Tuesday, May 31, 2011

Scarlet vs. Summer Tanager

Most male Scarlet Tanagers are probably unmistakable. These brilliant long-distance neotropical migrants bring us Minnesotans a taste of the tropics as these tanagers appear in the spring from their wintering grounds in northwestern South America. Among our breeding birds, this tanager's intense scarlet is non-peril. Scarlet Tanagers inhabit eastern deciduous woodlands, where they occur in low densities and, despite the threat of forest fragmentation, in stable numbers.  Eckert considers them to be uncommon in Minnesota. Nevertheless, birders can usually find them if they know where to search and are familiar with their songs.
A lesser known field mark of the Scarlet Tanager is the lower edge of the upper mandible, which usually shows a distinct "tooth."  This notch is clearly visible on the bill of the male tanager, banded today in Northfield.  It is less evident, but present in the second photo, a female Scarlet Tanager banded several years ago at the Nerstrand Big Woods State Park.
The last photo is of a Summer Tanager, rare but "barely regular" in Minnesota (Eckert).  Summer Tanagers usually breed in the southern United States. They winter from Mexico to South America. Female and immature tanagers can be difficult to identify.  Summer Tanagers are larger and more yellowish-orange, less olive than Scarlet Tanagers.  They usually lack the upper mandible notch you saw on the photo of the male Scarlet Tanager.  This Summer Tanager appeared at my South Dakota sunflower feeder on 18 November 2000, a late date for the state.

Sunday, May 29, 2011

Tennessee Warbler

I previously blogged about Tennessee Warblers. Today I write about our understanding of the evolution and taxonomy of some of our warblers.  One beauty of science is that our studies allow us to change our understanding of how the world works.  

Until recently, a number of warblers were considered to be closely related and, therefore, placed in the same genus, Vermivora. All have sharp, relatively thin bills. These species included, among others,  Tennessee, Orange-crowned, Nashville, Golden-winged, and Blue-winged Warblers.  Molecular studies indicate that only the Blue-winged and Golden-winged Warblers (along with the likely extinct Bachman's Warbler) are evolutionarily close.  The others are moved to a new genus, Oreothlypis. Furthermore, two Mexican warblers have been moved into the new genus.  Flame-throated and Crescent-chested warblers were formerly placed in the Parula genus (American Ornithologist's Union).

Changes in systematics only change our philosophical understanding of evolution.  The Tennessee Warbler's loud, ringing song remains one of abundant sounds of spring migration. Note the flute-like Wood Thrush song in the background of this file, used with permission from Thayer Birding Software.

Saturday, May 28, 2011

13-lined Ground Squirrel

Although I always knew that Minnesota is "the Gopher State," and that the University of Minnesota fields "The Golden Gophers," I had no clue those gophers are Thirteen-lined Ground Squirrels!  (Those of you not familiar with what a UM golden gopher looks like can click here for an illustration and history.)  Notice the mascot's tail stripes are vaguely similar to a Thirteen-lined Ground Squirrel.

I photographed this Thirteen-lined Ground Squirrel as it emerged from hibernation at the end of April at the River Bend Nature Center at Faribault.  These rodents are diurnal and eat seeds and a variety of small invertebrates.  They can damage gardens but also consume weed seeds, harmful insects, and even mice and shrews. 

Thirteen-lined Ground Squirrels become fat during the fall and store food in their shallow burrows.  By October they enter a special, deep hibernation chamber.  During hibernation,  their respiration decreases from about 150 to one breath per minute (Wikipedia). Getting fat and sleeping are probably excellent strategies for surviving Minnesota winters, but are probably ill-advised for succeeding in one's university career.

Thursday, May 26, 2011

Blackpoll Warbler

Spring-plumaged, male Blackpoll Warblers (here a Northfield bird banded in the 2011 spring) present few identification challenges.  Females and fall birds, like the fall 2008 Blackpoll in the second photo, present problems.
In all plumages, one key is in the feet and legs.  Blackpolls almost always show at least some yellow in the legs. The legs below, from the male above, are exceptionally yellow.  Even spring females often have legs like these.  In the fall, however, the yellow is often restricted to the birds' toes.  This field mark can be hard to see. 
Compare this leg with the foot of a fall-plumaged Bay-breasted Warbler that I shared with you in this blog on 5 September 2010.  (Click on the date to see the Bay-breasted foot.) A fall Blackpoll (below), demonstrates how reduced this yellow color can be (from 20 September 2010 blog post).

Tuesday, May 24, 2011

Rose-breasted Grosbeak

Rose-breasted Grosbeaks appear to be enjoying a banner year here in central Minnesota. Cutthroat is an archaic name for this species. At the end of Arpil, Erika and I found this three-some at a feeder at the River Bend Nature Center.  I banded and released the female in the second photo later in May 2011 in Northfield.

Its song, described as "a robin on steroids." is common in our forests (Thayer's guide to North American Birds, used with permission). Rose-breasted Grosbeaks, unlike other birds, are even known to sing from their nests. Both sexes attend to raising their young. 

Rose-breasted Grosbeaks winter in Central and South America.  Their return to eastern North America, after a long winter, is a welcome sight. This grosbeak inhabits both primary and secondary deciduous forests.  The bird also is found in parks and gardens, contributing to its healthy population numbers. Farmers have mixed emotions about grosbeaks. On one hand, they consume tree buds, flowers, fruits, and seeds.  But they also eat arthropods like beetle larvae and scale insects. Most of this information is gleaned from Wyatt and Francis (2002). Rose-breasted Grosbeaks are not my favorite birds to band-- their massive beaks can inflect quite a bit of pain.

Monday, May 23, 2011

Whooping Cranes in Rice County

Sunday morning we received a listserv email that two Whooping Cranes were found on Saturday east of Dennison in Rice County, Minnesota.  Unfortunately we were busy all day Sunday, and we could not check out the report until late in the afternoon.  I harbored little hope of finding the birds.  Strong south winds probably pushed these migrants on their way.  But Sunday was stormy, so perhaps the birds stayed down.  As you can see, we found the cranes.

I suspect these birds originated from Wisconsin, where the Wisconsin DNR and other organizations have initiated a recovery program.  Since 1999, cranes have been released in Necedah National Wildlife Refuge in central Wisconsin and migrate to Chassahowitzka NWR on the Gulf coast of Florida. Many birders saw two cranes in Rice County, Minnesota, last fall.  It surprises me that we are beginning to find Whooping Cranes in Rice Co., since we are west of a direct route between Wisconsin and Florida (but well east of the traditional crane migratory path between Texas and northwest Canada).
The Wisconsin program is an effort to establish a secondary crane flock to act as a population buffer in case the wild flock in Texas meets with disaster.  In 1941 only 15 individuals remained in the wild flock (that now numbers over 180).  By late October 2010, Wisconsin boasted about 96 wild birds.  About ten of these followed an ultralight aircraft to Florida.  Eleven cranes, banded and radio tagged, were let go near older, already released adults.  Presumably the birds found in Rice Co. are two of those 11.  Notice the radio transmitter on the left leg of the bird above.  The bird below is a second bird, as you can see by the differently colored bands on the right leg.  The two birds appeared to be a male and a female, but see my previously posted information about ascertaining the sex of living Whooping Cranes.  I will add more about these birds if and when I receive more information.
Update from International Crane Foundattion “Based on leg bands previously reported, these two birds are both juvenile males numbers 1-10 and 8-10.  They moved from Wisconsin into Goodhue County, MN for a short time and then made a brief trip back to the Necedah NWR  before returning to Minnesota to this location in Rice County just recently.One of them does have a satellite transmitter so if they move from this spot, we should get a location on them within a couple of days or so.”

Sunday, May 22, 2011

Lesser vs. Greater Yellowlegs

Yesterday's blog post, which showed yellowlegs in the background of the photograph, has me thinking about identifying Lesser and Greater Yellowlegs.  I took this photograph at the River Bend Nature Center in Faribault in August 2008.  When the two species are in the same pond and their sizes can be compared, you can usually tell the larger Greater (left) from the smaller Lesser Yellowlegs (right).


Size, however, is notoriously difficult to judge in solitary birds.  Note the bill shape and color.  The Lesser Yellowleg's bill is black, thin and needle-like.  The Greater Yellowleg's bill is broader at the base, bi-colored (at least in the non-breeding season), and often slightly upturned.

Most field marks, unfortunately, often overlap.  This variability inspired Sill and Sill, in their silly birding spoof, A field Guide to Little-Known and Seldom-seen Birds of North America, to add Middle Yellowlegs and the Least Yellowlegs to the North American birdlist. (This humorous book is curiously cited in the American Ornithologists' Union's opus Birds of North America, "further complications within this group are discussed by Sill et al. (1988).")

The calls of the two yellowlegs differ.  The Greater gives three or four sharp, clipped notes.  The Lesser gives two (or three) softer, shorter notes.  The differences in pitch are a more reliable field mark than the number of notes (songs are courtesy of Thayer Birding Software).

Saturday, May 21, 2011

Wilson's Phalarope

While we are enjoying a great warbler migration, shorebirds are few and far between.  Too much water this wet spring?  Erika and I did encounter a few Wilson's Phalaropes in southern Dakota County, Minnesota.  The three birds in the foreground of this photograph are phalaropes.  The birds behind them are Lesser Yellowlegs.

Female phalaropes are brighter than their dull-colored males.  In the photograph, a male is in the immediate foreground, with two females behind him.  On their breeding grounds, females compete for males, often breeding with more than one mate (polyandry).  After laying her eggs, the female deserts the male to compete for additional mates, leaving the first male all subsequent nesting duties (incubation, brooding, and other parental care).  

Phalarope endocrinology (hormones) is complicated. In other birds, males usually have high steroid levels, while females have more prolactin (a hormone associated with egg laying and caring for young).  Early studies suggested that male phalaropes have relatively low levels of testosterone, about the same levels as females.  More recent studies show that male phalaropes' testosterone levels spike early in the breeding season, but decline markedly as the season progresses. Prolactin levels in males are stimulated by the presence of eggs or young. Levels rise during incubation and then decline after the young hatch (Colwell and Jehl 1994).

Friday, May 20, 2011

Philadelphia vs. Warbling Vireo

During our bike trip on 18 May down the Cannon River Trail in Goodhue Co., Minnesota, Erika and I photographed a Philadelphia Vireo (first photograph).  We also heard Warbling Vireos.  The two species can be difficult to identify.

1. They have different songs (samples courtesy of Thayer Birding Software).  The Warbling Vireo sings "a single languid warble unlike the broken phrasiology of the other vireos" (Peterson).  The Philadelphia Vireo sounds like a slow, high-pitched Red-eyed Vireo. Listen for the insertion of three-quick notes within the song.  Since the Warbling Vireo is relatively common and breeds in Rice County, I often hear them.  Unfortunately I have only heard a singing Philadelphia Vireo once. (Philadelphia Vireos breed in forests across central and northern Canada, barely reaching the northern-most United States.)

2. Notice the lores of the birds in these photos.  The lore is the dark line that connects the bird's eye to the its bill.  The top two photos are Philadelphia Vireos.  Note that the lores are relatively dark. The result is a dark line through the eye.  Now look at the third photo.  This Warbling Vireo has much paler lores, giving its face an almost whitish look.

3. The crown of a Philadelphia Vireo is darker than that of a Warbling.

4. Philadelphia Vireos have yellowish throats.  Warbling Vireos have white throats. Be careful, however, of Philadelphia Vireos with relatively pale throats. (The second photograph was taken of a Philadelphia Vireo banded and released in Northfield, Minnesota.)
5. Both Vireos vary in the amount to yellowish on their flanks.  This variation can cause  confusion among birders, who might identify a yellow-sided Warbling Vireo as a Philadelphia, while correctly identifying a paler Warbling Vireo, like the bird in my third photo (a bird banded at Sand Lake National Wildlife Refuge in South Dakota).

6. Sibley notes that Warbling Vireos have a smaller bill.  This statement is a bit confusing.  I think he is comparing western Warbling Vireos to those east of the Rockies.  (The western birds may actually be a distinct species--eastern birds like those in Minnesota sing a slightly different song than do western Warbling Vireos.)  I have always thought that Philadelphia Vireo bills are smaller and definitely less obviously hooked than those of Warbling Vireos.  This field mark is good with a bird in the hand, but may be of less use in the field.

Thursday, May 19, 2011

Indigo Bunting

I last wrote about this bunting on 24 June 2010.  This year I have banded a male in Northfield (above) and observed a singing male at the Carleton Arboretum (below).  Listen to the song (used with permission of Thayer Birding Software).

Hatchling Indigo Buntings learn their songs from nearby males--not, as you might assume, from their fathers.  In fact, buntings raised in laboratories, only hearing their fathers' songs, grow up to sing strange songs unrecognized by wild buntings. Thus, in the wild, "song neighborhoods" are formed, with song themes that persist for up to ten generations.  These song types are fluid, and are affected by the songs of foreign buntings new to the neighborhood (Payne 2006).

Payne manipulated recorded Indigo Bunting songs (by slicing tapes in the days before computers). Buntings recognize their species by note pitch, spacing, and length. They recognize individuals by details of note structure. Indigo Buntings are more aggressive towards strangers. Birds also communicate their intentions by song length and singing rate (Lehner 1996).

Wednesday, May 18, 2011

Cerulean Warbler 2

Today (18 May 2011) Erika and I found a Cerulean Warbler in Goodhue County, Minnesota.  While biking the Cannon River Trail just east of old mile post 76, I heard a buzzy trill that I assumed was a Northern Parula--only to discover this Cerulean.  To date, I have also seen Cerulean Warblers in two locations in Rice Co.  On 11 May, I posted additional information on this species.

Tuesday, May 17, 2011

Magnolia Warbler

I blogged on the Magnolia Warbler in my post of 8 September 2010.  I was disappointed to miss seeing this species during last spring's dismal migration.  The Magnolia Warbler should be an abundant and easily seen bird.  I took the photo above in the eastern unit of the Cannon River Wilderness county park on 10 May 2011.  I banded the individual below on 17 May in Northfield, Minnesota. 

As I mentioned in my previous post, this species was discovered in 1810 during migration in a magnolia tree in Mississippi.  Magnolia Warblers breed in the boreal forests across central Canada and the northern-most United States.  Despite their being relatively abundant, very little is known about their breeding biology. They winter in the Caribbean and in Central America.

Monday, May 16, 2011

Brown Creeper

During the last three years of banding  in Northfield, I am surprised at the numbers of Brown Creepers that I catch -- between 30 to 36 each year.  The birds appear to be attracted to our water feature.  I have also seen them eating suet fallen from our feeders.

Brown Creepers are found across almost all of the United States, southern Canada, and in the mountains of Central America.  In most of its range, the species is a year-round resident.  Northern birds are migratory.  I band most of my birds in the spring and fall, so I assume most, if not all, are of northern migratory populations.

Sunday, May 15, 2011

Blue-winged Warbler

Gene B., Dave B., and I braved yesterday's rain and 46 degree temperatures to attempt a Big Birding Day in Rice Co.  You may recall that last May we tallied 129 birds.  This year we came up with 133 bird species.  Our success was mostly attributed to our finding huge flocks of migrating warblers.  One flock in the Cannon River Wilderness Area swarmed at all levels of the forest, even feeding on the ground.  They reminded me of a cloud of insects.  Like we birders, these birds must have been cold, wet, hungry and tired. We ended the day with 23 kinds of warblers.

The photo of the Blue-winged Warbler above is misleading.  This common warbler was one we missed yesterday!  The image represents, however, the serendipity of being in the right place at the right time (or not), both for birding and for taking photos.  Erika and I took this picture a few days ago in the wilderness park. I have previously posted information about Blue-winged Warblers (on 14 June 2010).

Wednesday, May 11, 2011

Blackburnian Warbler

Who is not startled by the brilliant beauty of a male Blackburnian Warbler?  On 10 May 2011, we were delighted to band and release two of these warblers. The species breeds in conifers in southeastern Canada and north-central and northeastern United States, continuing down the Appalachian Mountains.  Like the Cerulean Warbler, Blackburnians are vulnerable to deforestation in their wintering grounds in northern South America.  As much as 34% of their wintering grounds have been destroyed.  Blackburnians are also sensitive to timber operations and fragmentation of forest tracts in their breeding grounds. For now, nevertheless, their numbers appear to be stable.  The accidental importation of an East Asian bug in 1924 has caused massive die-offs of Eastern Hemlocks and Fraser Fir in the eastern United States and will undoubtedly adversely affect birds (like the Blackburnian Warbler) that depend on these trees (Morse 2004).

Cerulean Warbler

Erika and I found several singing Cerulean Warblers on 10 May 2011 in the eastern unit of the Rice County Wilderness Park.  This warbler is "uncommon, local and declining" in Minnesota (Eckert).  They are difficult to see, as they usually sing from the tops of mature deciduous forests.  Occasionally, like today, they are found lower in the forest.  Due to their treetop habitat, little is known about their breeding behavior.

Cerulean Warblers breed in scattered locations in Eastern North America.  They winter along the Andes from Columbia through Bolivia.  This species' numbers are cause for concern.  Some studies indicate a 50% decline in population during the last 40 years, and numbers have declined even since 1900.  Factors that may be contributing to this dire situation include loss of mature deciduous forest, fragmentation of these forests for human development, current early harvesting and shorter rotation of timber stands, loss of inmportant trees to disease (oaks, sycamores, and elms), tropical deforestation in their winter range, and loss of migratory stopover habitat, especially near the Gulf Coast (Hamel 2000).

Tuesday, May 10, 2011

Northern Parula

Last fall I posted a photo and blog entry on the systematics of Northern Parulas.  This spring I banded a couple of bright males.  Previously I have never noticed the small, bright-azure streak forward of their shoulders--you can see this color best in the photo above.  Parulas are birds of the eastern United States and southeast Canada.  They are seldom seen west of Minnesota; in 30 years of banding in South Dakota, I never caught one.  In Minnesota, Parulas are locally common breeders in our northeastern counties.  Elsewhere they are uncommon migrants (Eckert 2002). Listen for their ascending songs with a pip at the end.  If you listen to the call, you will also notice that Parulas also sing other buzzy notes.

The word "Parula" comes from the Latin for little titmouse. The word is variously pronounced as PAR-a-la or PAR-ya-la.  I have always said, par-U-la. The situation could be worse.  Audubon and other early ornithologists called the Northern Parula the Blue Yellow Back Warbler.

Monday, May 9, 2011

Chestnut-sided Warbler

Previously I have published Chestnut-sided Warbler posts on this blog (24 May 2010 and 20 August 2010).  Roger Tory Peterson called warblers "The Butterflies of the bird world;" I am reminded of small, brightly colored, tropical tanagers.

Male Chestnut-sided Warblers sing two songs.  Peterson described the best-known song as "'please please please ta meetcha,' with the last note dropping." Thayer's guide to North American Birds provides us with a sample of the this song (copy-righted file used with permission). This song is used to attract females. A second song, with an unaccented ending, is sung later to keep other males from the singer's territory.  According to Richardson and Brauning (1995), "The two song classes are learned separately. Birds require visual contact with tutor males to fully develop their repertoires."

Sunday, May 8, 2011

Wilson's Warbler

Last year I did not catch any Wilson's Warblers.  This year I banded one on 5 May. This warbler breeds across Canada and from Alaska south through the central Rocky Mountains. The species winters from the western Gulf Coast through Central America.

Wilson's Warblers seem, with a couple of exceptions, to be in decline. Recent studies show decreases of about 2% a year.  Exceptions to this trend may exist in logged areas that are currently in secondary growth.  Otherwise, the destruction of riparian habitat and the clearing of forested areas for human development may be contributing this trend (Ammon and Gilbert 1999).

Saturday, May 7, 2011

Ruddy Duck

Ruddy Ducks are in a separate tribe of waterfowl alongside the other ducks.  The tribe is called stiff-tailed ducks since they often hold their tails erect--often, but, as you can see in the female in the upper photo, not always.  (The photo is from the St. Marks National Wildlife Refuge in the Florida panhandle.) The Ruddy Duck is the only stiff-tailed duck expected in Minnesota.  Birders should be alert to the fact that Hooded Mergansers also occasionally hold their tails out of the water.

Breeding males are brightly colored, as in the lower photo taken several years ago at the Sand Lake National Wildlife Refuge in northeastern South Dakota.  Males bob their heads during courtship.  Pairs are usually monogamous, although some males are polygamous (Brua 2002).  Winter males are drably plumaged, sort of a white-cheeked version of the female.

Friday, May 6, 2011

Short-tailed Shrew

Short-tailed Shrews are found in most of northeastern North America.  They thrive in cold winters and indeed, temperatures over 95 degrees F can be lethal.  Below 77 degrees, these shrews must increase their metabolic rate to maintain their body temperature. They do this by increasing their food consumption during the winter, when they eat up to 43% more than in summer. They hoard food in caches.

This individual poked its head out from under the leaf litter as we raked under the bird feeder.  Short-tailed Shrews dig their own burrows and use passageways made by other mammals.  They eat up to three times their weight each day.  They eat bird seed, fungi, and a wide variety of animal prey.   They consume more vertebrates than do other shrews.  One reason for this larger prey is that Short-tailed Shrews are one of the few venomous mammals.  Their saliva contains a toxin that can kill small animals, and can be painful to people who attempt to catch them. The toxin is produced in their lower jaws and flows along a groove formed by their incisors.  According to Wikipedia (from which most of this information is taken), the toxin is being studied as drugs to control pain, to fight cancer, and to counteract high blood pressure.

Thursday, May 5, 2011

Louisiana vs Northern Waterthrush

The differences between Louisiana and Northern waterthrushes are subtle. On 3 May, we saw both species in the western unit of the Cannon River Wilderness Area in Rice Co. The first two photographs are of the Louisiana Waterthrush we saw; the second two are of Northern Waterthrushes, banded near Dundas in 2008 (third photo) and on 4 May 2011 (last photo).
So how do you tell these birds apart?

1) Throat.  In these photographs, you can clearly see that the throat of the Louisiana Waterthrush is plain white, unlike the finely speckled throat of the Northern Waterthrush.  This field mark is usually good, except these speckles can vary in both species.

2) Eyestripe.  The Louisiana Waterthrush's eyestripe is white and broad (specially behind the eye).  The Northern Waterthrush's eyestripe tapers to a point behind the eye and is often dusky.

3) Flanks.  The flanks of a Louisiana Waterthrush are often buffy, contrasting with the white breast.  This color may be subtle, as you can see in the photo above.

4) Leg color.  Note the bright pink legs on the spring Louisiana Waterthrush in the photos above.  The Northern Waterthrush tends to have dusky, horn-colored legs.

4) Size.  Most Louisiana Waterthrushes are at least a quarter of an inch larger than Northerns.  Good luck discerning this size difference in the field.
Just to make this situation a bit trickier, Northern Waterthrushes vary in underpart color.  Some are white, as is the bird above.  Others are yellowish, like the bird below. Louisiana Waterthrushes are always white-breasted behind the streaks. Yellowish Northern Waterthrushes have yellowish eyestripes quite unlike the white eyestripes of all Louisiana Waterthrushes. The eyestripe of a pale Northern Waterthrush, however, can be similar to the color in the Louisiana.

The songs of the two waterthrushes are perhaps the best way to tell them apart.  This field mark only works if the birds are singing!  In Rice Co., Louisiana Waterthrushes breed near limestone cliffs along the Cannon River. Northern Waterthrushes are migrants that breed further north and usually are not singing.  The Northern Waterthrush song ends in a diagnostic "chew-chew-chew." The Louisiana song begins with three clear slurred whistles, followed by a number of twittering notes dropping in pitch (Peterson 1947).  Thayer Birding Software graciously allowed me to use their copy-righted mp3 files of bird calls so that you can listen to the songs of the Louisiana Waterthrush and the Northern WaterthrushThayer Birding Software produces the DVD Birds of North America (Mac and PC versions available), which is well worth the price. This disk contains multiple bird photographs, videos, and bird calls of North American birds.