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.)
On Memorial Day weekend my neighbors noticed a tiny leak coming from their retaining wall. Within a day the leak had grown and caused the land to subside near the wall. The city-water pipe is leaking from the area near their water shut-off.
Since then the leak has grown into a creek while we wait for the water company to dig up the street and replace the pipe.
The neighbors aren’t happy but the birds are loving it. Grackles, robins, starlings, mourning doves, song sparrows, cardinals, and house sparrows visit the water feature every day. They bathe and drink and run through the stream.
They’re the only ones who will miss it when it’s gone.
(photo by Kate St. John)
Just because the red-tailed hawks didn’t nest this year on the Panther Hollow Bridge doesn’t mean they didn’t nest at all. This year they’re over by the golf course, a short flight from the bridge but conceptually far for us land mammals who must walk or drive around the Phipps Run valley.
Gregg Diskin photographed the family at their nest this weekend. One of the two babies is already stretching his wings. Click on the image above to see more baby pictures.
A few weeks ago Gregg also photographed one of the adults gathering food … really weird food … pizza.
I remember seeing that pizza at the Westinghouse picnic shelter as I walked to work one morning. The picnickers had carefully put the pizza in the garbage but the raccoons had pulled it out and scattered it. Lots of it! I put it in the garbage again.
The hawk found the pizza long before I did. I’m amazed he picked up a slice and carried it to a light pole.
Gregg has more photos of the pizza episode here.
I wonder if the hawk offered pizza to his family…?
(photos by Gregg Diskin)
The other day a mourning dove slammed into our bathroom window so hard it made me jump two rooms away. The impact left feathers stuck to the glass and scattered on the roof.
From our backyard feeders the window must look like a safe hole in the sky to escape the local Coopers hawk. But no. That dove probably died.
It wasn’t the first time the two upper windows on the back of our house have been hit but I hope it will be the last. I’ve ordered the thin bird tape shown above at American Bird Conservancy’s Bird Tape website.
I’m hoping for great results. The stripes have got to be better than the dusty outline of a dead dove on my window.
(photo from ABCbirdtape.org. Click on the image to visit the website.)
p.s. On a somber note, I read Lisa Ann Malandrino’s blog yesterday about the dead birds she found near her office in Jersey City on May 10. Window strikes in cities kill many, many birds on migration, a problem much larger than bird tape can solve. We need an organized effort in U.S. cities like the Fatal Light Awareness Program in Toronto, Ontario.
Ever since they returned from Peru last month the chimney swifts have been busy courting in the air.
You’ll often see a trio chittering loudly, flying fast, and turning sharply in unison. Studies have shown that the lead bird is usually a female and her followers are male. Their chases last more than five minutes, more time than I usually can spare to watch them.
After they form pairs the couples continue to fly together. Sometimes as they sail by the rear bird will raise his wings in a V. This happens more often after pair formation so scientists believe it’s part of pair bonding. I’ve seen pigeons do it too, without the “chitter.”
Chimney swifts have other amazing flight abilities. Did you know that…
- They fly almost constantly and only stop to roost or nest.
- They bathe on the wing by smacking their bellies against the water’s surface and shaking it off.
- If the opening is wide enough they can fly headfirst into a chimney and turn upright in mid air to cling to the chimney wall.
- They fly into narrow chimneys tail first.
- Their mean air speed is 29-30 miles per hour.
- They can fly at an altitude of 7,000 feet on the warm air rising ahead of a cold front.
It’s a joy to watch a bird that flies so well.
(photo by Jeff Davis)
We tend to think that birds with precocial chicks have an easier time as parents than those whose nestlings are naked and blind at birth, but this isn’t necessarily so.
Ducklings can walk, swim and feed themselves shortly after they hatch but their mobility is problematic. They have no idea where to find food nor how to stay safe. All they know is “Stay with Mom!”
Mother leads them to feeding areas and shows them what to taste. The ducklings peck in the vicinity until they find good food.
Her hardest responsibility is protecting them from danger. Baby ducklings are tasty morsels for raptors, minks, cats, dogs, large fish and snapping turtles. If you watch a mallard family day to day you’ll notice the number of ducklings decreases over time. Mom does her best but danger lurks.
This mother mallard has had pretty good success so far. Out of 8 to 13 eggs she still has six chicks.
Until they can fly she has mothers’ work to do.
(photo from Wikimedia Commons. Click on the image to see the original. Today’s Tenth Page is inspired by page 483 of Ornithology by Frank B. Gill.)
It’s breeding season for wild turkeys so the guys are putting on a show.
Which one will the ladies prefer?
Well, maybe they want to see them from this side, too, before they make up their minds.
(photos by Don Weiss)
On April 8 Charlie Hickey and his wife Carole heard a tapping at their front door but no one was there.
When the sound persisted they discovered a robin was attacking his own reflection in the door’s kickplate.
Convinced he was facing a rival, the robin would not give up. Here he tries to stare down that other bird.
And here he threatens him with the puff display. Look at the expression on his face!
Most birds don’t understand mirrors but I can understand why this bird is fooled. His reflection is that sharp!
When Charlie posted these photos on his Flickr account he alluded to Edgar Allen Poe’s Raven and wrote, “In spite of Carole opening the door and the trash pickup, [the robin] kept returning until Carole covered the kickplate with the door mat.”
What a relief when the door mat went up!
(photos by Charlie Hickey)
During incubation there’s not a whole lot of activity at a bird’s nest except for this: Mom (or Dad) periodically stands up, stares at the eggs and draws each one toward her with her beak. She’s not just rearranging the eggs, she’s turning them.
Other than a few notable exceptions, all birds turn their eggs because it’s required for the embryos’ survival. For instance:
- The temperature in the middle of a clutch is warmer than the edge. Birds move the outer eggs to the middle to keep them evenly heated.
- In the early days of incubation, it’s important that the embryo floats inside the egg while the membranes that support its life are growing and developing. Turning optimizes membrane growth.
- Eventually the chorion and allantoic membranes will be pressed to each other and to the shell. If these membranes adhere too soon the chick will not be able to move into the hatching position later and get out of the egg. Turning prevents premature adhesion.
- The albumen (the egg white) is the embryo’s fluid cushion and water supply. Turning the egg optimizes the fluid dynamics of the albumen so the chick can absorb it properly.
Egg turning is so important that it’s a wonder some species don’t do it. One notable exception are the megapodes who lay their eggs in compost heaps and let the heat of the decomposing vegetation incubate them. No turning there!
I’d rather watch a peregrines’ nest where things are happening, if only a bit of egg turning.
(photo of Dorothy turning her eggs from the National Aviary falconcam at University of Pittsburgh. Today’s Tenth Page is inspired by page 460 of Ornithology by Frank B. Gill.)
Most birds fly with flat backs and heads up but some have this rounded hunchbacked look.
Here a common merganser flies with dipped neck and tail. Loons always show this profile.
This shape is a good field mark. Can you name other birds that fly like this?
(photo by Steve Gosser)