Monday, June 28, 2010

Dissertations: His, Hers, and Ours

In the 1970s, when we were young and thought we were immortal, Erika and I pursued our doctoral research in the eastern lowland Ecuadorian jungle. I studied antbirds, a widespread tropical American family of birds that follow army ant swarms and feed off the arthropods fleeing from the ants.  The Ornate Antwren, below, is an example of an antbird.
I wondered if the antbirds (26 species inhabited my study area) obeyed Gause's Rule, that no two species can occupy the same niche.  What I found, briefly, was that these birds do divide up their resources so that no two species exploit the environment in exactly the same fashion.  In the jungle, we suffered through 15 feet of rain a year.  As we were on the equator, there was no dry season, which is when tropical birds often nest.  I was surprised to find that the antbird species appeared to breed all year.

Meanwhile, Erika studied the effects of intercontinental migration on the trematode fauna of Solitary and Pectoral Sandpipers.  These sandpipers breed in Canada and winter in South America.  The bird below is a Solitary Sandpiper.
Trematodes are internal parasites of many vertebrates.  There are many trematode species and some even inhabit humans.  They are found in many organs of their hosts. They are fascinating and beautiful creatures, as you can see in the photo below, which shows an hermaphrodite, the normal condition for a trematode, with both an ovary and two testes in the same individual.  Trematodes just sit there and fertilize thousands of eggs.  The trematode life cycle goes through several intermediate hosts, (always in evolutionary order!), before reinfecting their vertebrate host.
Erika discovered that Pectoral and Solitary Sandpipers have relatively few trematode parasites, and that the few they do have, hold on really tight.  The most amazing of these trematodes live in the birds' air sacs, which are extensions of birds' lungs.

Being of boundless energy, Erika and I also collected trematodes from my antbirds.  In effect, this study amounted to our doing a third dissertation!  There are two different feeding strategies among the antbirds, those that feed in the bushes, and those that always feed while walking on the ground, like the Striated Ant-thrush you see here:
We found that, despite some overlap, the ground walkers and the bush feeders harbor different trematodes.  Organisms that have close common ancestry often have the same parasites (ostriches and emus, for example).  Perhaps these two types of antbirds are not closely related.  Indeed, geneticists discovered that the DNA of the two groups of antbirds are not closely related.  Most ornithologists now place them in completely different families, Thamnophilidae for the bush inhabitants, and Formicariidae for the ground walkers.  In 1990, Erika and I presented this research at the International Ornithological Congress in Christchurch, New Zealand.

Thursday, June 24, 2010

Indigo and Lazuli Buntings

Genetic research is revolutionizing our understanding of how birds are related and of what constitutes a species.  The Yellow-shafted and Red-shafted Flickers I recently wrote about are a good example. They look different but they are genetically similar and they interbreed. Therefore they are considered to be the same species, now called the Northern Flicker.

At first glance, Indigo Buntings (the first photo taken in Northfield, Minnesota) and Lazuli Buntings (the second photo taken in Aberdeen, South Dakota) appear to be a similar example.  Although they look quite different, where the eastern Indigo comes in contact with the western Lazuli, these two buntings often hybridize. Thus, Alan Phillips, in his book Birds of Arizona, combined the two into a single species, which he named the Common Bunting.
Studies of certain enzymes suggest that Indigo and Lazuli Buntings are the same species, because the two buntings differ in enzyme frequencies in areas where they do not overlap, but these enzymes are similar where the ranges do overlap.  However, work with mitochondrial DNA suggests that Indigo Buntings' closest relative is the larger bodied and billed Blue Grosbeak (photo below from Fort Pierre, South Dakota). Furthermore,  Lazuli Buntings are relatively distantly related to any of the other North American buntings.  These results would imply that Indigo and Lazuli Buntings are distinct species that occasionally hybridize. Because of these conflicting data, most ornithologists have yet to lump Indigo and Lazuli Buntings into a single species.
Just to confuse matters a bit more, Indigo Buntings are also known to rarely interbreed with Painted Buntings in southeastern North America.  The photo below is a Painted Bunting in Florida.  I do not think anyone, however, suggests that Indigo and Painted buntings are the same species.

What is a "species?"  Most ornithologists adhere to the Biological Species Concept.  A species is a group of individuals that are at least potentially capable of interbreeding.  In other words, a species consists of individuals that share a common gene pool.  Other scientists lobby for the Phylogenetic Species Concept.  Here a species is a group of individuals that share a relatively recent common ancestry.  One result of this second concept is the recognition of many more species than are currently illustrated in our field guides.

My source for much of the genetic information is Payne, Robert B. 2006. Indigo Bunting (Passerina cyanea), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

Tuesday, June 22, 2010

Great Crested Flycatcher

The raucous calls of a pair of nesting Great Crested Flycatchers substitute as a very early alarm clock every morning. This bird belongs to the genus Myarchis, which is a large genus of flycatchers found from Canada through South America.  In Minnesota, the Great Crested is the only Myarchis flycatcher we encounter, which is perhaps fortunate, since identifying other species can be very difficult.  Our species is somewhat smaller than a robin and winters from southern Mexico to South America.

The Great Crested is the only eastern flycatcher that breeds in holes, even in man-made bird houses.  It often places snake skin at the cavity entrance.  Apparently the snake skin is for decoration rather than, as previously believed, scaring off predators.  These days cellophane or other shiny strips of trash are used in place of snake skins.

Friday, June 18, 2010

Red-eyed Vireo

All day Red-eyed Vireos sing, lazily whistling questions and  answering them.  An alternative name for this vireo is Preacher Bird, but "the song’s unending and monotonous character prompted Bradford Torrey in 1889 to reflect wryly, 'I have always thought that whoever dubbed this vireo the ‘preacher’ could have had no very exalted opinion of the clergy.'"  Click to hear the song, which can be heard from the treetops across much of North America.  Indeed, this species may be one of the most common birds of the eastern forests. The bird in the photo is an adult.  Age is ascertained by eye color.  This bird's eye is reddish.  Young birds have flat-brown eyes.  I will try to get a photo for you this fall.

Traditionally vireos were thought to be closely related to warblers, the vireos differing by their hooked beaks, more sedate feeding habits, and usually duller plumages.  The hook allows vireos to capture larger prey items than do warblers.  Recently, however, DNA researchers discovered that warblers and vireos are not closely related.   Vireos are genetically much more closely allied to crows,  shrikes, and a group of ancient songbirds that probably originated in Australia!  As a result, in their bird books, birders now find vireos towards the beginning of the songbirds rather than towards the end near the warblers.

The quote above is from Cimprich, David A., Frank R. Moore and Michael P. Guilfoyle. 2000. Red-eyed Vireo (Vireo olivaceus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

Wednesday, June 16, 2010

House Wren

Birders are often not enamored of House Wrens.  This wren has increased in numbers with the fragmentation of North American forests.  At they increase, they displace Bewick's Wrens.  Worse yet, they take over other cavity inhabiting species' nests (including Prothonotary Warblers, Tree Swallows, chickadees, and bluebirds) by destroying their competitors' eggs or killing nestlings.  The House Wren, indeed, can be responsible for the majority of nesting failures for these species. Not nice!

I enjoy their energetic, bubbly, flute-like song.  Others, however, describe it as "a long series of short, not very musical notes poured out in a rapid burst that suddenly rises and is a persistent singer, the the effect is remarkable more for bubbling energy than beauty" (Pough, 1949, Audubon Land Bird Guide).  You can decide by clicking here.
Finally, there is little remarkable in the House Wren's drab plumage.  Or so I thought until I looked closely at this wren that I recently banded.  The House Wren is really quite lovely, with cheeks adorned with pearl-like tears.

Monday, June 14, 2010

Blue-winged and Golden-winged Warbler

Today I banded a Blue-winged Warbler, a southern bird that has expanded its range since the 1800s into central Minnesota and the northeastern United States.  Ornithologists hypothesize that human cutting of eastern forests have facilitated this warbler's northward expansion--the bird likes shrubby habitat.
As Blue-winged Warblers move north, they replace or hybridize with Golden-winged Warblers.  The reasons for the displacement of Golden-wings by Blue-wings are not understood. This photo below of a Golden-winged Warbler is from Northfield last spring--I did not see one this year. Both species are also declining due to the destruction of scrubby habitat (for housing developments and farmland) in the US and to tropical deforestation in their wintering areas.
The genetics of these species' hybridization are fascinating. Golden-winged Warblers are homozygous dominant for white underparts (WW) and homozygous recessive for black throats (pp).  Blue-winged Warblers are the opposite: they are homozygous recessive for underpart color (ww), which gives them yellow underparts. Blue-winged Warblers are also homozygous dominant for throat color (PP)—this gives them plain (i.e., not black) throats.  (I hope you recall from high school or college that homozygous genes are the same—one from mom, and the other from pop—and  dominant genes usually mask recessive genes, which are only read when not masked by a dominant one.)

When Golden-winged and Blue-winged hybridize, the young get one gene from each parent, and thus carry WwPp genes.  They are heterozygous for both genes and have white underparts (because of the dominant W) and plain throats (due to the dominant P).  The recessive genes are just along for the ride. Because ornithologists did not know it was a hybrid, originally this hybrid was named Brewster’s Warbler.

Now things get complicated.  Watch what happens when two Brewster’s Warblers (WwPp birds) hybridize.  Each sperm or egg gets one of each gene, so might randomly contain WP, or Wp or wP or wp genes.  You can make a Punnet square, which shows what happens when these genes get back together when the sperm fertilizes the egg (remember that recessives gene is masked by dominant ones):




Brewster’s Warbler


Brewster’s Warbler


Brewster’s Warbler


Brewster’s Warbler



Brewster’s Warbler


Golden-winged Warbler


Brewster’s Warbler


Golden-winged Warbler



Brewster’s Warbler


Brewster’s Warbler
Blue-winged Warbler


Blue-winged Warbler



Brewster’s Warbler


Golden-winged Warbler


Blue-winged Warbler

So far, out of the same nest, on the average you are getting 9 Brewster’s Warblers, 3 Golden-winged Warblers, and 3 Blue-winged Warblers!  What about that 16th bird?  It’s genes are wwpp, which gives us a warbler we have yet to see.  A Lawrence’s Warbler has yellow underparts and a black throat.  Again ornithologists first thought it was a valid species.  Brewster’s Warblers are uncommon (I have only seen two in my career and I have never banded one), and only 1/16th of their young are Lawrence’s Warblers (I have never seen a Lawrence’s Warbler—I almost did once, but that is another story).

This discussion is inspired by Richard Pough’s Audubon Land Bird Guide (1949).  The genetics of these crosses is actually a bit more complicated, but this discussion will suffice as an introduction.

Saturday, June 12, 2010

Northern Flicker

In the photo above, a Northern Flicker is showing off her red nuchal (neck) collar.  She is a female, since she lacks a black mustache (malar) stripe.  Compare her with the male below.  His red nuchal collar is hidden (but present), and you can clearly see his black malar stripes.  Look closely at the female's right under-wing and the male's tail--the feathers are edged yellow.  These eastern birds used to be called Yellow-shafted Flickers.
The flickers in the western United States are quite different (see below). They lack the red neck collar and the male's mustache is red, not black. Similar to the eastern female, the western female lacks a mustache.  If you look closely at the tail and the wings of the western bird, you will note that they are edged reddish rather than yellow, hence these birds used to be called Red-shafted Flickers.
Until relatively recently the two types of flickers were considered to be distinct species.  However, they interbreed across the mid-west, from Texas to southern Canada and northwest to Alaska.  Hybrids have combinations of field marks and usually salmon-colored wing shafts.  I have seen hybrids in South Dakota with each wing containing both red and yellow-shafted feathers.  Recent studies show little significant genetic difference between these populations, despite the differences in field marks.  Yellow-shafted and red-shafted birds are all now considered to be one species named Northern Flicker.

The scientific hypothesis is that these flickers were isolated about the time of the last glaciation, about 10,000 years ago.  When the populations were separate, they differentiated.  As the populations came back into contact after the glacier receded, they had not changed enough to prohibit them from massively interbreeding.

The top photo is of a bird recently banded near Northfield, Minnesota; the middle on is at a feeder in Aberdeen, South Dakota; the red-shafted flicker is on a cottonwood in Missoula, Montana.

Thursday, June 10, 2010

American Redstart 2

I blogged about American Redstarts on 14 May 2010.  Here are a few new photographs of birds recently banded (and one old one) showing the difference between female and first and second-year male redstarts, and how the males, in their second year, molt into their black and orange plumage.
The flanks on the female above are flat yellow.  A first-year male's flanks, below, have an orange tint. 
During the next breeding season, second-year males begin molting into their familiar black and orange plumage.  Both the middle photo and the one below were taken in June, so some variation exists as to when this molt starts.
By the end of the second year, second year birds will look like the bird in the photo below.  By that time, however, a new batch of first year males will have hatched and will look similar to the second photo in this series.

Tuesday, June 8, 2010

Common Yellowthroat

The Common Yellowthroat is well-named.  This bird sports a yellow throat and is common over much of North America.  Because of the male's black mask, Erika and I often call him the Zorro Bird.  Other times we say, "There's a Witchity-witchity-witchity Bird" after its distinctive call. Common Yellowthroats are often found in marshy or grassy wetlands.  They usually respond well to birders' squeaking noises and come close to investigate. 
Females, like in the photograph below, are intrinsically more difficult to identify.  All are greenish above and mostly yellow below and have a slight chestnut wash on their forehead (this bird seems to have more brown on the head than normal.
Yellowthroat pairs are almost always monogamous, at least within a single season.  The female, however, is completely unfaithful to her mate and will copulate with other males.  These guys often hang around a mated pair's territory on the chance they will "get lucky."  (Guzy, Michael J. and Gary Ritchison. 1999. Common Yellowthroat (Geothlypis trichas), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

Monday, June 7, 2010

Red Admiral and Dame's Rocket

While strolling in the Carleton College arboretum, Erika and I found this Red Admiral butterfly atop a Dame's Rocket.  The flower is escaped from cultivation.  This mustard was brought to North America from Europe in the 1700s.  Dame's Rockets have but four petals, unlike the five of phlox.

The butterfly is holarctic, which means that it is found in the Old and New Worlds in both northern hemispheres.  In much of the Red Admiral's range, this butterfly is migratory in the spring, and perhaps also in the fall.  In North America this species overwinters from south Texas through Guatemala.

Sunday, June 6, 2010

Eastern vs. Western Meadowlark

I naively assumed that identifying Eastern and Western Meadowlarks is not impossible.  According to my first Peterson guide, although the two meadowlarks are nearly identical, the Western is paler on the back and has the "yellow of the throat edging a trifle farther onto the cheek; best recognized" The Eastern sings "two clear slurred whistles, musical and pulled out: tee-yah, tee-yair (last note 'skewy' and descending."  The Western, on the other hand, sings "a variable song of seven to ten notes, flute-like, gurgling, and double-noted; very unlike clear slurred whistles of Eastern Meadowlark."  Listen to these calls by clicking on these names: Eastern Meadowlark; Western Meadowlark.
I spent the last 30 years in South Dakota surrounded by Western Meadowlarks.  The Eastern Meadowlarks I am now seeing in Minnesota to appear to have darker backs than those South Dakota birds.  Look at the Eastern Meadowlark in the photo above (taken Thursday near Northfield, Minnesota).  The yellow of the throat does not go into the cheeks or the malar region behind the lower mandible and above the throat.  In the photo below of a Western Meadowlark from Fort Pierre, South Dakota, you can see that the throat's yellow color does invade the malar region on the sides of the face. 
Seems simple, if somewhat difficult to observe, at least for us in the upper Midwest (other races of meadowlarks from elsewhere in the United Stated complicate the situation). Enough variation exists in the yellow-on-the-face field mark (for example, see that some rare bird committees do not accept meadowlark identifications without accompanying tapes of the calls.

But the situation gets more complicated. Meadowlarks, where their ranges overlap (as they do in Minnesota), can learn and sing each other's (and other species') calls! (See Davis, Stephen K. and Wesley E. Lanyon. 2008. Western Meadowlark (Sturnella neglecta), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:  Furthermore, these two species occasionally hybridize.

Peter Pyle in his Identification Guide to North American Birds, a book used as an ultimate guide for banders, writes "this is one of the most difficult in-hand species identification problems."  According to Pyle, the complete lack of yellow in the malar region identifies female Eastern Meadowlarks, and extensively yellow ones indicate male Weaterns. What is a birder to do?  The answer must be to proceed VERY carefully when identifying meadowlarks!

Saturday, June 5, 2010


On my way to Nertrand Big Woods on Thursday, I stopped the car and listened for meadowlarks.  Instead I heard a very nearby Dickcissel, a bird that looks superficially like a meadowlark, singing from a roadside bush.  In his Audubon Land Bird Guide (1949) Richard Pough described the call as a repeated "dick, dick, dick, dickcissel...with the number of dicks and cissels varying."  Click here for the call and see what you think.

In my youth I read that the Dickcissel is the Jekyll and Hyde Bird because, while in North America Dickcissels eat mainly insects, in Venezuela (where most winter), they consume almost entirely rice and sorghum.  I have seen video clips of thousands of Dickcissels dripping like African locusts from Venezuelan sorghum.  This behavior does not amuse Venezuelan farmers and may be one reason for the Dickcissel's historic population decline.

Back in the USA, Dickcissels are polygamous prairie birds.  Females pick their mates by the quality of the males' territories, as measured by the availability of nesting sites (rather than food resources).  Males have been known to have up to six mates. On a yearly basis, Dickcissels tend to be nomadic, and therefore their numbers fluctuate annually.  One year they are abundant, the next they are absent.
The photo at the top of this entry was taken Thursday near Nerstrand Big Woods State Park; the lower photo was taken some time ago near Fort Pierre, South Dakota. Much of the information in this post comes from Temple, Stanley A. 2002. Dickcissel (Spiza americana), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

Friday, June 4, 2010


Today near Dundas I banded this Veery, which I originally banded two years ago, on 26 June 2008. Given the late June date of its original banding, I assume this Veery has a local breeding territory. The national longevity record for a banded Veery is 10-years, 1-month--banded and recovered in New Jersey. The Minnesota record is a Veery that was 4-years old, banded on 21 May 1977 and recaptured on 30 May 1981, both locations in the Lake Itasca region of Minnesota (data from Bird Banding Laboratory records).

The Veery breeds across southern Canada and northern United States. This species breeds throughout Minnesota, except for the southwest part of the state. Breeding Bird Survey data from 1994-2003 suggest, across the Veery's range, the species is especially common in northeastern Minnesota.

Thursday, June 3, 2010

Red-headed Woodpecker

Since both banding stations are amazingly unproductive, I spent the afternoon "chasing" Red-headed Woodpeckers at Nerstrand Big Woods State Park.  In any season, this park usually produces this relatively uncommon species. Today I immediately found at least one pair in the park's picnic area. "Chasing" is a poor verb.  I walked, the woodpeckers flew.  Totally unfair!  The birds fed on insect grubs (visible in the photo above) and acorns on the ground.

Why is this species uncommon?  Apparently this species ground-feeding habit makes it prone to automobile collisions and it is particularly susceptible to pesticides. This woodpecker's abundance, however, has varied widely for the past 200 years, and may be tied to fruiting trees and insect populations.