Common Whitetail: The Road to Pruinosity

One can hardly write about dragonflies without mentioning pruinosity, as I have done last July when blogging about Powdered Dancers last July. This year Erika’s garden has been full of Common Whitetails. We have counted up to 13 at once as the dragonflies basked on the warm side of our house.

Male Common Whitetails’ abdomens become Pruinose. Pruinosity is a powdery pigment “bloom on odonates that exudes from the cuticle and turns it light blue, gray, or white…” (Paulson). Pruinosity often reflects ultra-violet light. Pruinosity is more prominent on mature individuals and more often on males. The first three photos show Common Whitetails in various stages of becoming pruinescent. The last photo shows an unpruinescent female whitetail—similar to the female Twelve-spotted Skimmer (which has a yellow striped, rather than spotted, abdomen.

Common Whitetails make use of pruinosity for species and sex recognition, for making territorial displays, and, perhaps, to cool their bodies by reflecting solar radiation.

Robberfly

About a thousand species of Robberflies (Family Asilidae) inhabit North America (Maxson). The family has a worldwide distribution. Some, especially in the genus Lapria, mimic bumble bees (Bugguide). Looking like bees may frighten off potential predators, or make it easier for the robberfly to capture the bees. They also prey upon other arthropods, like flies, grasshoppers, beetles, moths and butterflies, and even dragonflies (Ecobirder). The robberfly bite paralyzes their prey, which is then injected with enzymes that digest the prey’s insides. The robberfly then drinks this soup by sucking it through their proboscis.

Six-spotted Tiger Beetle

This beetle is a relatively unspotted Six-spotted Tiger Beetle. The species is found in Minnesota and much of eastern North America. These beetles feed on other insects like caterpillars, ants, and spiders and thus are generally welcomed by gardeners.

After hatching, tiger beetle larvae make burrows, where they wait for their prey. Often they attack from the burrows “much like jack-in-the-boxes” (Wikipedia). The larvae live for about a year before pupating (and live for about 4 more years as adults). At night, adults return to their larval burrows. They also over-winter in the burrows (Mark Moran).

Six-spotted Tiger Beetles often have six spots on their emerald fore-wings. This field mark, as you can see, is not invariably present. I can make out two or three tiny spots on this individual. Others may have as many as ten.

Snapping Turtle

On our way down to the Bass Ponds in the Minnesota Valley National Wildlife Refuge, Erika and I stumbled over a Snapping Turtle. The reptile was probably touring, in search of a good egg-laying site. Note the leaches hitch-hiking on the turtle’s rear leg. No doubt the turtle provides both nourishment and a means of distribution for the leeches.

Despite being common (if not abundant) in Minnesota, Snapping Turtles are listed as a species of Special Concern in the state. Humans are about their only predator. Snappers are harvested for their meat, and the effects of commercial harvesting are unknown. Minnesota allows unlimited hunting of snappers with shells over a foot. Most of this hunting is in June, which is unfortunately just when turtles are laying eggs, thus affecting their reproductive potential. Snapping Turtles also harbour high levels of PCBs, which also may affect their reproductive capacity (and possibly also of that of humans who eat them) (MN DNR).

Snapping Turtles are sometimes thought to prey upon fish and waterfowl. They are, indeed, fairly omnivorous. These turtles, however, have been shown to eat “insignificat” numbers of game fish and mammals and large fish are a far more serious threat to nesting waterfowl (MN DNR).

Painted Turtle

I have previously blogged on Painted Turtles in 2011. Erika and I encountered this gorgeous individual at the Bass Ponds in the Minnesota Valley National Wildlife Refuge in Bloomington last week. This species is Minnesota’s most common turtle. They are omnivorous, they eat almost anything they can catch. They should not, however, be kept as pets. They require specific temperatures to thrive and tend not to do well with artificial diets. Furthermore, Painted Turtles carry salmonella, a very unpleasant digestive disease that does affect humans. Being hit by cars as the turtles try to cross roads is a major source of turtle mortality.

We flipped this turtle to see its colorful underparts. As we did so, the turtle responded by releasing copious urine. We set the turtle upright as we left it to its travels.

Blanding’s Turtle

The last thing Erika and I expected to see during a recent tour of Minneapolis water features was a woman with a Blanding’s Turtle under her arm. Any turtle would have been a surprise, but especially one classified as Threatened in Minnesota. This species is found from Minnesota and Nebraska east to New England. Nowhere is it common. Threats include habitat fragmentation and destruction and predators. Many are killed as they attempt to cross highways.  Females often nest in agricultural fields and thus are threatened by "chemicals, disking, machinery usage, increased nest predation, and shade produced by growing crops" (MN DNR).

Blanding's Turtles take 14 to 20 years to reach sexual maturity and may live up to 80 years. Typical of a long-lived species, they lay few eggs—only an average of eight per clutch (Wikipedia). This low reproductive rate makes recovery from ecological threats all the more difficult—mortality rates reaching 93% are reported for eggs and young (MN DNR).

They hibernate under mud and vegetation in ponds, from whence they may travel up to a mile (thus exposing themselves to the risk of automobiles on roads). They are agile swimmers and are omnivorous, consuming invertebrates, small vertebrates, and vegetation. Field marks include the spots on the upper shell and the bright yellow throat and chin.

The Minnesota Department of Natural Resources warns that possessing Blanding’s Turtles is illegal. The woman we met on our tour was quick to assure us that she found this turtle in the road near Farmington, and planned to release it in a wild area “up north.” My impression that the woman had contacted the DNR about her transplant plan—we just hope that this Blanding’s Turtle does not have strong homing instincts, crawling home across the highways of Minneapolis/St. Paul.

Review: The Warbler Guide

The Warbler Guide is a stupendous new book by Tom Stephenson and Scott Whittle, published by Princeton University Press. Each of the 56 species accounts contain at least a dozen photographs, emphasizing various plumage variations—in all, over 1000 stunning color photos grace the book. One of the unique features of this book is that many of these photos are taken from below, which is how you really see warblers in the field. Each account also contains photos showing distinctive features and comparison species. Range maps accompany each account.

The long introduction discusses what to look for when seeing a warbler. This section includes warbler photos showing field marks and suites of spring and fall warblers, all on the same pages (from the side, at a 45 degree angle, from below, as well as close-ups of warbler heads). The authors also launch into a long discussion of sonograms that illustrate warbler songs in each species account.

The book ends with a spreadsheet comparing warbler behavior and habitat (both also covered in the species accounts) and a short quiz emphasizing warbler identification. Also presented are a short series of birds likely to be confused with warblers (although I can’t imagine an Eastern Towhee could be confused with a warbler). Finally, a few photos of warbler hybrids are included. The book is sparsely referenced, but does include a few resources, in print, in audio and digital format, and on the Internet.

This relatively inexpensive book will aid birders of all abilities in identifying the warblers of America. The list price is $29.95. Prepublication orders (before the first week in July) from Amazon are $19.36!

Update: see my review of the audio files Cornell Ornithology lab has just published to accompany The Warbler Guide.

Field Sparrow

When we visited Faribault in May, Erika and I banded a Field Sparrow, a species I have ringed several times at our Dundas banding station. These sparrows are common in eastern North America. They breed in brushy pastures and scrublands, but, to their detriment, seldom in similar urban habitat. Across their range, Field Sparrows appear to be declining in numbers, either because their habitat is becoming forest or becoming urbanized (Carey et al. 2008).

Jade Clubtail

Until Wednesday, Jade Clubtails were known to occur from southeastern South Dakota (one record), Iowa, Indiana and Illinois south to eastern Texas and Louisiana (Odonata Central). On Wednesday, Erika and I made the first-ever observation of this dragonfly in Minnesota—at the Bass Ponds in Bloomington at the Minnesota Valley National Wildlife Refuge.

I immediately knew this was a dragonfly I had never seen—the chestnut tail told me that. Species identification was also aided by the critter’s green (not blue) eyes, black lines along the sides of the thorax, and the yellow appendages at the tip of the abdomen. The behavior and habitat also indicated a Jade Clubtail. This odonate perched on the ground near the bass ponds and the nearby forest. These clubtails prefer large, mud-bottomed lakes, sloughs, canals, and slow-flowing rivers (Paulson)—a perfect description of the Bass Ponds.

I shared these photos with Scott King, who concurred with my identification. Odonata Central also vetted the record.

Red-winged Blackbird

Because Red-winged Blackbirds are among the most abundant North American birds—they range from Alaska and northern Canada south through Central America—I have posted various photos of this handsome species. (See, for example, this post from 2011, or check out the species index tab at the top of this blog.) Familiarity, plus their huge flocks with their potential for damaging crops, may dampen our appreciation for these striking birds. (People are now one of the major causes of mortality for Red-winged Blackbirds (Yasukawa and Searcy 1995).)

Why is this blackbird so abundant? Their habitat includes both freshwater and saltwater marshes, the edges of ponds and streams, wet roadsides, dry meadows, and old fields (Allaboutbirds). I suspect the building of the Interstate Highway System has contributed to greatly expand the Red-wing’s range across North America—the highway right-of-ways are perfect habitat for this species.

Despite their abundance, I do not band many Red-winged Blackbirds. They seldom visit my urban bird feeders and are wary at our Dundas station. The male and female blackbirds on this post were banded and photographed during a public banding demonstration that Erika and I presented at the River Bend Nature Center near Faribault, Minnesota, this May. People attending had no trouble identifying the male, but had more difficulty recognizing the female below.