Archive for the 'Tenth Page' Category

Aug 23 2013

House Sparrows Bulk Up

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.)

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Aug 16 2013

No Birds Here

Downtown Pittsburgh from the Ft Pitt Bridge (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)

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."

Nope.  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.   Seed is also pre-treated with insecticide.

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.)

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Aug 09 2013

Ugly Ducks

Published by under Tenth Page

Mallard hybrid (photo by Andreas Trepte via 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's body.  They look like this because they're hybrids, a phenomenon that occurs easily in birds because Aves 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.

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 just "off" enough that they don't attract any females.

Did this hybrid mallard in Germany have a mate?  Perhaps the ladies think he's ugly.


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

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Jul 26 2013

The Sleeping One

Published by under 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.)

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Jul 19 2013

Man, It’s Hot!

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.)

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Jul 12 2013

Divorce Among Chickadees

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.)

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Jul 05 2013

Large Broods Wear Us Out

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.

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Jun 28 2013

Why Here?

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.

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Jun 21 2013

Light Cues

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.)

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Jun 14 2013

The Air Show

Published by under Peregrines,Tenth Page

Two juvenile peregrines learn independence in Wilmington, Delaware (photo by Kim Steininger)

June is "air show" month for our local peregrines.  Where the nests have emptied the action is in the air.

After they fledge, young peregrines are dependent on their parents for six to ten weeks while they learn to supply their own food.

Fortunately, as with all predators, they're born with an instinct to hunt.  Kittens instinctively stalk and pounce.  Peregrines are programmed to chase.  This means they can develop hunting skills without much parental assistance -- which is why hacking works.

In their first weeks after fledging, juvenile peregrines chase anything that flies: their parents, their siblings, butterflies, even turkey vultures.

After two to three weeks they begin to focus on prey the right size.  Eventually they capture something, almost by surprise.

In the meantime they play at all the right moves:  chasing, mock dogfights, roll-overs, talon grappling and prey exchanges.

Above a juvenile in Wilmington, Delaware chases his sibling who won the prize.

Keep looking up and you'll see the air show.


(photo by Kim Steininger.  This Tenth Page is inspired by and quoted from page 501 of Ornithology by Frank B. Gill.)

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