Expert Lanny Chambers ' Spring 2010 Migration Hypothesis

I assume that migration timing is an individual matter that varies on a bell curve, like many other inherited traits. A small number of males head north very early, and if successful may have an advantage in securing the best territories. In most years, the earliest migrants are at significant risk of mortality from starvation or exposure, but a few survive and pass the trait to another generation.

For a few consecutive days in early April, temperatures were above normal and the wind blew strongly from the south, across the whole midwest. For a few consecutive days in early April, temperatures were above normal and the wind blew strongly from the south, across the whole Midwest.

There was no stormy weather anywhere along the route, and a window opened for hundreds of miles of rapid travel. I think this favored the earliest male migrants, and resulted in record early FOY (first-of-year) dates as far north as southern Ontario. However, these birds were very thinly distributed, and few people saw them due to the small numbers.

Then the window closed: the weather changed, the typical pattern of cold fronts resumed, and north winds put the migration on hold for the vast bulk of birds, long enough to delay their progress for a couple of weeks. There's some evidence that the females have now caught up to the delayed males.

It's not reflected on my maps due to limited space, but I receive a steady stream of reports, even when the leading edge of the migration is not advancing. I used to consider such reports redundant, but now I realize that was shortsighted, and I'm glad to have the additional data. People from Texas to North Carolina were sending lots of first-bird reports in early April, and I can still see the fat part of the bell curve marching northward. Today, I got many reports stretching from Iowa to New York. I have no reason to believe a normal number of male Ruby-throated won't arrive eventually throughout their range, but if you live in its northern half, this year your first hummer may be a female.