A southerly flow of air created hot, muggy weather conditions in August. Fog enveloped the coast. Humidity prevailed everywhere. It’s normal for songbirds to begin leaving Maine as early as mid-August. Not this year. They bided their time until the weather changed.

Relief arrived on the last night of August. Northerly breezes greeted the dawn and southbound migrants streamed over Maine. Most of this activity was invisible, but there is a location in Yarmouth where birders can watch the movement. Nocturnal migrants can get caught offshore, settling on islands until they get reoriented. At daybreak, they cross back to the mainland. Sandy Point on Cousins Island is such a place. Local birders know the point will be bustling with songbirds on mornings after a clear night of northerly breezes.

Usually you’ll find Derek Lovitch standing there. Lovitch is a professional birding guide and owns Freeport Wild Bird Supply. On the morning of Sept. 1, he tallied 486 songbirds trying to cross the channel. Nearly 40 percent of them were American redstarts. Derek counted 73 northern parulas making the attempt. A third of the birds were too distant to identify, but he recognized 22 different species that morning.

Songbirds typically migrate at night, relying on the stars to guide them, the chilly air to cool them and the darkness to protect them. On a clear night with a light breeze from the north, you can actually hear them pass over. Many can be identified by their distinct flight calls — an expertise that far exceeds my skill level.

Waterfowl migrate in daylight, when they can follow rivers and recognize landmarks. They have less to fear from predation. Canada geese are famous for their “V” formations. This allows members of the flock to see each other easily, and each bird flies just outside the turbulence created by the wing flaps of the bird in front of it. Double-crested cormorants follow the same strategy, and many large flocks are milling about the skies right now, preparing to head south.

Hawks are streaming southward. Mid-September is prime time for most migrant raptors, but the movement persists into October. The hawk watch atop Cadillac Mountain in Acadia is the best-known local viewing spot. Rangers and volunteers scan the horizon for incoming birds and explain the identifying field marks as they pass.

All raptor species take advantage of the Cadillac updrafts, but some do it more than others. In the first five days of this month, 300 sharp-shinned hawks passed the summit. More than 100 American kestrels rode the winds past the peak. Larger, slower raptors favor these updrafts, and the early trickle of vultures, ospreys and harriers is growing into a torrent. Some broad-winged hawks also pass the summit, but most prefer a route over our inland mountain ranges. A few merlins and peregrine falcons occasionally pass by the Acadia hawk watch, but these raptors generally follow a seashore route, preying on shorebirds as they go.

Birds are smart enough to avoid migrating against a headwind if they can avoid it. Soaring hawks can overcome unfavorable conditions merely by riding a southerly breeze high into the sky and then gliding to the next peak. On such occasions, they quickly circle too high to watch. Birders know the best time to watch hawks is right after a cold front has passed. A northwest breeze the following morning sends the hawks streaming low past the summit, giving close views.

Want proof? On Sept. 1, a favorable northwesterly breeze wafted over Cadillac. Hawk watchers tallied 237 hawks by mid-afternoon. A muggy wind from the south prevailed Sept. 2. Only two hawks passed the peak that day.

Whenever weather discourages migration, birds settle down for the day and forage. They take advantage of the opportunity to refuel while awaiting better conditions. Songbirds feed on bugs; raptors feed on songbirds. Songbirds cope by grouping together into mixed-species foraging flocks, seeking safety in numbers. More eyes mean more vigilance whenever a sharp-shinned hawk sneaks in for the kill. Mixed flocks make for fun fall birding, because several species may occupy the same grove.

We’ll have a continuing flow of fun throughout September. Even after our birds depart, Canadian birds will fill the void, falling out here at daybreak. Maine is a migratory speed bump. Birds from Newfoundland to Nova Scotia flow down the coast of Atlantic Canada until they have no choice but to cross the Gulf of Maine. We’re right here waiting for them.

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.