Wednesday, August 31, 2011

August Warblers 2

August bought two additional early fall migrants to our banding station.  The first, a young Canada Warbler, is a subdued version of its bright, spring plumage.  Canada Warblers are not local breeders.  The second could be a local bird, and is definitely more of a challenge to identify.  It is a young Common Yellowthroat.  Field marks here include the ochraceous yellow on the throat and the brownish tinge to the fore-crown.

Tuesday, August 30, 2011

Shadow Darner

Sunday evening I rescued this Shadow Darner from my bird net. Shadow Darners are common across northern North America. Among the largest and fastest-flying dragonflies, Shadow Darners prefer shady areas, usually near water. They fly into the late evening and sometimes even at night (Montana Field Guide). They also fly late into the fall. Already our evenings and nights have been cool, with temperatures in the 60s F.

Shadow Darners can take advantage of these cool climates, habitats, and times because they can regulate their body temperatures. A number of factors contribute to this phenomenon. When I removed the darner from the net, the dragonfly acted lethargic (as you can see as it perched on my finger). Later I placed the darner on a lily leaf. Here the animal began to quiver its wings, a behavior called "wing-whirring." Like shivering, this action can elevate the body temperature.  Furthermore, a darner can control heat loss by altering the circulation between its thorax and abdomen. Finally, large dragonflies like darners more efficiently retain body heat than do smaller ones (May 1976). When I returned from closing my nets for the night, the Shadow Darner had flown.

Monday, August 29, 2011

Blue-fronted Dancer

Blue-fronted Dancers are damselflies named for their bouncy flight. This summer I found them to be common along many area waterways.  Males, like the one in the first photo, are fairly distinctive.  Field marks include their blue bodies (with very thin black lines separating the body parts) and the terminal azure abdomen segments.
I find dragonflies and damselflies to be difficult to identify. Immature males can resemble other damselflies. Female Blue-fronted Dancers complicate matters by coming in two forms, blue and brown. Blue females look like males, but lack blue-tipped abdomens. Brown females are similar to other female dancers, and I have relied on Scott King for my identification of the brown female below. (Kirk Mona recently blogged, "What if everyone could tell if you'd had sex? Ask a Dragonfly." I am tempted to title this post, "What if your prospective mates look like different species?")

Saturday, August 27, 2011

August Warblers

Fall warbler migration in the Upper Midwest begins in the second half of August. This year I banded a Chestnut-sided Warbler on 21 August, an Ovenbird and a Mourning Warbler (both on 22 August), followed by a Black-and-White Warbler on 26 August. All were young and all but the Mourning were conceivably local birds.  I banded none of these species, however, earlier in the summer.
Last fall the migration appeared to began earlier. In 2010 I banded a Blackburnian and a Canada Warbler on 12 August; my first Black-and White Warbler was captured on 19 August (along with a second Blackburnian). The next day I banded three Chestnut-sided Warblers. I ringed over a dozen additional warblers as the month progressed.
Photos: Chestnut-sided Warbler (top); Ovenbird (second); Black-and-white Warbler (third); Mourning Warbler (bottom).

Friday, August 26, 2011

Least Skipper

Skippers are hard to identify. With a little bit of help from my friends, I labeled this one as a Least Skipper. Field marks include its small size, rounded wings, and dark forewings. The checkered antennae also help.

The Least Skipper inhabits the eastern United States and southern Canada. This butterfly is often abundant, but the flight can be short-lived.  Least Skippers fly about damp, tall grasses along roadsides, streams, and meadows.  I found it in unmowed grass along a small creek at the Dennison, Minnesota, sewage treatment ponds.

Wednesday, August 24, 2011


Duckweed is our smallest flowering plant. It floats on pond surfaces, often turning lakes green. The plant does not grow in moving water and favors nutrient-rich water. Duckweed reproduces both sexually (via a tiny flower) and asexually (by budding). A single duckweed produces a daughter bud about once a day. In about two weeks, this rate of reproduction results in about 17,500 plants! A pond covered with duckweed suffers from few underwater plants and usually low oxygen levels that cause fish to die. Koi, goldfish, and grass carp will eat duckweed, but prefer other plants. Ducks eat duckweed, and also disperse duckweed that stick to their feathers. When people complain about duckweed, however, I reply that I prefer a pond filled with a flowering plant rather than slimy algae. Furthermore, duckweed is a high-protein food source for waterfowl (and, potentially, for people). The plant, with its extraordinary reproductive ability, has the potential as a renewable resource for clean energy--an energy source that actually removes carbon-dioxide from the air.

Tuesday, August 23, 2011

Summer Azure

The Azures comprise almost a dozen forms that were once considered to be a single, variable, and abundant species across North America. Now several species are recognized, but their taxonomy is confusing, even for experts. Kaufman in his Field Guide to Butterflies of North America suggests that amateurs simply enjoy these bright blue-backed, white-undersided butterflies as Azures. Let the lepidopterists argue about species. In mid-summer in Minnesota, however, the choices are somewhat limited. I suspect the odds are excellent that this photograph is of a Summer Azure.

Many Azure caterpillars have a symbiotic relationship with ants. The caterpillars secrete a sugary substance that feed the ants, while the ants protect the caterpillars from predators. In other species the caterpillars feed the ants while on the caterpillar host plants, but then move into ant nests and begin feeding on ant larvae. Nevertheless, the ants continue to protect the butterfly pupae. The adults break out of the pupae case and must crawl out of the ant nest before the butterfly can take flight (Wikipedia).

Monday, August 22, 2011

American Dagger Moth Caterpillar

At Afton State Park, Erika and I happened upon this caterpillar of the American Dagger moth. Anything this bright must be an example of aposematic coloration--"be careful, I'm poisonous!" In this case, you'd be correct. Many people develop a nettle-like rash from handling this caterpillar. Seeing as how this critter was grazing on Poison Ivy, the habitat would get you if the caterpillar didn't! The moth is found east of the Rockies, primarily in the United States.

Sunday, August 21, 2011

Slender Spreadwing

Slender Spreadwings are identified by their long, thin abdomens and by the whitish wing edges. Note that the wings narrow to stalks where they attach to the body. In July, Scott King found this individual at Lake Byllesby County Park in Dakota County. They favor ponds, wetlands, and streams.  Eastern Spreadwings are found acorss a wide area of eastern North America. I was tickled to learn from Scott that the Spanish for Odonata is Caballitos del Diablo--Devil's Ponies.

Saturday, August 20, 2011

Henslow's Sparrow

On 19 August 2011, Erika and I strolled through the Afton State Park interpretive prairie loop.  Dragonflies were our main goal. Aware that Henslow's Sparrows were a possibility, I stopped short when I heard a distinctive, single, hiccup-like "tsi-lick" from within the grass. (In this link, used with permission of Thayer Birding Software, the song is repeated a bit more rapidly than what we heard.) Using the Sibley App on my smart phone, Erika and I quickly confirmed that this was a singing Henslow's Sparrow. The location of the call and the bird were difficult to ascertain. In the photo above, the sparrow is in the dead center of its preferred prairie habitat.
To our surprise and delight, the Henslow's Sparrow flew up and continued to sing from to the top of a nearby goldenrod. Visually this sparrow proved far more difficult to identify than was its song. The olive-green characteristic of this species in the spring was reduced to a patch on its nape and a very faint wash across the head. The underparts were also only very faintly buffy. Although the bird showed a few flank streaks, the breast was faintly, if at all, streaked. This relatively lack of color and streaking may be the result of the bird's being in a very worn late summer plumage.
On the other hand, the double "mustache" stripes are quite visible (specially in the photograph just above). These field marks are actually a subauricular line and lateral throat-stripe. Furthermore, the bill is large and conical and the top of the head profile is relatively flat. The rusty wing coverts and tertial feathers are also characteristic of a Henslow's Sparrow. The spots on the head are also good field marks.
Recently Henslow's Sparrow populations have declined at rates approaching 10% a year. This decline is the steepest of any North American grassland bird (Herkert et al. 2002). The main reason for this decline has been their shrinking grassland habitat.  Local population increases have been associated with the Conservation Reserve Program and with efforts at prairie restoration such as at Afton State Park. But these conservation efforts are probably not sufficient to buck this species' downward population trend.

Friday, August 19, 2011

Black Saddlebags

Black Saddlebags are gliding aerial predators. The name comes from the black bands on their hind wings. The back wings are broadened to aid in gliding. Males are black. Females are larger and have a spotted pattern on their dorsal abdomens, visible in the third photo. Females and young males tend to have paler heads than do males. Saddlebags rarely perch, but will rest high in trees. When prey insects are plentiful, saddlebags often form feeding swarms.
Black Saddlebags are common from southern Canada south to Mexico, Bermuda and Cuba. I took the first of these photos at a farm a couple of miles north of Northfield. The middle two photos were of Black Saddlebags flying over a field near the Cannon River on the north end of Carleton College's arboretum. Among the several saddlebags at this last location glided a paler dragonfly, probably a female Red Saddlebags. This species is found across the eastern United States. Male Red Saddlebags are red-bodied, but females are light brown or pale orange with white and brown eyes. 
As they glide and chase after their flying insect prey, all saddlebags are difficult to photograph. Capturing images requires patience, manual focusing, and large memory cards (to deal with an inevitable plethora of out-of-focus images)--and a fair amount of dumb luck.

Thursday, August 18, 2011

Northern Rough-winged Swallow

Last week, Erika and I canoed the Cannon River from Northfield to Cannon Falls. Along the way we saw a few Northern Rough-winged Swallows as they perched on exposed timber over the river. This swallow breeds across North America, from southern Canada through most of the United States. Our birds migrate south in the winter to join resident populations from Mexico through much of Central America.

Why is this bird called a Northern Rough-winged Swallow? The outer-most primary of this swallow has a rough edge. In adult birds, the outer primary edge lacks barbules. Males have curved hooklets and females have thickened spines that give the feather a rough edge. De Jong (1966) writes, "The possible adaptive significance of this feature remains a mystery."

Why is this bird called a Northern Rough-winged Swallow? Rough-winged Swallows were thought to range as groups of interbreeding races from North America through South America. In 1981, researchers in Costa Rica discovered a break in this species's range. Northern birds breed in the mountains, whereas southern birds are restricted to lowlands. Formerly considered to be races and although very similar in appearance, northern and southern birds can be told apart.  Since they do not interbreed, we have the Northern Rough-winged Swallow. The Southern Rough-winged Swallow is found from Costa Rica on south.

Wednesday, August 17, 2011

Wandering Glider

Scott King alerted me to the presence of Wandering Gliders, although I found them zig-zagging over Carleton College's arboretum prairie rather than over parking lots full of shiny cars to which, according to Scott, they are often attracted. 

Found on every continent except Antarctica, the Wandering Glider is probably our most widespread dragronfly. It is found from northeastern, southern, and southwestern North America to southern Argentina and Chile. It also inhabits southern Africa, the Arabian Peninsula and most of the Middle East, west and north across the Indian subcontinent (they are recorded from over 20,000 feet elevation in the Himalayas) to China, Japan and Korea. It is known from Southeast Asia to Australia. You can look for Wandering Gliders across the Pacific--the species is the only dragonfly on Easter Island and was the first Odonata to recolonize Bikini Atoll after the nuclear bomb testing (Wikipedia). They have landed on ships hundreds of miles from land (Mead). Only Europe and northern portions of the Old World seem to lack breeding Wandering Gliders, but even in those northern locations these dragonflies are occasionally reported. In colder parts of their range, Wandering Gliders are migratory. 

Tuesday, August 16, 2011

Avian Pox

During a relatively unproductive banding day on 15 August 2011, I caught this juvenal Chipping Sparrow that suffered from a bad pox infection. Avian pox is a virus that affects many different species of birds. The virus is commonly seen in songbirds. This slow-developing disease comes in three strains (fowl, pigeon, and canary pox virus).

Mosquitos carry the virus, which is also transmitted by contact with other infected birds and by contaminated food or water, particularly at bird feeders. Two forms of the disease exist. The first causes warty growths around eyes, beaks, feet, and unfeathered skin. The second causes growths in the respiratory system.  Birds with either form of pox are often weak and starving. This Chipping Sparrow, with its crusty warts and yellowish fluid around its nostrils, appears to show symptoms of both forms of avian pox.

Birds, particularly Wild Turkeys and Bald Eagles, suffer significant mortality from pox. Birds can survive, as apparently did an American Crow reported by The Minnesota Birdnerd blog site. Survivors acquire at least limited immunity from the disease. No treatment is known for avian pox in wild birds. Washing infected areas with antiviral drugs often just spreads the disease.  Birds can be saved by wildlife rehabilitation units, but require supportive care and protection from secondary infections. Bird feeding areas should be decontaminated with 10% bleach. Removing infected birds may reduce transmission of the disease but is illegal. Mosquito control is also a possible remedy. Fortunately humans are not known to be susceptible to avian pox infections. People who handle birds should take precautions to avoid spreading the disease between captive birds. This information was gleaned from the National Wildlife Health Center and the Michigan Department of Natural Resources.

Monday, August 15, 2011

Eastern Pondhawk

The Eastern Pondhawk was one of the first dragonflies I listed last year in Erika's garden. This summer Scott King showed me the male above at Lake Byllesby in Dakota County and I found the female below in Rice County. 
This dragonfly is a fierce predator, taking other insects, some even larger than the pondhawk. They will take other dragonflies and even their fellow Eastern Pondhawks. In the photo below, the victim's identity is uncertain, but may be a meadowhawk or a Blue Dasher.

Saturday, August 13, 2011

Chipping Sparrow

Because juvenal-plumaged Chipping Sparrows are not included in some field guides, these birds can be difficult to identify. As you can see in theses photographs, juvenals are streaky below and lack the adults' rufous caps. This plumage is acquired quickly by nestlings--by eight days hatchlings are recognizably in juvenal plumage and, after a month, they are fully molted. The time young birds spend in juvenal plumage varies greatly. They begin molting into their winter (basic) plumage as soon as two weeks or as late as a month after hatching. Early broods stay in juvenal plumage longer than later hatched birds. Birds in eastern North America tend to molt out of juvenal plumage in their summer range. Western birds suspend their molt, completing it after they migrate to their wintering grounds (Middleton 1998).

Friday, August 12, 2011

White-tailed Deer

Erika and I saw several White-tailed Deer fawns along the Cannon Valley Bike Trail on 9 August.  Over the past several decades, many deer populations have exploded. In parts of North America, deer are considered to be pests--they eat garden plants and damage trees. Deer are also a favored host of the deer tick, which carries Lyme Disease. The cutting of forests for timber and for human habitation has resulted in an abundance of deciduous food sources for deer.  Natural predators have also been greatly reduced or eliminated. Deer are further attracted to highway rights-of-way, as these produce a plethora of grasses. The results include collisions with commuters and the ire of gardeners and farmers. Deer population control efforts, however, tend to be contentious.  

Thursday, August 11, 2011


Woodchucks (Groundhogs) are really over-sized squirrels.  They are also true hibernators, sleeping away the winter. Groundhogs are mostly vegetarians, preferring wild grasses and occasionally crops.  Their burrows can do damage to cropland and house foundations.  Erika and I found this Woodchuck along the freshly-mowed Cannon Valley Bike Trail in Goodhue County.  I assume this mouthful is to gain weight--these squirrels can begin hibernation in October, only two months from now. The freshly cut grass must have been like a fast food restaurant.  I have not seen reference to their lining their burrows with grass.

Wednesday, August 10, 2011

Ruffed Grouse

On 9 August 2011, Erika rode our bikes along the Cannon Valley Bike Trail in Goodhue County.  About two miles west of Welsh Station, Erika suddenly stopped short and pointed into the woods.  "What is that?" she exclaimed.  I hopped off my bike, my camera ready. She discovered a Ruffed Grouse.  Although they are known from the counties along the Mississippi River, this grouse is the first I've seen south of Duluth.
This Ruffed Grouse proved to be exceedingly tame, as grouse often are, so I was able to photograph the bird from relatively close range.  Examining the photo above closely, I noticed that the tip of the upper mandible seems to be missing. This defect may have been from a natural injury, birth defect, or wound from an encounter with a shotgun blast.
Across most of their range across Canada and parts of the northern United States, Ruffed Grouse numbers fluctuate an a ten-year cycle.  According to Rusch et al. (2000), these cycles are caused by Snowshoe Hare cycles that affect predators such as Northern Goshawks and Great Horned Owls. When rabbit populations crash, the predators turn to grouse. When rabbits are not present, the starving predators also migrate out of Canada into the northern United States, where they feed on grouse (and other prey).  
Grouse cycles and the reasons for them are less apparent in southeastern Minnesota and in other southern parts of the Ruffed Grouse's range that lack the Snowshoe Hares. Researchers in Minnesota found no direct correlation between grouse populations and migrating raptors. Furtman, in The Minnesota Conservation Volunteer, reports that Ruffed Grouse depend on aspen buds for winter food. In years with many Tent Caterpillars, stressed aspens may produce less palatable buds. Ruffed Grouse switch to less abudant or less palatable food and consequently their populations decline.  Warm winters may also adversely affect grouse.  Without snow cover in which to burrow and keep warm, grouse may overeat scarce food sources. Without snow burrows, the grouse may be more visible to predators. Whatever the reasons for grouse cycles in Minnesota, the cycle is generally at its low point in mid-decade and at its high point in years at the end and beginning of the decade.

Tuesday, August 9, 2011

Eastern vs. Spotted Towhee

All spring and summer, an Eastern Towhee called near my banding nets. A few times a male or female peered inquisitively at my net. Today I finally banded the male. Listen to the call of the Eastern Towhee, who says, "Drink your tea;" then listen to the Spotted Towhee's drawn-out "chweee." (These files are shared with permission of Thayer Birding Software and their great DVD, Birds of North America.)
As you can see in the photograph above (a bird from Northfield, Minnesota), except for their white wing patch, Eastern Towhees have unspotted backs and wings. Compare this bird with the bird below, a Spotted Towhee from Aberdeen, South Dakota. These species' biology is complicated. Eastern Towhees breed from southernmost Manitoba, through Minnesota and Iowa, and southward. They are absent from much of extreme western Minnesota. Spotted Towhees breed in the western United States, east to extreme western areas of the Northern Plains (ND, SD, NE, and on south). Areas of hybridization lie along the Missouri and Platte river drainages as well as along the Souris River across North Dakota and southern Manitoba. Towhees do not breed along the James River in North and South Dakota, or along the Cheyenne River in eastern North Dakota.
Normally Ornithologists conclude interbreeding birds indicate that the populations involved are simply races, not separate species. Until relatively recently, Eastern and Spotted towhees were both considered to be a single species, the Rufous-sided Towhee. However, in the range of hybridization, most of the birds you see in the western states are Spotted Towhees. Eastern Towhees predominate along the Platte River, in southeastern South Dakota, and in Manitoba. Biologists conclude that assortative mating is taking place, and that the two species do not interbreed except when no alternative exists. In the hybrid zone you often see pure Spotted or Eastern towhees. This discrimination leads to a gene barrier, albeit a leaky one, between the two populations.  

During my 30 years of banding birds in Aberdeen, in northeastern South Dakota, I caught towhees only as migrants.  Although I caught a few Easterns, most of the birds were Spotted Towhees.  Once in southern South Dakota, just west of the Missouri River, I found a Spotted Towhee singing a perfectly clear Eastern Towhee song. In fact, I have never seen an unspotted towhee in western South Dakota. Thus the biology of these forms is likely a bit more complicated than I described in this post.