Is there a phenology of migration triggers?

Yesterday afternoon we drove a circuit on the local roads around a large chunk of Carlos Avery Wildlife Management Area in Chisago County. We were looking for robins and red-winged blackbirds. Not a feather of either was to be seen, although we did see an osprey and two turkey hens on the northern leg, plus the waterfowl we've been reporting, and the Better Half spotted a cluster of pussy willows near a wetland on the southern leg.

Spring arrival, male red-winged blackbird

Photo by J. Harrington

This morning we had to drive the southern leg of the same loop to run an errand, picking up heart worm and flea & tick meds for the dogs. Blond SiSi showed the season's first tick the day before yesterday. On our way to get the meds, we noticed two robins and two or three red-winged blackbirds. Where were they yesterday? Did they just arrive overnight? Was the time of day a significant factor? We'll probably never know, but their recent appearance puts the season's migration phenology back into a more usual framework.

Elsewhere, Journey North shows that both robins and blackbirds have been arriving in much of Minnesota only within the past week or two, while monarch butterflies and ruby-throated hummingbirds are still well south of our North Country. According to All About Birds:

The mechanisms initiating migratory behavior vary and are not always completely understood. Migration can be triggered by a combination of changes in day length, lower temperatures, changes in food supplies, and genetic predisposition.

Redwing Blackbird

Feet firmly perch 
thinnest stalks, reeds, bulrush. 
Until all at once, they attend my 
female form, streaked throat, brownness.

Three fly equidistant 
around me, flashing. 
Each, in turn, calls territorial 
trills, beckons ok-a-li, ok-a-li! 

Spreads his wings, extends 
inner muscle quivering red 
epaulet bands uniquely bolden. 

Turn away each suitor, 
mind myself my audience. 
Select another to consider, 
He in turn quiver thrills. 

Leave for insects. 
Perhaps one male follows. 
Maybe a few brood of young, 
line summertime. 

Silver Maple samaras 
wing wind, spread clusters 
along with mine, renewing Prairie. 

As summer closes, I leave 
dragonflies, damselflies, butterflies, 
mosquitoes, moths, spiders, crickets for 

grain, see, Sunflower; 
join thousands to flock Sky— 
grackles, blackbirds, cowbirds, starlings— 
Swarming like distant smoke clouds, rising.

Allison Adelle Hedge Coke 

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