Though it’s nearly mid October I saw monarch butterflies migrating through Pittsburgh on Thursday and Friday October 10 & 11. Their timing seems late, but they were given a boost by August-like weather early this month.
Now that the weather has changed unwelcome insects will invade our homes including Asian ladybeetles (Harmonia axyridis) that resemble native ladybugs but don’t act like them. Also called “harlequin ladybirds,” they overwinter indoors, make a stink, and bite when frightened.
A hundred years ago we thought this bug was a great idea and repeatedly introduced it to the U.S. to control aphids. The introduced ladybeetles never made it in the wild until a population was found thriving near New Orleans in 1988. After that they spread like wildfire across the eastern U.S. and into Canada.
Thirteen years later they became established in South America and Europe(*). By 2004 they were in southern Africa. They hadn’t been introduced. How did they get there?
A 2010 study of their genetic markers revealed that those three continents were invaded by the eastern North America population. In a move called the bridgehead effect, Asian ladybeetles in the U.S. used our continent as a jumping off point to colonize Europe, South America and Africa.
In the American West there’s a 3-inch long katydid called a Mormon cricket (Anabrus simplex) that cannot fly but it sure can walk.
We hardly notice Mormon crickets until millions swarm and march across the landscape, advancing more than a mile a day like a Biblical plague of locusts. Naturally scientists wondered what makes them do it.
A 2006 study discovered that the swarms are driven by hunger and fear. The crickets are hungry for protein and salt so they start to migrate, but the bugs are cannibals and will eat each other if they can. Those at the back of the pack pursue the front line to catch and eat them. Fear forces the crickets to keep track of their neighbors and constantly on the move.
Despite the danger from behind, individuals sometimes double back into the crowd. If enough of them do it the whole swarm changes direction. How does this happen? What signals such a change?
We concluded that the mechanism through which locusts agree on a direction to move together (sometimes with devastating consequences, such as locust plagues) is the same we sometimes use to decide where to live or where to go out: we let ourselves be convinced by those in our social network, often by those going in the opposite direction.
We don’t necessarily pay more attention to those doing the same as us, but many times [we pay more attention] to those doing something different.
Songbird migration is underway across the continent but we can’t see it happening outdoors because the birds travel at night. However, we can watch them online.
Radar can see birds in flight so Cornell Lab of Ornithology’s BirdCast uses national radar data to plot where, when and what direction the birds are moving. Click the BirdCast link to see the most recent video. Watch sunset (red bar) sweep across the continent and the birds start to move, then sunrise (yellow bar) sweep across and migration stops for the day. The date above the map is a pulldown menu for selecting prior nights.
The BirdCast screenshot above was taken on Tuesday 3 September on a night when many birds left Pittsburgh on their way to the Gulf coast. At 4:50am you can see them lighting up the BirdCast map from southwestern Pennsylvania to Mississippi.
Before BirdCast existed, I watched weather radar for a snapshot of current bird activity. BirdCast filters the weather map so you see only the birds. The Weather Service does not so you’ll want to check out this vintage article — Watch Migration On Radar — for a quick tutorial on how to read the map.
The screenshot below was taken from Great Lakes weather radar on the same date and time as the BirdCast snapshot at top. Notice the differences!
Wisconsin and Lake Michigan are brightly colored on the weather map because of heavy rain. That same area is a dark spot on BirdCast because birds don’t migrate in a storm. BirdCast also shows no birds moving in Florida; Hurricane Dorian was there.
Last night, Sep 4-5, the wind was from the north and skies were clear west of the Appalachians. BirdCast and weather radar both show birds on the move from Pennsylvania and Illinois to the Tennessee and Mississippi Valleys.
Every year, beginning in late August, broad-winged hawks (Buteo platypterus) head south on a 4,500 mile journey from their nesting territories in North America to their winter grounds in Central and South America. It’s a journey many of us witness at Pennsylvania hawk watches.
Unlike other hawks, broad-wings usually travel together. Though not in organized flocks they cue off each other to find the best travel conditions. This brings them together on migration.
The Allegheny Front Hawk Watch, 1.5 hours from Pittsburgh, saw 119 broad-winged hawks last Saturday but will peak September 13-15 with close to 2,000. Other Pennsylvania hawk watches will count even more.
Visit Hawkcount.org to see the latest statistics and find a hawk watch near you. Plan a visit soon.
Meanwhile, keep looking up. There’s a good chance you’ll see a broad-winged hawk overhead in the next couple of weeks.
(photos from Wikimedia Commons; click on the captions to see the originals)
In August 2019 a rare bird showed up every evening at an industrial park in Duquesne, PA. The bird was outside his normal range, but this is not surprising for a juvenile yellow-crowned night-heron.
Related to egrets and bitterns, yellow-crowned night-herons (Nyctanassa violacea) live near water and eat mostly crustaceans. Some live year round in Central and South America. Others breed in North America and migrate south for the winter as shown on the map below.
However, juvenile yellow-crowned night-herons are great wanderers. As Cornell Lab’s All About Birds explains, “After the breeding season, young birds often disperse to the north or west before heading to wintering grounds.” That’s how they end up in Newfoundland, North Dakota and Duquesne, PA.
At 4pm on Sunday August 18, I went to see him at the industrial park but he wasn’t there because (duh!) he’s a night-heron. So I went back at 7:20pm.
He attracted a small crowd. Five of us watched him roam the sidewalks and grass beneath the pine trees at American Textile Company. He was so unafraid of humans that he walked right past two people standing on the sidewalk. This bird is completely focused on cicadas.
To give you an idea how close he came, here are photos from Oliver Lindheim (at top) and Amy Henrici, two of the many birders who’ve made the trek to Duquesne.
As soon as the glut of cicadas is over, this bird will be on his way.
UPDATE 26 August 2019: This bird is gone. He didn’t show up on the evening of August 21.
NOTE: If you went to see the yellow-crowned night-heron and you use eBird, please mark his location as the new “Stakeout” Hotspot created specially for him called “stakeout, yellow-crowned night-heron at City Center, Duquesne, PA.
Eastern monarch butterflies, famous for their autumn migration from North America to Mexico, have declined 80-90% in the last 20 years. To help the butterflies many people collect eggs and caterpillars in the wild and captive-raise them to increase their chances of survival. Unfortunately this well-meaning act can damage the insect’s ability to migrate.
Researcher Ayse Tenger-Trolander at Univ. of Chicago stumbled upon this when she purchased captive-bred butterflies for her monarch migration study. To measure their autumn migratory drive she placed them in a flight simulator and noted the dominant direction they wanted to fly. Wild migratory monarchs orient South. The captive-bred monarchs chose random directions, unlikely to migrate.
To further test the butterflies, Tenger-Trolander collected wild monarchs and raised a new generation indoors, mimicking outdoor autumn conditions. Here’s what she found.
Furthermore, rearing wild-caught monarchs in an indoor environment mimicking natural migration-inducing conditions failed to elicit southward flight orientation. In fact, merely eclosing(*) indoors after an otherwise complete lifecycle outdoors was enough to disrupt southern orientation.
Chip Taylor, Director of Monarch Watch, pointed out on NPR that some captive-bred monarchs do make it to Mexico, but added that “The real reason for raising monarch butterflies is for the enjoyment, the education. [T]he idea of individuals saving caterpillars as “monarch rescue” is misguided. “That’s simply not going to work as a way to boost the population,” says Taylor. “What we really need to do is to improve the habitat.”
We’re learning that monarch migration is complex and very fragile. It’s easy to break it in a single generation.