Woodchuck

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.

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.

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.

Halloween Pennant

On 6 August, Erika and I found Halloween Pennants along the large, artificial pond next to Circle Lake in Rice County, Minnesota. With its orangish wings with dark bands, the species is unmistakable. They are generally the most common Pennant.  We disagree with the BugGuide.net that claims that the males are not territorial.  We saw males chasing other males away before returning to their perches.

Male Halloween Pennants have red-topped abdomens. Females can be reddish or yellow. When perched, this pennant holds its forewings higher than the back ones, a trait evident in the photo below.

This species is found from Central America, across eastern North America, often to southern Canada. Although they can be found away from water, they prefer lakes and ponds. This dragonfly is a hardy species, even encountered on cool, windy, rainy days (Mead).

Eastern Amberwing

During a dragonfly expedition on Thursday to Circle Lake in Rice County, I happened upon several Eastern Amberwings.  The amberwings defended small territories around sticks protruding from the lake. I took this photo as I leaned over the rail of a lakeside dock.


A couple of days ago I blogged about how Viceroy Butterflies are examples of Müllerian Mimics. If entomologists are correct that the amberwing mimics wasps, then this dragonfly is certainly an example of Batesian Mimicry, where harmless creatures resemble poisonous ones.  The amberwing acts like a wasp, bobbing its abdomen up and down while waving its wings.  The goal is to dissuade potential predators who have had unfortunate encounters with wasps.

Pectinate Toes

I have long been aware that herons have a pectinate toe.  This is a comb-like, serrated structure on the edge of their midde claw.  The comb is used as a preening tool.  Despite many attempts at photographing heron toes, like those of the Snowy Egret above, my efforts to illustrate pectinate toes have been unsuccessful.

My friend Tami V. is the Communications Director of the Wildlife Rehabilitation Center of Minnesota.  She and her colleagues recently released Great Blue Heron chicks rescued from a colony destroyed by last May's tornado, which damaged many parts of north Minneapolis. I asked Tami to take photos for me.  The bird above is a Green Heron, a close up of its pectinate toe is below. I believe this structure is even more fully developed on adults.

Tami went a step further and photographed the pectinate toe on one of their other patients, a Common Nighthawk. Aside from other nightjars, as far as I know, the only other birds with such toes are Barn Owls. I do not know why more birds possess pectinate toes.

I appreciate the assistance of the Wildlife Rehabilitation Center of Minnesota and Tami's enthusiasm for pursuing my request for photographs. Both Tami and the Center are busy without odd requests from ornithologist bloggers.

Müllerian Mimicry

On 2 August 2011, Erika and I found both Viceroy and Monarch butterflies in Carleton College's arboretum. Note the distinctive line across the hind wings on the Viceroy above. Despite their similar patterns, the Viceroy and Monarch are not closely related. Although both are in the same Family, Nymphalidae, the Viceroy is in the genus Limentis (the same genus as the Red-spotted Purple.)  The Monarch is in the genus Danaus. 

For over 30 years I've taught that these two butterfies are examples of Batesian mimicry.This type of mimicry is when good tasting creatures look like poisonous ones. Because Monarchs store toxins from milkweeds, they are distasteful, if not poisonous to birds. The good-tasting Viceroys just have to less common than Monarchs, so that the birds to not catch on to the Viceeroys' disguise. But researchers have discovered that Viceroys contain their own distasteful chemicals. These distasteful butterflies have come to look alike, so as not to overly tax the birds' learning abilities. The birds only have to learn one pattern.  This convergence, where toxic critters look similar, is called Müllerian mimicry. 

Odonata Sex

Sex is complicated among the Odonates.  First a male transfers sperm from his testes at the end of his tail (abdomen) to a structure under his body (thorax).  Then he grabs his mate by holding on to the back of her head with claws at the tip of his tail.  The female then reaches her abdomen up to the sperm storage organ under the male's body.  Once connected, the dragonflies are said to be in the Wheel Position.  The pair of White-faced Meadowhawks in the photo above are in this Wheel Position.


Copulation, which can occur in flight or when perched, commences with the male flushing other males' sperm out of the female.  Next he deposits his own sperm.  Fertilization can last an hour or more. Next the female needs to lay her eggs in the water.  Often the male guards against other males' mating with her. As in the photos of the two Stream Bluets below, he flies attached to her until her eggs are laid. Otherwise another male may come along, flush the first male's sperm out, and replace it with his own.

Eastern Comma

The Eastern Comma is another butterfly with punctuation on its lower wing.  You may remember I recently posted about another such critter, the Question Mark.  Besides lower wing punctuation, the upper wing pattern of the two species differ slightly (Kaufman). 


Last week, Erika and I found this Eastern Comma on a bench along the Cannon Valley Bike Trail in Goodhue County.  The butterfly appeared to be sucking sweat left by overheated bikers.  This species does not usually visit flowers, instead preferring sap, rotting fruit, dung, salts and minerals (Wikipedia).   Eastern Commas are found across most of eastern North America.

Giant Swallowtail

In March I blogged about seeing a Giant Swallowtail in Key West.  At the time, I mentioned that this butterfly occasionally strays to Minnesota.  Yesterday Erika and I came upon this Giant Swallowtail feeding on a flower basket in Prescott, Wisconsin (across the St. Croix River from Minnesota). Two key field marks for this butterfly are the yellow spots on its tails and the yellow "X" formed by the wing spots.  


This summer I have seen a few others along the Canon River Bike Trail in Goodhue County. Last summer I observed none in Minnesota (although others reported them). They are most common in the Deep South and Mexico and normally, in our part of the country, range to northern Iowa and southern Wisconsin.