If I were to make a list of the top 10 North American birds least likely to show up in Maine, a crested caracara would be on that list. Although it is a member of the falcon family, it has more in common with vultures. Its favorite food is carrion. It’s capable of taking live prey but prefers critters that already are deceased. Unlike other falcons, it is slow and is comfortable walking and hopping along the ground.

The crested caracara is such a tropical bird that it is the national bird of Mexico. Its nickname is the Mexican eagle. Its range extends into the southern United States, and I have seen it in Texas, Louisiana and Florida. It’s rare enough in Florida that it is listed as a threatened species. Fossil records indicate it colonized Florida shortly after the last Ice Age, when the Sunshine State was still a savannah dominated by oak trees.

The crested caracara prefers open country, preferably arid, though pastureland will suffice. Maine is nearly 90 percent forested, and our state is waterlogged. What is this bird doing here? Some birds get lost in migration, but the caracara doesn’t migrate. A strong storm might blow a caracara northward, but not this far north and there were no storms during the time of its arrival.

We may never know the answer. Sometimes, individual birds just wander. There is an account of an appearance in Ontario in 1892. In the last decade, several have turned up in New Jersey. More recently, sightings have occurred in Massachusetts and Nova Scotia. But the present caracara is the first known record in Maine.

During summer, most birds are exactly where they are supposed to be. In autumn, all bets are off. Storms can push migrants off course. Some birds are just prone to wandering. A few birds can even be genetically misdirected.

Most waterfowl learn migration routes from their parents, but the majority of songbirds have the directions to their wintering grounds hardwired into their DNA and follow the route by instinct. A genetic malfunction can give individual birds the wrong map, causing them to migrate in the opposite direction.

Wandering birds are called vagrants or accidentals. The phenomenon occurs more often in autumn because there is a large number of young birds making their first, inexperienced migration. In spring, some northbound birds overshoot their destinations. Out-of-range birds add spice to birding. There is always the chance of finding the unexpected.

Vagrancy is usually disastrous for the accidental wanderer. Away from its natural home, the chances of survival are slim. But vagrancy can be good for the species. Successful nomads colonize new habitat and expand the range of the species. It helps some species adapt to environmental changes. The northern cardinal, tufted titmouse and red-bellied woodpecker all have moved northward into Maine over the last half a century. Turkey vultures were a rarity when I was a wee lad.

The genetic imprint of migration routes shows up as weird historical anomalies in certain species. Several northern breeders follow a route to the tropics that originally was determined by the extent of glaciers during the last Ice Age. As the ice receded, these birds colonized new areas and those new migration routes are still genetically hardwired 10,000 years later. Swainson’s thrushes and blackpoll warblers, which breed over the western end of their ranges, fly east before heading south, along the edge of where the glaciers once were. Bohemian waxwings breed in western Canada. They, too, tend to wander along this eastward route during their nomadic search for food during the winter. Flocks of thousands descend into Maine during the colder months.

Research conducted in Maine demonstrated the genetic coding is so strong in shorebirds that they are imprinted on specific mudflats along our coast and have difficulty finding nearby mudflats if their historical sites have been compromised. As humans alter the landscape, shorebird numbers are plummeting. Of course, development is not the only reason for this. Climate change is affecting their breeding grounds far north of civilization. The resurrection of the peregrine falcon is also taking a toll.

None of this explains why a crested caracara has turned up in central Maine. Sometimes, they just roam. That’s fine with us. Birders like surprises.

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