Last week I used a term I hadn’t defined yet.

Mandible means jaw and comes from the Latin mandere which means to chew.  In mammals the mandible refers only to the lower jaw but in birds it’s the name for the two parts of the beak, upper and lower. 

The best bird to illustrate this is the black skimmer who has very large mandibles for his size.  Related to terns, this bird lives at the coast and feeds on small fish near the surface of the water. 

His beak is his fishing tool.  Not only is it huge and colorful but if you look closely at this picture you’ll see that his lower mandible is much longer than the upper. 

To catch fish the black skimmer flies just above the water dragging his lower mandible in the sea.  When a minnow is caught in his beak, he snaps his bill shut and swallows. 

The technique looks like skimming, hence his name.  Click here to see what he looks like when he’s fishing.

(photo by Steve Gosser)

The shape of a bird’s beak matches its lifestyle.

• Raptors have sharp, hooked beaks for tearing meat.
• Crossbill beaks have crossed tips so they can pull seeds easily out of pine cones.
• Avocets have long, thin, upturned bills because they skim the water with their lower mandibles to capture aquatic food.
• Conversely, flamingos have wide downturned bills because they sweep the water with their upper mandibles.  They turn their heads upside down to eat.

Why do ducks have long bills with serrated edges?  Why do woodpeckers have pointy beaks?  Why do pelicans have pouches?

The answers are easy if you know something about their lifestyles and what they eat. 

See if you can figure out the reasons for the rest of the beak shapes shown above. 

Keep in mind the illlustration is fanciful.  Our spoonbills don’t have orange-brown heads and our buntings don’t have yellow eyes and bills. 

(Frankly I couldn’t refrain from changing the title of the bunting picture.  It was originally labeled “night hawk” but the beak shape is so unlike a common nighthawk’s that I couldn’t stand it.)

(image from www.infovisual.info. The name “night hawk” was altered to “bunting.”  Click on the image to see the original.)

Now that we know where the birds’ ears are positioned, today’s lesson is easy to understand.

Auriculars is another name for cheek feathers (indicated by the red arrow), so-called because they cover the bird’s ears.

According to the Sibley Guide to Birds, auriculars are a “complex set of feathers that channel sound into the ear.  Feathers at the rear border are short, sturdy, and densely colored.  Feathers over the ear opening are lacy and unpatterned.”

On owls, these feathers create a pronounced facial disk that funnels the faint sounds of their prey into their ears.

Click here to see the facial disk — including the auriculars — on a great-horned owl.

(photos by Chuck Tague)

23 July 2010

I was going to talk about head feathers today but some of them are named for the body part they cover.  So what are those feathers covering?  I asked two vultures to help me out.

Vultures don’t have head feathers because of their lifestyle. When they eat carrion they stick their heads into rotting carcasses and get their heads very dirty. Since head feathers are hard to clean, vultures just don’t have them.

Pictured here are a turkey vulture at left and a black vulture on the right.  Notice that you can see their ears!  (red arrows)  Birds’ ears are below their eyes on the edge of their cheeks.   On the turkey vulture you can see that the end of his smile comes pretty close to his ear.

These birds also give us a good view of their nostrils, called nares (yellow arrows). The size is quite different between the two species because turkey vultures have a keen sense of smell (big nares) and black vultures don’t. 

And finally, who can avoid noticing those wrinkles?  I’m glad most birds cover them.

(photos by Chuck Tague)

Have you ever noticed that feathers are different shapes depending on their location on a bird’s body?   This is especially true of flight feathers: remiges (wings) and rectrices (tails).

Shown above are six primary and six secondary feathers from a sharp-shinned hawk.  The feathers are lined up in the order they appear on the bird’s wing with the wingtip at left.

Notice how each feather is a slightly different shape than the one next to it.  This difference allows each feather to contribute its own contour to the overall flight surface of the wing.  In this illustration there’s a contour gap after feather P5 because only six of the sharp-shin’s ten primaries are shown — P10 to P5 — before jumping to the secondaries.

Look closely and you’ll see that the edges of the sharp-shin’s primaries are not uniformly curved. (Click here for close-up.)  Instead they have notches on the wide vane and emarginations on the narrow vane.

Sharp-shinned hawks pursue small birds through the forest and make quick turns through narrow openings to avoid obstacles.  This means their wings are short and their primaries are deeply notched and emarginated to accommodate their hunting style.

Peregrines’ flight requirements are much different.  They dive at top speed in the open air to capture their prey.  They don’t need to avoid trees so their wings are long and their feather edges are nearly smooth for rapid dives and precision flight.  Click here to see that peregrines’ primary feathers are less curved the sharp-shins’.   Only their P10 feather has a noticeable notch.

You can examine the feathers of many birds at The Feather Atlas website where I found this photo.  It’s a National Forensic Laboratory project of U.S. Fish and Wildlife in which they make high-resolution scans of the primaries, secondaries and tail feathers of each species.  There are separate scans for juveniles and females/males if the feathers look different.

I’m sure you’ll enjoy browsing the site and learning more about feather shapes.

(photo from The Feather Atlas. Click on the photo to see the original webpage.  NOTE: It is illegal to possess any feather without a permit.  Click here for details.)

If you have a bird bath I’m sure you’ve noticed a lot more activity there during these long, hot days.

Tuesday evening my bird bath was so popular that nine birds lined up waiting while a robin monopolized the water.  The group included song sparrows, mourning doves, starlings and house sparrows.

When the robin finally gave way it was fascinating to watch everyone drink.  All of the birds except the doves put their beaks in the water then turned their faces to the sky to swallow, just like the blue-winged goose pictured at left.

The doves were different.  They put their beaks in the bird bath and sucked up the water like the pigeon shown at right.

Why do they drink so differently?

The answer is complex and depends upon the species.  It’s partly related to their anatomy (#4) and partly style.  Birds have at least five different ways of drinking:

1. Sip and Tilt up:  Most birds use this method (and the next one) to collect water in their beaks.  Then they turn their heads up to send the water to the back of their throats.
2. Suck and Tilt:  Looks a lot like the first method but is quicker because they collect a lot more water by actively sucking it up.
3. Sucking without raising their heads:  This is the method favored by Columbiformes (doves and pigeons) and helps identify birds as members of this order.
4. Tongue drinking:  Birds who sip nectar are experts at this method because their tongues are specially formed for their favorite food.  Watch hummingbirds and nectar eaters, such as lorikeets, and you’ll see them use their tongues to drink.
5. Drinking in flight:  Swifts and swallows skim the water with their lower jaw, scoop up the water and swallow.

Next time you quaff a cold beverage, think about which method you’re using.  😉

(photos from Wikimedia Commons.  Click these links to see the original photos:  blue-winged goose and rock pigeon)

2 July 2010

Before we can go any further on the topic of feathers — and there’s a lot further to go — we need to learn some terminology.

Feathers are made of keratin, just like our hair and fingernails, but they seem a lot more complex because we don’t live with them every day.  Fortunately this cool illustration from Wikimedia inspired me to delve into the parts of a feather.  And here they are:

Calamus or Quill:  (Pronounced KAL-e-mes)  The large hollow portion of the shaft that attaches the feather to the bird’s skin or bone. It doesn’t have any barbs on it. 

Rachis or Shaft: (Pronounced RAY-kiss)  The long, slender central part of the feather that holds the vanes.  It’s like the mast that holds the sails.

Vane: The plumed part of the feather that grows from the central shaft.  The vanes are like the canvas sails on a mast.  Notice that the two vanes of this feather are about equally wide.

Barb:  The barbs grow from the rachis.  Each barb is a feather within a feather with a little shaft and little barbs of its own called barbules.  When viewed as a whole the barbs are the vane. 

Barbules (too tiny to show above):  Barbules are mini-barbs that grow from the central shaft of each barb.  The barbules on one side of the shaft are smooth.  Those on the other side have tiny little hooks called barbicels that grab the smooth barbules that lie next to it.  When properly preened the barbicels all hook up to their nearby barbules and the feather vane is smooth.  See the bottom row in the illustration below.

Afterfeather: The downy, lower barbs.  They lack barbicels and don’t “hook up” because they’re used for warmth, not flight.

I’ll write more about feathers in the coming weeks, so you may want to bookmark this blog and refer to it later.

(image from Wikimedia Commons.  Click on the image to see the original.)

After nesting is over, what’s the next big item on a bird’s agenda?  

Molting.

Birds lose their old feathers and grow new ones because their feathers wear out. 

Shown here are four primary feathers (remiges) molted by a black-legged kittiwake.  It’s easy to see that these feathers are no longer in good shape for flight.  Their edges are not smooth.

Notice how eroded the white barbs are compared to the black ones.  That’s because pigment adds strength to the feather.  The darker the pigment, the stronger the feather.  For this reason many sea birds have black tips on their white flight feathers and some birds have completely black primary or secondary feathers. Here are three examples of black-tipped wings on …

For more information on feather wear and how it affects the appearance of shorebirds, see this very helpful blog (written from Malaysia).

(photo from Wikimedia Commons.  Click on the caption to see the original)

If you watch birds preening you’ll often see them twist their necks over their backs, touch the tops of their tails with their bills, and groom their feathers.

The spot they’re touching is the uropygial or preen gland.  It has nipple-like pores that secrete preen oil to keep their feathers supple and suppress parasites.

Preen oil also provides some waterproofing.  Perhaps that’s why this gland is best developed in petrels, pelicans and ospreys.

Preening is vital for birds’ survival.  Besides removing feather and skin parasites and spreading preen oil, birds do it to peel the scales off pin feathers and comb the feather barbules back into place.  Feathers must be in their original shape with all the barbules interlocking in order to fly well and stay waterproof.  Preen oil probably holds the feathers in their combed position just as our oily hair products keep our hair in place.

Not all birds have preen glands — ostriches and emus don’t — but waterfowl do.  In this photo a female common eider is pointing her long white bill directly at her preen gland.  You’ll see this often if you watch ducks.

You’ll also see it if you watch peregrines because they must keep their feathers in tip top shape for precision flight.

Does preening waterproof them?  When my friend Karen sees the Pitt peregrines touch their preen glands she says, “It’s going to rain.”

(photo by Chuck Tague)