Thursday, March 24, 2016

Spring 2016: Will we have an early migration?

Excellent numbers of Fox Sparrows are now moving through habitats near the Lake Erie shoreline in northwestern Ohio. Photo / Kenn Kaufman.

Thursday, March 24: After an exceptionally mild winter in northwestern Ohio, we've had many questions about how the weather might affect the timing of migration in spring 2016. 

The short answer is that the mild season may alter the timing for a few species, but not for most. To understand the difference, it helps to think of migratory species in two categories, obligate migrants and facultative migrants. (These are really two ends of a spectrum, not two distinct categories, so these definitions are somewhat oversimplified.)

Most migratory birds, especially those going long distances, are obligate migrants. That is, the timing of their migration is instinctive and hard-wired. A Blackpoll Warbler that leaves Brazil in April to start moving north toward Canada is not responding to local weather anywhere; it is going on instinct. This is true for the vast majority of the warblers and other Neotropical migrants that create so much excitement in northwestern Ohio in late April and May. No matter how harsh or mild the winter might be in the U.S., it won't change the timing of their flights. At most, an extremely cold, late spring in the southern U.S. might delay the arrival of these birds in Ohio by a few days--that is, they might linger for a few extra days in the southern states if conditions are bad. But a warm, early spring in the south won't speed up their travel. 

Some short-distance travelers, especially those moving in early spring, are facultative migrants. Within general outlines of the season, they may move earlier or later, for greater or shorter distances, depending on what the weather is doing. This is true to some extent for many of the waterfowl in early spring. In a cold season, when northern waters may still be frozen solid, they may linger later at our latitudes. Sandhill Cranes are facultative migrants, and in recent years they have been moving later in fall and earlier in spring, and not going as far south for the winter as they formerly did. 

At this point in late March, the spring migration is well under way. In areas near Lake Erie, such as Magee Marsh Wildlife Area, Ottawa National Wildlife Refuge, and Maumee Bay State Park, recent days have produced good numbers of typical early migrants such as Wilson's Snipe, Eastern Phoebe, Tree Swallow, Winter Wren, Brown Creeper, Golden-crowned Kinglet, Fox Sparrow, and Rusty Blackbird. Eastern Towhees and Field Sparrows also have begun to appear (both species have been seen at the feeders at Black Swamp Bird Observatory). American Woodcocks have returned in force, and on calm evenings they can be heard performing their flight displays in damp meadows near woods. 

During the next week or so, we should continue to see more of the typical early birds. Pectoral Sandpiper, Greater and Lesser Yellowlegs, Hermit Thrush, American Pipit, Vesper Sparrow, Savannah Sparrow, and Purple Martin are among the species to watch for. Some of the short-distance migrants might arrive earlier than usual. But as for those colorful warblers, tanagers, orioles, and the like, coming from the tropics, we should expect those to appear at their usual times in April and May. 

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