallest. On the East Coast, we see American kestrels, merlins and peregrine falcons. They chase down birds and insects in midair. Thus, they are streamlined like fighter jets, with short tails and pointed wings. They are very agile in the open skies, able to change direction at high speeds. Kestrels can snatch a dragonfly in mid-flight. That gives them a rather floppy flight-style, rising and falling, twisting and turning quickly. Larger falcons fly faster and more powerfully.

Accipiters are the next size up. These include sharp-shinned hawks, Cooper’s hawks and northern goshawks. Accipiters are stealth hunters, flashing in for the kill before the victim sees them coming. They have short wings and long tails, giving them quick acceleration and good maneuverability through forest. Thus, their flight styles in migration are more direct than the falcons, often in a flap-flap-glide rhythm. They soar and circle in the sky more readily than falcons, but less than buteos.

Buteos are larger. These include broad-winged hawks, red-shouldered hawks and red-tailed hawks. They are slower-flapping raptors, with wide wings and spread tails. They soar and circle easily, and often sit on perches, scanning for prey upon which to pounce. In migration, they can glide long distances without a wingbeat. Even from 5 miles away, it’s obvious.

Lastly, there are the big raptors — eagles, vultures and ospreys. From 5 miles away, they appear as the biggest specks on the horizon. Each one holds its wings differently.

An eagle flies with its wings straight out, as if a board was laid across its back. Vultures have a deep V-wing shape, flap reluctantly and teeter a lot. Ospreys have an inverted gull-wing shape. Their wings point up at the shoulders, but down at the tips. They’re also bright white on the belly, obvious at a distance. All these guys are easy to identify.

The Cadillac Mountain hawk watch is Maine’s oldest, now in its 27th year. Schoodic Institute has coordinated the event for the last decade. Anyone can pop in without notice, and join the fun between 9 a.m. and 2 p.m. However, reservations are required to drive to the summit of Cadillac through Oct. 19.

So watch the weather, and plan ahead. Consult recreation.gov.

Bob Duchesne, Good Birding

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.