For the Birds – Talks at the Ecological Society of America meeting

I recently returned from Memphis where I attended the annual meeting of the Ecological Society of America. In this column, I will review several talks I attended on birds to give you an idea of some new research being done on birds.

Gabriel Colbeck of Washington State University is conducting doctoral research on Black-throated Blue Warblers at the Hubbard Brook Forest in New Hampshire. Specifically, Colbeck is interested in the acoustics of bird song.

We know that low frequency sounds (lower pitched sounds) carry better through dense habitat than higher frequency sounds. Also sounds with slower elements tend to be distorted less in dense habitat than sounds with faster elements.

Colbeck is seeking to determine if Black-throated Blue Warblers adjust their characteristic buzzy “zur zur zur zwee” song to the nature of the habitat. Colbeck compared areas in Hubbard Brook that were damaged by the ice storm of January, 1998 to undamaged areas. In the damaged area, the ice storm downed many canopy trees and now the understory is dense with shrubs and saplings, contrasting with the more open understory of undisturbed areas.

Black-throated Blue Warblers sing a high- and low-frequency song. Colbeck expected low-frequency songs to be given more in the disturbed areas but found no difference in the proportion of these two types of songs in the disturbed and undisturbed habitats. He did however find that slower paced songs were more prevalent in the dense, disturbed area. The results suggest that these warblers adjust the nature of their songs to acoustic features of their environment.

Rebecca Tittler and colleagues at Carleton University in Ottawa presented a paper on dispersal distances of North American songbirds. The authors seek to determine how far breeding birds in one year moved from either their breeding site in the previous year or, for birds in their first breeding season, from the site where they were born. The authors used the Breeding Bird Survey (BBS) dataset to examine changes in abundance of 51 species from one year to the next. The authors looked for a high number of birds along BBS routes in the year after a high number of birds on a BBS route within the same state or country. The results suggest that songbirds disperse between 5 and 60 miles between years, a value much larger than previous work based on recapture of banded birds.

David Brown of Lousiana State University and Tom Sherry of Tulane reported on the wintering behavior of Ovenbirds in Jamaica. Two classes of birds were found: sedentary birds that have a fixed home range overlapping with neighbors and floaters that shift their habitat based on food availability. The classes were not related to age or sex.

Finally, Dee Boersma of the University of Washington gave a fascinating talk on Magellanic Penguins. She has been studying the largest colony of these penguins in the world at Punta Tomba along the south coast of Argentina for the past 22.

The climate at this site is temperate and the penguins nest on beaches above the tideline in burrows in the sand. The burrows are usually adjacent to a small bush that provides shade. Over the past 22 years, this population has decreased by 80%.

Two eggs are laid in the burrow of each pair. The mother and father take turns incubating the eggs with each shift lasting ten to 15 days. The eggs hatch after seven weeks. The chicks are incubated for an additional five weeks. Immediately after relinquishing incubation duties, the very hungry parent heads out to sea to feed on small fish and squid.

Using satellite transmitters placed on the backs of some male Magellanic Penguins, Boersma has shown that the penguins are now swimming much farther north and seaward to feed. Global climate change is proposed reason for this change in foraging behavior. Warmer ocean waters may have forced the preferred food of these penguins to be found in cooler offshore waters. Climate change may have affected the ocean currents along the coast as well.

The upshot is that the penguins must swim farther to find enough food to replace their fat reserves before they come back to take their mate’s place in incubating. It is possible at some point that an incubating parent may be forced to abandon the nest if the other parent is away foraging for too long.

Penguins that arrive late on the breeding grounds tend to be in poorer physiological condition, lay smaller eggs and have lower reproductive success. The late arrival is also driven by the necessity to feed farther offshore than in earlier years of the study.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at [email protected] Previous columns and other information on Maine birding can be found at his blog: http://www.mainebirds.blogspot.com/

For the Birds – Colorado Birding

My wife Bets went to Colorado a couple of weeks ago to attend a business conference. I flew to Denver afterward for a few days of birding with her. This column will describe some of our birding adventures in that beautiful state.

The latter third of July is not the optimal time for a birding excursion to Colorado. Most birds were tending fledged young so bird song was infrequent and birds were therefore harder to detect. Some birds like the Mountain Plover had finished breeding and departed for their wintering areas. Nevertheless, we managed to see many species of birds with a little effort.

Our destination for the first day was the Pawnee National Grassland, about 90 miles northeast of Denver and 30 miles east of Fort Collins. This national treasure includes some 193,000 acres of federal land interspersed with private farmland. The area is crisscrossed by north-south and east-west roads, making it easy to explore the area.

The Pawnee Grassland results from the climate of the area. Annual rainfall is only about 12 inches a year. Summer temperatures are usually high; it reached 109 degrees when we there. The low moisture means that trees are rare and virtually all of the habitat is shortgrass prairie. Despite the harsh climate, bird life is surprisingly abundant.

Horned Larks are everywhere. Driving along the roads, flocks of larks, sometimes 100 or more, flew up in front of the car. Western Meadowlarks were common as well.

For most of the grasslands, the highest points are fence posts and wire fences. Birds often perch atop them. Checking these perches yielded lots of Western Kingbirds, Brewer’s Sparrows and Lark Buntings. We never tired of seeing male Lark Buntings with their bright white wing patches on otherwise black bodies and the associated females with their more muted plumage.

One of the specialties of the grasslands is McCown’s Longspur. One male gave us fantastic looks only ten feet away, allowing us to see the characteristic white and black pattern on the tail and the rufous patch in the wing.

We only saw five hawks on our trip but they represented five different species: Red-tailed Hawk, Swainson’s Hawk, Ferruginous Hawk, Northern Harrier and American Kestrel.

Prairie dogs are abundant on the Pawnee Grasslands. These rodents provide habitat for Burrowing Owls. We had no problem seeing many of these charming owls. In one small field, we saw nine at once!

A chat with a local farmer revealed some of the tension that occurs where agriculture and nature meet. This farmer indicated he did not like prairie dogs on his horse farm because they provided nesting sites for Burrowing Owls. The farmer indicated the owls were killing his barn cats, leading to too many mice in his horse barn.

A pronghorn antelope was a nice treat along with several species of ground squirrels and two rabbit species scurrying over the grasslands.

Two days later, we planned a trip into the Rocky Mountains to escape the heat wave that was plaguing the Denver area. We chose to explore Golden Gates State Park northwest of Denver.

We began our birding at the Visitors Center, quickly finding Mountain Chickadees, a Hammond’s Flycatcher and Dark-eyed Juncos. The juncos were the gray-headed forms, differing from out eastern slate-colored forms by the distinctive black lores in front of the eyes on the otherwise gray head and the rufous “backpack”.

From the Visitors Center, we drove up Mountain Base Road. This road has parking areas and picnic sites every half-mile or so, conveniently allowing birders to stop safely. We encountered several families of Western Bluebirds and Mountain Bluebirds, the parents working hard to feed their begging fledglings.

We did well with the crow family, finding Clark’s Nutcracker, Steller’s Jay, American Crow, Common Raven and Black-billed Magpie. Alas, no Gray Jays.

The bubbling song coming from a moist thicket gave away the presence of a Lincoln’s Sparrow. We heard the wonderful cascading song of a Canyon Wren, unseen from a cliff along the road. We found several Yellow-rumped Warblers, differing from our eastern yellow-rumps in having a yellow rather than white throat.

We ultimately reached the high point of the road at 9,200 feet at Panorama Pass. Here one could see over 100 miles of the Continental Divide with mountain after mountain in view. A flock of Red Crossbills called as they flew overhead.

Returning to the Visitors Center, we drove up Crawford Gulch Road. A short hike there yielded a Townsend’s Solitaire. We found a singing Warbling Vireo, whose song is buzzier than for our local birds. A stop at a feeding station on the way out of the park yield three hummingbird species: Broad-tailed, Rufous and Calliope for a nice flourish on a fine day of birding.

[First published on July 31, 2006]

47th Supplement to The Check-list of the Birds of North America

The most recent supplement to the Checklist of North American Birds was published in July by the AOU Check-list Committee. You can download a copy of the report at: http://www.aou.org/checklist/Suppl47.pdf

Two splits are reported in this supplement. First, the Cape Verde Shearwater , formerly considered a form of Cory’s Shearwater, has been split off as a valid species. The Cape Verde Shearwater is now called Calonectris edwardsii. Some nice photographs of the two species can be seen at: http://www.patteson.com/CVShearwater.htm. To date, there is only one North American record of Cape Verde Shearwater.

A second split is the recognition of Blue Grouse as two different species. The Sooty Grouse (Dendragapus fuliginosus) is found in the Pacific Northwest while the Dusky Grouse (Dendragapus obscurus occurs in the Rocky Mountains. Earlier workers noted differences in plumage and vocalizations between the Blue Grouse in the two different areas. Recent DNA comparisons support the split of Blue Grouse into two species.

Some changes in scientific names affect Maine birds. The Willet is transferred from the genus Catoptrophorus to Tringa. The two species of tattlers (genus Heteroscelus) found in western North America are also transferred to Tringa.

The skuas and jaegers are elevated from the subfamily Stercorariinae within the family Laridae to their own family, the Stercorariidae. This change was made because recent research indicates the skuas and jaegers are more closely related to the auks (Alcidae) than the gulls.

A number of terns formerly in the genus Sterna are assigned to different genera to better reflect our understanding of the evolution of the group. Here are the new names if you want to update your field guide.

Sooty Tern Onychoprion fuscatus
Bridled Tern Onychoprion anaethetus
Aleutian Tern Onychoprion aleuticus

Least Tern Sternula antillarum

Gull-billed Tern Gelochelidon nilotica

Caspian Tern Hydroprogne caspia

Royal Tern Thalasseus maximus
Sandwich Tern Thalasseus sandvicensis
Elegant Tern Thalasseus elegans

Common Tern, Arctic Tern, Forster’s Tern and Roseate Tern remain in the genus Sterna.

One final change affecting North American birds is the transfer of Gray Hawk from the genus Asturina to Buteo. The scientific name of the Gray Hawk is now Buteo niditus.

For the Birds – Common Loon

The Common Loon has to be one of the most beloved birds in the state of Maine. Their other worldly calls evoke a feeling of wilderness. Their striking black and white plumage is a beautiful sight to behold.

Common Loons play a role in Native American folklore. A Chippewa tale details the creation of the world by a loon. A Micmac story describes Kwee-Moo, a loon who was the special messenger of Glooscap, a tribal leader and hero. The folklore from a number of western Native American tribes describes how the loon came to acquire its necklace.

Common Loons have a northerly breeding distribution whose southern limits follow the upper tier of states all the way from Maine to Washington. A disjunct breeding population occurs in northwest Wyoming.

Historically, Common Loons nested further south. Breeding populations were known from northeastern California, southern Minnesota, northern Iowa, northeastern Pennsylvania, northern Ohio and southern New England.

Outside of North America, Common Loons are regular breeders in Greenland and Iceland. Nesting occurs rarely in remote portions of Scotland. During the winter, Common Loons occur more broadly throughout Europe.

The allure of loons is likely the best explanation for the effective conservation efforts that have arisen to evaluate and protect Common Loon populations. Loon Ranger programs have sprung up in a number of states. Loon Rangers are volunteers who monitor the nesting of Common Loons.

Such programs in the northeastern United States were effective in stemming declines of Common Loons and in educating the public about threats to Common Loons. These programs became models for other loon conservation programs from Alaska to Iceland.

Maine Audubon sponsors an annual loon count in Maine. In fact, the 2006 count is being held today. This program is an extremely popular one; all of the volunteer positions for the 2006 were filled.

These counts have shown that Maine has about 4,100 loons nesting in lakes throughout the state. Minnesota is the only state with more loons (over 10,000). Wisconsin has the third largest loon population with about 3,000 adults.

Results from the 2005 count (available at: http://www.maineaudubon.org/conserve/citsci/loon2.shtml) indicate the highest loon populations were on Moosehead Lake (58 adults), Damariscotta Lake in Lincoln County (52 adults), Cobbossecontee Lake in Kennebec County (51 adults), China Lake in Kennebec County (38 adults), Great Moose Pond north of Skowhegan (41adults) and two of the Belgrade Lakes (Great Pond with 47 and Long Pond with 38 adults).

Based on the 2005 data, Maine Audubon biologists estimate that the loon population in the southern half of the state is about 3,000 birds, the highest value since the count started in 1983. This rosy estimate suggests that the Maine loon population is not declining and may in fact even be growing.

Vermont’s loon population is considerably smaller. In 1987, the species was placed on the state Endangered Species list following poor nesting success in the 1980’s. In 1994, only 14 pairs nested, producing 17 chicks. Conservation efforts seem to be effective; last year 191 adults were nesting in the state.

What can you do to help conserve loons in our state? We need to start with a bit of nesting biology. Loons build a nest just above the water line. The nest is made of aquatic vegetation that the loons throw from the water onto the nest site.

Loons are particular about the placement of their nests. The birds prefer to nest on the sheltered side of islands. For smaller lakes without islands, the loons seek a site on the lee side of the water body. This choice of microhabitat is clear; the loons do not want their eggs to be covered by water from waves. After prolonged rains when lake water levels rise, nests may be inundated. The loons will then abandon their first nesting attempt and try again with a nest a bit higher up.

A female loon generally lays two eggs. The chicks are able to swim soon after hatching. They rest on the back of a parent when they are tired. Chicks can barely dive below the surface on their first day but can reach the bottom after the first week. Chicks become fully feathered by their eighth week and fly after 11 weeks.

Chicks succumb to turtles, fish and other predators. However, a study in New Hampshire indicated that 15% of loons died from boat collisions. Boats failing to obey the no-wake zone close to shore may inundate nests. Boaters seeking to get close-up views of loons may collide with a loon, particularly a young loon.

The bottom loon: keep your distance from loons while boating and let other boaters know as well, particularly if the boats get too close to loons or their nests.

[First published on July 15, 2006]

For the Birds – Purple Martin

Maine provides breeding ground for six species of swallows. Tree Swallows, the first to arrive in the spring, are the most abundant. Barn Swallows are nearly as common. As colonial nesters, Cliff Swallows and Bank Swallows may be locally abundant. Rough-winged Swallows even less common in the state. But the least abundant is the Purple Martin.

Purple Martins are the largest swallows in North America and among the largest in the world. They are an extremely popular bird, recognized by many non-birders. Males are completely covered with a glossy blue black plumage and are the only swallows in North America with a dark belly. Females with brown upperparts and lighter underparts are similar to other female swallows but can be distinguished by their large size and the prominent brown or gray collar around the nape. A martin’s chattering vocalization adds to their charm.

Although Purple Martins are scattered in parts of western North America (parts of the desert Southwest and coastal areas from British Columbia to central California), they are continuously found throughout most of the eastern states. However, they occur discontinuously in New England. In Maine they occur in a broad swath proceeding northeastward from coastal York County to the Calais region of Washington County. This band continues northeasterly into New Brunswick ending at the northwestern tip of Nova Scotia.

The Maine Department of Inland Fisheries and Wildlife estimates there are probably not more than a couple of hundred pairs in the state. Purple Martins are colonial nesters but Maine colonies are typically smaller than the large colonies one sees in southeastern states.

Although Purple Martins nested in natural cavities before the development of the United States by European immigrants, nearly all eastern birds now nest in human-made apartments. Elaborate martin houses may be used as well as gourds, hollowed out, and hung close together. The provision of houses may have caused martins to become colonial. Martins in the west often nest solitarily in natural cavities. Eastern martins have nested exclusively in human-made cavities since 1900. The geographic difference in nest-site choice is one of the most pronounced of any bird over its range.

Because of their popularity, incorrect information about Purple Martins gets published and reprinted, becoming fact in the eyes of unskeptical readers. Some of these myths pertain to the diet of Purple Martins. Manufacturers of martin houses often encourage the purchase of their products by touting the effectiveness of martins in controlling mosquitoes. Don’t believe it!

Martins tend to feed several hundred feet above the ground and always take flying insects. Their prey are mostly large species like dragonflies, wasps, bees, and Japanese beetles. Martins feed only during the day.

Mosquitoes on the other hand tend to be found in damp grass close to the ground during the day and may only be active at night. No study of martin diets has ever shown mosquitoes to be a significant component of their diet. I suspect that martins may even aid mosquitoes by reducing the populations of dragonflies, which are often effective mosquito predators.

Depending on flying insects for sustenance, Purple Martins are subject to the vagaries of the weather, particularly in New England and the Maritime Provinces. Cold or extended rainy weather during the early part of the summer can reduce the number of flying insects and spell disaster for Purple Martins.

The nesting process is slower than in many other songbirds. Incubation takes place for 15-20 days before hatching. The female does most of the incubation although the male may take a turn while the female leaves the nest to feed. The young do not fledge until 28 or 29 days after hatching.

As one would expect, nesting begins earlier in more southern parts of the range. Females begin laying eggs around the end of March in Texas but not until the first ten days of June in Maine and Nova Scotia.

It’s wonderful to have a martin colony on your property. However, getting a colony established in Maine is a tough proposition. Besides their low population numbers in Maine, martins have specific requirements for their nest boxes. The nest box needs to be higher than trees in the local area and no tree should be within 60 feet of the martin house. The martin house can be placed between 30 and 120 feet from human habitation. Research has shown that martin houses further than 120 feet from human houses are usually avoided. Martins have learned that proximity to a human house lowers the risk of predation. Another challenge is keeping House Sparrows and European Starlings out of the nest cavities.

Lots of useful information can be found at two websites: http://www.purplemartin.org and http://www.purplemartins.com/

[This column was originally published on July 1, 2006]

For the Birds – Ruby-throated Hummingbird

Over 320 species of hummingbirds have been described. This family of birds occurs only in the New World and most species are found in Central America and South America. With a little effort, it is not hard to find a dozen species in places like southeastern Arizona. But in eastern North America, we have a single species, the Ruby-throated Hummingbird.

Ruby-throated Hummingbirds have a broad distribution occurring in the United States eastward of the 100th meridian everywhere except the southern tip of the Florida peninsula. In Canada, ruby-throats occur from the Maritime Provinces westward into Saskatchewan. No other species of hummingbird in North America has a broader geographic range.

It’s hard to think of a Maine bird whose summer arrival is more anticipated. Who is not fascinated by these little sprites? The red throat feathers (called a gorget) of a male Ruby-throated Hummingbird may seem to sparkle in the right light. Their throat feathers refract light, giving the bird an iridescence that makes the feathers seem to shimmer as the bird moves its head.

Ruby-throats winter from Mexico south to northern Panama. To migrate to eastern North America, these birds often fly non-stop over the Gulf of Mexico, a flight of 500 miles. Such a trip requires a lot of fuel and Ruby-throated Hummingbirds fatten on insects and nectars, nearly doubling their weight before the trans-Gulf flight.

The mating system of Ruby-throated Hummingbirds appears to be polygyny; one male may mate with many females. No long-lasting pair bonds are forged. A male will court a female through complicated flight displays. When a female flies into his territory, he begins with a dive display, flying U-shaped loops starting from as high as 30 feet above the female. If the female perches, he switches to very fast, side-to-side flights, with his gorget extended, within two feet of the female. If the male is acceptable as a mate, the female will cock her tail feathers to one side and lower her wings, inviting the male to mate with her. Mating lasts only about 2-3 seconds and that is the end of the male’s contribution to the offspring.

The female builds the nest by herself. The base is made of the down from dandelions and thistles and is attached to the upper side of a branch, much like a saddle over the back of a horse. The sides of the nest are made of plant down, bud scales and spider webs. The plant material is woven into the nest with the spider silk.

The eggs are usually two in number and, as you might imagine, are tiny. An average egg is half an inch long.

Incubation takes 12-14 days and the young hatch as naked, blind chicks. Feeding usually begins soon after hatching and the young fledge about 20 days after hatching.

We think of Ruby-throated Hummingbirds as depending on nectar for their sustenance. However, these birds also take spiders and insects (mosquitoes, gnats, fruit flies and small bees). Although no quantitative study has been conducted, some ornithologists have examined ruby-throat feces and estimate that 50-60% of the diet is insects.

As nectar-feeders, hummingbirds, along with many insects, serve as pollinators for a number of plants. Trumpet creeper, a forest vine, seems to be primarily pollinated by Ruby-throated Hummingbirds.

Of course, the fondness of hummingbirds for nectar makes it easy for us to attract hummingbirds to our gardens and backyards. Hummingbirds will visit many types of flowers but generally those with long, tubular flowers are most attractive. Bee balm, for instance, is a favorite of ruby-throats.

An offering of sugar water is an effective way to attract hummingbirds through artificial means. The nectar produced by hummingbird-pollinated flowers is rich in sucrose (table sugar). On the other hand, flowers that are pollinated by songbirds like Cedar Waxwings and European Starlings are rich in two other types of sugar, fructose and glucose. Experiments with Rufous Hummingbirds using solutions made from these three sugars showed a preference of the hummers for sucrose.

The best recipe for making sugar water for hummingbirds is one part sugar to four parts of water. You can heat the water to make the sugar dissolve more easily but heating the water is not necessary.

Don’t add red dye to your sugar water. The most common red food dye, Red Dye Number 40, is approved for human consumption in the U. S. but not in several European countries. We also know that substances that seem to be safe for humans may be harmful to other vertebrates. Tylenol, for example, has strong negative effects on cats. Arguments about the safety of red dyes are moot to me; most hummingbird feeders have some red on them anyway and the addition of red dye does not make the feeder more attractive. At best, red dye is useless. Why bother with it?

[First published on June 17, 2006]

For the Birds – Bicknell’s Thrush

Maine has seven members of the thrush family among its breeding birds. These include Eastern Bluebird, American Robin and five species of thrushes with various amounts of spotting on their breast. These spot-breasted thrushes are among the finest of avian songsters. Their flute-like songs are magical, in part owing to the fact that these thrushes can control the left and right side of their syrinx, the organ that produces sound in birds. Thrushes can harmonize with themselves!

The Wood Thrush, more common to our south, but can reliably be found throughout the state. Veeries are found throughout the state. The Veery sings a song that spirals downward in pitch; the name of this thrush comes from its characteristic call note, Veer. Swainson’s Thrush, whose song spirals upward rather than downward like the Veery’s song, is a bird of spruce-fir forests. This species is therefore scarce in the southern third of Maine. Hermit Thrushes are widely distributed in the state, nesting in bogs as well as conifer forests. The final species, Bicknell’s Thrush, is the least known of our thrushes and is restricted to high elevations.

Bicknell’s Thrush has only been recognized as a full species for the past decade. It was formerly considered a subspecies of the widely distributed Gray-cheeked Thrush, which occurs from Alaska to Newfoundland in boreal habitats. Thanks to the work of the late Henri Ouellet, ofthe Canadian Museum of Nature in Ottawa, the Check-list Committee of the American Ornithologists Union elevated Bicknell’s Thrush to species status.

Ouellet built the case for Bicknell’s Thrush being a valid species with several lines of evidence. He began by demonstrating that Bicknell’s Thrushes differ in the color of the upperparts, the tail feathers, the throat and the undersides from Gray-cheeked Thrushes. Ouellet also showed that Bicknell’s Thrushes are smaller than Gray-cheeked Thrushes from the same latitudes. But morphological differences do not necessarily demonstrate that Gray-cheeked Thrushes and Bicknell’s Thrushes do not breed with each other. However, he was able to show that Bicknell’s Thrushes and Gray-cheeked Thrushes do not overlap in either nesting areas or wintering areas.

To really make his case, Ouellet needed to demonstrate that the two forms are reproductively separate. He analyzed the songs of Gray-cheeked and Bicknell’s Thrushes, finding distinct differences. Furthermore, Bicknell’s Thrushes on their breeding grounds did not respond to playbacks of Gray-cheeked Thrushes.

Ouellet’s final piece of evidence was a comparison of the DNA of the two forms. The analysis showed that the DNA differed by an amount similar to differences between other closely related species. The analysis suggested that the ancestral group split into Gray-cheeked Thrush and Bicknell’s Thrush about a million years ago.

The nesting range of Bicknell’s Thrush includes the Adirondack region of New York, and portions of Vermont, New Hampshire, Maine, Nova Scotia, New Brunswick and Quebec.

In northern New England, Bicknell’s Thrushes are generally found above 3000 feet in elevation although these birds may occur as low as 2,050 feet on some Maine peaks. Bicknell’s Thrushes like stunted spruce-fir forest, particularly areas that have been disturbed by fir waves or rime ice accumulation during the winter. They may nest along the edge of ski trails. The thick re-growth of these disturbed areas is often nearly inpenetrable, necessitating patience if you want to see one of these birds.

Male Bicknell’s Thrushes sing throughout the day until the middle of June and then singing stops abruptly. Birds will occasionally call after singing drops off but the dense habitat and secretive nature of the thrushes make them very hard to find. In short, if you want to see a Bicknell’s Thrush on its breeding habitat in Maine this year, you better plan a trip soon!

The entire population of Bicknell’s Thrushes is certainly no more than 50,000 individuals, making Bicknell’s Thrush a species of concern for environmental managers. These birds do nest at fairly high density (average of about 50 pairs per 100 acres) so habitat alteration of even a small area at high altitude can have serious repercussions for the species.

Conservationists worry about winter habitat degradation as well. The entire population winters on only four islands in the Greater Antilles.

In 1992, The Vermont Institute of Natural Sciences (VINS) launched a survey of Bicknell’s Thrushes in the northeastern United States. You can find lots of information on Bicknell’s Thrush at their website including maps of mountains with breeding Bicknell’s Thrush and downloadable recordings of songs and calls. Their URL is: http://www.vinsweb.org/cbd/mtn_birdwatch.html

You can download a copy of Henri Ouellet’s paper and two papers from the VINS research team, all published in the Wilson Bulletin, by going to: http://elibrary.unm.edu/sora/

Type in Bicknell’s Thrush in the search box. The second, third and fourth entries are the ones you will want to see.

[Originally published on June 3, 2006]