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It’s In Your Nature: Can different weather patterns affect migrations?

Published November 16. 2024 08:05AM

For our perching birds such as swallows, catbirds, flycatchers, scarlet tanagers or Baltimore orioles, our diminishing amount of sunlight (for the most part) triggers their migration timing.

Looking back at my copious bird notes, the local barn swallows depart our region between Aug. 15 and Aug. 22. They sense an approaching frontal system during that time frame and most leave with the most favorable winds. They can’t wait too long because they are long migrants heading to areas in or near Argentina.

Scarlet tanagers arrive here from the tropics about the first week of May, and generally by late August into early September they are moving southward. Besides the need to travel so far as a reason for their short-term stay in the breeding area, they feed primarily on leaf eating insects. Fewer and fewer caterpillars are available to find as August wanes.

Raptors are quite predictable, too, especially the broad-winged hawks. They have a long migratory trip to accomplish. It is safe to say that 90% of the broad-winged migrants passing by the Hawk Mountain hawk watch are between Sept. 10 and 20 each year. A few trickle through earlier, and maybe a few dozen are still seen the first few days of October.

They will move, barring horrible weather conditions like a hurricane, because the need to get to Peru or Bolivia and it’s a looooong trip. But “broadies” don’t rely on deflection winds blowing across the ridge tops to help them; they use thermals to rise upward and then drift down ridge. This year’s weather patterns did little to affect their routine.

But, our bald eagle, golden eagles and red-tailed hawks have been affected this autumn by some unusual weather. The extreme dry pattern we are in is in direct correlation to areas of rather stagnant high-pressure systems parked over us. We haven’t experienced the powerful cold fronts pushing rain our way and the normal strong northwest winds that follow the frontal passage. So, yes, weather patterns can have an impact on some migrants, especially the aforementioned raptor species.

As of Nov. 6, 419 bald eagles had been spotted passing Hawk Mountain. Last year by that same date, 639 bald eagles had been recorded. Similar data is shown for red-tailed hawks; this year, 608 “red tails” were recorded. Last year, there were 989 by that date. Even more drastic a drop can be seen in golden eagle migrations. By Nov. 6, 28 “goldens” had been recorded, compared with 101 last year by that date.

Well, you could surmise that their populations have dropped, but all three of these species have not seen a population decline, so weather must be a factor. I’m betting that when colder weather arrives on the heals of a number of cold front passages, that the numbers will gradually get closer to last year’s data.

So, the swallows and tanagers weren’t affected too much by a weather pattern change this year, but the three raptor species that traditionally ride the deflection winds above the ridge tops are lagging back awaiting more favorable winds. (Our exceptional drought conditions are related to these persistent high-pressure systems, too.) Nature can be affected so drastically by alterations in even short-term weather pattern changes.

If we get a couple of good, windy days in the next few weeks, you can check the migration data online at either the Bake Oven Knob or Hawk Mountain websites to see I have made the correct assumptions. But, no matter, get out there.

Test Your Outdoor Knowledge: True/False — Eastern bluebirds and robins are both actually species of thrushes.

Last Week’s Trivia Answer: Saw whet owls will migrate southward from the colder areas and could be seen now and into the winter months.

Email Barry Reed at breed71@gmail.com

Bald eagles, like this juvenile soaring over a ridge top, rely on strong northwest winds to help them cover sometimes 20 miles in an hour as they move southward. This autumn has had fewer favorable days, resulting in lower migration totals. Records from the last three years show about 600 bald eagles were recorded by mid-December, so the next few weeks could bring bigger numbers. BARRY REED/SPECIAL TO THE TIMES NEWS
Red-tailed hawks like the cold and blustery winds of November to help them conserve energy as they migrate. “Red tail” numbers are lower this year because of those missing winds.
Accipiters, such as this Cooper’s hawk, use deflection winds to migrate more efficiently. Maybe some cold fronts later this month will “push” a few more along the ridge top.
Barn swallows are daytime migrants that travel to southern South America. They leave in mid-August, often on the morning of a cold front passage day.
Most of our perching birds, like the scarlet tanager, migrate at night. They also leave this area by late August to travel to Central and South America. This male was photographed in late August a few years ago and was beginning to molt to his winter yellow plumage.
Cedar waxwings are variable migrants. Most do leave this region for areas to our south. Their migration times may vary, especially with unusual weather patterns like this year’s. Some will even over-winter in areas where dried berries or fruits are plentiful.