European starlings (Sturnus vulgaris) are famous for their ability to fly in tight formation. When under attack by a peregrine falcon, they evade him in amazing ways.
Starlings under pressure fly closer together and shape-shift the flock like a giant blob in the sky. This makes it hard for the peregrine to choose a single bird as prey and gives their flocks a special name, a murmuration.
This winter Chad+Chris Saladin have been filming murmurations in Lorain, Ohio. Above on 30 December 2018, below on Christmas Day.
Why does this red-tailed hawk throw up a long gray lump? Is he sick? Not at all. He’s casting a pellet.
Birds’ digestive systems are very different from ours, beginning with their beaks. Since birds don’t have teeth they swallow most of their food whole. The rest of their digestive system is geared to deal with this.
Birds have little saliva and few taste buds compared with mammals, which chew and physically process food as the first step and then subject it to chemical processing as the second step. Birds reverse this sequence. They start chemical digestion in the proventriculus [then the food] undergoes physical processing in the gizzard.
Ornithology, 3rd Edition by Frank B. Gill, page 164
We chew with our teeth and spit out the bones. Birds chew with their gizzards which then collect the bones, fur, and other indigestible bits into a lump. The bird spits out the lump when it’s a convenient size.
Owls, eagles, hawks and falcons cast pellets but so do many other birds “including grebes, herons, cormorants, gulls, terns, kingfishers, crows, jays, dippers, shrikes, swallows, and most shorebirds.” (quote from Wikipedia)
Scientists examine pellets to find out what the bird ate. One of the long-eared owl pellets below was dissected to reveal the rodent bones inside.
For whatever reason, it’s rare to see a bird casting a pellet so consider yourself lucky if you witness it, as Chad+Chris Saladin did in the photos above.
A NOTE ABOUT HANDLING OWL PELLETS from Wikipedia: Some rodent viruses and bacteria can survive the owls’ digestive system so wear gloves and sterilize the pellets in a microwave oven before handling. A 2005 study found outbreaks of salmonellosis at elementary schools associated with dissection of owl pellets: Smith KE, Anderson F, Medus C, Leano F, Adams J, 2005. Vector-Borne and Zoonotic Diseases,5, 133–136.
(red-tailed hawk photos by Chad+Chris Saladin; pellet photo from Wikimedia Commons; click on the captions to see the originals)
Unimpressed by the University of Pittsburgh’s scarecrow recordings, Pittsburgh’s winter crow flock continues to roost on campus. On Saturday evening, 29 December 2018, Claire Staples and I counted them for the Christmas Bird Count. It was harder than it sounds.
We began at 4pm at the highest vantage point we could find — the top deck of a parking garage between Trees Hall and the Petersen Events Center. From there we could see two huge streams of crows arriving from the south and east, pouring into the trees near Kennard Playground. Unfortunately the playground is over the edge of the hill so those crows went out of sight as soon as they landed.
By 5pm there were so many crows that new arrivals were landing on Trees Hall roof. We were pretty confident we’d counted 10,000 … and then they began to leave. What?!
The crows were headed for Schenley Heights so we followed in the car. We thought they might roost in the Heights but they were restless and on the move. Those in the air were headed for the Cathedral of Learning. We chased them down the hill.
Sure enough, Tennyson Avenue between Alumni and Clapp Halls was “Crow Central.” It was impossible to count them in the air as you can see in Claire’s video.
On 11 March 2011 the town where ICRC is located, Otsuchi, Japan, was devastated by nearly 30 foot waves from the Great East Japan Earthquake and tsunami. The photo below of the Kirikiri section shows how Otsuchi was wiped out.
The International Coastal Research Center headquarters was severed damaged as well (the three-story building in the photo below).
The first two floors were wrecked, as seen in two photos from the ICRC website. (Click here to see more photos of the damage.)
However, by 2015 the local jungle crows (Corvus macrorhynchos) could not resist stealing the damaged materials inside the building. During the nesting season they flew into the open building, ripped insulation off the pipes and carried it to their nests.
To get rid of the crows the ICRC asked for help from Tsutomu Takeda, an environmental scientist and crow expert. Rather than using scarecrow tactics he hung large signs on the pipes, visible from outdoors, that said “Crows Do Not Enter.”
Can the crows read the signs? No, but people can and when they do they look up to see if crows are in the building. The crows hate it when people watch them stealing nesting material so they stopped doing it.
If the signs worked on jungle crows in Japan, perhaps they’ll work on American crows, too. I wonder if our winter crow flock would stop roosting at the University of Pittsburgh if they put “Crows Do Not Enter” signs in the trees. 😉
Pigeons (Columba livia) and the raptors who hunt them have evolved together for millions of years. The raptors’ successful hunts leave only the fastest, most maneuverable pigeons. Speedy, elusive pigeons mean only the most skillful raptors can survive. Most of us never get to see this interaction so this dramatic video from Romania is a real treat.
The pigeons stay in a tight flock because raptors can’t pick out a victim in a moving ball of birds. The raptors try to separate one bird from the group by slicing through the flock. If it works, the raptor pursues the lone bird.
When you’re vulnerable to predators it pays to stick together and have a good lookout to warn you of danger.
The dusky-throated antshrike (Thamnomanes ardesiacus) doesn’t look important but he’s quick to notice the presence of hawks and falcons and has a distinctive alarm call that wakes up the forest to impending danger. It turns out that he’s key to the foraging location and cohesion of his mixed species flocks in the Amazon.
Early this year, a study by San Francisco State University temporarily removed dusky-throated antshrikes from their mixed species flocks in Peru. They discovered that within hours the flocks left their semi-open mid-story locations for denser parts of the forest. Often the flocks without an antshrike completely dissolved.
What does the alarm call sound like? Is it loud? Does it grab your attention? You bet! Here’s the sound of a worried dusky-throated antshrike:
His role in the flock works so well that the same mix of species sticks together for generations. As San Francisco State Professor Vance Vredenburg remarked, “You come back to the same habitat after 20 years, and the same flocks are using the same areas of the forest.”
While you’re out running errands here’s something to do while you wait for the stoplight to change …
Are there birds on a wire near you? What are they doing?
Are they all facing the same way?
Birds face the wind when they’re perched so the air doesn’t ruffle their feathers and make them uncomfortable and cold. They also land and take off facing the wind so they actually arrived in that direction.
The direction the birds are pointing tells you the direction wind is blowing … except …
if the birds are not facing the same way, the breeze is very light or the air is calm.
(photo from Wikimedia Commons; click on the caption to see the original)
Barn swallows (Hirundo rustica) are found on every continent except Antarctica, breeding in the northern hemisphere and wintering in the southern hemisphere with one notable exception: a small population breeds in Argentina.
This behavior was unknown until 1980 when scientists confirmed that northern-born barn swallows had decided to nest during South America’s spring. They’ve even shortened their return migration, traveling only as far as the equator during South America’s winter.
Scientists speculate that the birds are breeding in Argentina because we changed the landscape to their liking. 99% of barn swallows prefer to nest on man-made structures including farm buildings, bridges and boathouses. They found what they like near Buenos Aires.
Because these swallows have flipped their north-south patterns a Cornell University study reports that this could be the first step toward a new species, similar to terns and skuas that have distinct northern and southern species (example: great skua and south polar skua). For now, though, the Argentinian barn swallows still recruit northern-born swallows to join them.
While we’re cold up here in North America, some barn swallows are starting families in November.
In a study conducted in Italy, researchers released racing pigeons fitted with GPS backpacks from sites 20 to 80km from home (12.5 to 50 miles). In over 200 flights, the data showed that experienced pigeons preferred to follow roads and rail lines in the early and middle parts of their trips. As they got close to home they left the road grid and made a beeline for the loft.
On the first trip from each site pigeons didn’t use the grid, but the more they made the same trip the more they used big roads.
Why do they do this? Scientists suspect that easier navigation above major roads makes up for taking slightly longer routes. The birds don’t have to think about where they’re going and can focus on flying fast and watching for predators.
That’s why I take expressways in my home town, even when they’re clogged at rush hour. I know the back roads but I’d rather not think about navigating.