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,

http://www.nwhc.usgs.gov/disease_information/avian_botulism/index.jsp, 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.

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 (http://herpnet.net/Minnesota-Herpetology) 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.

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: http://bna.birds.cornell.edu.bnaproxy.birds.cornell.edu/bna/species/582.

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.

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?

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.

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.

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.

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: http://bna.birds.cornell.edu.bnaproxy.birds.cornell.edu/bna/species/247

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.