January 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]