Entries Tagged as 'Migration'
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]
Tags: Behavior · Migration
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]
Tags: 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]
Tags: 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]
Tags: Foraging · Migration
Abundant evidence exists to show that the earth has been warming over the past century. This evidence includes the melting of the polar ice caps with the consequent rise in sea level, earlier leaf-out dates for trees and bushes, earlier ice-out dates of lakes and the northern range expansion of various species.
The spring arrivals of migratory breeding birds are also sensitive to a warming world. With leaves emerging earlier, caterpillars become active earlier, providing earlier food for warblers and vireos. Nectar for hummingbirds should be available earlier.
A number of studies have documented earlier arrivals of migratory breeding birds. Bird clubs in the Worcester, Massachusetts area and in the Ithaca, New York area have been compiling first arrival-dates of migratory birds for over 100 years. The data clearly show earlier arrivals in recent years for nearly all species of migratory birds frequenting those areas.
In 1994, I began a citizen-science project to monitor the arrival dates of over 100 species of Maine migratory breeding birds. Each volunteer is asked to note the first arrival of each species along with the location of the sighting. This on-going project has taught us much about the nature of spring bird migration across the state. We know have over 55,000 arrival dates in the dataset. The collective contributions of so many volunteers have made this project possible.
We know over the period 1994 to 2014 that some bird species arrive a bit later in cold springs and a bit earlier in warm springs. However, Maine does not have a continuous record of arrival dates to rival those of the Ithaca and Worcester bird clubs.
Maine however did have a bird organization, the Maine Ornithological Society, active around the turn of the 20th century. This organization published the quarterly Journal of the Maine Ornithological Society (JMOS) from 1899-1911. The journal regularly published arrival dates of Maine birds along with censuses of birds. Danny Kipervaser, Scott Lilley and I collated the arrival date data from the JMOS to compare to contemporary arrival dates. Our expectation was that birds should be arriving earlier now compared to then. Our predictions missed by a mile.
We only had sufficient data from the JMOS for 80 of the species I track in the current arrival date project. Of those 80 species, only nine are now arriving earlier in modern years. These included inland Common Loons, Great Blue Herons and Red-winged Blackbirds, all of which need open water in their lake or marsh habitats. The other six species were American Woodcock, Ruby-throated Hummingbird, Tennessee Warbler, White-throated Sparrow, Rose-breasted Grosbeak and Indigo Bunting. Most of these species arrive between four and eight days earlier now.
The most common result was to see no significant change in arrival dates across the time span. Fifty-one species are arriving at the same schedule now as they did a century ago. Quite a contrast with the Worcester and Ithaca records.
Remarkably, 20 species are now arriving significantly later than they did around the turn of the 20th century. These species include seven aerial insectivores (swallows, nighthawks), three warblers, four sparrows and Bobolink.
What’s going on here? I see two possible biases. First, the amount of forests we have in Maine now is far greater than in 1900 when farmland was more extensive. As a result, habitat for the sparrows and Bobolinks that seem to be arriving later were almost certainly more abundant then than they are now. Thus, the chances of seeing an early arriving bird were higher a century ago.
Second, the JMOS birders were likely more in tune with nature than we are. Outside on foot or on horse-drawn carriages, these observers would be less likely to miss a first arrival. Despite our fine optics, the JMOS ornithologists might well have been keener observers than we are.
[Originally published on May 16, 2015]
Tags: Migration · Weather
Purple Finches are regular if erratic visitors to our feeders. The gorgeous males with their deep red breasts and heads can only be confused with male House Finches. A male House Finch has brown streakings on the flanks with less extensive red (more reddish-orange) on its head.
Female Purple Finches are mostly brown and white. The breast has dark streaks. A bold white stripe lies just above the eye; this white supercilium is absent in female House Finches.
Have you noticed that male Purple Finches are usually outnumbered by females at your feeder? Not so fast. First-year males are dead ringers for female Purple Finches. You really have to have them in hand to tell them apart by examining the wear of the primary coverts and the shape of the tips of the outer tail feathers. Some of those streaked Purple Finches at your feeder are first-year males.
Purple Finches belong to the suite of irruptive finches popularly called the northern finches. Purple Finches breed across the northern tier of the U.S. from Maine to Minnesota and across the southern tier of the Canadian provinces. A breeding population also occurs west of the Cascades and Sierra Nevada from California to British Columbia.
Strong southerly irruptions occur every other year in this species. These biennial irruptions are thought to be driven by variation in the production of cone crops of the conifers on which the Purple Finches depend.
To gain some insight into these movements of Purple Finches, my wife Bets Brown and I analyzed all of the banding data on Purple Finches from the Bird Banding Laboratory over the period of 1921 until 2008. Over 745,000 finches were banded over this period and almost 20,000 of those banded birds were subsequently recaptured (or in a few cases, found dead).
We were particularly interested in three questions. During irruptions, do birds from one area like New England move straight south or do they spread across the continent (Purple Finches can be found throughout North America)? Do Purple Finches show fidelity to breeding sites? Do Purple Finches show fidelity to wintering sites?
The analysis of banding data presents many challenges. Banding effort is never constant either across space or time. Most of the banding records come from the period 1960-1985. Banding effort varies greatly among states and provinces. Nevertheless, some general patterns can be discerned.
Birds banded in VT, NH and ME were re-encountered broadly but mostly in the eastern United States, curling eastward through the Gulf Coast states. A few reached Texas and modest numbers occurred in MI, ONT, WI and MN. A similar pattern emerged for birds originally banded in NY.
We also analyzed birds first banded in PA, NJ and NC. These areas are south of the breeding range and were banded in the winter. Re-encounters of these birds occurred mostly in the the New England and the eastern provinces. The re-encounters are consistent with the data from birds originally banded in New England.
Moving to to the Midwest, birds originally banded in MI, WI and MN also were re-encountered broadly but most irruptions were due south.
Only 275 Purple Finches banded in the Pacific states or BC were re-encountered. However, a consistent pattern was that those birds migrate west of the Cascades and Sierra Nevada.
We did find some evidence of breeding site fidelity across as many as five years. Some wintering site fidelity was evident as well over periods of one to six years. Uneven banding efforts prevent us from knowing how prevalent such fidelity is.
I’ll end with the most impressive distance between captures. A Purple Finch banded in Maine in 1966 was subsequently captured two years later in Texas, a distance of 1792 miles.
For a copy of our paper, visit http://bit.ly/1BntjMb
[Original published on March 29, 2015]
Tags: Identification · Migration · Species Accounts
We have certainly had no shortage of storms this winter. Perhaps you have wondered how birds can deal with the cold, the wind, and the snow to survive such challenging spells of bad weather. The research done on birds’ ability to anticipate storms has provided some insights but much remains to be done. In today’s column, I’ll discuss the results of two recent papers that shed light on the effect of impending storms on bird behavior.
The first paper by Henry Streby of the University of California and colleagues was published earlier this year in the journal Current Biology. The researchers had 20 Golden-winged Warblers fitted with geo-locators in April of 2013. These small dataloggers continuously record light-levels and time. From the data, a researcher can track the longitude and latitude of a migrating bird. Birds must be captured so that the data from the geolocator can be read.
In April of 2014, Streby and colleagues tracked the arrival of nine of these marked birds back to their mountainous breeding territory in northeastern Tennessee from wintering areas in South America. The birds arrived in Tennessee between April 13 and April 27, 2014.
Between April 27 and April 30, a massive storm that spawned over 80 tornadoes developed over the middle of the United States. The eastern Tennessee Golden-winged Warblers were able to detect the impending storm well before it arrived. What did the birds do? All nine of the warblers vacated their breeding grounds. Five of them did return after their storm and their geolocators were resampled. All five of these birds took evasive action to avoid the storm.
On April 27, tornadoes were being generated from Kansas to Texas. By the following day, the storm was less than 100 miles from the Golden-winged Warblers’ breeding area. The storm was quite powerful when it arrived in northwestern Tennessee, generating winds of over 100 mph.
But the wind posed no problem for the five warblers. They had moved to Florida’s Gulf Coast, beyond the range of the storm. One of the birds even flew to Cuba.
How did the birds know the tornadoes were coming? The authors believe that the birds were detecting infrasound, sound whose frequency is far too low for humans to hear. Tornadoes generate infrasounds that are propagated through the ground.
Storms are usually associated with low-pressure systems so falling barometric pressure could be a cue that a storm is approaching. A recent paper by Creagh Breuner and colleagues examined this phenomenon. The paper was published in 2013 in the Journal of Experimental Biology.
When humans hear that a blizzard is approaching, we see a run on groceries, batteries and candles. Shouldn’t birds prepare for inclement weather as well? The Breuner team addressed this question by studying White-crowned Sparrows on the breeding grounds at high altitude in Montana. Spring snowstorms are frequent.
In particular, the researchers searched for a relationship between falling barometric pressure and behaviors that might help the birds weather the storm. The researchers predicted that falling barometric pressure should cause an increase in mass (due increased feeding rate_, an increase in the rate at which fat is deposited and hormonal changes associated with stress. They also did experiments on captive birds by artificially lowering the air pressure and looking for changes in behavior.
The results were mixed. The authors clearly showed that the sparrows could detect changes in barometric pressure in their lab experiments. In the field, falling barometric pressure did not result in an increase in mass or in stress hormone production. The researchers did find a significant relationship between fat deposition and barometric pressure but the effect was very slight. In the lab, birds sometimes increased their feeding rate as pressure dropped but again stress hormone levels did not change. We have much more to learn about these intriguing responses.
[Originally published on March 1, 2015]
Tags: Behavior · Migration · Physiology · Weather
The irruption watch is on! Will Common Redpolls, Bohemian Waxwings, White-winged Crossbills, Snowy Owls and Pine Grosbeaks grace us with their presence this winter? Initial observations are promising as redpolls, Bohemian Waxwings and Snowy Owls have been reported widely in the state already.
These irruptive migrants are driven from their northerly breeding grounds by lack of food. Birds are remarkably tolerant of cold weather as long as they can find sufficient sustenance to keep their greedy furnaces stoked. When food on the Arctic tundra or the taiga becomes scarce, be it birch seeds, conifer seeds, lemmings or fruit, birds dependent on a particular food must move south or perish.
The Northern Shrike is another irruptive species. They are absent in Maine in some winters and occasionally common. At least a few Northern Shrikes have been seen in Maine. We’ll explore the biology of Northern Shrikes in today’s column.
The breeding distribution of Northern Shrikes spans the northern part of North American from Quebec to Alaska. When they withdraw from their breeding areas due to lack of food, they come farther south in the western United States, reaching southern Utah and Nevada. In the east, Northern Shrikes rarely occur south of Massachusetts and New York. This species also occurs in Eurasia where it is called the Great Grey Shrike.
Northern Shrikes are boldly marked birds, reminiscent of a bulky Northern Mockingbird. Northern Shrike adults have a gray back and crown with a narrow black mask through the eye. The wings are black with a prominent white patch. The tail is black with white outer tail feathers. The gray dorsal surface, white wing patches on black wings and white in the tail make it easy to dismiss a shrike as a mockingbird. The undersides are whitish-gray.
Immature Northern Shrikes look like washed out versions of adults. The upper parts are generally buff-colored; the mask is thinner and less darkly colored. The most distinctive feature is the prominent scaling on the breast and belly.
The similarity with mockingbirds ends when you check out the bill. The bill of a Northern Shrike is strongly hooked, used to kill small mammals, rodents and sometimes insects. A shrike is a hawk wannabe!
Northern Shrikes habitually perch at the top of a tall shrub or tree, appearing peaceful and docile. But when a potential prey is spotted, the shrike springs into action. A shrike usually captures insects or small mammals with its bill. Birds are pursued through the air and usually captured with the feet. Although the toes of shrike are not shaped like the talons of a hawk or owl, the feet are very strong. Friends of mine who band shrikes wear leather gloves when taking shrikes out of mistnets to avoid wounds from shrike feet clamping down on the banders’ hands.
Once a prey item has been secured, the shrike quickly kills it with a bite to the neck, severing the spinal cord at the level of the cervical vertebrate. The prey is typically impaled on thorns or barbed-wire, often left as a cache for later use. This macabre impaling behavior is the basis for the folk name of butcherbirds for shrikes.
While studying the effect of winter bird feeding on Black-capped Chickadees in a remote section of the North Woods east of Flagstaff Lake, I quickly learned when a Northern Shrike was in the neighborhood. The chickadees, woodpeckers and other birds frequenting the feeder would freeze. The cacophony of birds at the feeder halted; dead silence prevailed. Woodpeckers pressed themselves tightly against a tree trunk. The birds were perched stock-still in mortal feat. I never saw a shrike take a bird in this situation but they often captured a vole that made the unfortunate decision to emerge from the snow pack to grab a fallen sunflower seed.
[Originally published on December 7, 2014]
Tags: Migration · Species Accounts
Where did the summer go? The departure of most of our swallows and flycatchers indicates the fall migration has begun. Thr flood gates will soon be open as warblers, vireos and hummingbirds will leave us followed by sparrows and hawks. Today’s column is a potpourri of short items based on the theme of migration.
We delight in the spring arrival of migrating birds and claim them for our own. But when you think about it, the many species of birds that migrate from the tropics to nest in temperate North America spend only a minority of their time on our continent. A Ruby-throated Hummingbird nesting in Maine is here for only about three months. Migration to and from Costa Rica might require another two months or so. These hummingbirds are really Central American birds that grace us with their presence for a short time each year. The same can be said for Bobolinks in Argentina and Bolivia, Cliff Swallows throughout South America, Baltimore Orioles throughout Central America and numerous other migratory species.
Birding for songbirds during fall migration requires more effort than is needed during the spring migration. Fall migrants do not sing and have molted into their less conspicuous basic plumage. The phrase “confusing fall warblers” is so true.
Although most passerines do not migrate as a flock, migrants in a particular patch tend to gather in mixed-species flocks as they forage to fatten up for the next migratory leg. Fall birding in a forest is therefore hit-or-miss with often long periods of misses. A good trick is to find the chickadees. Migrant warblers and vireos often forage with the chickadees.
As an example, I was recently at West Quoddy State Park in Lubec with a couple of friends. We had walked over a mile with scarcely any birds. At the margin of the bog, I heard a couple of chickadees. I began pishing (saying the word pish quickly – if you don’t know the technique of pishing, do a YouTube search for pishing). As expected, the chickadees approached to investigate the source of the pishing but so did about 25 warblers. We were surrounded by Black-and-white Warblers, Black-throated Green Warblers, Yellow-rumped Warblers, a Common Yellowthroat and a Red-eyed Vireo for good measure.
We know that population numbers of many of these migratory songbirds are declining. One of the most important drivers in these declines is the cutting of tropical forests. A particular problem is cutting of timber on protected conservation land. These parks and preserves are difficult to police with limited staff and resources.
The monitoring of illegal timbering is done mainly with aerial or satellite images. Environmental managers may not get the photos for several days by which time the timber thieves have moved on.
Rainforest Connection, a start-up company in California, has developed a way to repurpose old smartphones to detect illegal timber activities quickly. A smartphone is covered in a water-proof case and powered with a solar battery. The phone is mounted high on a tree. A sensitive microphone is attached to the phone. The smartphone detects chain saw noises and gunshots. Each five minutes, the smartphone sends a packet of data to a central server. If the server detects the sound of chain saws, local enforcement officers, alerted by cell phone, can catch the ecocriminals in the act. Similarly, recordings of gunshots can aid in the capture of poachers.
Each phone can monitor an area of about one square mile. Cell phone coverage has penetrated deeply into equatorial forests throughout the world. The service plan costs for these phones are modest, only a few dollars a month in most tropical countries. Such a cost seems like a bargain in exchange for preventing the loss of thousands of dollars of wood or endangered animals. I suspect we will see the widespread use of this technology.
[Originally published on September 13, 2014]