Entries Tagged as 'Migration'
Are they coming this winter or not? One hears this question a lot in birding circles at this time of year. The question centers on the group of birds called the northern finches or winter finches, higher-latitude birds that grace us with their presence in some winters but not in all. The only predictable feature of northern finch abundance is unpredictability.
The northern finches include Purple Finch, Pine Siskin, Evening Grosbeak, Pine Grosbeak, White-winged Crossbill, Red Crossbill and Common Redpoll. Although some of these species nest in Maine, most individuals of these species nest well to our north.
All of these species depend on the seeds from trees for their sustenance, particularly during the winter. Redpolls are fond of birch seeds and the rest specialize on conifer seeds (firs, hemlocks, spruces, larches and pines). Pine Grosbeaks have a taste for fruit as well.
When seed abundance is adequate on the breeding grounds, these finches will forgo a southern migration and spend the winter on their breeding grounds. The birds spare themselves from the significant cost of migration. However, seed production by the trees the finches depend on varies dramatically from year to year. In a year of low seed production, the northern finches are forced to be nomads, wandering south until they encounter the seeds they need.
These southern migrations are called irruptions. The birds irrupt or move into areas away from their breeding grounds.
In our neck of the woods, three conditions have to arise for us to see an irruption of Common Redpolls, White-winged Crossbills or other irruptive species. First, seed production on the finches’ breeding areas has to fail. Second, seed production of those trees has to be high in Maine. Third, the irruptive finches have to happen upon our abundant seeds in their wanderings.
For the past 20 years or so, Ron Pittaway in Ontario has been putting out a winter finch forecast. He gathers data on the cone production of various conifers, birch and fruit trees. He has been remarkably good in predicting flights of irruptive finches. His data for southern Ontario mirror abundances in neighboring provinces and states.
According to Pittaway, this winter will likely be poor in Maine for Pine Grosbeaks. Mountain Ash in the boreal forest produced many berries this summer. Pine Grosbeaks will have no need to irrupt.
On the other hand, cone production by several species of conifers across the boreal forest was modest at best. Pittaway expects White-winged Crossbills, Red Crossbills and Pine Siskins to stage irruptions. Purple Finches have already started to appear in Maine in good numbers at feeders.
The Evening Grosbeak has had a couple of excellent breeding years so their population seems to be on a bit of an upswing after several decades of declines. Pittaway thinks these birds are likely to be seen at feeders in southern Ontario and northern New England.
So far, he seems right on the money. In the past week or so, I have heard reports of Evening Grosbeaks in Machias (100 birds!), Newcastle, Bangor, Wells, Skowhegan, Gardiner, Milbridge, Pittsfield, Biddeford, and Yarmouth. You get the picture; it is an irruption! I am not alone in hoping we have an abundance of these beautiful finches here all winter. Keep those sunflower feeders filled.
Red-breasted Nuthatches depend on conifer seeds during the winter as well. Unsurprisingly, their irruptions tend to coincide with those of Purple Finches, Pine Siskins and White-winged Crossbills. I’ve seen more Red-breasted Nuthatches this fall than I have in the past few years.
Blue Jays also show irruptive behavior, responding to the abundance of their preferred winter food, acorns. Acorn production has been low this year in central Maine, perhaps due to the dry summer we had. Many of our Blue Jays will move south for the winter.
[First published in mid-November, 2016]
Tags: Foraging · Migration
On September 29, Rhonda Little-Aifa posted photographs of an unfamiliar hawk on the Maine Birds Facebook page. The bird was at the Millinocket Airport on Medway Road, first seen a few days earlier.
Doug Hitchcox, the Naturalist at the Maine Audubon Society, recognized the bird as a Swainson’s Hawk. Swainson’s Hawks nest on cliffs near grasslands in western North America and spend the winter in South America, as far south as Argentina.
Clearly, this was a bird out of place. The Maine Birds Checklist Committee recognizes only two prior records for the state, one seen on May 3, 2009 in Pownal and on seen on September 23, 2013 in Harpswell. Eight other reports of this species, dating from 1883 to 2005, have not yet been reviewed by the Checklist Committee.
A major migration of birders to Millinocket began on September 30. Dozens of birders got to see this cooperative bird, particularly over the weekend. The hawk was last soon on the morning of October 4. You can see pictures at: http://ebird.org/ebird/view/checklist/S31826769
Swainson’s Hawk belongs to the genus Buteo, the genus that also includes the familiar Red-tailed Hawk and Broad-winged Hawk. Swainson’s has proportionally longer wings and a smaller bill than the similarly-sized Red-tailed Hawk.
Swainson’s Hawk has colloquial names of locust hawk and grasshopper hawk. The hawks feed often on the ground, chasing grasshoppers, a favored food. The Millinocket Bird spent most of its time perched on the fence surrounding the airport or walking/running on the ground, chasing down grasshoppers. Louis Bevier made a video of the hawk capturing a grasshopper: You can watch the video at: https://vimeo.com/185072912
Swainson’s Hawks will also catch dragonflies and other large insects on the wing.
Normally, Swainson’s Hawks migrate south from their western breeding grounds, through Central America and then spread out in South America. Like most Buteo hawks, Swainson’s Hawks are averse to migrating over water.
Swainson’s Hawks are one of the most abundant species migrating through the Isthmus of Panama. Hawk watchers in Panama City counted 900,000 soaring migrants (mostly Swainson’s Hawks and Turkey Vultures) passing overhead on a single day in November of 2013. That record was eclipsed on November 2, 2014 when 2.1 million birds passed over. What a spectacle that must have been!
This hawk joins a long list of vagrants to Maine from western North America. These birds include White-winged Dove, Western Flycatcher, Calliope Hummingbird, Hermit Warbler, Brewer’s Sparrow, Black-throated Sparrow and Western Meadowlark.
I think it is significant the the Millinocket Swainson’s Hawk was a young bird, born in the summer of this year. Many birds that appear in unexpected places during migrations are naïve, inexperienced birds. Young birds are much more likely to make navigational errors than more experienced birds.
Navigation during migration involves two abilities. Most migrants are capable of vector navigation, maintaining a particular compass direction for a specified length of time or distance. True navigation requires that a bird knows exactly where it is, even if it is displaced by a storm or wind.
Experiments demonstrate differences between the navigational abilites of juvenile and adult birds. Imagine Yellow-rumped Warlers banded on their breeding grounds in Maine that normally would migrate south to North Caroina for the winter. Vector navigation in a south-southwest trajectory will get those birds to their wintering grounds.
Some ornithologists have experimentally captured such birds and displaced them eastward or westward. Let’s fly some warblers from Maine to Minnesota and release them there in the fall. Adult birds have true navigation; they realize where their displaced position is and will migrate in a southeasterly direction to get to North Carolina. The young warblers are poor at true navigation. Most will use their vector navigation skills and head south toward Texas. Vagrant birds therefore tend to be young birds that are much more likely to get lost.
Tags: Foraging · Identification · Insects · Migration · Species Accounts
In the last column, I provided some tips on how to predict when migrating birds are likely to be seen in your local patch. Experiencing a fall-out of migrants is exhilarating. In today’s column, we will explore ways that you can experience migrating birds while they are in flight.
Some birds migrate during the day. We have all thrilled to skeins of Canada Geese or Double-crested Cormorants, winging their way in V-formation to more favorable areas. Hawks, eagles and falcons are diurnal migrants as well. They are adept at taking advantage of the vertical winds, called thermals, that form during the day due to uneven heating of the earth’s surface. A rocky outcrop will warm more rapidly than an adjacent forest. The rocks warm the air, the air rises and is replaced by cooler air from the adjacent forest. That cool air warms, rises and you get the picture. Hawks are masters at soaring from thermal to thermal, scarcely beating a wing.
A sunny day with winds in the right direction produces spectacular numbers of these soaring migrants. Mt. Agamenticus in the Ogunquit area and Cadillac Mountain in Acadia National Park have several thousand raptors migrating over them each fall. Bradbury Mountain in Pownal can be great for spring hawk migrants.
Hawk watching is a boom-or-bust activity. Make sure the weather conditions are right and you may be rewarded with more hawks than you can follow.
Shorebirds and most of our songbirds are nocturnal migrants. Advantages of night-time migration are three-fold. The risk of predation from raptors is low. The air is cooler; migrating birds raise their metabolic rate so high they must constantly dump heat or they will overheat. The cooler air helps them balance their heat budget. Finally, the air is less turbulent at night, making powered flight more efficient.
Migrating songbirds mostly migrate at altitudes of 2,000 to 4,000 feet. Shorebirds may fly a bit higher.
How can you see these birds at night? Get your binoculars or, better yet, a spotting scope and train it on the surface of the moon. If migration is occurring, you will see the silhouettes of birds passing in front of the moon’s image. Don’t expect to see birds flying at their normal migrating height but as birds take off or descend, they are easily seen against the moon. The technique works well for birds that are no more than several hundred feet above the surface of the earth.
You can also appreciate migrating birds at night from radar images. In the early days of modern radar in the early 1940s, mysterious blips were detected on radar screens. They proved to be no threat to military aircraft. These echoes were called angels. Now we know that the angels are small flocks of birds.
The Doppler radar used now for weather forecasting is perfect for detecting bird migration. Here is the URL for a great tutorial on how to use the freely available NEXRAD radar images to monitor migration: http://www.woodcreeper.com/videos/NCAR_Tutorial-desktop.m4v
Yet one more way to appreciate nocturnal migration is to use your ears. Nocturnal migrants are noisy, regularly emitting short flight notes. In some cases, the flight notes are similar to the calls the birds give while they are on the ground. In many cases, however, the flight notes are only given during a nocturnal flight.
Bill Evans has been a pioneer in the study of nocturnal flight calls. Visit his website at http://www.oldbird.org/ He has sonograms for a number of warblers and sparrows.
On a night that is not too windy, you can hear the flight notes above. However, a microphone will capture many more of those vocalizations. Evans provides directions on how to build a microphone system using cheap materials like a plastic flowerpot, saran wrap, a dinner plate and an inexpensive microphone.
Tags: Migration · Weather
The southward migration of five billion birds in North America is a staggering phenomenon. These migratory movements provide us with the chance to see a diversity of birds, often in very high numbers. I will devote the next columns to ways to fully experience the fall migration.
Migrating birds are flying right on the edge of survival. Flight is energetically taxing, requiring that a bird’s metabolic rate be raised five times or more above its resting rate. With the exception of birds like swallows, swifts and kites that feed on insects on the wing, migrating birds cannot refuel during flight. One way migrating birds try to maximize the length of a migratory leg is to take advantage of favorable winds.
A weather map offers you a tool to predict when migrations will be strong by looking at the relationship of low- and high-pressure systems. Generally, high-pressure systems alternate with low-pressure systems, moving from west to east across the continent.
A high-pressure system has winds that circle the center of the system in a clockwise pattern. The leading edge of the high-pressure system therefore has winds that flow from north to south.
A low-pressure system has winds that flow counterclockwise. The winds on the backside of a low flow to the south.
To determine when conditions are perfect for a wave of fall migrants, all you have to do is find the nearest cold front (indicated on the weather map by a line with triangles). At the cold front, an area of cool air from a high-pressure system moves underneath the less dense, warmer air of the low-pressure system. The rising air cools, usually causing a line of precipitation.
As the front passes, a strong flow of wind blowing to the south occurs with the interaction of the trailing edge of the low-pressure system and the leading edge of the high-pressure system. Depending on the rate at which the high-pressure system moves, spectacular migrations may be seen for several days.
If you see a warm front passing across your neighborhood, you do not need to worry about getting up at the crack of dawn to look for migrating warblers or sparrows. A warm front (indicated by a line with semicircles on your weather map) is caused when a low-pressure system slides over and above a high-pressure system. In this case, the winds at and behind the front will flow to the north. Birds migrate mostly when the winds are favorable and will stay put if the winds are opposite their migratory trajectory.
On a favorable night, birds will fly as long as they can, settling down sometime in the wee hours of the morning. Sometimes, precipitation can cause birds to land en masse. By luck, a given spot may be hopping with birds.
Where is the best place to look for a fallout? Frankly, serendipity plays a huge role here. Sometime fallouts are broad, occurring over a county-sized area; at other times, the fallouts may be quite restricted.
However, some places are more likely to produce fallouts. Shrubby areas along the immediate coast are often productive. Birds that are migrating just offshore will seek landfall to rest and refuel. A dawn excursion to a coastal area can produce a stream of tired birds, welcomed by dry land. Fort Foster in Kittery, Two Lights State Park in Scarborough and the Eastern Promenade in Portland often harbor many fall migrants. I have experienced fallouts at West Quoddy State Park in Lubec. Any patch of coastal real estate with some bush and tree cover can be productive.
Migrating birds may look for islands of habitat in areas that are heavily developed. The Evergreen Cemetery in Portland is one such magnet.
Finally, migrants need water so checking ponds, streams and rivers can produce excellent fall migrant numbers.
Tags: Migration · Weather
It’s late Augusts and the fall migration is well underway. Where did the summer go?
Migrations are tremendously expensive undertakings for birds. They must pack on fat to fuel each leg of their long journey. To see fall migratory birds, finding an abundant food source is a good strategy. Putting on fat quickly is an imperative for migrating birds so they know the best places to eat.
My wife and I spend a lot of time in Lubec on Cobscook Bay. The area is a wonderful birding destination with lots of accessible conserved land. During the fall migration, my wife and I use the strategy of going to the food to find the birds. If you want to see diners, go to a restaurant.
The South Lubec Sand Bar can be hopping with shorebirds and other water birds from August into October. This bar is about a mile long and is adjacent to an expansive sandflat along the South Lubec Road. This sandflat is the best restaurant in the area for sandpipers and plovers.
Sandpipers forage by rapidly probing into the sediment, capturing invertebrates by feel. Their bills are well equipped with touch receptors. The sandpipers prey on small shrimp-like crustaceans called Corophium as well as polychaete worms, marine relatives of earthworms. These invertebrates are found in the lower to middle part of the intertidal zone.
Plovers use a different feeding technique, relying more on their vision than their touch. A plover stands and looks for movement in the sediment. The plover then runs to that unsuspecting prey animal and captures the ragworm, bloodworm or other invertebrate. This form of feeding is called ambush predation or run-and-peck predation.
The plovers and the sandpipers are dispersed broadly across the flat at low tide. Birding at this stage of the tide is fruitless.
The trick is to let the rising tide bring the birds to you. As the tide starts to cover the productive part of the flat, the birds seem to redouble their feeding efforts as they are forced higher and higher in the intertidal zone. They congregate right along the rising tide line, seemingly oblivious of the humans staring at them.
For an hour or so, large number of shorebirds will be congregated in a narrow swath, affording great views. Eventually, the tide will force the birds to higher ground. The birds fly off to local fields or other open habitats and the show is over.
I have found that arriving at the sand bar four hours before predicted high tide is optimal. The birds will start congregating within the next hour. By two hours before high tide, the birds will have gone to roost.
Of course, it is possible to arrive at high tide and wait for the birds to return. I have had less success with this method as the birds seem to be more aware of human presence.
We walked the sandbar recently with a group of friends. Diversity and numbers of birds varies from day to day. We had a corker of a day but not high bird diversity. We enjoyed stunning close-up views of many Least and Semipalmated Sandpipers. The Leasts with their reddish-brown upperparts and yellow-green legs are lovely birds.
We had fun picking out the occasional White-rumped Sandpiper from the flocks. These birds are easy to identify in flight by their namesake white rump. On the ground, they are similar in color to the gray Semipalmated Sandpipers but a bit larger. The tail of a White-rump extends well beyond the folded wings, unlike the shorter tail of Semipalmated Sandpipers.
A few Semipalmated Plovers and Greater Yellowlegs rounded out our list for the day. We often see a Merlin, Peregrine Falcon and even a Parasitic Jaeger hunting the shorebirds but not that day.
Of course this technique of letting the tide bring the shorebirds to you works on any intertidal mudflat. Give it a try!
Tags: Foraging · Identification · Migration
The next two weeks (late April into May) will produce the peak of spring migration. Some of the migrants will pass through on their way to more northerly, even Arctic, breeding grounds and others will nest here. A few species like Red-headed Woodpeckers and Blue Grosbeaks overshoot their intended breeding grounds and generally backtrack to where they should be.
Avian migration is largely driven by food availability. Leaf-gleaning insectivores like warblers and vireos don’t arrive back in Maine until the leaves of deciduous trees are out. Swallows and flycatchers need to delay until insects are on the wing. Birds with broader diets like Red-winged Blackbirds and Common Grackles have an easier time of it, arriving en masse in Maine in March.
Then, we have the hardy birds that scoff at the rigors of a Maine winter and grace us with their presence all year long. Most of our woodpeckers fall into this category of resident birds. Hairy Woodpeckers and Downy Woodpeckers are common at feeders and in woodlands. Pileated Woodpeckers are fairly common birds, seen less frequently than one would expect based on their crow-size bodies and raucous vocalizations. Red-bellied Woodpeckers have been increasing in Maine over the past two decades and are now regularly seen. Our two three-toed woodpeckers, the Black-backed Woodpecker and the American Three-toed Woodpecker, are infrequently encountered.
All six of these woodpeckers make a living by extracting insect larvae from their galleries or tunnels in wood. The powerful bill excavates a hole to gain access to the gallery and then their long harpoon-like tongue explores the gallery until resistance is fine. A quick poke and it’s time for lunch. Perhaps you are aware of the amazing length of the tongue of a woodpecker. It is so long that it extends behind and then across the top of the skull in a sheath just beneath the skin. A woodpecker tongue can be three times the length of the bill.
In addition to this sextet of residents, we have two other woodpeckers in Maine that are migratory. Each relies on food that is only available during the warmer months.
The first is the Northern Flicker. These large woodpeckers sometimes excavate wood in search of insect larvae. However, they prefer to feed on the ground, having a particular taste for ants. A flicker’s tongue is modified as an efficient ant-harvesting tool. It is shaped less like a harpoon and more like a brush. The many tips of the tongue effectively allow a flicker to easily harvest ants. You may see a flicker pounding on the ground. The bird is excavating an ant colony with a particular goal of getting access to the soft, nutritious ant larvae underneath the soil surface. Beetles make up an important part of their diet as well.
We do see Northern Flickers lingering late into the winter or even overwintering in Maine. Flickers are quite adaptable and can make ends meet by feeding on seeds and berries.
To our south, Northern Flickers may be resident birds. In Maine, the snow prevents flickers from their favored means of ground foraging in the winter.
Our other migratory woodpecker is the Yellow-bellied Sapsucker. The name is amusing enough and its way of making a living is fascinating. These woodpeckers maintain elaborate systems of sap wells in trees. A sapsucker creates these shallow holes and then feeds on the sap that exudes from the wells. The sap attracts insects and sapsuckers will prey on these insects as well, particularly when feeding young. The protein-rich insects are just the ticket for growing nestlings.
A sapsucker visits its wells daily, enlarging them as necessary to insure the continued flow of sap. Ruby-throated Hummingbirds take advantage of these wells. Hummingbirds frequently nest near sap wells and follow a sapsuckers as it works its trap line of sap wells.
Flickers and sapsuckers, it’s good to have you back for a while.
Tags: Insects · Migration · Species Accounts
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