Cooler temperatures this week are giving Michiganders a break from air conditioning and a chance to pull out their fall sweatshirts.
For birds, it’s migration time — with more than 3.6 million birds moving across the state last night.
The first to leave Michigan are insect-eaters such as warblers and songbirds. Their movement can be tracked in real time on Cornell University’s BirdCast website, which uses U.S. weather radar data to show the intensity of nocturnal migration from sunset to sunrise.
Migration typically runs from August through November, with most birds heading to Central and South America or the Caribbean.
As insect activity slows with dropping temperatures, birds take advantage of moving cold fronts, said Kirk Waterstripe of the Grand Traverse Audubon Club.
“They're hopping the tailwind. The reverse is true in the spring... But this time of year, when the wind's anywhere out of the north — anywhere favorable — they'll hitch a ride," said Waterstripe, "Makes life a lot easier."
While migration appears to be on schedule this year, warmer-than-usual falls can delay the journey. Milder winters — which are becoming more common in Michigan — can cause many migratory birds are stay longer.
While many robins stay in Michigan, Waterstripe said. They typically return in March, but “the year before last, we had nearly 300 robins counted in mid-December. So they're no longer the harbinger of spring.”
Just last year, an extended warm spell in Wisconsin kept robins and bluebirds around longer than normal.
Despite that, Waterstripe said, delays in fall migration affect birds little — the bigger impact being in the spring.
" Migration has become fairly finely tuned to arrive at the breeding grounds when food supplies are available," said Waterstripe.
But climate change, he continued, is causing insects to hatch earlier, but birds are still largely triggered by day length. As a result, when they reach the breeding grounds in spring, peak food availability may have already passed, which could lead to reduced overall breeding success.
You can also subscribe to BirdCast email alerts here, which notify you on evenings when migration activity is forecast to be especially high.
