This column is the first of three summarizing the results of some of the recent Christmas Bird Counts in Maine. The count period began on December 14, continuing through January 5. We’ll travel widely across the state today.
As you know, the weather in November and December was unusually mild. Most freshwater bodies of water were still open. We therefore expected the Christmas Counts to have some lingering species that normally would be further south. The open water could provide habitat for waterbirds that are usually forced south by ice on ponds and lakes.
The Augusta Christmas Bird Count (hereafter, CBC) took place on December 19 and produced 53 species. Common Loons have usually departed from this area by December but seven were found this year. Two Great Blue Herons were present as well. The count of 33 Bald Eagles was not too shabby. Four Iceland Gulls and a Glaucous Gull were found among Ring-billed Gulls, Herring Gulls and Great Black-backed Gulls.
Lingering landbirds included a Carolina Wren, three Eastern Bluebirds and a Yellow-rumped Warbler. Not as many lingerers as expected.
This winter is shaping up as a poor one for irruptive species, those species that occasionally move south into Maine from areas to our north. The only irruptive species were a single Northern Shrike and six Pine Siskins.
The Lewiston/Auburn CBC was held on the same day. Counters there found 51 species.
Ten species of waterfowl were detected. The more unusual sightings were 20 Greater Scaup, 35 Lesser Scaup, 20 Buffleheads and one Barrow’s Goldeneye among the 39 Common Goldeneyes. The extensive open water accounted for the five Common Loons and a Belted Kingfisher.
Lingering species included a Hermit Thrush, eight Northern Mockingbirds and a Pine Warbler. I’m sure the counters were hoping for a better showing of late-departing birds.
Like Augusta, Lewiston/Auburn hosted few irruptive birds. Three Pine Siskins were the only winter invaders found.
We’ll head to the coast now, starting with the York County CBC. This count was held on December 14. A total of 81 species were counted.
Waterfowl diversity is always high on this count; 15 species were tallied this year. The highlights included 1,083 Common Eiders and 66 Harlequin Ducks. Two loon species were present: 86 Common Loons and 13 Red-throated Loons.
We expect Great Cormorants in the winter and Double-crested Cormorants during the summer in Maine. This year, one Double-crested was found among the 39 Greats.
This count produced an excellent diversity of lingering birds. These hardy birds included nine Great Blue Herons, a Northern Harrier, four Belted Kingfishers, two Northern Flickers, two Carolina Wrens, a Ruby-crowned Kinglet, 59 Eastern Bluebirds, one Hermit Thrush, six Northern Mockingbirds, a Yellow-rumped Warbler and a Baltimore Oriole.
Two rarities were found: a Dickcissel and a Clay-colored Sparrow. A dozen Pine Siskins were the only irruptive birds.
On downeast to the Schoodic Peninsula. The Schoodic Count was held on January 1. A total of 58 species were found, including an eye-popping rarity.
Thirteen species of waterfowl were present. A single Red-throated Loon was found along with 65 Common Loons. Fifty Horned Grebes and 95 Red-necked Grebes were nice counts. A single Razorbill was found ; 21 Purple Sandpipers were seen foraging on the rocky shore.
Lingering birds included a Northern Harrier, a Belted Kingfisher, two Northern Flicker, five Yellow-rumped Warblers, a Fox Sparrow and a White-crowned Sparrow.
One Northern Shrike was the only winter invader on the count.
The highlight of the count was a Black-throated Sparrow found by Ed and Debby Hawkes and Chuck Whitney. This species is normally found in the deserts of the southwestern states and Mexico. The sighting is the first confirmed record for Maine (a 1983 record provides only sketchy details) and only the fourth confirmed record for New England. Fantastic!
Categories: Christmas Count Summaries
This column is the second of two on the history of bird feeding in North America. A major resource for this column is a recent book, Feeding Wild Birds in America by Paul Baicich and co-authors.
We pick up the story in the 1941 when the Audubon Guide to Attracting Birds was published, just a week before Pearl Harbor was bombed. Roger Tory Peterson wrote several of the chapters.
Of course, the war effort prevented bird enthusiasts from spending freely on birdseed. Many found that oatmeal, bread crumbs and peanut butter served to attract birds. By the late 1940s, several companies were formed specializing in the retail sale of birdseed.
The 50s decade was a prosperous one. Suburbs proliferated everywhere and suburbanites engaged in various home-based leisure activities, including bird feeding. John Dennis was a particularly influential person through his column “Guide to Bird Attracting” in Audubon magazine. John Terres wrote the 1953 book, Songbirds in Your Garden that further stoked the popularity of bird feeding.
Two men, Simon Wagner and Bill Engler, from competing companies joined forces to develop birdseed packaging suitable to grocery shoppers. The plastic bags allowed the buyer to seed the product before purchase. A shopper could buy food for the family and for the birds at the same time.
John Barzen was one of the first to realize that most birdseed mixes sold in the 50s were actually cheap seeds (cracked corn, millet, milo) that attracted undesirable birds like House Sparrows. European Starlings and Brown-headed Cowbirds. Barzen found that sunflower seeds, safflower seeds and peanuts were better at attracting birds like Northern Cardinals, chickadees and jays. The first commercial suet cakes appeared in 1958.
Bird feeding continued in popularity in the 1960s. Nyjer seed (sometimes called niger seed or thistle) was introduced as a popular attractant for finches. Most of the nyger we use is imported from Ethiopia or India.
The importation of nyger has sometimes been halted because seeds of noxious weeds are often unintentionally mixed in with the nyger. Most of the nyger seeds are now heat-treated before sale; nyger seeds are more resistant to high temperatures than the weed seeds.
In 1969, Droll Yankee introduced the tubular feeder with a number of feeding ports, perfect for feeding sunflower seeds to hungry birds. A tubular nyger feeder was first produced in 1972.
The first Earth Day in 1970 accelerated the environmental movement, given a strong push earlier by Rachel Carson’s Silent Spring, her 1962 expose of the impacts of DDT on birds. Bird feeding took on added importance as a way to protect birds.
Birdseed was sold in bulk for the first time, often by yearly sales conducted by bird clubs or environmental groups. Stick-on window feeders made it possible to put up a feeder just about anywhere.
Although people had been feeding hummingbirds for decades, better hummer feeders appeared in this decade.
People became more sophisticated with their bird feeding in the 1980s, often targeting particular species. This practice was made possible by a landmark study by a U.S. Fish and Wildlife Service biologist, Aelred Geis. He conducted extensive choice experiments, determining the preferred foods of many feeder birds.
Specialty birding chains appeared in the 80s. These included Wild Birds Unlimited, Wild Bird Centers of American and Wild Bird Marketplace.
In 1987, Project FeederWatch (PFW) was hatched. This program was actually an expansion of the Ontario Bird Feeder Survey. Homeowners maintain feeding stations and record feeder visits at specified times. PFW participants are generally diligent about keeping their feeders stocked continuously.
By the 1990s, one-third of all U.S. citizens over the age of 16 fed the birds. In this decade, scientists first started to look at the impacts of feeding (increased survivorship and nutritional status, range expansions of species like Red-bellied Woodpeckers, Tufted Titmice, Carolina Wrens, House Finches and recently arrived Eurasian Collared-Doves).
In the last column, I discussed the positive benefits of bird feeders and noted that no evidence exists to show that birds become dependent on feeders. Growing and selling birdseed is big business with sales of seed and feeders exceeding two billion dollars per year. Over 50 million Americans are involved with some level of bird feeding and observation around their homes. Such broad interest has not always been so.
Today, we’ll look at the history of bird feeding in North America. This topic has long been a research interest of mine. This column benefits greatly from information in Feeding Wild Birds in America by Paul Baicich and others.
Bird feeding is a two-way street. We feed the birds to help them survive but also feed to lure the birds closer to us so that we may enjoy their beauty and behavior.
We can start in 1854 with Henry David Thoreau. In his classic reflection Walden, he writes of tossing half a bushel of unripe corn just outside his cabin and watching the various animals that were attracted to the corn, including Blue Jays and Black-capped Chickadees.
We fast-forward to 1898 when Florence Merriam Bailey began teaching bird classes to teachers in the District of Columbia. Bailey had recently graduated from Smith College and had been actively involved in battling the harvest of egrets. These birds were being slaughtered in large numbers because their breeding plumes had become fashionable in women’s hats.
Bailey showed that nailing a few bones and suet to a tree attracted a diversity of birds. She recommended grains and table crumbs as well.
At the same time, Elizabeth Davenport in Vermont fed the birds a diversity of seeds as well as cornbread. She kept careful records, documenting over 20 bird species at her feeders.
Anna Botsford Comstock, a professor at Cornell University, started the Nature Study program for children. Kids were encouraged to feed birds and make observations on them. The Nature Study program continued into the 20th century.
The venerable table feeder was in use by the end of the 19th century. Window feeding-trays appeared in the early 1900’s. Bird feeding was encouraged by the National Audubon Society’s magazine, Bird-Lore and by two books on attracting birds by Bradford Torrey and Njelte Blanchan.
Even at this early stage of bird feeding, authors and observers noted the dual benefits of bird feeding: helping birds survive and attracting birds to enjoy them. Suet was recommended as a most valuable food. We concur with this advice as fat is more calorie-rich than carbohydrates or proteins. Birds store fat to fuel their migrations, their over-night shivering and other activities.
By 1910, more sophisticated bird feeders began to appear. Hans Berlepsch, a German, had begun to design bird feeders that minimized waste. His bird bell (a silo-like contraption in which seeds fell onto a tray) was one of the most popular.
Waldo Lee McAtee, a federal biologist, advocated using coconuts or tin cans with small holes as feeders. Such feeders minimize the loss of food. The holes could be made small to allow chickadees access but not larger birds that tended to outcompete chickadees at a feeding table.
The first suet feeders appeared at about this time. Rather than simply tying or nailing suet to a tree, people began to make suet boxes from wood or metal. Some people mixed seeds in with the suet.
House Sparrows sometime dominated bird feeders. Many people found this introduced species undesirable. Clever inventors produced feeders that allowed agile chickadees to get to the food but not relatively clumsy House Sparrows.
Commercial bird feeders became widely available in the 1920’s and bird feeding continued to increase in popularity. To be sure, World War I and the Great Depression forced cutbacks in bird feeding but bird feeders were a common sight in 1940. We’ll continue in the next column.
[Originally published on December 13, 2015]
A number of readers have contacted me recently with a concern about bird feeding. Holiday travel means that our bird feeders may be depleted while we are away, depriving birds of our handouts. Readers are asking if we are doing harm to birds by providing and then removing food.
This query requires us to answer two questions. First, do birds benefit from bird feeding? Second, do birds become dependent on bird feeders?
The answer to this first question is yes. One line of evidence comes from a technique called ptilochronology, a daunting word that refers to the rate of feather growth. Did you know that you can see daily growth bars on a feather? Each contour feather a bird produces has a record of how quickly it was formed.
Tom Grubb and his students used this technique to examine the impact of bird feeding. They captured Downy Woodpeckers, White-breasted Nuthatches, Carolina Chickadees and Tufted Titmice in the winter in Ohio. The researchers plucked one of the tail feathers of each bird. The birds quickly started replacing that missing feather.
Half of the birds had access to bird feeders and the remainder were found in areas where only natural food was available. After a month or so, the birds were recaptured and their regrown tail feather was examined. The birds with access to supplemental food regrew their tail feathers at a faster rate; the daily growth bars were longer in these well-fed birds. So, bird feeding increases the nutritional status of birds.
Margaret Brittingham and Stan Temple examined the impact of bird feeding on the winter survivorship of Black-capped Chickadees in Wisconsin. They banded over 500 chickadees. Some populations were given access to unlimited sunflower seeds and some populations had to depend on natural food. Over the course of three winters, Brittingham and Temple found that winter survivorship of banded birds with access to supplemental food was 67% compared to 37% for birds without sunflower seed handouts. That’s a pretty striking result.
The researchers found that the greatest risk to the control (unfed) birds was in the coldest months with more than five days with subzero temperatures. Chickadees with supplemental food were also heavier than the control birds.
These results have been corroborated in similar studies done in Pennsylvania and Ontario.
Birds therefore benefit from the food we provide for them. But is there a risk that birds become dependent on our handouts? The answer to that question is no to the best of our knowledge.
We return to research done by Brittingham and Temple in Wisconsin. Having shown that bird feeding increases winter survival of Black-capped Chickadees, these ornithologists set up an experiment to test for feeder-dependence. In one area, chickadees had been given sunflower seeds continuously for several years. In the second area, no bird feeders were ever present. The authors took away the bird feeders from the first area where birds had been feeding on sunflower seeds for years and monitored winter survivorship of both populations.
If the population given sunflower seeds in previous years had a lower survivorship than the population with no bird feeders, one could claim that the birds in the first area had become dependent on the sunflower seeds. But there was no difference in survivorship for the two populations. The previously fed chickadees did as well in the following year feeding on natural food, as the unfed chickadees did that never experienced the bounty of bird feeders.
Similar studies have not been done for other North American species that frequent feeders but I expect that results would be similar. Depending on a single source of food is risky for any winter bird. Winter songbirds commonly range over areas of 10 to 25 acres. Much of this area is regularly patrolled and food is taken from a number of different parts of their winter area.
[Originally published on November 30, 2015]
It’s now mid-November and the images of swallows flocking in August as they prepare to migrate are distant memories. Yet, the fall migration still continues. The fall spectacle is a wonderfully protracted event.
The schedule of bird migration is largely governed by food. Migratory birds leave Maine when their preferred food is no longer sufficient. The first to leave are the aerial insect-eaters like swallows, swifts and nighthawks. Leaf-gleaning insect-eaters like warblers, vireos and tanagers are next on the calendar. The caterpillars and other insects on which these birds depend can be found through September. Few warblers linger into October.
Sparrows occur throughout October as the seeds of grasses and other plants are available for these ground-feeders. Most sparrows will depart before the first snows cover their food.
The migration we are enjoying now is waterbird migration. As long as lakes are unfrozen, these birds can find the sustenance they need.
Fall birding on lakes and ponds can be exciting. You never know what you might see. In late October, I took one of my two ornithology lab sections to Sabbatus Pond, a known hotspot for ducks and other waterbirds in autumn. The first day we saw the expected Buffleheads, Ring-necked Ducks, Greater Scaup, Lesser Scaup, Ruddy Ducks and American Coots.
The next day, those same birds were present but a student pointed out a group of birds in the middle of the Pond. Several hundred dark ducks were arranged in a line, a common behavior in Black Scoters. Sure enough, that is what they were. The orange bills of these birds seemed to be illuminated from within.
The flock took flight and we were able to pick out two White-winged Scoters. Bill Hancock saw these birds later in the day near sunset. He watched the flock fly south from the lake, making this sighting a one-day wonder.
Black Scoters nest at high latitudes on small ponds. They winter along the coast. The hopscotch migration of these seaducks gives us a chance to see them on freshwater bodies.
In early November, a smaller flock of Black Scoters and White-winged Scoters visited North Pond in Smithfield. They were accompanied by a few Red-necked Grebes, another species that winters along the coast.
On November 6, Tom Aversa and Bruce Barker found some remarkable waterbird diversity on Sebasticook Lake in Newport. They saw the expected freshwater species like Canada Goose, Mallard, American Black Duck and Green-winged Teal. But, if you just saw the rest of their list, you would certainly think Tom and Bruce were birding at a coastal site. They saw Common Eiders, Black Scoters, White-winged Scoters, probable Surf Scoters, Long-tailed Ducks, a Red-throated Loon, a Red-necked Grebe, four Horned Grebes and Bonaparte’s Gulls. As is normally the case, these coast-bound migrants did not linger. Striking it rich with fall waterbirds is a hit-or-miss proposition.
On that same day at Lake Josephine in Aroostook County, Bill Sheehan found a Greater White-fronted Goose among the 800 Canada Geese there. He was also able to find two Cackling Geese, a miniaturized version of the Canada Goose.
November can be a good time to see vagrant species as well. On November 1, Derek and Jeannette Lovitch, Kristen Lindquist and Evan Obercian found a Gray Catbird and two Orange-crowned Warblers in Portland.
On November 7, Lisa Dellwo and Bill Schlesinger found a Yellow-billed Cuckoo in Lubec. On November 9, Don Reimer found a Blue-winged Warbler at Sebasticook Lake.
Although none have been reported this year to my knowledge, Cave Swallows occasionally appear along the New England coast in November. The closest breeding population is in east Texas.
The big excitement this November has been the Franklin’s Gull Lake Sebasticook, present for several days. This vagrant from breeding areas in the Great Plains provides the tenth record for the state.
[Originally published on November 25, 2015]
Taking a walk around the neighborhood, I was treated to one of the great sounds of late fall, the honking of Canada Geese in flight. Looking up, I saw a small V of geese heading south. Have you ever wondered why these geese fly in V-shaped flocks? Such flight formations yield a significant savings of energy.
As a bird flies, eddies of air swirl off the tips of the wings. Some ornithologists began to wonder if trailing birds could take advantage of these upward eddies to gain lift. Using a computer model developed by aviation engineers, these ornithologists found that birds flying in V’s could realize an energy savings of 71%, compared to birds flying alone. The model showed that greatest benefit would result when a trailing bird has a wing overlap of about 5 inches with the next bird ahead. In other words, if a bird moved abreast to the next bird ahead of it, the wing of the trailing bird would overlap by five inches with the wing of the bird next in line. The model also showed that each bird except the leader should be between one and three yards behind the bird in front for greatest energy savings. Finally, the model shows that the birds in the flock should beat their wings in perfect synchrony.
Films of migrating Canada Geese were used see how well the positions of the geese agreed with the computer model. In many cases, the wing overlap was right around five inches, the most desirable position. Distance to the next bird and synchrony of flight were not always as predicted, probably because of turbulence in the air . Nevertheless, the performance of the geese suggested that an energy savings of 36% resulted from flying in V’s.
In a V of geese, the leader receives no benefit of the flight formation. Geese do switch positions so take turns as leader. The social status of the leader(s) has not been studied.
Canada Geese are not the only birds that fly in V-formations. Most geese species, including Snow Geese, fly in V’s. I’ve also seen Tundra Swans, White Pelicans, and Double-crested Cormorants flying in such formations.
Some ornithologists have begun to use microtechnology to better understand the behavior of birds flying in V’s. Henri Weimerkirsch fitted migrating pelicans with heart rate monitors. He found that pelicans toward the back of flight formations had lower heart rates, demonstrating the advantage of mooching lift off of birds flying ahead of you.
Stephen Portugal provides even more remarkable data. He fitted endangered Northern Bald Ibises with small data loggers that recorded the position of birds and their flapping rate several times a second. The data loggers have to be recovered to collect the data. The Northern Bald Ibises were the perfect species to overcome this challenge.
Portugal and others were trying to reintroduce this species into central Europe where they had been extirpated. Portugal’s team raised young birds and taught them the old migration route by leading them in a microlight airplane. At the end of each day’s migratory leg, the ibises were captured and their data loggers were read.
The data showed that the birds are bang on with theoretical predictions: the birds beat in synchrony and the distance behind and to the left or right of the next bird in the V conform to the predictions.
Some ibises prefer to be on the left side of the flock and others on the right. They do switch positions frequently and take turns being the leader.
When the migration was first begun, the ibises did not fly in a regular formation. No adults were present to teach them how to fly in a V. Nevertheless, they quickly discovered on their own the advantages of flying in a V.
[Originally published on November 11, 2015]
Categories: Behavior · Migration
The Common Eider is a common species of sea duck in northern coastal regions of North America, Europe and eastern Siberia. A common breeder in Maine, Common Eiders nest as far south as Massachusetts in New England. Common Eiders are important members of arctic breeding bird communities well to the north of us as well.
Common Eiders withdraw from their more northerly breeding areas after nesting and winter in coastal flocks. Winter aggregations may number in the thousands. In Maine, this species is present year-round.
Common Eiders are distinctive birds, often recognizable merely by their silhouette. The combination of a long, sloping bill (think ski jump), long neck and peaked head give them a distinctive look. At a length of two feet, Common Eiders are among our biggest ducks.
Adult drakes are subtly beautiful birds. The crown is black but the cheeks, neck and dorsal body are mostly white. A close look in favorable light reveals a light green wash on the posterior side of the face and nape. The mostly black wings contrast with the white sides when an eider is on the water. The bill is a dull yellow.
Like most ducks, the adult females are much less brightly marked. The body is barred with irregular dark and light brown stripes. The head is mostly brown.
First-year males are highly variable with brown heads like females but with splotches of white and brown on the dorsal surface. The breast is white.
Common Eider females make a nest on rocky islands, not far above the high tide mark. A female plucks down from her breast to line the nest. The down used to create soft, warm pillows, coats and sleeping bags often comes from eider down.
Harvesting eider down is typically done after the nesting season. A down collector simply gathers the down from the nest once the young eiders have hatched. However, synthetic insulating materials have been developed with comparable insulating properties to eider down. These synthetic products are relatively cheap to produce so an eider down-filled vest or coat will cost you a pretty penny compared to a product made from a synthetic material.
By the way, some down used for insulation comes from geese. That down has to be plucked directly from the geese. Goose down is inferior to eider down in insulating properties.
A hen eider may lay up to 14 eggs. When the ducklings hatch, they are covered with a down coat and leave the nest soon after hatching.
Once the ducklings have hatched, they aggregate into crèches of 100 birds or more. These eiders are watched over by the moms as well as non-breeding females.
The ducklings start to form their contour feathers in their second week and complete feather growth by seven weeks after hatching. They take their first flight nine or ten weeks after hatching.
Common Eiders dive in search of invertebrate food from the sea bottom. Mussels are one of the most common prey items taken although crabs and sea urchins are important components of their diet as well. An eider swallows a mussel whole, crushing the shell of the mussel in its powerful gizzard. For a crab, an eider removes the legs first and then swallows the de-legged crab for crushing in the gizzard.
The fondness of Common Eiders for mussels poses a challenge for mussel mariculture. Not surprisingly, the dense aggregation of mussels attracts eiders. Nets seem to be the only practical way to protect the mussels from the eiders and other sea ducks.
Common Eiders are doing well now with an estimated population of two million birds in North America and Europe. Our New England population was nearly decimated by market hunters by the end of the 19th century. Fortunately, the eiders have recovered.
[Originally published on October 18, 2015]
Categories: Reproduction · Species Accounts
Let’s consider the wonder of bird migration today starting with a shorebird. During the summer, Semipalmated Sandpipers breed on the arctic tundra all across North America. As precocial birds, the Semipalmated Sandpiper chicks hatch fully feathered and can find their own food soon after hatching. The parents provide some protection from predators for the young birds but the chicks largely feed themselves. In July before the chicks can even fly, the adults depart the tundra to work their way to their wintering areas near the mouth of the Amazon River in South America. Once the chicks learn to fly, they depart a few weeks later to fly to an area where they have never been.
Semipalmated Sandpipers and other shorebirds are not the only birds whose young find their way unaided to wintering areas. Young-of-the year Magnolia Warblers find their way to Central America, Kirtland’s Warblers to the Bahamas and Swainson’s Hawks to Argentina. Geese and cranes are among the minority of birds that lead their young to wintering grounds. Most birds have their migration genetically encoded.
These internal maps are often amazingly precise. It is not unusual for a songbird over the course of its lifetime to use the same breeding territory in Maine and spend the winter in the same wooded area in Mexico. Clearly, birds have marvelous navigational abilities. How do they do it?
The sun is an obvious guide for navigation. Captive European Starlings become restless as the time for migration approaches. These birds attempt to fly from the cage in a particular direction, corresponding to their known migration direction. On cloudy days when the sun is obscured, the birds do not orient in the proper direction.
Most songbirds migrate at night so the sun is not a visible cue during their migratory legs. However, some night-migrating songbirds use a sun-compass by judging the proper direction of migration as the sun is setting and then remembering that direction when they begin their migration in the darkness.
Some migrant birds navigate using the stars. Captive songbirds that are ready to migrate orient in the proper direction on cloudless nights but move randomly when clouds block out the brighter stars. Some interesting experiments have been conducted in a planetarium. Birds inside the planetarium orient in particular directions based on the patterns of the stars. When the map of the stars is rotated so that north and south are reversed, the birds orient in the right direction as indicated by the stars but the wrong direction as indicated by the earth’s magnetic field. Some of our local birds that are known to use the stars to guide their way are Black-billed Cuckoos, Rose-breasted Grosbeaks and Bobolinks.
The earth’s magnetic field can be used to navigate by some migrating birds. Early experiments with pigeons showed that placing small magnets on the pigeons’ necks interfered with their ability to orient properly. More sophisticated experiments have been recently done where birds are fitted with small helmets which reverse the direction of the magnetic field around the bird. The north pole of the experimental magnetic field around these birds is actually south and the apparent south pole is north. As expected, the experimental birds orient in exactly the opposite direction.
Some birds that migrate during the day use visible landmarks for navigation. Hawks and Hawk and eagles may follow mountain ridges. Some landbirds may follow the coastline.
Finally, some birds actually use their sense of smell to find their way. Homing pigeons with their nostrils plugged with cotton are not able to find their homes as well as pigeons without plugged nostrils. Some seabirds like the Leach’s Storm-Petrel locate their nest burrows by smell.
As many of our birds leave us until the spring, we can thankful these birds can navigate so well. We know we will see many of them again next spring.
[Originally published on October 4, 2015]
Categories: Migration · Weather
We are in the middle of one of the great ornithological spectacles of the year, the fall migration. It’s fun to track the appearance and disappearance of migratory species as they traverse the continent. We can learn much by our collective observations of the pace and route of bird migration at the species level.
But ornithologists are also interested in populations (isolated groups of one species) of birds. As an example, do Black-throated Green Warblers breeding in Maine overwinter in the same tropical areas as the Black-throated Green Warblers nesting in Michigan or in the Great Smokies? And what are the migratory pathways for these populations starting from different longitudes? To answer these questions, individuals have to be identified. A tried and true method is bird banding.
The Bird Banding Lab (henceforth, BBL), a federal agency in the U. S. Geological Survey, coordinates banding activities of native North American birds. To band native birds, one must obtain a Master Bander Permit, possible only after extensive experience in assisting a licensed bander. The BBL provides banders with aluminum bands, each with a unique, nine-digit number. The bander captures birds either in mist-nets or traps and fits the bird with a numbered band using special banding pliers. The banding process can be done quite quickly, minimizing the stress to the captured bird.
The bander sends the BBL records for all birds banded, including age and sex. The banded bird thus provides a record that a particular bird was at a particular place at a particular time. But the real value of banding comes when a banded bird is recovered. Sometimes banded birds are found dead while others are captured by banders at a different banding station.
The re-encountered bird is reported to the BBL workers who close the loop, letting the finder know where the bird was banded and letting the original bander know where the bird was re-encountered.
The power of bird banding relies on the re-encounter of banded birds. As you might imagine, the odds of re-encountering many species of birds are pretty slim. As an example, 745,000 Purple Finches have been banded in the United States and Canada but only about 20,000 have ever been re-encountered (2.7%). As a scientific tool, banding requires that many individuals be banded.
The band numbers for most bands are too small to be read through binoculars (as if a bird would hold still for you to read its digits!) so most birds must be recaptured to determine their unique band number. However, the numbers of bands on large birds like swans can sometimes be read with a spotting scope, obviating recapture of the bird to discover its identity.
Here are a few of the ornithological discoveries that have been made possible by banding birds. Arctic Terns are known to migrate from pole to pole, twice a year. We have learned much about where different populations of birds winter. For instance, Palm Warblers do an interesting crisscross in migration. Populations breeding in the upper Midwest and Prairie Provinces migrate southeast to winter in Florida while our eastern Palm Warblers migrate southwestward to winter along the Gulf Coast.
Re-encountered birds provide us with information on the longevity of birds. Recently, a Ring-billed Gull that had been banded 53 years earlier was found alive, blowing away the previous longevity record.
Some banding records can cause your jaw to drop. For instance, a Semipalmated Sandpiper banded in Nova Scotia was recaptured four days later at the mouth of the Amazon in South America. The bird had flown 2800 miles, non-stop, over the Atlantic Ocean in just 96 hours!
John James Audubon was the first bird bander in North America. He tied some aluminum wire to some nestling Eastern Phoebes in Pennsylvania and found that the birds returned the following year to nest.
[First published on September 20,2015]
Categories: Banding · History · Migration
The fall migration is well underway. Swallows are scarcer than hen’s teeth now in Maine. We will bid adieu to most warblers and vireos this month.
Migration is a tremendously expensive and arduous undertaking for a bird. As warm-blooded vertebrates, birds have a high metabolic rate. Smaller birds have a tougher time of it than larger birds. On a per gram basis, it is much more expensive to be a hummingbird than a robin.
To complete a migratory journey, birds require predictabl food all along the way. Many migratory songbirds rely on fruits to help meet their fueling requirements. Before Europeans settled in North America, migratory songbirds took advantage of fruits like winterberries, pin cherries, mountain ash fruits.
The relationship between the fruit-bearing plants and the fruit-eating birds benefits both parties. The birds disperse the seeds of the plants in return for a bit of nutritious fruit.
Human colonization has resulted in both the intentional and accidental introduction of exotic plants. I am writing this column in Lubec and I can look out the window and see large banks of the invasive Japanese knotweed across the way. Bittersweet, Japanese barberry, Tartarian honeysuckle, Morrow honeysuckle, autumn olives, multiflora rose and two species of buckthorns are other well-established invasive plants in our state.
Invasive plants often outcompete native plants. An invasive plant is usually free of herbivores and pathogens that it has to contend with in its native habitats. Such ecological release is a huge advantage in competing with native plants with their own herbivores and pathogens.
We know that invasive plants are causing reductions in the abundance of native fruit-bearing plants. What implications do these changes have for migratory birds?
Brie Drummond addressed this question for her Honor’s thesis at Colby College in 2003 and published her work in the Northeastern Naturalist in 2005. She studied two representative introduced plants, Tartarian honeysuckle and multiflora rose and two native plants, a viburnum species and silky dogwood.
She found that the fruits of the honeysuckle and dogwood degrade quickly. All were either eaten or rotted by the end of November. The rose and viburnum fruits persisted into the winter, offering wintering birds (primarily waxwings and American Robins) some sustenance.
Brie measured the energetic content of each of the four types of fruits using an instrument called a bomb calorimeter. The fruits of the two native species had higher caloric content than the two invasive species. However, choice experiments with the rose and viburnum fruits showed that birds did not show a preference between the two fruits. Perhaps, Brie thought, birds are selecting fruits based on carbohydrate or fat content rather than total energy content. Digestibility of the fruits may play a role as well.
Susan Smith and colleagues at the Rochester Institute of Technology did a more detailed analysis of fruit quality. They published their work in 2013 in the Northeastern Naturalist. These researchers examined five native plants: three species of dogwoods, arrowwood viburnum and spicebush. In addition to the invasive plants studied by Brie, the RIT team examined buckthorn fruits.
The researchers determined total energy content and fat content of each type of fruit. They found that the caloric content of native plants was slightly higher than the caloric content of the invasives. However, striking differences in fat content emerged. No invasive fruits had higher than 1% fat content while the fat content of native fruits ranged from 6% to 48%.
Migrating birds primarily use fat to fuel their migration. Fats are more energy-dense than carbohydrates or proteins so a gram of fat provides more energy to a migrating bird. One would predict that fall fruit-eating birds would prefer the native fruits.
Smith and colleagues measured preferences of fall migrants and found results that fit their predictions: fall frugivorous birds prefer native dogwood fruits to the fruits of the four invasive species.
[Originally published on September 6, 2015]
Categories: Foraging · Migration