Migration

Probably the best-known and perhaps most fascinating bird instinct is migration. “Somehow” each bird knows when it is time to fly south (or back north). The birds know which pathways to travel and what their destinations should be. The “somehow” is explained in an incredibly wise God who taught each bird what to do. “Even the stork in the sky knows her seasons; and the turtledove and the swift and the thrush observe the time of their migration” (Jeremiah 8:7). “Is it by your understanding that the hawk soars, stretching his wings toward the south?” (Job 39:26).

The vast majority of birds migrate twice each year, in the spring and again in the fall. For many, that means going from Canada or the U.S. to Central or South America. For some birds, the shift is less dramatic, and they may move from far-northern Canada to southern Canada, or from the northern U.S. to the southern U.S. Some cold-loving birds move back and forth between the northern and southern arctic zones. In general, most birds do not want to winter in frigid areas. (Can you blame them?)

This means, at least where I live in Pennsylvania, that winter is not the most active time for birding. There just aren’t that many year-round residents. For Lebanon County, of the 304 (last time I checked) bird species ever reported on eBird, only 43 have been reported or would be likely to see in all twelve months. These year-round birds include Canada geese, mallards, doves, vultures, bald eagles, a few hawks, most woodpeckers, corvids, starlings, bluebirds, robins, titmice, chickadees, nuthatches, finches, some sparrows, and cardinals. Of course, there are additional birds that are here only during the winter. (I actually love winter birding, because it is so quiet and peaceful, as well as invigorating and refreshing.) 

Spring, however, is the most exciting time for many birders, for two reasons. First, after the drabness and dearth of winter, birds are returning for the summer, and birders watch for their feathered friends to come back in a predictable pattern. The early mornings become alive with bird songs. Second, migrating birds pass through on their way to points further north, often Canada, and a few weeks or months in spring provide the brief opportunity to see them. As a bonus, most spring-migrating birds are in breeding plumage.

There is a consistent schedule for migration, and this pattern guides birders in what to look for and which habitats to frequent. (The below observations are based on south-central Pennsylvania.) Winter birding often focuses on waterfowl. The migration of ducks, geese, swans, and allies varies some, because these birds are dependent on open water. Some years the ice melts early, and other years it stubbornly lingers. As a general rule, waterfowl migration starts early in February and peaks in mid-February to mid-March. It really tapers off through the month of April.

Raptors start migrating in March, and various species take their turns through at least late-April, before winding down by mid-May. (More about this next time.)

Shorebird migration is an extended season. Early shorebirds can start arriving in March. April becomes busier, and May is prime. Some migration can even continue into June.

Some birders really love raptors, and others work hard to become proficient at tricky shorebirds, but the overall favorite group of birds tends to be songbirds (passerines). It’s tough to see returning songbirds before April, but in March some of the bravest species start trickling in. Many people consider the arrival of robins to be the first sign of spring (more about that in a minute), but probably the true harbingers of spring are brown-headed cowbirds, common grackles, tree swallows, and eastern phoebes.

The beginning of May introduces prime time for songbirds, and it features that exciting time known as warbler season. Some warblers nest in the area, but for others there is a two- to three-week window in which to spot them on their way through. Yellow-rumped warblers can winter over, but the first migrating warblers are palm and pine warblers, which could start sneaking in mid-March. Black-throated green warblers are next, possibly starting at the beginning of April, and each week introduces new arrivals, ending with Cape May warblers in mid- to late-May. While this sounds like nearly a two-month warbler season, there is a difference between when the first few appear and when the main crowd arrives. For almost every warbler, the peak time frame falls within the first three weeks of May.

By the end of May, pretty much every bird that is coming back or passing through has done so. If someone wants to go birding only one week of the entire year and wants to choose the most exciting time with the highest potential number of species, the second week of May is the time to go. This year’s “biggest week in American birding” was celebrated May 8-17, with “Big Day” on May 9. There is also a fall “Big Day” to coincide with fall migration. This year it was October 10.

Fall migration is kind of like saying goodbye. Summer residents return to their winter homes. Generally, those that arrive earliest in the spring are the last to leave, and the birds gradually disappear. Sometimes you notice them gathering in preparation for mass migration (tree swallows, chimney swifts). Often, though, one day you find yourself thinking, “I haven’t seen a __ in a while. I guess they’re gone until next spring.” Birds seen only during migration also pass through, usually in reverse order of when they came. Fall birds for almost all species are more challenging to identify; they are in non-breeding plumage, and less-marked immature birds are mixed in – hence, one of the great challenges of birding – “confusing fall warblers.”

Some species are partial migrators: robins, goldfinches, blue jays, and Canada geese, to name some of the more common examples. For these birds, some will migrate and some will overwinter. Robins generally hide out in the woods, and a careful observer can find them all year; in winter, they are more likely to be in the treetops than on the ground. Goldfinches lose their bright coats, but many of these drab birds frequent feeders all winter. Large groups of blue jays are on the move in October, and honking V’s of Canada geese take off each morning, but some remain for the winter. At least for some of these species, or so the theory goes, the local winter population may not be the same individuals as the local summer population. It is possible that the entire group of Canada geese, for example, shifts southward, and Pennsylvania might become the northern edge of the range instead of somewhere in the middle.

I tend to be a pretty local birder, but avid birders often travel to other locations for migration. That’s because there are invisible pathways in the sky. Certain routes are most advantageous for birds. Flying long distances over water is draining, and some birds are visual flyers, relying on landmarks like mountain ridges and lakes. Migrating birds also need places to rest and feed. They will divert to avoid weather events, and of course, the shortest distance between two points is a straight line. There are four major migration routes in the U.S., and these determine the hotspots for birders, but there will always be a smaller number of birds that don’t strictly follow those routes.

The Atlantic Flyway (shorebirds, waterfowl, warblers) and the Pacific Flyway (shorebirds, raptors, Western songbirds) follow the coastlines. In the interior of the U.S., there is the Mississippi Flyway, which gets the lion’s share; some people call it a superhighway. Closer to the Rocky Mountains is the Central Flyway (cranes and waterfowl). Warbler-manic birders go to Ohio (specifically, Magee Marsh) or to Cape May, NJ. I prefer quiet and peaceful over commotion and crowds, so I don’t feel a burning urge to go to the “best” places. There is enough of God’s beauty and wonder to satisfy me in quieter spots.

Migration, on the one hand, is a complex ecological picture, with many interwoven factors. On the other hand, it is quite precise and individualized, with each species having unique plans designed by God. Each species knows when to go, which path to take, and where its destination is.

Scripture taken from the NEW AMERICAN STANDARD BIBLE ®, Copyright © 1960, 1962, 1963, 1968, 1971, 1972, 1973, 1975, 1977, 1995 by The Lockman Foundation. Used by permission.