Yearly Archives: 2010

Anatomy: Wax Eaters

Bird Anatomy
Yellow-rumped warbler in breeding plumage (photo by Chuck Tague)

5 November 2010

Last week we learned that the stages of birds’ digestive tracts are in a different order than our own so that the heaviest parts are at their center of gravity while they fly.

After birds swallow their food they chemically digest it (proventriculus), then “chew” it in the gizzard.  If they swallow something indigestible and bulky, they regurgitate it as a pellet.  Some species even get nutrition from normally indigestible substances, a talent that has further modified their digestive systems.  The yellow-rumped warbler is one example.

Wax is impossible to digest for most animals and birds.  Its description as a “saturated long-chain fatty acid” even sounds dangerous (saturated!  fatty!) yet the yellow-rump depends on wax for its winter food.  This makes it unique among warblers, most of whom eat insects and must leave North America by September to survive.  The yellow-rump sticks around because it switches its diet to wax-coated bayberries.

How has the yellow-rump’s digestive system adapted to do this?  They have higher levels of gall bladder and intestinal bile-salt than other birds and their digestive system absorbs the food more slowly.  They probably even process it for a longer time, possibly moving it back and forth so the gizzard can grind it again.

The yellow-rumps’ love of bayberry myrtle also gave them an alternate name.  The eastern subspecies is called the “myrtle warbler.”

So now you know why yellow-rumped warblers don’t go far south in the winter:  They’re eating waxy berries.

(photo of a springtime yellow-rumped warbler by Chuck Tague)

Biofuel Affects Bird Diversity

Musings & News, Plants & Fungi


If you garden for birds you know that what you plant has a huge effect on the variety of birds in your yard.  This applies on a larger scale as well.

In recent years our government has encouraged the development and manufacture of biofuels to replace our dependence on foreign oil.  The typical method is to grow corn and refine it into ethanol.  This has spawned a debate on the wisdom of converting valuable farmland into acreage devoted to fuel instead of food and using the corn supply to feed our cars. 

But corn, a labor intensive crop that must be planted every year, is not the only source of biofuel.  Perennial grasses like switchgrass work as well.

When our government provides subsidies to grow biofuel feedstock, even marginal land will be converted to this purpose.  Does it matter what we plant?  Indeed, it does.

Last month two researchers from the University of Wisconsin-Madison published a study on the effect of bioenergy crops on bird diversity in the Upper Midwest.  Using bird surveys and land use maps, Claudio Gratton and Tim Meehan calculated the change in bird diversity when marginal land is planted in annual monocultures (corn) versus a mixture of perennial prairie plants and grasses.

Their results are shown in the maps above.  Brown is bad — species decline up to 50%.  Blue is good — species increase up to 200%. 

Can you guess which map is which? 

The lefthand map shows bird diversity declines up to 50% if we plant monocultures of corn for biofuel.  The righthand map shows that bird diversity doubles if we plant diverse grasslands.

It’s no surprise that monocultures are bad but the results are frightening.   Click here to read more about this in Science Daily.

(image linked from Science Daily.  Click on the image to read the article.)

Most of the Trees Are Bare?

Phenology, Trees
Bare trees at Shenango Lake, 31 Oct 2010 (photo by Kate St. John)

2 November 2010

Western Pennsylvania was a changed landscape last Sunday, 31 Oct 2010, when I drove to Shenango Lake.

Only a week before the trees showed some fall color and many still had leaves, but now most trees are bare except for russet stands of oaks and lone tulip poplars with yellow tops like candle flames.

For many years I kept track of the date when the trees lost their leaves.  It’s a useful marker for scientific studies.  For instance, it’s the first piece of local information you need for doing a deer density count(*).

Once I started tracking the dates when “Most Trees Are Bare” and “Most Trees Have Leaves” (real leaves, not just hints) I realized there are leaves on our trees only six months of the year.  In the City of Pittsburgh, where our growing season is longer because of urban heat, most trees are bare by November 15 and most have leaves by May 5.

You can track this too.  The oaks still had their leaves last weekend so I’ll wager none of you have reached the “Most Trees Are Bare” stage.  But that date is coming very soon.

Keep watching.

(photo by Kate St. John)

(*) To calculate deer density, you walk a transect counting the number of deer scat piles on top of winter’s fallen leaves.  Use the number of scat piles, the number of days since all the leaves fell, and the average number of times a deer drops scat per day to calculate deer per square mile.

Quiz: Not a Thrush?

Migration, Quiz, Songbirds

1 November 2010

Yesterday, 31 Oct 2010, I was happy to see a flock of these birds on the exposed, dry mud at Shenango River Lake.  I know their identity but they’re tricky, so here’s a quiz. 

First clue: He’s not a sparrow because his beak is too thin.  Sparrows have deep seed-cracking beaks, this bird does not.

Perhaps he’s a thrush?  He has a striped breast, short neck, thrush-like stance, almost-thrush-sized bill, and he walks a lot. 

A longer look reveals many “Not Thrush” things about him. 

  • He’s a little smaller than a Swainson’s thrush.  Unfortunately his size is hard to gauge because he’s rarely near anything that gives him scale.
  • He is only found in open tundra-like landscape, never in the forest.
  • He has wing bars.  Our eastern thrushes do not.
  • His outer tail edges are white.  (You can see this when he flies.)
  • When he walks he darts and jabs in a quick manner that’s different from the deliberate walk-and-pause of thrushes.
  • He pumps his tail and almost wags it.  Hermit thrushes raise then slowly lower their tails. The top side of his tail, which you can’t see in this photo, is not rusty like that of a hermit thrush.
  • In flight this bird is bouncier than a goldfinch.
  • And like a goldfinch he always calls when he flies.  His call is a dead giveaway.  He says his name.

Final hint:  This bird is a treat to see because he neither breeds nor winters in Pennsylvania.

Ready for the answer? Check the comments.

(photo by Steve Gosser)

Happy Halloween!

Books & Events, Insects


Here’s a trick: You won’t find these dragonflies in western Pennsylvania in late October. 

The Halloween Pennant, named for his orange and almost-black colors, is only here in the summer. 

Here’s a treat: If you live in Florida, Halloween Pennants are present year-round.  For you, today’s a good day look for this timely insect.  You’ll find him on the tip of a weed, riding the wind.

(photo by Julie Brown.  Click on the photo to see the original.)

Almost November, what will we see?

Phenology


Yesterday morning was cloudy, cold and blustery.  As I waited at the busstop hundreds of grackles flew south over Greenfield.  Perhaps they were leaving the roost.  Perhaps they were leaving town.

In only two days it will be November.  The variety of birds is dropping though the number of crows, robins and starlings is growing.

Soon the north will freeze and migrating ducks and swans will stopover on Pennsylvania’s lakes.

Yesterday Karen DeSantis reported a flock of tundra swans over Westmoreland County, the first this fall.  I can hardly wait to see a V of swans myself.

What else will we see in November?

There’s a list on my phenology blog “What to Look For in Early November” and at Chuck Tague’s “Welcome to the Dark Side.”

(photo of migrating tundra swans by Chuck Tague)

Anatomy: Where Are Their Teeth?

Bird Anatomy
Diagram of bird digestive system (linked from Fernbank.edu)
Diagram of bird digestive system (linked from Fernbank.edu)

29 October 2010

Birds have the same basic internal equipment that we do but the location and shapes of their body parts are modified because they fly.

So here’s a puzzle.  Teeth are heavy, so where are their teeth?

Millions of years ago the ancestors of birds had teeth but modern birds don’t have even a vestigial tooth.  Yet they eat food that ought to be chewed: meat, nuts, and entire mice and fish swallowed whole.

Birds do indeed “chew” their food but not in their mouths.  Teeth are heavy equipment for the front end of flying animals and if they had to escape suddenly while chewing a big meal, the food would add extra weight to their heads, a real challenge to flight.

Birds’ bodies have an elegant solution to these two problems.  The chewing mechanism and main holding compartment are the same organ, the gizzard, located at the center of gravity under the wings.

The gizzard is a muscular stomach that breaks up food by grinding it with the grit birds eat to aid digestion.  The gizzard grinds and turns the food among the grit, breaking it into smaller bits the same way we chew with our mouths.

As you can see from the diagram, the gizzard is the third digestive organ in most birds.  The first is the crop, a bulge in the esophagus where food waits to be processed.  The second is the glandular stomach or proventriculus where enzymes break down the food before passing it to the gizzard where it’s “chewed.”

So now you know.  Birds’ teeth are on the inside.

(image of a bird’s digestive tract, linked from Fernbank Science Center in Atlanta, Georgia.  Click on the image to read more about birds’ digestion.)

Why the Leopard Got His Spots

Mammals


In 1902 Rudyard Kipling answered How the Leopard Got His Spots.

According to Kipling, the Ethiopian and the Leopard originally hunted on the High Veldt where they and their prey matched the plain, sandy landscape.  Their prey moved to the forest but when the Ethiopian and Leopard followed them there, the animals they hunted were camouflaged while they “show[ed] up in this dark place like a bar of soap in a coal-scuttle.”  They couldn’t catch a thing.

“The long and the little of it is that we don’t match our backgrounds” said the Ethiopian, so he changed the color of his skin and offered to help Leopard change too. “The Ethiopian put his five fingers close together (there was plenty of black left on his new skin still) and pressed them all over the Leopard, and wherever the five fingers touched they left five little black marks, all close together.” 

So, says Kipling, that’s how the Leopard got his irregular spots.  And why?  He needed camouflage in the forest.

More than 100 years have passed.  Can science support this story?

Last week the BBC reported on a new study that confirmed Kipling’s “why,” but not his “how.” 

Using mathematical models, scientists analyzed the pattern complexities of wild cats’ coats and correlated the complexity levels to the cats’ lifestyles.

Do wild cats have spots and stripes for social reasons?  Do the patterns attract mates or repel rivals?  No.  The models showed that cats living in trees and at low light levels are the most likely to have complex and irregular coat patterns.  Notice how the tree-dwelling leopard’s spots are similar to the dappled leaves behind him.

Which brings me to a cat I know very well.  She is not wild, she does not live in trees, and she doesn’t have to operate at low light levels.  Nevertheless Emmalina has four colors on her coat (white, beige, taupe and black) in an irregular pattern of blotches and stripes. 

In our house we’ve learned this pattern makes her disappear when crouched on the kitchen counter, an amazing adaptation for modern life.

(leopard photo from Wikimedia Commons.  Emmalina’s photo by Kate St. John.)

Crabapples and Rain

Bird Behavior, Weather & Sky

Thank you, everyone, for your comments, emails and phone calls about yesterday’s quiz.

My local experts — Marcy Cunkelman, Dianne Machesney and Chuck Tague — agree that the tree is a crabapple.   My photo didn’t provide enough information to identify the cultivar but Marcy suggested a Sargent’s Crabapple, Dianne gave us a list and Chuck Tague emailed this comment:

“Dianne and Marcy are correct.  It is one of the ornamental crabs.  It resembles the trees at Chatham Village in Mt. Washington, Showy Crabapple “Malus floribunda”.  The top of one is close to my second floor office window. It is not a favorite of birds until after the first hard frost.  Then, usually a week or two before Thanksgiving, swarms of fruit-eaters descend on the tree.  American Robins and Cedar Waxwings bounce from crabapple to crabapple in a frenzied feast.  Mixed in are House Finches and House Sparrows.  Eventually a brigade of European Starling swoops in and the fruit is stripped clean in a few hours.”

Chuck sent a photo of a cedar waxwing tossing back a crabapple, but I chose this one of a robin in the rain — on Chuck’s crabapple tree — because it ties two themes together.

Yesterday’s storm and heavy rain reminded me that there’s a link between weather, birds and food.  We might guess that heavy rain puts birds under stress.  Now we have some proof.

Alice Boyle of the University of Western Ontario studies white-ruffed manakins in Costa Rica.  They’re fruit-eating birds the size of chickadees who, like chickadees, must eat all the time and, like chickadees, change elevation in the winter.

Winter in the Costa Rican rain forest isn’t cold but it’s very, very wet.  Alice Boyle and her colleagues discovered that when particularly long, heavy rain storms plagued the area, the white-ruffed manakins migrated to lower elevations.  Blood tests of rain-affected birds showed they had high levels of stress hormones and were burning fat.  In other words, they were hungry and stressed out.

Boyle says that the stress of rain may be what prompts the birds to fly downhill to drier ground, “These rainstorms have really strong effects, both behaviorally and physiologically, in ways that nobody knew before.”

Her study might not translate to all birds, but it supports our guess that rain means stress.

Read the article and see a picture of the white-ruffed manakin here.

(photo by Chuck Tague)