Feather Pigments

By in Morphology, Physiology

None of us is so foolish as to think that winter is over.  However, the spring bird migration is about to begin.  It is likely that Red-winged Blackbirds will begin to appear in Maine before the month is over.  March will bring Common Grackles, American Woodcock, Turkey Vultures, Eastern Phoebes and Osprey.

As spring approaches, many songbirds will change from a drab winter plumage to a more gaudy breeding plumage.  Males are much more likely to “get dressed up” for the breeding season.  This change in costume is accomplished by molting of feathers.

Like our fingernails, bird feathers are dead structures once they are formed.  In fact, feathers are mostly composed of keratin, the same material that makes up our fingernails.  As feathers are formed in special structures called follicles, various pigments are deposited as small grains in the feather that gives a feather its distinctive coloration.

By far the most common type of pigment in bird feathers are the melanins.  Melanins of different types impart black, brown and other earthy tones to a feather.  Humans produce melanins too.  The black skin of a person of African heritage is caused by the high concentration of melanin in the skin cells.  Lighter-skinned humans produce melanins when exposed to strong sunlight.  That’s how we get a suntan.  Melanins are produced by the cellular machinery of birds by recombining amino acids from the breakdown of proteins.

Besides providing color to feathers, melanin has another important function in birds.  The presence of melanin grains strengthens the feathers.  You can probably think of a number of large birds that have black wing tips.  Northern Gannets, Snow Geese, Tundra Swans, White Ibis, Wood Storks, American White Pelicans, and Swallow-tailed Kites are good examples.  For a flying bird, the outer feathers of the wing experience the most stress during flight.  The birds above are not close relatives.  All of them have evolved black-tipped wings to reduce the wear on their outer wing feathers.  The presence of similar structures in unrelated species is called convergence; black wing tips are an excellent example of convergence.

Lots of our local birds have brilliant red, yellow and orange feathers in their breeding plumage.  In most birds, these colors are imparted by pigments called carotenoids.  Unlike melanins that a bird can manufacture, carotenoids cannot be made by a bird’s cells.  Rather, the carotenoids are acquired in the diet either by consuming plant material or indirectly by eating animals like caterpillars that consume plants.  Carotenoids are made by plants.  The brilliant yellows, reds and oranges of fall trees come from carotenoids in the leaves that are unmasked only after the green chlorophyll pigment is resorbed in the fall.  Birds retain carotenoids from their plant food for their own decoration.

The amount of carotenoids in the diet of a bird can determine how colorful that bird’s breeding plumage is.  For instance, a male House Finch typically has deep red feathers on its head, breast and rump.  Males that are good at finding food rich in carotenoids have deep red feathers.  Males on deficient diets are yellowish rather than red.  Research has shown that female House Finches choose their mates based on the color of the plumage.  Red males are preferred.  Females seem to know that if a male is good at finding food for itself, his food-finding abilities will come in handy when it is time to feed hungry nestlings.  Yellow male House Finches will normally not be picked as mates by females.

A third type of pigments in bird feathers are called porphyrins.  These compounds are similar to the hemoglobin molecules in our blood.  Porphyrins generally impart reddish and brownish tones.  These pigments are found in a number of owls.  One characteristic of porphyrin pigments is that they fluoresce under ultraviolet light.  Birds can see into the ultraviolet portion of the spectrum so porphyrins are likely more vivid for birds than they are for us.

Eastern Bluebirds, Blue Jays and some other local birds have what appear to be blue feathers.  However, there are no blue pigments in bird feathers.  The appearance of blue is brought about by the particular structure of the feathers.   That structure allows all the different colors of visible light (all the colors of the rainbow) to enter the feather but only blue colors are reflected back out.  All the other colors are absorbed by the feather and can’t be seen.   So, a Blue Jay appears to be blue not because of blue pigments but by selective reflection of light.  As I tell my students, blue color in birds is a pigment of your imagination.

[Originally published on February 21, 2010]

Maine Christmas Bird Count Highlights III

By in Christmas Count Summaries

This column is the last in a series of three documenting the highlights of Christmas Bird Counts in Maine, held between mid-December and early January.  We’ll take a whirlwind tour all over the state today.

The results from the counts covered today mirror the general trends of other counts in Maine: low numbers of irruptive winter finches, Bohemian Waxwings and northern owls and a good diversity of lingering species that normally are found well to our south.

The Sweden count produced 36 species.  A Red-headed Woodpecker was an excellent find.  Lingering birds included two Wood Ducks, a Great Blue Heron and three Rusty Blackbirds.   The 50 Cedar Waxwings provided a notably high count for this year in Maine.   The Sweden counters established a record high count for an introduced bird, the House Sparrow with 529 tallied.

Let’s fly out to Monhegan Island where a total of 47 species were found.  Of course, the usual seaducks and loons were present.  This island usually harbors some waifs at any time of year and this December was no exception as a Sedge Wren was found.  This species is an extremely rare breeder in the state so any record of the species is notable.  Fourteen Carolina Wrens were present as well.

Lingering species included a Double-crested Cormorant, a Hermit Thrush, a couple of Yellow-rumped Warblers, a Common Grackle and a Red-winged Blackbird.  White-crowned Sparrows migrate through Maine between their more southerly wintering areas and northerly breeding areas so one found on Monhegan was a very nice find.

Continuing along the coast, our next stop is the Bath Christmas Count.  This count yielded an impressive 83 species.  This total included 19 species of waterfowl, high-lighted by both Lesser Scaup and Great Scaup, a Ring-necked Duck and 17 Barrow’s Goldeneye.  The 254 Red-necked Grebes far outnumbered the 38 Horned Grebes as well as the Red-throated Loons and Common Loons.  Three species of alcids were found with three Thick-billed Murres and 58 Razorbills joining the more expected Black Guillemots.

Birds of prey included 23 Bald Eagles, a Sharp-shinned Hawk, a Cooper’s Hawk, a Red-shouldered Hawk and five Red-tails.

The Freeport count produced a list of 61 species.  Sixteen species of waterfowl were highlighted by an impressive count of 1,871 American Black Ducks.  Grebes and loons were in short supply.

Lingering birds included a Double-crested Cormorant, two Belted Kingfishers, a Ruby-crowned Kinglet and a Fox Sparrow.  The 235 American Robins made for an impressive count.

Let’s head up the St. Croix River to the estuarine region around Calais and St. Stephen.  That count yielded a list of 34 species.  The most common waterfowl were Common Goldeneye and Common Merganser.  Most of the species this year were expected residents or winter visitors.  Lingering birds were a Common Grackle and a Rusty Blackbird.

Lingering species included nine Great Blue Herons, three Belted Kingfishers, a Hermit Thrush, an American Pipit, one Orange-crowned Warbler, 44 Yellow-rumped Warblers, a Common Yellowthroat and a Red-winged Blackbird.

I always like to compare the results of the Bangor count with the Orono-Old Town count.  The count circles are quite close together so one would expect most of the same species and similar abundances.

This year, the Bangor count yielded 43 species while the Orono count produced 48 species.  By and large, common species were found in approximately equal densities in the two areas.

These two counts were among the “finchiest” counts this year with Pine Siskins (scarce as hen’s teeth in most parts of Maine this winter) found on both counts.  A single Pine Grosbeak was found in Bangor along with 14 Purple Finches.  The 1,0003 American Goldfinches set a new high-count record for Bangor.  Orono has three Purple Finches and 275 American Goldfinches.

Other notable birds in Bangor included a Gray Jay, two Northern Mockingbirds, 14 Bohemian Waxwings and a dozen White-throated Sparrows.  Good finds on the Orono count included a couple of Barrow’s Goldeneyes, a Merlin, a Belted Kingfisher, a Northern Shrike, a Northern Mockingbird and rarest of all, an Orange-crowned Warbler.

The Farmington Count resulted in a tally of 39 species.  Only a single House Finch was found this year.  Tufted Titmice continue to move northward and westward into Maine; Farmington had 23 of these delightful birds this year.  The 13 Brown Creepers set a high for the count.  Waxwing numbers were pretty impressive with 159 Bohemians joined by 63 Cedars.  The Farmington count circle has a lot of open land so the 102 Snow Buntings were not unexpected.

Other notable birds were a single Wilson’s Snipe, two Common Loons and seven Brown-headed Cowbirds.

[First published on February 7, 2010]

Maine Christmas Bird Count Highlights II

By in Christmas Count Summaries

This column is the second in a series of three documenting the highlights of Christmas Bird Counts in Maine, held between mid-December and early January. Let’s take a trip along the coast of Maine, visiting six Christmas Count circles.

The Biddeford count tallied a fine total of 82 species on January 5. Snow Geese in Maine during the winter are unusual, so the two found here were good finds. Twelve other, more expected species of waterfowl were found.

Red-throated Loons are usually much less common than Common Loons during the winter in Maine; 13 and 146 of these species, respectively, fit this pattern. Red-necked Grebes (93) were outnumbered by Horned Grebes (176).

The 377 Purple Sandpipers were joined by a lone Dunlin for the only shorebirds found this year. Regularly occurring Black Guillemots along with the more unusual 14 Razorbills and two Thick-billed Murres made for a nice trio of alcids.

Some migratory breeding birds or migrants linger in Maine into the winter. Such birds included a Great Blue Hero, a Northern Flicker, a Gray Catbird, a Field Sparrow, three Savannah Sparrows and a Lincoln’s Sparrow. The total of 675 American Robins was impressive.

Four finch species were found with the nine Purple Finches and nine Pine Siskins being the most notable. These two species are tough to find this winter in Maine so far.

The count held in the Pemaquid/Damariscotta area produced a list of 69 species. This area usually has abundant Common Eiders so the 1,421 found this year were expected. Not expected were a King Eider and a Ring-necked Duck.

This area is also a good place to look for foraging Northern Gannets just offshore; 87 were counted this year.

A Turkey Vulture was an exceptional find this year; most have migrated from Maine by the end of October.

The rocky shores in this area are great for Purple Sandpipers and 223 were present this year. Less expected were the dozen Ruddy Turnstones.

Three species of alcids were found with three Dovekies and a singleton Razorbill joining the 22 Black Guillemots.

Three Belted Kingfishers either found open freshwater or fished in the ocean for their food. Lingering landbirds included an extraordinary nine Chipping Sparrows, a Fox Sparrow, a White-crowned Sparrow and two Common Grackles.

The Thomaston/Rockland count produced 72 species. The 15 species of waterfowl included a Snow Goose, an impressive 541 Buffleheads and three Ruddy Ducks. A Pacific Loon was an excellent find.

Six species of raptors were found including a couple of Rough-legged Hawk and an impressive total of 20 Red-tailed Hawks.

Four Bonaparte’s Gulls and a single Black-legged Kittiwake were present along with much more numerous and common Herring Gulls, Ring-billed Gulls and Great Black-backed Gulls.

Lingering birds included four Northern Flickers, a Belted Kingfisher, a Ruby-crowned Kinglet, and a Swamp Sparrow,

The North Penobscot Bay count, including the town of Belfast, yielded 50 species. Waterfowl diversity was good with 12 species recorded. American Black Ducks (206) outnumbered Mallards (140). This region is reliable for Barrow’s Goldeneye. One was tallied this year along with 173 Common Goldeneyes.

Loon and grebe abundance was low with only five Common Loons and a single Horned Grebe found.

A Red-bellied Woodpecker was a nice find; this species continues to make inroads into Maine. A Carolina Wren was unexpected. This species is sometimes described as “half-hardy”; they can tolerate a moderate New England winter but not a severe one.

As I noted in the last column, this winter does not seem to be particularly promising for invasions by Pine Siskins, Common Redpolls and other northern finches. But in the Belfast area, Pine Siskins (26) and Common Redpolls (25) nearly outnumbered the 35 House Finches.

Further downeast, the Schoodic Point count yielded 62 species. A Northern Pintail was the most unusual of 12 species of waterfowl. The 244 Red-necked Grebes were particularly abundant this year.

Less common gulls included two Bonaparte’s Gulls, a Glaucous Gull and 14 Black-legged Kittiwakes.

Most of the landbirds found this year were either residents or regular wintering species. The few lingering birds were two Belted Kingfishers, a Northern Flicker and five Common Grackles.

I’ll end with the northernmost count in Maine, the Presque Isle count. Participants found 29 species, about the average number of species on this count. The 180 Common Ravens outnumbered the 54 American Crows. Two Gray Jays were good additions.

Bohemian Waxwings had invaded with 412 counted. This area has lots of open fields, providing habitat for 2,342 Snow Buntings. The only finches were 39 Purple Finches and 14 Pine Siskins.

[Originally published on January 24, 2010]

Maine Christmas Bird Count Highlights I

By in Christmas Count Summaries

Christmas Count season is upon us.  Organized by the National Audubon Society, this census effort has given us a valuable snapshot of early winter bird distribution for over the past 100 years.  Over 20 counts are held in Maine.   This column is the first in a series describing the highlights of the 2009/2010 counts.

Each winter, bird abundance in Maine is increased by varying numbers of irruptive (meaning moving into) birds from our north.  Such species include Common Redpolls, Pine Grosbeaks and other northern finches as well as Bohemian Waxwings.  In some years, Snowy Owls, Great Gray Owls and Northern Hawk Owls grace us with their presence for the winter.  Alas, this year is a poor one so far for these erratic winter visitors.

Maine’s southernmost count, the York count, was held on December 14 and produced a fine list of 86 species.  With lots of coastal and freshwater habitat, this count circle usually produces a nice diversity of waterfowl.  This  year’s count was no exception with 16 species found.  The most notable waterfowl were three Snow Geese and two  Gadwall.  Harlequin Ducks in eastern North America seem to be declining so the 86 individuals of these handsome birds on the York count were nice to see.

The combination of the southerly location of this count and early date for this count in the nearly three-week counting period resulted in a number of birds that were lingering later than normal for this species.  I am sure most of these birds have found their way farther south now!

These lingerers included  Double-crested Cormorant, Great Blue Heron, Black-crowned Night-Heron, Northern Harrier, Wilson’s Snipe, Belted Kingfisher, Yellow-bellied Sapsucker, American Pipit, and Savannah Sparrow.  I suspect many of the 51 Eastern Bluebirds tallied have sought warmer climes now.

Six species of gulls were counted.  The most unusual was a Black-headed Gull.  Black-legged Kittiwakes were represented by a fine total of 35.

Shorebird diversity was excellent with the expected Purple Sandpipers and Sanderlings joined by a Killdeer, two Ruddy Turnstones and two Dunlin.

The most common alcid in coastal waters is the Black Guillemot and 10 were found this year.  Razorbills usually winter well offshore so the count of 22 birds is noteworthy.

The best rarity on the count was a Yellow-throated Warbler.

The Lewiston/Auburn count was held on December 19.  A total of 43 species were found by the 25 participants.  The 326 Mallards were by far the most common of the six species of waterfowl found.  Two lingering Common Loons were nice finds.  Five species of diurnal raptors were found with the dozen Red-tailed Hawks and the two Peregrine Falcons being the most notable.

Red-breasted Nuthatch abundance varies greatly from winter to winter.  This year seems to be a bit of a down year; only 14 were found in Lewiston/Auburn.

Lingering birds included a Hermit Thrush and a Field Sparrow.  Three Northern Mockingbirds and 60 Cedar Waxwings were good additions to the count.  The 50 Northern Cardinals indicate this species continues to increase in Maine; the species was quite uncommon in Maine only 30 years ago.  Only two finch species (American Goldfinch and House Finch) were found this year.

The Bunker Hill (in Lincoln County) count produced 50 species on December 21.  Eleven species of waterfowl were tallied with a Redhead, a Ring-necked Duck and a dozen Greater Scaup being the most notable.

Birds that normally depart from Maine by this time included a Great Blue Heron, two Eastern Bluebirds and, most unusually, a Vesper Sparrow.

Three Red-bellied Woodpeckers were found along with three other species of woodpeckers: Downy Woodpecker, Hairy Woodpecker and Pileated Woodpecker.

Only two species of finches were found:  114 American Goldfinches and a single House Finch.

The Waterville count was held on December 20 and produced 53 species.  Open water was limited but counters were able to find a Greater Scaup, a lingering Ring-necked Duck and a single Barrow’s Goldeneye (multiple individuals of this species are usually found on the Kennebec River here).

Diurnal raptor diversity was good with the highlights being a Rough-legged Hawk, several Red-tailed Hawks and a Merlin.

Two observers must have been amazed to find an Eastern Phoebe, pumping its tail, at this late date.  Other unexpected birds included a Lincoln’s Sparrow and a pair of Rusty Blackbirds.

One Bohemian Waxwing was picked out of a flock of Cedar Waxwings.  A large dairy farm north of Fairfield usually produces a nice mix of ground-feeding seedeaters.  The counters were not disappointed this year, finding Horned Larks, Snow Buntings, and a single Lapland Longspur.

[Originally published on January 10, 2010]

Species Concepts III

By in Speciation

In the last column, I began a discussion of the different concepts of species used by biologists. How do we know what a “good species” is? The column ended with the Biological Species Concept (BSC, for short), in which the ability to interbreed determines if two populations should be combined into one species.

Determining species limits is tricky because hybrids often occur when two presumed species overlap. Orioles provide a nice example of the changing winds of bird taxonomy. Prior to 1983, birders could see Baltimore Orioles in eastern North America and Bullock’s Orioles in the west. Based on the fact that these two species interbreed at their region of overlap in the Great Plains, the AOU Check-list Committee combined the two species into one, called the Northern Oriole. Subsequent work revealed that the two species have very different molting patterns. DNA comparisons indicate that Baltimore Oriole and Bullock’s Oriole are not even their closest relatives. So the Check-list Committee reversed itself and split Northern Oriole back to two species.

Our current taxonomy has some inconsistencies. The American Black Duck and Mallard interbreed freely. Waterfowl biologists are concerned that hybridization with Mallards may be swamping the genetic constitution of the black ducks. Similarly, the Golden-winged Warbler is declining throughout much of its range, due in part to extensive hybridization with the Blue-winged Warbler (a species that is rapidly increasing its range). So despite the ability of these two pairs of species to interbreed freely, we recognize each pair as two separate species.

Compare that situation to the Yellow-rumped Warbler, one of the most familiar warblers nesting in Maine and indeed throughout North America. Two forms of this species are recognized, our eastern Myrtle Warbler and the western Audubon’s Warbler. Male Myrtle Warblers have white throats and male Audubon’s have yellow throats. The two types of yellow-rumps interbreed in a very limited area in the southern Canadian Rockies. Despite the more limited interbreeding than the two species pairs above, the two distinct forms are combined into a single species.

This discussion leads us to consideration of the last species concept, the Phylogenetic Species Concept (PSC, for short). Advocates of the PSC argue that the ability to interbreed is a misguided approach. Rather, these advocates define a species as a group of individuals that all share at least one characteristic found uniquely in that group. If individuals sometimes interbreed with other species but still maintain those unique characteristics, it’s no big deal. Each species has its own history (or phylogeny). Use of the PSC would cause the Myrtle Warbler and Audubon’s Warblers to be split into two species. The limited interbreeding does not alter that fact that the two types of yellow-rumps have unique throat colors.

Unique songs or calls can be used to define a species under this approach. From the work of Jeff Groth and Tom Hahn, we know that there are at least nine populations of Red Crossbills with distinctive flight calls. The different call types do show some morphological differences and differences in choice of cones they feed on. The PSC would result in these nine call types being split into nine species.

Genetic differences can be used to define species using the PSC. If all individuals in a population have a unique sequence of DNA, that information can be used to define a species. Of course, a DNA sequencer is a bit unwieldy for birders to carry in the field!

One upshot of using the PSC is that the number of recognized species of birds will increase. I have seen one estimate that the number of bird species could be doubled to about 20,000. That is one way to work on your life list.

Regardless of the species definition chosen, biologists will continue to be confused for some species or groups of species. Populations change and diverge through time in response to changing climate, increases in competition or changes in predator numbers. To drive this point home, let us end with Herring Gulls.

Herring Gulls occur around the globe in higher latitudes of the northern hemisphere. European Herring Gulls are the lightest in color. They interbreed with the slightly darker American Herring Gulls. American Herring Gulls from Alaska interbreed with even darker Vega Herring Gulls in Siberia. The Vega gulls interbreed with the darker yet Herring Gulls in central Russia and they interbreed with Lesser Black-backed Gulls in Europe. But at the end of this ring, the Lesser Black-backed Gulls and European Herring Gulls can’t interbreed! Where do we draw the species line?

[Originally published on December 13, 2009]

Species Concepts II

By in Speciation

In the last column, I wrote about the scientific classification of birds.  I pointed out that the families and orders into which birds are classified are pigeonholes defined by scientists.  The only taxonomic unit that is defined by nature is the species.  Recognizing species is not as easy as one might think.  We’ll begin to explore this prickly subject today.

A recent scientific review showed that there are over 60 definitions of species.  I will collapse this list to three basic concepts and discuss the strengths and weaknesses of each.

The morphological species concept is based on the idea that all members of a species should be similar.  Of course similar is a subjective adjective.  I like to show my introductory biology class a portrait of the basketball player Wilt Chamberlain next to the jockey Willie Shoemaker.  An alien would scarcely suspect that these two mean, differing so much in height and skin color, belong to the same species.  Strike one for the morphological species concept.

Sibling species, species that are deceptively similar, also pose a problem for the morphological species concept.  Prior to 1973, certain flycatchers with eye-rings and wing-bars were identified as Traill’s Flycatchers.  Fieldwork showed that some male Traill’s Flycatchers gave a sneezy fitz-bew song and others gave a fee-bee-o song.  Researchers found that some Traill’s females responded only to the fitz-bew songs and others only to the fee-bee-o songs.  Traill’s Flycatcher is actually two very similar species: the Willow Flycatcher and the Alder Flycatcher.  Distinguishing the two species in the field is nearly impossible and even in-hand identification is not always possible.  Strike two for the morphological species concept.

Ernst Mayr, one of the greatest biologists of the 20th century, developed the biological species concept, defining a species as a population of interbreeding organisms that are reproductively isolated from other populations.  This concept is widely held and is the predominant view of the members of the American Ornithologists Union Check-list Committee that rules on taxonomic changes for the birds of the Americas.

The critical aspect of this concept is the ability to breed with other individuals to produce viable offspring.  Different species should be unable to hybridize; they should be reproductively isolated even if they are found in the same area.  Isolating mechanisms include songs, displays and infertility that prevent members of different species from mating or producing viable young.

Two problems arise with his concept.  First, how do you treat populations that are geographically separate from each other?  Consider the scrub jay complex.  Scrub Jays are very common birds west of the Rocky Mountains, essentially occupying the ecological role of our Blue Jays.  But there is a population of Scrub Jays in south Florida.  Also, the Scrub Jays on Catalina Island, off the coast of Southern California, look a bit different from western Scrub Jays.  How can you apply a test of the ability to interbreed for populations that are not in contact with each other?  The answer is that it becomes a judgment call.  Formerly, these jays were all treated as one species, the Scrub Jay.  More recent work, based in part on DNA differences, has split the scrub jays into the Florida Scrub Jay, Western Scrub Jay and Island Scrub Jay.  We still don’t know if these different populations can interbreed.  Strike one against the biological species concept.

Another problem is that a lot of birds do hybridize.  More than 10% of bird species care capable of creating viable offspring with members of other species.  Ducks are the most notorious birds in this regard with over 400 hybrid combinations known.  Mallards hybridize with over 50 species of ducks and geese.  Wood Ducks hybridize with over 40 species.  Over 10% of the American Black Ducks and Mallards in New England are hybrids.

Hybrids occur regularly in wood warblers as well.  Lawrence’s Warbler is a well-known hybrid between a Golden-winged Warbler and a Blue-winged Warbler.  The Cincinnati Warbler described by Audubon is now known to be a cross between a Blue-winged Warbler and a more distantly related species, the Kentucky Warbler.

Even though hybrids often are capable of reproduction, in some cases their mixed-parentage offspring are not fertile.   Some hybrids capable of reproduction may have more difficulty in securing a mate than pure-breed individuals.

But many hybrids can secure mates and produce offspring that are fertile.  In such cases, ornithologists measure the proportions of hybrid to “pure” offspring where two populations overlap.  The two populations are judged to be the same species if hybrids are common.  In the next column, we will see this rule in action.  I will also present a third, more controversial, species concept.

[Originally published on November 29, 2009]

Species Concepts I

By in Speciation

Taxonomy is the branch of biological science that is concerned with the classification of organisms. To use birds as an example, all birds are classified into the Class Aves within the Subphylum Vertebrata (which includes all animals with backbones) and the Phylum Chordata (which includes sea squirts as well as vertebrates).

The Class Aves is divided into a number of orders. For example, the Order Gaviiformes includes the loons while the Passeriformes includes all the perching birds. In turn, each order is broken into a number of families. The Corvidae (jays and crows) and the Vireonidae (the vireos) are but two of the many families in the Order Passeriformes. Families are broken down into genera (the singular is genus). Finally, each genus contains one or more species. Following the convention developed by the Swedish taxonomist, Carolus Linnaeus, every species is referred to by its genus and species name. The scientific name of the Black-billed Cuckoo is Coccyzus erythropthalmus. It’s a good thing we have standardized common names for our birds!

Ideally, the taxonomic system should reflect the relatedness of the species within a group of organisms. So, all species that belong to a particular genus are more closely related to each other than they are to other members of their family that are in different genera. Let’s consider the sparrow family, the Emberizidae. Within this family, the White-throated Sparrow and White-crowned Sparrow both belong to the genus Zonotrichia. Our classification suggests these two species are more closely related to each other than either is to the Chipping Sparrow, classified into the genus Spizella. But all the sparrows, classified into many different genera, are all considered more closely related to each other than to any member of another family like the finches (Fringillidae) or tanagers (Thraupidae).

Of all the different levels of a taxonomic system, the species is the only one that is defined by nature. We have techniques that allow us to determine if a population of organisms constitutes a species. All of the other levels are defined by humans. There is no formal definition of what constitutes a genus or a family or an order.

Taxonomy operates on a system of priority. The first classification of a group of organisms is the one that is usually followed. Revisions to taxonomy can be published to reflect better understanding and new discoveries but such revisions have to be reviewed and approved by other taxonomists before an older taxonomy can be changed. As an example, barnacles used to be classified in the Phylum Mollusca, the group that contains snails, clams and squids. Like most mollusks, barnacles have a calcareous shell around the body. Careful examination of the internal structures of barnacles showed them to be crustaceans, more closely related to lobsters, shrimp and crabs. Barnacles were re-classified into the Phylum Arthropoda. The rapid increase in our knowledge of DNA sequences of many organisms has caused us to revise many taxonomic classifications.

Different groups of organisms were originally classified by different taxonomists. Each taxonomist had a subjective notion of how similar species should be to allow them to be classified into the same genus. There are 500 species of marine tropical snails called cone shells. All 500 of these species are classified into the genus Conus. The frog genus Pristimantis contains over 400 species of frogs native to South America and northern Central America. Different taxonomists might have defined each genus more narrowly and might have established ten or more genera for the same groups of species. At the other extreme, some species are considered so distinctive that they are put into their own genus. The Gray Hawk is the only species in the genus Asturina. The distinctive Shoebill from Africa is not only the sole species in its genus but the only member of the family Balaenicipitidae. The Black Skimmer is one of only three species in the family Ryncopidae. Birds are split into smaller genera than many other groups of organisms.

In the end, taxonomy is a way of organizing earth’s biodiversity. A taxonomic system is really a collection of pigeonholes, nested within larger pigeonholes. It is up to each taxonomist to decide how large a genus pigeonhole or a family pigeonhole should be. In other words, all taxonomic units above the level of the species are artificial groupings created by taxonomists.

We recognize the species level as the base of all taxonomy. Species are not artificial units created by scientists but groups determined by the biology of the organisms. However, recognizing a species is tricky and often controversial. We’ll jump into that fray in the next column.

[Originally published on November 15, 2009]

Life Lists

By in Birding and Birders

Shopping lists, grocery lists, to-do lists.  People love to keep lists.  That habit is found in many birders who keep lists of birds they have seen.  Such lists are called life lists.

The first mention of a bird life list that I can find appeared in an editorial in 1927 in the Wilson Journal of Ornithology.  A life list was defined as “a total list of birds with which the observer has made a field acquaintance”.  The editorial writer advocated listing of species but not subspecies because the latter cannot often be identified in the field.  The writer thought that a life list of 150-250 birds would be a reasonable expectation for most regions of the United States.  Higher totals would require the observer to travel.

The editorial concluded with thoughts on the value of a life list.  Keeping the list and adding to it is certainly enjoyable.  But is knowing a few species well better than having a passing acquaintance with many species?

Although the concept of the life list was associated with ornithologists, most people who keep bird life lists are not professional ornithologists.  For a portion of these birders, a life list represents the medium of a competitive sport.

The American Birdwatchers’ Association (now the American Birding Association) was organized in 1968 primarily to support birding (and listing) as a hobby.  List totals of subscribers were published so members could see how their lists compared to others.  The game was on!

A great milestone was reached in 1972.  Joe Taylor reported a North American list of 700 species, the first person to reach this then lofty goal.

The ABA continued to grow, fueling the growth of competitive birding, but also through the pages of Birding magazine, providing tips on identification of tricky species and site guides to birding hotspots.

Each year, ABA members have the option of reporting their list totals for publication.  Much has changed since Joe Taylor first cracked the 700 species barrier.  Increased communication has made reporting of rarities much more efficient.  In the 1970’s and 1980’s, one could pay to subscribe to a North American telephone rare-bird-alert to learn of unusual birds on our continent.  With the development of the Internet, cell phones and digital cameras, reporting of rarities became even more timely.  Now, a birder on a remote Alaskan island can send photographs of a Terek Sandpiper to the world only minutes after taking the photograph.

The twin effects of increased competition and efficient communication can be seen by looking at the most recent Life List report, reporting totals through 2008.  One can see that 282 birders have cracked the 700 species barrier and 28 birders have seen 800 species or more.  The highest total reported is that of Macklin Smith, an English Professor at the University of Michigan; Smith reports 879 species.  The next closest is Ted Koundakjian of California at 868 species.

Competing at this level is difficult because of the time and financial resources required.  If a super-rarity shows up in southeastern Arizona, these birders need to make a special trip because their competitors will likely be making the trip.

Both Smith’s and Koundakjian’s lists are notable because they do not contain any heard-only birds.  The ABA allows the listing of birds that are heard but not seen.  In part, this rule is an effort to minimize disturbance of nocturnal birds like owls or secretive birds like Yellow Rails or Black Rails.  These species can usually be reliably identified by voice.  There are purists, however, who will not put a species on their life lists unless they see the bird.

For birders with more limited time and money, life lists can be kept at more local levels.  People can report state lists for the ABA Life List Report.  For Maine, 423 species have been reported in the state.  Julie Suchecki reported the highest total of 349 species with Frank Paul a close second at 338.  I suspect other birders in the state have comparably impressive lists but choose not to report their totals.

Some people keep county or township lists.  Yard lists are popular as well.

Annual lists are kept by many birders.  These lists can be over large geographic areas (world list, North American list) or more local areas.  For 2008, Doug Hitchcox reported the highest total of species in Maine (219 species).

Some birders do not bother to keep any life lists.  Others will maintain lists for their own personal satisfaction but do not report them.  And yet others enjoy the competitive side of birding that listing provides.

[Originally published on December 27, 2009]

Recent Ornithological Literature

By in Recent Ornithological Literature

Today’s column will be a review of recently published articles in ornithology that I hope will be of interest.

Foot waggling in Common Loons

If you have spent much time watching Common Loons, you surely have seen a loon on the water raise one foot into the air and either hold it there briefly or shake it, often several times in succession. This behavior is called a foot waggle. After waggling the foot, a loon may put the foot under the wing, a behavior called shipping.

The reasons for foot waggling have been discussed for years but not adequately tested. Some ornithologists suggest foot waggling occurs most frequently in birds that are about to sleep or rest and interpret foot waggling as a comfort movement. Other scientists think that the large foot of the loon with its extensive system of capillaries may be used to regulate body temperature. A foot out of the water might lose heat quickly by evaporation of water into the air. Other ornithologists have suggested that food waggling may function as a social signal.

A recent paper in the Condor by James Paruk describes his work to investigate the function of the loon foot waggle at several sites in the Upper Peninsula of Michigan. He found that 81% of the foot waggles observed occurred while a loon was either preening or resting. Foot waggling was therefore judged to be primarily a comfort movement. Occasionally, a loon would give a single foot waggle in a stressful situation such as after encounters with boaters or a Bald Eagle or after loud thunder. Because only some loons used the foot waggle in such situations, Paruk claims that the behaviors are idiosyncratic – some birds use the behavior and others do not.

The loons did waggle their feet more on sunny days than on cloudy days. The dark bodies of loons heat up more in direct sunlight. This relationship suggests that regulating body temperature may be a secondary function of foot waggling.

By the way, foot waggling is seen in other aquatic birds as well including grebes, Ruddy Ducks, scaups and their relatives, and mergansers.

Tail pumping in Eastern Phoebes

The tail-pumping behavior of a perched phoebe is a good feature to use in identifying this flycatcher. The function of this behavior has been the subject of much conjecture. Michelle Carder and Gary Ritchison recently published an article in the Journal of Field Ornithology that presents a test of possible explanations for the behavior.

They tested four hypotheses by extensive field observations. The first is that phoebes use tail pumping to maintain their balance on a perch. The authors measured tail-pumping rates on perches of different stability (thin versus thick branches) and under different wind speeds. They found no correlations and reject this explanation. A second hypothesis was that phoebes use tail pumping as a territorial display to other males. Through playback experiments, this explanation was also rejected.

Thirdly, tail pumping might be use to aid foraging by flushing insects. The authors found no support for this hypothesis.

The predator-deterrent hypothesis was supported by the author’s data. A phoebe should increase its tail wagging in the presence of a predator to let the predator know “I see you”.  Lower rates of tail wagging when predators are not seen may discourage those predators from attacking a phoebe.

Altitudinal ranges of birds and climate change

As global warming proceeds, marked changes occur in the climate of mountains. The warming means that species restricted by temperature can move higher up a mountain.

For mobile species like birds, scientists expect that the distribution along an altitudinal gradient will occur. Birds must move higher up a mountain to find the temperature regime that best suits them.

Recently, Morgan Tingley and colleagues published a paper that explores this phenomenon. They resurveyed bird abundance in the Sierra Nevada mountains of California along four elevational transects, first established nearly a century ago. Climate information indicates that any site along the transects is warmer now than it was a century ago. The workers focused on 53 bird species and found that 48 of them had shifted their range higher up the mountains over the past century.

[Originally published on October 18, 2009]

Bird Sleep

By in Physiology

With the arrival of cool weather, I expect activity at your feeders has increased. I like to monitor when the chickadees, goldfinches and other feeder birds leave the feeder in the afternoon. The birds are going off to their roosts and the timing of their departure for their roost, relative to sundown, is remarkably constant from day to day.

At their night-time roosts, most birds spend most of the night sleeping. Birds spend about half of their lives sleeping but the amount of sleep they get depends greatly on the latitude and the season of the year. During the early part of the Maine summer, birds may sleep less than nine hours when the night is so short. On the other hand, Maine birds in the winter sleep more than 15 hours a night.

Birds living in the vicinity of the equator experience near equal days and nights each day so spend twelve hours a day sleeping throughout the year.

Some birds spend the night in communal roosts. European Starlings and American Crows are good local examples. In more southern parts of North America, huge roosting flocks of Common Grackles and Red-winged Blackbirds are common.

Migration poses a real challenge for birds in terms of getting adequate sleep. Most songbird migration occurs at night and then the birds must forage during the following day to restock their fat reserves. Not a lot of time for sleeping.

A recent study of migrating Swainson’s Thrushes revealed a behavior that helps these birds fight sleep deprivation. The birds take minute-long naps through the day. During these short siestas, a thrush will puff its feathers out and squint their eyes. A migrating Swainson’s Thrush will spend up 15% of its day sleeping in these very short bouts.

Many birds choose solitary roosts. Red-tailed Hawks, Bald Eagles, Black-capped Chickadees and Purple Finches are good examples.

Particularly during the winter, the choice of roost site can mean the difference between life and death. Many of our northern finches (Common Redpolls, Pine Siskins, Purple Finches) roost in evergreen trees. Such trees offer protection from the chilling effect of winter winds. The birds can also absorb a little of the infrared radiation emitted by the trees. In the brutal economy of a Maine winter, the little bit of heat absorbed from the environment can be critical for a wintering bird.

Woodpeckers, nuthatches and chickadees will spend the night in cavities, often the same cavities used for nesting during the breeding season. House Finches will seek out the eaves of houses for a relatively warm roost site.

Some birds sleep on the ground. Members of the grouse family are typical of this sleep behavior. Northern Bobwhite arrange themselves in tight circles on the ground with the heads facing outward. If a predator disturbs the roost, the birds explode in all directions, certainly giving the predator a dramatic shock.

The posture of a sleeping bird can important in conserving heat during a long winter night. The unfeathered bill is a potential source of heat loss. Many sleeping birds will turn their head under their scapular feathers while they sleep. Mourning Doves turn their head down, nestling it in their dense breast feathers. Some birds sleep while standing on one leg, reducing by half the heat loss across the unfeathered legs.

Aquatic birds may sleep while floating on the water. The Common Eider, abundant along the Maine coast in the winter, snoozes while bobbing on the ocean surface at night. The down feathers of the eiders, renowned for their warmth, keep the eiders warm.

Some birds are able to sleep while on the wing. Some species of swift spend months in the air without landing. Albatrosses often spend months at sea. Sleeping on the surface of the ocean is possible exposes the birds to fish and whale predators. Similarly, Sooty Terns are reported to stay airborne from the end of one nesting season to the beginning of the next breeding season. Ornithologists believe these birds spend time sleeping in flight.

Have you ever wondered why birds do not fall off their perches while they are sleeping? Songbirds have a flexor tendon in the lower part of each leg. When they perch, the flexor tendon tightens, causing the toes to curl around the perch. The tendon essentially locks, keeping the toes firmly around the perch during sleep. The same type of tendon is useful in raptors when they are carrying prey. Once a fish is in the talons of an Osprey, that fish has no chance.

[Originally published on November 1, 2009]

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