Category Archives: Tenth Page

Birds On The Wires

Bird Behavior, Tenth Page

European starlings on wires in Germany (photo from Wikimedia Commons)

Early this month Beth Lawry asked about the noisy flocks of songbirds now congregating in the Pittsburgh area.  She wrote, “I am seeing strings of them along the signs on the Parkway –- sometimes 50+.”    And on the wires.

These are flocks of European starlings (Sturnus vulgaris), some of the 200 million descendants of 100 starlings introduced in Central Park, New York in 1890-91.

Flocking has helped them survive and thrive in North America.  In flocks they have:

  • Better foraging success:  Individual starlings get more to eat when they can see their flock mates eating (Fernandez-Juricic, 2005).  They watch each other as they methodically walk across my yard eating grubs.
  • Reduced predation:  In flocks they have statistical safety in numbers, more look-out birds to warn of danger, and the ability to hide within the flock when they’re under attack as shown in this video of starlings evading a peregrine falcon in Torino, Italy.
  • Thermoregulation at the roost: Starlings hang out with each other all day and then gather into huge roosts at night where they huddle to stay warm.  At very large roosts they swarm at dusk, as seen in this amazing video from Ireland.

And they are noisy.  They mimic other birds (poorly) and make wiry sounds and wolf whistles.  Click here to hear.

The starling flocks we see this month are only a hint at what we’ll see by the end of the year.  More starlings are on their way.  Those who live in the northern part of their range fly south for the winter.  Those who live south of 40oN latitude do not.

Guess where Pittsburgh is.  40oN.  We’re probably a starling hotspot because our local birds stay put and the northern crowd joins them.

By the end of December we usually have 6,000 starlings(*).

Thousands of birds on the wires.

 

(photo from Wikimedia Commons. Click on the image to see the original. Today’s Tenth Page is inspired by page 320 of Ornithology by Frank B. Gill.)

 

(*) average of Pittsburgh and Pittsburgh-South CBC counts, 2001 through 2011.

House Sparrows Bulk Up

Bird Anatomy, Tenth Page

House sparrow molting, Sept 2008 (photo by Remi Jouan via Wikimedia Commons)

Have you noticed that a lot of birds are molting now?  On the extreme side I’ve seen a bald male cardinal and Mary DeVaughn reported a bald blue jay, both of whom shed all their head feathers at once.

Less extreme-looking but still ragged are the house sparrows.  Ten or more of them line up at my bird bath to splash wildly and loosen their old feathers.

Birds must molt to replace worn feathers but house sparrows, who don’t migrate in North America, have an additional reason.  In August they put on heavier plumage that will keep them warm over the winter.

According to Ornithology by Frank B. Gill, the plumage on house sparrows weighs 0.9 grams in August.  By the end of September they’re wearing 1.5 grams of feathers.

Our house sparrows are bulking up.

(credits: photo from Wikimedia Commons. Click on the image to see the original. Today’s Tenth Page is inspired by page 154 of Ornithology by Frank B. Gill.)

No Birds Here

Musings & News, Tenth Page
Downtown Pittsburgh from the Ft Pitt Bridge (photo from Wikimedia Commons)
On the Fort Pitt Bridge, Pittsburgh (photo from Wikimedia Commons)

Which place has fewer birds:  a city?  or a cornfield?

When birders visit cities they often think, “There are no birds here.”  This isn’t accurate, but I think so, too, until I realize there’s a very high quantity of birds but low quality — lots of pigeons, starlings and house sparrows.  It’s the lack of diversity that prompts the comment.

Bird diversity is highest where the habitat provides a wide variety of food, cover and nesting sites.  A 20-year study of abandoned fields on Long Island found that bird diversity increased with the foliage height.  Since there’s not much foliage in cities the birds we find here are those who nest on or in buildings and eat human refuse or handouts — and the birds who prey on them (peregrines!).

Most songbirds eat insects and invertebrates which are hard to come by in the asphalt jungle. Even hummingbirds who sip nectar feed insects to their young.  If you want birds you must have insects.

Places without insects are biological wastelands because they’re also missing everything that depends on insects, all the way up the food chain.  Here’s a picture of a wasteland.  There are no birds here.

Cornfield in Penn Yan (photo by Jamie Lantzy via Wikimedia Commons)
Cornfield (photo from Wikimedia Commons)

I bet you’re thinking, “That’s not possible. There are plants in that cornfield. There have got to be insects and birds there too.”

No. There aren’t.  Today in the U.S. we use more pesticides than we did when Rachel Carson warned us about them in Silent Spring.(1)

90% of the corn we grow is genetically engineered to survive the assaults of herbicides, fungicides and insecticides.  This allows cornfields to be sprayed frequently(2) without hurting the corn.   Corn seed is also coated with insecticide, neonicotinoids, that imbue the plant with poison.

There are no insects in cornfields, no birds, and no plants except corn.  I was amazed when I found out about this at Cornstalks Everywhere But Nothing Else, Not even a Bee.

Not even a bee!  Hmmmm…

(credits: photo of Pittsburgh from the Fort Pitt Bridge and a cornfield, both from Wikimedia Commons.  Click on the images to see the originals.  Today’s Tenth Page is inspired by page 620 of Ornithology by Frank B. Gill.)

Ugly Ducks

Tenth Page
Hybrid male mallard (photo from Wikimedia Commons)

We’ve all seen them — ugly ducks that defy identification.

They have mallard heads with blotchy white bodies, or yellow legs instead of orange, or a wild duck head with a domestic duck’s body.  They look odd because they’re hybrids, a phenomenon that occurs easily in Aves because birds have retained a high level of genetic compatibility.

Hybrids confuse ornithologists.  Brewster’s and Lawrence’s warblers were classified as unique species until they discovered that both are hybrids of blue-winged and golden-winged warblers.  Dr. Frank Langdon fell into the hybrid trap with his Cincinnati warbler, revealed 100 years later to be a Kentucky and blue-winged hybrid.  The AOU famously lumped Bullock’s and Baltimore orioles into the “northern oriole” in 1983, thinking that their hybridization meant they were the same species.  Not!  Fifteen years later the orioles were split back into Bullock’s and Baltimore. (Whew!)

Hybrid birds aren’t always sterile but when they are it happens to the females.  Sterile females lay eggs that never hatch because their genetic blend causes their embryos to die during development.  In the early days of peregrine falcon reintroduction, management agencies removed sterile hybrid peregrines so the male could find a fertile mate and increase the species.  This happened at Cleveland’s Terminal Tower in 1993 (Zenith moved into that opening) and in Harrisburg, PA in 1998.

Male hybrids are fertile but they often fail to find a mate because their plumage, voices and courtship displays are “off” enough that they don’t attract any females.

Did this hybrid mallard in Germany have a mate?  I wonder if the ladies think he’s ugly.

(credits: photo by Andreas Trepte, www.photo-natur.de via Wikimedia Commons.  Click on the caption to see the original. Today’s Tenth Page is inspired by page 590 of Ornithology by Frank B. Gill.)

The Sleeping One

Tenth Page

Common Poorwill (photo by Dominic Sherony via Wikimedia Commons)

While reading about birds’ response to heat stress I came across this amazing story of a bird that appears to hibernate!

The common poorwill (Phalaenoptilus nuttallii) is the smallest North American nightjar, a member of the family Caprimulgidae that includes the common nighthawk and eastern whip-poor-will.  He lives in the arid West and, like his relatives, hunts for insects on the wing at dusk and dawn and on moonlit nights.

Flying insects are an unpredictable food source so when the weather’s bad or food supplies are low the poorwill prevents starvation by entering torpor.  He roosts, drops his body temperature to as little as 4.3oC (40oF) and reduces his oxygen intake by more than 90%.  He can do this on a daily basis if he has to and can even enter torpor while incubating eggs.

Poorwills take torpor to an extreme.  Rather than leave North America for the winter as nighthawks do, the poorwills remain in northern Mexico and the southwestern U.S. where winter can be too cold for flying insects.  They cope by entering torpor and staying there for two to three months!

To help themselves wake up they choose a location where the sun will warm them.  It needs to be a safe place because it takes seven hours for them to fully heat up.  This is probably why they are small.  The larger the animal, the longer it takes to leave torpor.

The Hopi knew this bird’s amazing trait and named him Hölchoko — “The Sleeping One.”

 

(photo from Wikimedia Commons. Click on the image to see the original.  Today’s Tenth Page is inspired by page 160 of Ornithology by Frank B. Gill.)

Man, It’s Hot!

Bird Behavior, Tenth Page

Dorothy panting to cool off after the banding (photo by Donna Memon)

Man, it’s hot here in Pittsburgh!  Yesterday the heat index was near 100 degrees.

We stay inside air conditioned buildings to avoid the heat but birds can’t do that.  Instead they use both obvious and amazing techniques to stay cool.

Just as we do, birds avoid heat.  They…

  • Reduce activity by roosting during the hottest part of the day.
  • Stay in the shade:  At midday Pitt’s peregrines roost on the north face of the Cathedral of Learning where it’s always shady.
  • Soar where the air is cool.  (Wish I could do that.)

Birds actively lose heat.  Dorothy used four of these techniques when she was overheated on Banding Day 2012 (pictured above).  Birds…

  • Pant.
  • Hold their wings slightly open.
  • Sleek their feathers to squeeze heat out of their downy undercoat.  That’s why Dorothy looks so thin here.
  • Expose the skin on their legs, wattles, etc. to lose water through their skin. Dorothy moved the feathers away from her legs so we can see her bands.
  • Gular fluttering:  Seabirds and nightjars can vibrate the muscles and bones in their throats to increase heat loss.  You’ve probably seen gulls doing this.
  • Bathe: We go for a swim, birds take a bath.  Vultures and storks don’t even have to find water.  They defecate on their legs to cool them off.
  • Turn on fans:  I’m not kidding. Scientists trained pigeons in 1975 to turn on fans when they were hot and thirsty.

And finally, some birds actually raise their body temperature.  This is amazing!  If your body temperature is warmer than the air you lose heat.  Hyperthermia can lead to heat exhaustion or death but some desert birds can raise their body temperatures in a controlled fashion to keep themselves cool.  Ostriches raise their body temperatures 4.2o C (7.5o F) every day. This saves water because they don’t lose any to cool off.

The weather forecast says today is the last of the unbearable heat before thunderstorms usher in a cold front.  I sure hope so!

In the meantime don’t be surprised to see birds with their mouths open.  They pant even when they fly.

 

(photo by Donna Memon.  Today’s Tenth Page is inspired by page 160 of Ornithology by Frank B. Gill.)

Divorce Among Chickadees

Bird Behavior, Tenth Page
Black-capped chickadee (photo by Shawn Collins)
Black-capped chickadee (photo by Shawn Collins)

“Birds are classically among the most monogamous of all organisms,” writes Frank B. Gill in Ornithology.

Many birds mate for life.  Swans and geese, parrots and eagles, albatrosses and even pigeons choose a mate once and for all.  Among those species divorce is rare.  That’s why a Bewick’s swan couple caused a stir when they arrived on their wintering grounds in 2009, apparently divorced and remarried.  They were the only Bewick’s swans known to do it in 40 years of study.

Do other monogamous birds ever divorce?  Is it typical behavior that we hadn’t noticed?

In 2000, Scott M. Ramsay and his team published an eight year study of black-capped chickadee social life.  Using bird bands and DNA testing they discovered that young females who have low confidence in their mates initiate divorce after their first breeding season and remarry on a more permanent basis for their second year of motherhood.  The team even found out why.

When black-capped chickadees pair up the males sing to maintain their territories and the females listen to determine who’s strongest.  When a first-year female hears her mate fail she remains with him but mates with other males as well, producing a clutch of mixed paternity.  She and her husband incubate and raise the nestlings but before the next breeding season she files for divorce and marries someone of higher social rank.

The study found that the ladies who “messed around” were the ones most likely to divorce.

No surprise there.

Read Ramsay’s famous study here.

(photo by Shawn Collins.  Today’s Tenth Page is inspired by page 360 of Ornithology by Frank B. Gill.)

Large Broods Wear Us Out

Birds of Prey, Nesting & Courtship, Tenth Page

Common kestrel nest in Germany (photo from Wikimedia Commons)

Any parent can tell you that raising kids is hard work and even harder if there are multiple infants the same age. (Think triplets!)

Most birds experience this multiple effect every time they nest.  In fact, the work is so exhausting that having “extra” kids beyond their normal clutch size decreases the parents’ life expectancy in some species.

This was shown in studies of common kestrels in Europe in the 1980s.

A team led by Cor Dijkstra artificially lowered and raised brood sizes of common kestrels by removing eggs from some nests and adding them to others.  Kestrel parents whose brood size of five remained normal or was reduced to three experienced the typical winter mortality of 29%.  On the flip side, adults whose broods were augmented were much more likely to die the next winter.  60% of the kestrels who raised two extra chicks were dead by the following March.

For thousands and thousands of years the clutch size of the common kestrel has been honed by the deaths of those who raised too many.  The birds settled on the number five.  More than that can kill them!

 

(photo of common kestrel nest in Germany from Wikimedia Commons. Click on the image to see the original.
Today’s Tenth Page is inspired by page 521 of Ornithology by Frank B. Gill.)

Why Here?

Nesting & Courtship, Peregrines, Tenth Page

Peregrine about to land on the Tarentum Bridge (photo by Sean Dicer)

Why do peregrines nest on buildings and bridges instead of cliffs?

“Raptors imprint on their natal nest sites.  Consequently, they choose a similar situation several years later when they reach maturity.”(1)

This explains why they’ve chosen to nest at the Tarentum Bridge, pictured above.  The adult female, nicknamed Hope, was born on the Benjamin Harrison Bridge in Hopewell, Virginia.  That bridge is such a dangerous place to fledge that Hope was hacked in the Shenandoah Mountains, but she remembered where she was born and picked a bridge when she chose a place to nest.

There are exceptions to the natal imprint rule.  Though Dorothy’s daughter Maddy was born on the Cathedral of Learning, a 40-story Late-Gothic Revival building, she chose the I-480 Bridge in Valley View, Ohio.  I can’t think of anything less like the Cathedral of Learning than this.  (The nest is at a broken patch of concrete on the bridge support.)

Maddy's nest at the I-480 Bridge, Valley View (photo by Chad+Chris Saladin)

The exceptions have saved at least one species from extinction.

Mauritius kestrels used to nest in tree cavities but monkeys were introduced to the island and ate the eggs and young. By the 1960’s the kestrels were down to two pairs — almost extinct — when one of the pairs decided to nest on a cliff ledge where the monkeys couldn’t reach them. That nest was successful, their youngsters nested on cliffs, and the species rebounded.

The exceptions benefit the rule.

 

(photo of Hope at the Tarentum Bridge (blue structure) by Sean Dicer.  Photo of Maddy’s nest site at the I-480 Bridge at Valley View (busy highway) by Chad+Chris Saladin.
Today’s Tenth Page is inspired by and includes a quote(1) from page 444 of Ornithology by Frank B. Gill.)

Light Cues

Bird Behavior, Peregrines, Tenth Page

Peregrine falcon tail feather (photo from Shutterstock)

Though Pitt’s peregrines, Dorothy and E2, are courting again today’s solstice will change that.

All living things have endogenous biological clocks that can run without light cues but we get out of synch with each other and the seasons in the absence of our external timekeeper, the sun.   Today our clocks struck twelve and began to head down again.

For peregrines in northern mid-latitudes the summer solstice ends their breeding cycle (initiated by the winter solstice) and triggers molting and preparation for migration.

Molting is a chilly and energy intensive activity in which birds replace all their feathers.  Since feathers provide warmth it’s cold to lose them.  Growing thousands of new feathers requires protein, increased blood to the feather sites, and changes in the birds’ calcium distribution.  And while flight feathers are being replaced flying is somewhat less efficient, an important consideration for precision-flying peregrines.

It makes sense to schedule this activity for a time when food is abundant and temperatures are warm.  Dorothy and E2 molt their flight feathers in July and August.  Good timing!

Our peregrines don’t migrate but arctic peregrines face an additional challenge.  They begin their molt in the arctic but don’t have time to complete it before they must leave on migration. Their bodies have adapted by starting the molt in the arctic, pausing during migration, and resuming at their wintering grounds in South America.  Very ingenious!

So when the sun paused this morning our birds got in synch.

We did too, we just don’t realize it.

(photo of a peregrine falcon tail feather from Shutterstock. Today’s Tenth Page is inspired by page 262 of Ornithology by Frank B. Gill.)