Saturday, July 31, 2010

Wells Lake Rookery: Possible Botulism

On Friday morning, John H. and I canoed to the Wells Lake Rookery near Faribault in Rice County, Minnesota.
The majority of the birds present were Double-crested Cormorants.
We were careful not to overly disturb the birds so we did not disembark.  Many cormorants flew overhead.
Also nesting in the rookery were dozens of Great Egrets.
And a few Great Blue herons.
All, however, was not well at the rookery.  Dozens of cormorants were dying along the shore. They displayed the symptoms of avian botulism. This diagnosis should be confirmed through laboratory analysis of the carcasses.  Other species at the rookery did not seem to be affected.
According to the National Wildlife Health Center,, avian botulism is a paralytic disease caused by a toxin produced by the bacterium, Clostridium botulinum. The toxin affects the birds' nervous systems, leaving them unable to use their wings and legs, neck muscles (as in the photo above) and other muscles. Although we only saw a few dozen crippled or dead cormorants, avian bacteria can strike thousands of waterfowl at once.

Botulism comes in several strains.  Type C affects birds, mostly waterfowl, shorebirds, colonial waterbirds, and other species.  Humans, dogs, and cats are resistant to this strain.  Only a few cases are reported from people and their pets.  We have to worry about Types A, B, and, perhaps E.  A and B are contracted from eating improperly preserved canned products.  Type E is from poorly cooked fish, and affects gulls, loons, and other birds. Thorough cooking destroys all types of botulism, according to the National Wildlife Health Center.

John and I immediately reported this mini-outbreak to the Minnesota Department of Natural Resources. Outbreaks can be controlled by collecting and destroying carcasses and, if dealt with promptly,  through intervention by wildlife rescue organizations.

Thursday, July 29, 2010

Spiny Softshell Turtle

The final highlight of Erika and my stroll on Monday to the Carleton College Arboretum was our encountering this soft-shelled turtle along the banks of the Cannon River.  Separating Smooth Soft-shell Turtles from Spiny Soft-shells proves to be difficult.  To identify them, you usually have to have the turtle in hand.
In the photo below, you can make out bumps along the leading edge of the shell.  I suspect these structures indicate that this turtle is a Spiny Soft-shell. In both species, males are much smaller than females.  This turtle seemed very large to us, so we suspect she is a female.
The Spiny Soft-shell is more common than the Smooth, which is considered a species of special concern in Minnesota.  In any event, the Minnesota website on Minnesota herps ( shows Rice County oddly lacking records for either species.  Certainly this hiatus is due to oversight.  Erika and I previously have paddled by softshell turtles on the Cannon River.

Wednesday, July 28, 2010

Sedge Wren

While Erika and I walked by a fairly dense stand of Big Bluestem in the Carleton College Arboretum (see last post), we were startled by a loud bird song only a few feet from our trail.  
I made "spishing" sounds, and up popped a Sedge Wren. Erika continued to "spish" while I took photographs. The wren circled and called back at us.  Click here to hear the call. Often, before I could auto-focus my camera, the wren darted into the grass and out of view.
The Sedge Wren is an odd bird.  This wren is nomadic, breeding in an area during one year but not the next.   Furthermore, Sedge Wrens many breed in the spring, depart the breeding grounds, and, in the same season, breed again elsewhere.  Often they nest in May and June in Minnesota, Wisconsin, North Dakota and Saskatchewan.  A second nesting season occurs in July and September, with birds moving into Nebraska, Kansas, Missouri, Vermont, and Massachusetts.  Our July Sedge Wren definitely appeared to be territorial.  I do not know if it was a local bird making a second breeding attempt or if it was one of those nomads from a foreign breeding area.
Male Sedge Wrens may be polygynous--they may mate with more than one female--and females may be serially polyandrous--they may mate with more than one male.  Females in a Minnesota study, however, had higher reproductive success when they mated with monogamous males.  On the other hand, polygynous males have higher reproductive success than do monogamous males.

Our Monday stroll had one more surprise, which I will share with you in the next blog post.

This information is gleaned from Herkert, James R., Donald E. Kroodsma, and James P. Gibbs. 2001.  Sedge Wren (Cistothrous platensis), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

Tuesday, July 27, 2010

A Walk in the Carleton College Arboretum

One reason Erika and I retired to Northfield, Minnesota, is the Carleton College Arboretum.  Located on the north edge of town, this 880-acre preserve is a wonderful resource for both the college and the Northfield community.  The arboretum contains riparian and upland forest, oak savanna, and restored tallgrass prairie.  In late summer, Erika and I especially enjoy 140 acres of prairie.  Wildflowers and birds abound.
On Monday we took an hour's walk in the arboretum.  On our way to the prairie we came upon a plant with which I am unfamiliar.  Being a casual botanist, encounters with unfamiliar wildflowers are not that uncommon for me.  The plant in question is a Common Evening Primrose (Oenothera biennis).  These yellow flowers bloom in the evening and wither the following morning.  The plant has a plethora of medical uses ("eczema, asthma, migraines, inflammations, premenstrual syndrome, breast problems, metabolic disorders, arthritis and alcoholism"), and, infusions of the plant, as a folk tea or coffee substitute (Coffey, 1993. The History and Folklore of North American Wildflowers).
The prairie was awash in purple Wild Bergamot and yellow sunflowers.  The Compass Plant (Silphium laciniatum) was difficult to identify.  Thanks to the director of the arboretum for help with this one. The basal leaves of this plant tend to point north and south, thus the name.  The North American prairies were once awash with this species.
Big Bluestem (Andropogon girardii) is a grass that is emblematic of the tallgrass prairie.  When European settlers first rode their horses into this prairie, Big Bluestem was so tall that they sometimes lost their way.  (Perhaps the first Europeans had small horses, since now this grass grows to about 10 feet.)  In this photo you can see why an alternative name for this grass is Turkeyfoot.  This species is a dominant member of the prairie ecosystem.  It is a warm-weather plant, and does not become mature until relatively late in the summer, allowing other earlier-spring plants to complete their life cycles earlier in the spring.

As Erika and I walked along a path through Big Bluestem, a small but vociferous bird called forth from within the tangles.  I will report on that encounter in my next blog post.

Sunday, July 25, 2010

Great Blue Heron Gular Fluttering

By opening their bills, and vibrating their upper throat muscles and bones, herons (and a few other bird families) are able to increase the passage of air across the mucus membranes of their throats.  This behavior, called gular fluttering, increases heat loss on hot days.  Because of its permanent down coat and lack of sweat glands, the ability to lose excess heat is important to a bird.
On Friday I happened upon this Great Blue Heron gular fluttering. Temperatures, high for Minnesota, reached the mid-80s F.  In the photo below, you can see that the upper throat is expanded in this process, thus expanding surface area.  Blood flow in the throat is also increased and vessels are dilated to facilitate heat loss.
I am surprised that the bird, in order to cool off, did not wade into the water.  I suspect, however, that relatively little heat is lost through a heron's feet.  Heron feet contain counter-current exchanges between their arteries and veins, which have evolved to maintain heat during cold winter days.  I suspect that these exchanges can not be turned off and on.
While I watched, the heron occasionally peered into the water below its perch and speared small minnows. The heron successfully caught a small fish in each of the three attempts I witnessed. After consuming the minnows, the heron returned to gular fluttering.

Wikipedia incorrectly writes, "birds also avoid overheating by gular fluttering, flapping the wings near the gular (throat} skin."  Good Heavens!  You CAN'T believe everything you read on the Internet?

Friday, July 23, 2010

Why Do Birds' Knees Bend Backwards?

Reading my recent Song Sparrow post, with my comment on wing bones, I am led to ask, "Why do birds' knees bend backwards?"  Trick question!  Bird knees bend the same as ours....

The leg joint of this Great Egret is actually the bird's ankle.  The foot bones are elongated and, just like with us, connect the ankle with the toes.  Above the angle run the tibia and fibula, which connect on the upper end, to the femur.  Birds' femurs (thigh bones) usually lie close to the body.  The knee is at the lower end of the femur. Check out the next turkey or chicken that you carve.

Thursday, July 22, 2010

Eastern Wood-Pewee

On Monday I banded an Eastern Wood-Pewee.  Although common in Eastern forests, not much is known about its breeding habits. One problem is that this flycatcher nests high in the forest canopy. 

Other birds of note: a Black-capped Chickadee originally banded on 21 August 2008 was recaptured on 19 July 2010; a Northern Cardinal banded on 18 April 2008 was recaptured on 20 July 2010.

Wednesday, July 21, 2010

Song Sparrow Juvenile Plumage

I recently banded this juvenile Song Sparrow.  Young are born naked and molt into this juvenile plumage, which lasts until the first fall, when birds obtain their basic (winter) plumage.  Sibley's Birds of North America is one of the few field guides to illustrate this plumage.  The underparts of these young birds have brown stripes against a buffy background (unlike the white background of older birds).  Often they are so buffy that the beginning birder might mistake them for Lincoln's Sparrows.

Note also the radius and ulna bones visible on the underside of this bird's wing.  The outer end of these two bones are the bird's wrist.  The secondary flight feathers attach to the ulna.  The outer bones on the wing are the bird's carpels and digits (modern birds have but three).  The primary feathers attach here.  Thus birds regulate their flight with their hands.

Tuesday, July 20, 2010

Yellow-throated Vireo

For almost three years, I have heard Yellow-throated Vireos at our Dundas banding station.  Surprisingly, this is the first one we've caught. Usually this species is outnumbered by Red-eyed Vireos, a similar-sounding bird, in the forest edge habitat they share. In the Northeast during the early 1900s, Yellow-throated Vireos almost disappeared.  Birders thought the population decline was caused by spraying for Dutch Elm Disease.

Yellow-throated Vireos are monogamous.  To attract females in the spring, unmated males begin building nests.  The females take over, and the male accompanies the female to and fro, even if he does not help with subsequent nest construction. He begins calling if he loses contact with his mate.  Once the young have fledged, each member of the pair goes its own way.

As often in this blog, my primary source of information is the AOU's The Birds of North America, in this case: Rodewald, Paul G and Ross D. James. 1996.  Yellow-throated Verio (Vireo flavifrons), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

Monday, July 19, 2010

Cabbage White Butterfly

The Cabbage White Butterfly, accidentally introduced into North America from Europe, is now found in every state of the United States.  Cabbage White's with two wing spots are females.  Males have but one, and spend the day trolling for females (see photo below).  After mating, the female lays her eggs on the underside of leaves.  The pupa hibernate. Cabbage Whites can be pests on cultivated cabbages, kale, radishes, broccoli and horseradishes.  The Cabbage White above landed on a variegated nasturtium in Erika's garden, which will be my hunting ground for future butterfly blog posts.

Sunday, July 18, 2010

House Sparrow

Digital photography has revolutionized my birding. I am excited even to take a picture of the lowly House (or English) Sparrow. They are despised and ignored by most birders and banders. Not only have these sparrows been introduced from England and Germany, they are ubiquitous (they have a nearly world-wide distribution) and take over nesting cavities of native species. Why were they introduced? I read that people wanted every bird mentioned in Shakespeare (or maybe birds of the Bible) to inhabit Central Park. In any case, the English tend to introduce British birds around the world.

House Sparrows prove to be interesting. The species demonstrates evolution at work. Since their introduction to Brooklyn in 1851 (and San Francisco in 1871, and Salt Lake City in 1873), House Sparrows have evolved! Today House Sparrows are smaller in the southern parts of North America and larger in the north. Furthermore, they have longer limbs in warm climates and shorter ones in cooler areas. (Similar size trends are noted for many species. Larger birds retain heat better than smaller ones since the larger ones have less of a surface to body mass ratio. And you would want shorter legs in cool climates to protect you from heat loss.)

Lowther and Cink (2006) also cite an 1898 study of House Sparrows after a Rhode Island ice-storm. Half of the 136 birds brought in to a lab died. Larger males survived more often than smaller ones. Females showed different survival patterns--average-sized females survived better than larger or smaller ones. This study is a clasic example of natural selection.

Friday, July 16, 2010

Michigan Lily

Today Erika and I rode our bicycles along the Sakatah Singing Hills State Trail.  Just west of Warsaw, we zipped by a few lilies in a marshy area below the trail-side.  In college I contemplated becoming a botany major, but a number of events conspired against that path. I remain, however, interested in wildflowers.  Over the years, I have taken a few wildflower photos (the flower photos are after all the birds), which you can see at:

In any case, today's lilies struck me as small but intense orange, with their petals oddly reflexed towards the sky.  We stopped and peddled back to the flowers, Michigan Lilies, Lilium michiganense. They are found across much of the Midwest. This plant is threatened in Tennessee and endangered in New York.  In Minnesota, it has become uncommon due to conversion of wetlands to farmland and because of roadside maintenance destroying habitat (Moyle and Moyle, Northland Wildflowers, U MN Press 2001).

By the way, this lily's nomenclature is a bit confusing.  Moyle and Moyle call this flower the Turk's-cap Lily. The USDA plant database (, however, reserves this common name for Lilium superbum, a plant not known to occur in Minnesota.

Thursday, July 15, 2010

Barn Swallow

Mid-July is upon us and we have the first sign of fall: Barn Swallows beginning to congregate on area power lines.  These swallows winter in Central and South America.  This species may be our only long-distance migrant that also breeds in its wintering grounds: Barn Swallows are known to nest in the austral summer in northern Argentina. These birds may be becoming southern residents and not making the return migration to North America.

Barn Swallows historically nested in caves, but now almost exclusively use human habitations.  This abundant species breeds across North America, Asia, and Europe, and its range is spreading along with human populations.

My source for most of this information is Brown, Charles R. and Mary Bomberger Brown. 1999. Barn Swallow (Hirundo rustica), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

Tuesday, July 13, 2010

American Robin

The American Robin is the most abundant of the North American thrushes.  Robins are so numerous that many folks don't appreciate their beauty.  I banded this male robin (you can tell it is male because of its dark head--females have much grayer heads) on 6 April 2009 and recaptured it on 12 July 2010. Male robins are monogamous during the breeding season, but usually take different mates in subsequent years.
I am fascinated by robin subspecies.  Turdus migratorius migratorius, found across much of North America, is the most common robin and is the one found in Minnesota.  T. m. propinquus is larger and paler than our birds and lacks the large white spots on the outer tail feathers. This race is found in the western US from British Columbia and Montana, south into Mexico and the Great Plains.  Two subspecies of interest to Minnesotans are T. m. caurinus of the rain forests of western Washington north to southern Alaska and T. m. nigrideus of the damp coniferous forests of eastern Canada.  Both of these races are darker-backed than our birds and both might be expected to appear in Minnesota in the winter.  In the northland, many non-birders are surprised when they see robins in the winter.  But robins are not uncommon during the winter and I have noticed that they are usually much darker-backed than are our breeding birds.  For both of these races, spending the winter in Minnesota counts as a southern vacation!  Nevertheless, be warned, I am aware of no verified records of either subspecies from the state. (Three additional robin races exist, one the the southeast US and the other two in Mexico.)

Sunday, July 11, 2010

Cedar Waxwings

The Cedar Waxwing is one of our two birds with yellow-tipped tails (the other is the Bohemian Waxwing).  The species is primarily a fruit-eater; waxwings have been known to become drunk on fermented berries.  If the berries are near a road, this can be fatal for the birds. We all know that being drunk on a highway is a poor strategy.
Waxwings derive their name from the red, wax-like tips to their secondaries.  You can see these structures in the photo above.  These are odd feather growths because they can be present on males or females. Older birds, however, tend to have more red tips than younger ones. The bird below is a male without the feather tips. You can tell it is a male because the black on its throat is more extensive than on a female (which sports only a very narrow line of black below the bill).
Flocks of Cedar Waxwings are often found in cedar (and other fruit) trees.  I did not expect to find these birds on a barbed wire fence at the Dennison Water Treatment ponds near Northfield.  Their unkempt, long crests also surprised me.  Usually waxwings have handsome, slick plumage.

Friday, July 9, 2010

Dakota County Common Loon

Susan P. mentioned that she found an adult and young Common Loon at Kingsley Lake near Lakeville, Dakota Co., and that the birds could probably be photographed.  Because loons are my favorite birds,  Erika and I were not long in searching.  We immediately found the birds along the southwest corner of the lake. The adult gave several clear and piercing yodels as we approached.
I did not know that Common Loons nest this far south in Minnesota.  Janssen, in his book, Birds in Minnesota, indicates that Dakota Co. is the southern limit to their nesting range.  Non-breeding loons are found south of their nesting range.  Historically, loons may have bred as far south as the Iowa border.
If you look for these loons, watch your toes.  The lake is guarded by this aggressive snapping turtle.  If you look closely, a leech is riding the turtle's back. Perhaps the turtle is one reason there is only one young loon. 
More perils await both loon parent and young, since their main wintering area in the Gulf of Mexico is awash in spilled oil.  These birds are probably doomed unless they are fortunate enough to winter, as some loons do, along the Atlantic coast.

Thursday, July 8, 2010

Recaptures and Chickadee Tails 2

In my recent post about ageing birds by tail feather wear, I compared a Black-capped Chickadee to a Northern Cardinal.  Today I banded an adult female chickadee, and I thought comparing two tails from the same species made more sense. The worn tail on the left is from the adult chickadee, while the pointed tail feathers on the right is from the young bird.
I also recently recaptured three birds from last year--two House Wrens: one banded on 11 May 2009, recaptured on 28 June 2010; the other banded on 19 May 2009 and retrapped on 8 July 2010.  A Chipping Sparrow caught today, 8 July 2010, was banded exactly one year ago.

Tuesday, July 6, 2010

Speaking of Cloacae

Roxie Laybourne, who spent her career at the National Museum in Washington, was one of my mentors.  Among her claims to fame was that she was the only person who could identify the sex of a living Whooping Crane.

Whooping Crane sex is important.  The Fish and Wildlife Service took eggs from wild nests in Canada and hatched them in Maryland.  They bred these birds to build a captive flock, thereby assuring survival of the species in case anything happens to the wild birds (oil spills, late season hurricanes?). 
The problem is that Whooping Cranes form life-long pair bonds.  If you accidentally try to mate two males, they may form a homosexual pair bond, and you have just wasted two very valuable birds.  Roxie developed a machine, basically an ophthalmoscope with tweezers, to peer into a Whooping Crane's vent and into the cloaca (see last post).  Male birds have two testes, but females normally have but one ovary.  Thus, the male cloaca has five internal openings (two sexual ducts, two urinary ducts, and the digestive tract); the female has four (only one sexual duct).  By counting those openings, Roxie knew the sex of those birds.  (Of course, the cranes were not crazy about having their cloacae examined.  Wildlife technicians caught the captive birds and placed them in special straight jackets before Roxie went to work.)

Monday, July 5, 2010

Cloacal Protuberances

I last posted about some of the ways banders identify a bird's age.  Often both sexes of birds are similar.  The photo below is of one of these species, the Chipping Sparrow. In the photo, the bird is on its back, with the tail going towards the upper right and the belly feathers moved out of the way. 
When breeding, most male birds have a swollen cloacal protuberance, the structure in the center of the photograph.  A female's cloaca is, by comparison, never so swollen. Structurally, the cloacal protuberance is not a penis.  The swollen cloaca is also not a cloacal phallus (an organ of ducks and ratities), which I wrote about in my 2 April 2010 post.

The cloaca is a chamber into which empty the digestive tract (the anus empties into the cloaca; the exit of the cloaca is called the vent), sexual ducts, and urinary tubes.  Cloaca comes from the Latin for sewer.  Male birds get the job done with a cloacal "kiss," with little or no penetration of the female. I will have more to write about cloacae (I assume cloacae is the plural of cloaca) in my next post.

Saturday, July 3, 2010

Tail Tip Tales

The Black-capped Chickadees, as evidenced by my banding 12 recently fledged young, have fledged their first broods.  Many young birds look very similar to adults, and discerning the ages can be difficult.  One method of aging birds is by the ossification of their skulls.  Young birds have almost transparent "windows" in their skulls.  These windows become ossified and opaque as the bird ages. Observing the relative ossification of bird skulls, however, requires practice and experience.

Tail tips also give a clue to age.  Look at the tips of this recently fledged Black-capped Chickadee's tail. The tips of the tail feathers are pointed and unworn.  These are relatively new feathers, grown as the bird molted from its nestling feathers (juvenile) to its current basic (winter) plumage.

Compare the shape of those tail tips to those of an adult female Northern Cardinal.  The adult bird does not molt all its tail feathers at once--the molt into winter plumage takes weeks and does not occur until after the breeding season is finished.  Thus the adult feathers are squarish (not pointed like in the chickadee) and relatively worn.