And here’s a potential food source — a flock of dunlin.
The peregrine is looking for a bird that’s easy to catch. The dunlin are sitting ducks (er… dunlin) if they stay on the ground so they fly and flock as soon as they see a peregrine. This interaction has made dunlin more fit in the years since the peregrine population has recovered from the DDT crash.
A 2009 study at the Fraser River delta on the Pacific coast backs this up. Peregrines never went extinct on the West Coast but they were very scarce in the 1970′s. During this period wintering flocks of dunlin safely roosted on the sand at high tide and became fat — and a bit slower — in early winter.
The peregrine population began to recover in the 1990′s and soon found tasty dunlin meals as they migrated past the Fraser River delta in fall and spring. The dunlin quickly learned it was unsafe to roost at high tide during the day because peregrines were on patrol. Instead they began to spend high tide flocking over the open ocean, flying and flying for three to five hours. With this exertion they became much more fit and are now are measurably thinner in early winter, the time when peregrines are passing by.
Peregrine falcons have provided dunlin with a fitness program. Be fit or be eaten.
Click here to read more about the Fraser River dunlin study.
While songbirds, hawks, and dragonflies are migrating this month there’s a bird whose journey beats them all.
The arctic tern sets long distance records in its pole-to-pole round-trip migration of 44,000 miles (71,000 km). Since arctic terns can live 30 years, an individual can rack up a lifetime achievement of 1.5 million miles (2.4 million km).
The data behind this amazing feat was published in 2010 by the Arctic Tern Migration Project which studied arctic terns that nest in Greenland and winter in Antarctica.
To track the terns the scientists used tiny geolocator tags from the British Antarctic Survey, the same tags used to track wood thrushes. In both studies scientists captured each bird, affixed a tag, then had to find the same bird on its breeding grounds a year later and recapture it to gather the data. Wood thrushes don’t put up a fight but arctic terns relentlessly dive bomb their enemies to drive them away. This study had bird hazards.
Attacking terns were not the only hazards. Camping on an island off the coast of Greenland is no picnic. “Our tents blew out to sea in the storm.” Yow!
Watch this video from the Encyclopedia of Life to see the terns’ amazing migration and why it’s worthwhile for these birds to travel so far.
Just when you thought you’d mastered white wading birds, a wildcard shows up!
It’s the time of year for white little blue herons. I was reminded of this when I visited Scarborough Marsh last week and encountered great egrets, snowy egrets and little blue herons, all of which were white. Great and snowy egrets are always white, but little blues are blue … except when they’re young.
Little blue herons (Egretta caerulea) don’t breed in western Pennsylvania but juvenile birds disperse widely — they even fly north! — so it’s possible to find them outside their normal range in August and September. Because they’re very rare in Pittsburgh I was surprised to find three at Scarborough Marsh but I should have checked the range map. They breed in southern Maine.
With so many white wading birds how did I figure them out? Beaks and legs!
p.s. (*) Jim Valimont points out that along the southern, Gulf, Caribbean and Pacific coasts the white morph of the Reddish Egret adds to the confusion. Its beak resembles the immature little blue heron’s except that it’s two-tone pink and black. It’s not found in Maine and Pennsylvania.
p.p.s Steve Gosser contributed this photo of a white-morph reddish egret. Compare it to the first photo at top. Confusing? Yes! But his legs are black and he only visits saltwater.
It seems hard to believe but the subspecies Branta canadensis maxima (Giant Canada Goose) was nearly extinct in 1900 due to overhunting and habitat change. Many states conducted reintroduction programs to help the geese along. Here in Pennsylvania the birds so did well that there are nearly 280,000 resident maxima Canada geese, almost double the management goal of 150,000.
How do you determine the citizenship status of a Canada goose? By time of year and location. Only Pennsylvania residents are here in September. Migratory geese won’t be leaving Canada until the lakes begin to freeze in October and even then the South James Bay population visits the northwest corner of the state (Lake Erie to Pymatuning) and the Atlantic population stays well east of the Appalachians and south of I-80. In most of Pennsylvania, Canada geese are residents.
Why don’t our resident geese migrate?
Geese travel in family groups which collect at staging areas to join larger flocks. The young geese learn the migratory paths from their parents. If their parents don’t migrate the whole family stays put. The reintroduced geese had no one to teach them to migrate so they and their descendants live here year round.
The resident geese know our habits and will gather in the no-hunt zones this month. You may see more of them on our city rivers and in county parks in the days ahead.
Meanwhile, remember that fall is here and with it comes hunting season. Wear blaze orange, especially if you visit State Gamelands where it’s required even if you’re not hunting.
(photo of Canada geese in Ottawa, Ontario from Wikimedia Commons. These geese are migratory. Click on the image to see the original)
When fishermen and trappers abandon their lines in the water, they hurt unintended victims. One careless individual nearly killed a great egret in York County, Pennsylvania.
Thanks to John Beatty, Ann Pettigrew, TriState Bird Rescue and a whole host of caring volunteers the bird was saved. Here’s the story in John Beatty’s words:
On August 8th 2013 at William Kain Park I noticed an Egret was trailing behind some high-strength fishing line with a hook attached inside of the corner of its mouth. It was later discovered that this line was left behind by someone attempting to catch Snapping Turtles in the lake. I called the Fish & Game Commission and they dispatched out an officer but before he arrived a couple of local York County Parks employees happened to stop by as well. With a coordinated effort they were able to corral this bird into the woods, capture and retrieve it. By another coincidence there happened to be a veterinarian (Ann Pettigrew) of the Leader Heights Animal Hospital out taking photographs and she offered her help to bring the bird back to her office. The hook was removed from the bird’s throat and after being treated and nursed back to health it was released on August 18th. It was very nice that they invited me to come and take photos at the release of the bird.
Above, the egret struggles to remove the line but the hook is lodged in his throat. In fact it has gone through and is protruding from his neck.
Below, county park naturalists Fran Velazquez and Kelsey Frey slogged through mud, water and thorns to catch the bird. Wrapped in a towel, they are holding its beak (through the towel). You can see its black feet near Kelsey’s gloved left hand.
At Leader Heights Animal Hospital, Dr. Ann Pettigrew removed the hook and heavy-duty string and treated the bird. Then she took it to Tri-State Bird Rescue for rehab. In only ten days it was healthy and ready for release.
Shorebirds are migrating but we’re not likely to see them in Pittsburgh because we don’t have a shore. However there’s an excellent place north of us that does: the harbor at Conneaut, Ohio.
Conneaut’s harbor was formed where Conneaut Creek flows into Lake Erie. The lake’s waves can be rough so the harbor has been sheltered by two breakwaters. These allowed the creek (and probably the harbor dredge) to deposit a sand spit and mud flat so extensive you can park on it.
Visiting shorebirds feed at the water’s edge and rest on the sand. Sometimes they’re so close you have to back up to see them with binoculars!
The harbor is more than two hours away but the trip is well worth it. Steve Gosser photographed this marbled godwit there in July.
Click here for a map and the harbor’s eBird checklist. The best place is called the “sand spit” on the map.
We all recognize the Doppler effect when an ambulance siren rises in pitch as it speeds toward us, then drops as it recedes. (Click here for a car horn example.)
Here’s a bird that uses that sound effect.
American avocets have many techniques for protecting their nests from predators. They pretend to incubate a fake nest, then walk a few steps and pretend again. They distract the predator by walking toward him in a teetering tightrope walk with wings outspread. And they mob aerial predators before they can reach the nests.
But the most amazing technique is reserved for ground predators. When avocets swoop to chase them away they shout at them, modulating their pitch to resemble the Doppler effect. This is done so convincingly that the predator thinks the bird is approaching much faster than it actually is. Run away!
Tex Sordahl discovered this while studying American avocets and black-necked stilts in the 1970s and ’80s. Both use the Doppler sound effect. I’m sure he got a dose of it during his study.
(photo by Ingrid Taylar via Wikimedia Commons. Click on the image to see the original.)