For the Birds Radio Program: Migration
Today Laura Erickson talks about the hows and whys of fall migration. 3:44
Migrants are coursing through the northland, and birdwatchers are joining in the annual ritual of watching them. Like waxwings, some birders are easily found in sociable flocks, eating and talking as they bird–you can find gaggles of these gawkers gathering at Hawk Ridge in Duluth. Less sociable birders are drawn to sewage ponds and other shorebird spots like hawks drawn to the same thermals. But many people watch the fall migration pageant in their own backyards, or even from the comfort of their dining room or kitchen, looking out the window.
The best days for backyard birding during migration tend to be drizzly or foggy, when birds are laying low. Migrant warblers passing through a neighborhood may feel lost or lonely when they’re by themselves, strangers in a strange land, so they quickly search out a chickadee flock to join. Warblers don’t eat bird seed, but whenever chickadees appear at a feeder, check out the trees just in case some warblers are tagging along. Flycatchers, vireos, tanagers, and other birds sometimes join these groups–that’s how I’ve built up my yard list over time.
Birds migrate not directly because of the coming cold weather–after all, every bird comes equipped with a built-in down jacket. What they need to avoid isn’t cold but hunger. Cold-blooded prey animals die or hide out when the temperature dips to freezing. Aquatic animals and plants aren’t accessible once ice covers lakes and rivers. And mice and many kinds of seeds become hidden and often inaccessible beneath deep winter snows. So birds that depend on any of these food sources must go south for the duration.
For some species, migration is no big deal. Swallows, hummingbirds, and Sharp-shinned Hawks spend their days in flight no matter whether they’re traveling or staying in one area–the Barn Swallow flies about 600 miles per day just weaving around catching bugs. But some birds expend an enormous amount of energy migrating compared to living their normal day-to-day lives. Some of these birds put on huge amounts of fat before they can leave at all. The huge numbers of robins that died from DDT poisoning during the 1950s and early 60s succumbed during migration–the pesticide accumulated in fatty tissue, where it could do little damage until the birds burned up all that fat during serious flying. When they haven’t ingested poisons, birds have no trouble metabolizing huge amounts of fat. Most long-distance migrants have longer wings than close relatives that go shorter distances, perhaps in part to accommodate the higher weight load when they’re fattened up.
But for some species, that extra weight makes long distance flying difficult or even prohibitive. Some warblers leave the north woods still pretty lean, trusting that their metabolic needs will be met with food they find along the way until they reach the Gulf of Mexico, where they apparently gorge themselves on Cajun or Tex-Mex food before striking out over water.
There are so many aspects to migration that watching birds is a rich way to spend the fall. Within a few weeks, most of our abundant birdlife will be gone until spring. Enjoy them while you can.