Just about every year up here in northern Minnesota, we have a few days in March when the temperature reaches 50 or higher. It feels like spring! On the news yesterday, March 9, they said the thermometer hit 55 at Duluth International Airport, breaking our all-time high for the date. Having my windows open a bit felt wonderful!
Despite the old saying that you can’t fool Mother Nature, you can fool a lot of her creatures—at least, her human creatures. We know how much we want real spring to begin without ever figuring out that changeable weather is exactly what real spring is. Thawing and then freezing again, balmy days and then a blizzard. The unpredictability is quite predictable. There’s a reason April Fool’s Day is set in spring.
Because we’re only human, we can’t help but worry about birds. And many really are killed during migration. The reason migratory birds fly back and forth despite the mortality is because sticking it out would mean a higher mortality rate for them, but there are still a lot of losses during their long travels, and weather is one major reason. So over millennia, migratory birds have evolved strategies for minimizing the danger.
Because weather is so very changeable, most bird migration is triggered by daylength, or at least, most birds reach migration readiness in spring due to increasing daylength. Neotropical migrants—that is, the ones who return here from Central and South America—return within a week or ten days or so around the same date every year. The journey may start out very precisely timed to daylength, but weather of course influences their progress.
Daylength also affects the migratory readiness of many early migrants—the ones that wintered in the central and southern states—but many of them become primarily keyed in on weather, motivated to get crackin’ as temperatures rise. The early bird really is hoping to get the worm, if that early bird is a robin, but those worms won’t emerge until the ground thaws.
Geese and swans eat some worms, too, but their main needs as they return north are open water and snow-free patches on grain fields. So it makes sense that the vanguard of both robins and geese tracks the 37-degree isotherm, when snow is disappearing from large swaths of ground, the frozen soil is starting to melt, and ice is yielding on some rivers and streams. Some people up here panic when they see robins early in March, knowing full well that in the next two months, snow is very likely to cover the ground again, but if those worms suddenly grow inaccessible again, robins have a backup plan—feeding on fruits still clinging to trees and shrubs. The last robin of winter, making infrequent call notes, will suddenly change his tune, and by the very act of singing that most welcome robin song, he transforms himself into the first robin of spring.
This spring, Frank Nicoletti is once again keeping track of migration at Hawk Ridge Bird Observatory’s Spring Raptor Count, conducted at Skyline Parkway in West Duluth. The count is supposed to begin on March 1, but Frank understands that birds use cues unrelated to our human calendar, so he jumped the gun this year and started on February 22. We may think February is the dead of winter, but on February 27, he counted 80 Bald Eagles, and as of the end of the day March 9, he’d totaled 691 Bald Eagles, 20 Golden Eagles, and 5 Red-tailed Hawks, 3 Rough-legged Hawks, 2 Cooper’s Hawks, and a single Goshawk and Merlin. So far he’s only tallied 5 Canada Geese and 2 Trumpeter Swans moving through. Those numbers will change enormously in the coming days and weeks. You can count on this mild spell ending—it is just March 10—but spring really and truly is here.