Shorebird migration is peaking now in Maine as southbound birds head for warmer climes for the non-breeding season. We get two cracks a year with these passage migants as they move through Maine each spring and late summer/fall.
Two species of yellowlegs, Lesser Yellowlegs and Greater Yellowlegs, are common migrants through Maine. They are more likely to be seen on coastal mudflats but regularly appear in inland wetland areas as well. The bright yellow legs make it easy to identify a large sandpiper as a yellowlegs but which one is it? Separating the two is an identification challenge.
As befits the name, the Greater Yellowlegs is larger than the Lesser, weighing twice as much as its smaller relative. Greater Yellowlegs are chunky, bulky birds compared to the slim, graceful shape of Lesser Yellowlegs. A Lesser is 10-11 inches long while a Greater is 14-15 inches long. Nevertheless, it is difficult to accurately gauge the size of birds when there are not other known species around to provide a yardstick. Fortunately, other characteristics can be used to distinguish the two species.
A somewhat subjective but useful feature is the facial appearance. The face of a Lesser appears has a kind, gentle demeanor compared to a Greater’s harsher mien.
A Greater with its bulkier body has a relatively small head and thin neck. The neck frequently has a kink in it, like a heron. The breastbone is strongly angled and bulges from the chest. The neck of a Lesser is relatively thick and shorter, rarely showing the kinked appearance. The head does not seem small relative to the body.
The bill of a Greater is absolutely and relatively longer (relative to the head). You can use the length of the head viewed from the side as a measuring stick. The bill length of a Greater exceeds the length of the head. Measurement of museum specimens indicates the bill averages about 1.3 times the length of the head. A Lesser’s bill is pretty close to the length of the head.
The bill of a Greater Yellowlegs is slightly upturned compared to the straight bill of a Lesser. Outside of the breeding season, the bill of a Greater Yellowlegs is broader at the base and usually two-toned (gray at the base and black at the tip). The tip of the bill is somewhat blunted. A Lesser has a straight, thin, needle-like bill with a sharp tip. The bill is uniformly black along the length.
Your ears can provide the most convincing cues for a correct identification. A Greater Yellowlegs gives a loud, piercing whistle that is often rendered as “tew tew tew”. A Lesser Yellowlegs gives a softer, less strident call rendered as “tu”, that may be given as single notes or a couple of notes. A great website to hear recordings of these two species is www.AllAboutBirds.org; just type in the species name of interest in the search box and press Enter. On the species screen, you will see a tab called Sound. Click on that tab and you will be taken to links for a number of recordings.
The difference in the vigor of the calls is reflected in the foraging behavior. A Greater is a hyperkinetic forager, dashing back and forth along a mudflat. A Lesser is a more sedate, less frenetic forager.
Most of the other large members of the sandpiper family that pass through Maine lack yellow legs and hence are not likely to be confused with one of the two yellowlegs. However, Stilt Sandpipers can cause some confusion. These birds have greenish-yellow legs and are about the size of a Lesser Yellowlegs. In fact, they often forage with Lesser Yellowlegs. Proportionally, the head of a Stilt Sandpiper seems large. The bill is relatively heavy and shows a pronounced droop.
[First published on August 18, 2013]
In today’s column, I’ll provide a summary of some recent scientific articles on birds that occur in Maine. All of these articles appeared in the most recent issue of the Wilson Journal of Ornithology.
Christina Masco describes research she did in Maine on Appledore Island on interactions among nesting Great-blacked Gulls. These gulls nest at high density and a pair aggressively defends its small territory (about 350 square feet) throughout the breeding season. Real estate on Appledore is hard to find so most territories abut several other territories.
If an intruding gull enters the territory of a gull, aggressive interactions ensue. But some of these fights are avoided by the use of threat displays, warning another gull that it should leave or prepare for a fight.
One of these threat displays is a distinctive vocalization that sounds like “yeow”. This call tells an adjacent bird that an attack is imminent. Masco used play-back experiments to determine if Great Black-backed Gulls can recognize individuals based on their “yeow” calls. She found that a territorial gull will hold alert postures longer in response to unfamiliar “yeows” compared to the “yeow” given by a mate or neighbor.
This finding is an example of the dear enemy phenomenon. Animals get used to adjacent enemies and tend to respond less vigorously to them than to strangers. In other words, it is better to deal with the devil you do know rather than the devil you don’t know.
The Eastern Wood-Pewee is a fairly common breeding bird throughout our state. Felicity Newell and colleagues wrote an article describing surprising reproductive traits of this species in Ohio.
Before this research, ornithologists had presumed that Eastern Wood-Pewees were monogamous, with a pair-bond cementing one male and one female together. Newell and colleagues present research that challenges this assumption of mate fidelity. They color-banded 79 pewees with unique color combinations. Much to their surprise, they found one male that was simultaneous feeding young at two different nests. The same male was polygynous (mated to more than one female) the following year as well.
Polygyny is advantageous for a male because he can father twice as many young as a monogamous male. Polygyny can be disadvantageous for females because their presumed faithful mate is devoting half of his time to a different family.
Aside from habitat destruction, bird mortality from bird-window collisions represent the greatest human-associated source of bird deaths. Bird deaths from window collisions number in the billions.
Dan Klem of Muhlenberg College has been studying bird-window collisions for over 30 years. Klem and Peter Saenger wrote an article in which they evaluate the effectiveness of selected visual signals to deter bird-window collisions.
Their work was based on a carefully controlled experiment where they placed wood-framed picture windows in an area of mowed pasture in Pennsylvania. They placed a platform feeder 10 meters from each window.
Experimental treatments included using clear glass, reflective (mirrored) glass, ORNILUX Mikado glass, and Acopian bird savers (vertically hung parachute cords spaced three or four inches apart). The ORNILUX glass reflects more ultraviolet light than other types of glass as well as the Acopian bird savers. Unlike humans, birds can see a portion of the ultraviolet spectrum.
Klem and Saenger recorded the number of bird collisions (some of which were fatal) with the picture windows equipped with the three different types of glass. They also tested the effectiveness of the Acopian bird savers.
In one experiment testing the three types of glass, no difference in total collisions was found. However, fatalities were lowest at clear glass (10%) and highest at the ORNILUX glass (58%). The ultraviolet-reflecting glass had the opposite effect expected.
A second experiment showed that parachute cords were very effective in preventing collisions, hung outside of either clear or reflecting glass.
Visit http://www.birdsavers.com/ to learn more about Acopian bird savers.
First published on August 4, 2013]
Categories: Bird Conservation · Recent Ornithological Literature · Reproduction
After a wet and cool June, the warm temperatures in July convince us that summer has finally arrived. However, birds operate on a different calendar. Tree Swallows and Barn Swallows can be seen by the tens and even hundreds perched on utility wires with migration on their minds. Least Sandpipers, Greater Yellowlegs and Short-billed Dowitchers are appearing on coastal mudflats. The fall migration has begun. Perhaps, a less confusing term would be post-breeding migration but I think the phrase fall migration is here to stay.
Some ornithologists have estimated that five billion birds in North America migrate south every year. In today’s column, we will consider the why and when of the fall migration.
To begin, we need to recognize two types of migrating birds. First, we have species that breed locally but winter to our south. We can call these species migratory breeding birds. Second, we can see species that breed to our north and winter to our south. We only see these birds, called passage migrants, during their migration to and from their breeding grounds. Various sandpipers and Snow Geese are examples of passage migrants through Maine
You may wonder why Tree Swallows depart southward from Maine when the summer weather is just starting to become glorious. The answer is food. The need to migrate is not impelled by temperature but rather by lack of food. Given sufficient food, birds are capable of tolerating markedly extremes of temperature. The abundance of flying insects, on which the swallows depend, is beginning to decline. The reduction in food necessitates an August departure for most of our swallows.
Cuckoos, warblers and vireos rely heavily on caterpillars and other insects, which feed on the leaves of trees and shrubs. The abundance of these insects is sufficient to allow leaf-gleaning birds to stay in Maine well into September. After the first killing frosts of autumn, leaf-eating insect abundance declines markedly and our warblers and vireos are forced to migrate south. Except for Yellow-rumped Warblers and Palm Warblers, most of our warblers will depart by the beginning of October.
A number of our migratory breeding birds are seedeaters. Seeds from herbaceous vegetation can be found through the fall until a snow cover accumulates. White-throated Sparrows, Chipping Sparrows and Rose-breasted Grosbeaks can longer well into October.
The movement of passage migrants begins in July with the arrival of post-breeding shorebirds. Birds breeding above the Arctic Circle have a narrow window of opportunity for breeding. Insect and fruit abundance in the Arctic is amazingly abundant during the time of the midnight sun but rapidly shortening days and cooling temperatures take their toll on food availability for birds.
The Semipalmated Sandpiper, a species I have studied on its migration, provides a typical example of the migration of sandpipers. Semipalmated Sandpipers arrive on their Arctic breeding grounds in late May or early June. Both the female and the male incubate the eggs and tend the young.
Before the young sandpipers can fly, the females will begin their fall migration. They are followed a week or so later by the males. The young are left on the tundra, barely capable of flying but obviously able to find food and avoid predators. They begin their migration about a month after their parents have departed. the juveniles inherit the instinct to migrate and find the way to their South American or Caribbean wintering grounds without the benefit of a guide.
I encourage you to get out this summer and to enjoy the fall migration! The post-breeding migration is much more protracted than the spring migration. Spring migration is characterized by an urgency to get back to the breeding area and secure a good territory and mate. The fall migration is more leisurely, lasting into November when the last of our sparrows and hawks depart.
[First published on July 19, 2013]
The bird field guides available today represent an embarrassment of riches. Until the National Geographic Guide was published in 1983, birders had two guides, one by Roger Tory Peterson and one by Chan Robbins, for help in field identification. I cut my ornithological teeth on these two field guides. I well remember the plates in the Peterson guide called confusing fall warblers. Confusing they are!
The classification of the New World Warblers is confusing as well. In the past couple of years, major changes in our understanding of how these warblers are related have emerged. Many of these insights come from the use of DNA comparisons to assess relatedness. Field guides published in the next few years will have a different arrangement and different scientific names for many of our warblers. As an example, Hooded Warbler, Wilson’s Warbler and Canada Warbler were thought to be closely related and all were placed in the genus Wilsonia. Recent research shows that Hooded Warbler is actually closer related to warblers like Northern Parula and Palm Warbler and shares a genus name with these species now. Canada Warbler and Wilson’s Warbler remain in a different genus.
An extraordinary new field guide will do much to reduce our confusion over field identification and get us used to the new classification scheme of warblers. This book is The Warbler Guide, written by Tom Stephenson and Scott Whittle. Both are accomplished birders and each brings another talent to this guide. Stephenson is a musician and Whittle is a professional photographer.
This soft-bound book is 560 pages long. At 6×9 inches in size, it’s a bit large for a pocket but easily fits in a backpack for field use.
The first 100 pages provide an introduction to the use of the guide and warbler-specific tips for identification. Most pages are adorned with uniformly excellent photographs of warblers. This guide has literally hundreds of photographs.
The authors begin with a topographic tour of wablers. The photographs are excellent for showing various feather tracts that are often useful in field identification. Then the authors describe various features to notice on a warbler (with many photos), such as facial contrast, shape, eye-arcs, wing panels and flight-feather edging. A useful section on sexing and ageing warblers is provided.
The introductory section concludes with a primer on auditory identification. The authors’ approach is perhaps the most innovative aspect of the guide. We learned to identify a male Chestnut-sided Warbler by its “pleased-pleased-pleased-to-meetcha” song. The authors use a different, more objective approach. Songs are broken into phrases and elements, superimposed on element qualities and speed. Sonograms of songs are a prominent feature of this guide.
The authors next provide Visual Finder Guides and a Song Finder Guide to allow an observer to quickly home in on an identification. A Face Quick Finder has 86 photos of side views of all the faces of warbler species on two facing pages. Similar layouts are provided for sideviews, underviews and oblique views of the full body.
The Song Finder Guide relies on the observer noticing numbers of phrases, the timbre of the notes, changes in pitch and other vocal characteristics to reach an identification.
The bulk of the guide is made of the individual species accounts. Each account begins with a few symbols showing the shape in silhouette, the tail pattern, general color, range map and specific habitat (e.g., tops of trees).
Let’s take the Blackburnian Warbler account as an example. Ten pages are provided with 50 color photos (along with 8 photos of warblers that can be confused with Blackburnian). Telegraphic text descriptions augment the photos. Two pages, replete with sonograms, describe the songs of this species.
This book will be published on July 24. A companion app with sound recordings will appear soon as well. Grab a copy of this guide in time to help with those confusing fall warblers.
[First published on July 7, 2013]
Categories: Field Guides
As the most mobile of all vertebrates, birds pose a challenge to ornithologists seeking to understand the where and why of bird movements. Banding captured birds is a time-honored technique. It is, however, fundamentally inefficient because a banded must be recaptured to get an endpoint for its movement. Furthermore, a Common Redpoll banded in Maine and recaptured in New Jersey may have taken a circuitous route from one point to the other.
Radio-transmitters can be used to track bird movements. A transmitter and antenna are attached to a captured bird. Each transmitter emits a unique frequency. Using scanners, field workers get a fix on a bird and by triangulation determine the position of the bird at a particular time. Typically, the transmitters are only effective over distances less than a mile. Although these transmitters are miniaturized, they are still too heavy to place on most songbirds and other small birds.
Satellite-transmitters are similarly attached to birds but their signals can be identified all ove the world. It is possible to follow the movements of an albatross or Osprey with a satellite-transmitter from a computer desktop. But like radio-transmitters, satellite-transmitters are not small enough to place on smaller birds.
In today’s column, I want to concentrate on a relatively new method of determining bird movements that can be used on smaller birds. The device is called a geolocator and is brilliant in its simplicity.
A geolocator is a light-recording device with a computer chip to collect sunrise and sunset data daily along with the time of day and date of each event. It is easy to figure out where the bird is on a particular day from that information. As an example, if the sun comes up at at 4:56 AM EST and sets at 8:31 PM on June 15, I must be in Rangeley, ME. An area further south will have a shorter daylength and an area further west will have a later sunrise and sunset.
These geolocators are quite small, weighing as little as 0.5 gram (a penny weighs three grams). Thus, these devices can be put on birds as small as vireos and large warblers. The devices are mounted on the rump, attached with a harness that runs around the upper legs of a bird.
The trick, of course, is to recapture the bird and recover the geolocator. In most of the work with geolocators done so far, ornithologists take advantage of the fact that migratory birds show a high degree of fidelity to their breeding sites. Thus, a Tree Swallow can be tagged with a geolocator one April and then recaptured in the same area the following April with daily data on sunset and sunrise for every day it wore the geolocator. Pretty cool! The investigators download the data and get a day-by-day map of the movements of that bird.
The most recent issue of the ornithological journal, The Auk, has a series of articles on remarkable discoveries using geolocators. Here are a couple of examples. Geolocators show that Tree Swallows from a range of breeding areas use southeastern Louisiana as a stopover area during fall migration to Central America. The technology shows that Red-eyed Vireos have a much slower migration than most neotropical migrants. Spring migration from South American takes about 45 days, only 13 of which are spent flying.
To me, the most amazing result of geolocator research concerns seven Arctic Terns that were banded on the breeding grounds in the Netherlands. This species hold pride of place as the the longest-distance migrant. But these seven birds showed the migration is even more impressive than formerly thought. These birds migrated after breeding south along the west coast of Africa, eastward to Australia (to New Zealand in one case) and then southwest to Antarctica for the austral summer. The movements for one year were over 55,000 miles! One year!
[First published on June 23, 2013]
Tourist season is upon us again. On May 28, Maine hosted a visit by a Eurasian Collared-Dove. This bird showed up at a feeder in Falmouth. It represents the first record of the species in the state of Maine. Alas, this tourist did not tarry and was not seen subsequently.
From the picture taken by Doug Hitchcox, you can see this dove is a striking bird with a sandy-gray plumage and a distinct black band, edged with white, across the nape. The tail is squared off rather than pointed like the tail of a Mourning Dove. The call (koo-KOO-kook, with the second syllable accented) is distinctive.
As the name suggests, Eurasian Collared-Doves are not native to North America. The arrival of the species in Maine is a long story with a few interesting twists.
Eurasian Collared-Doves were originally native only to India, Sri Lanka and Myanmar (formerly, Burma) where they typically occur in open, dry areas often associated with agricultural areas. Now they are found over much of Europe and Asia, having expanded east to China and west to Portugal. We know quite a bit about the pattern of colonization of the species in Eurasia.
In the 1600’s, these birds expanded into Turkey and the Balkans. We do not know if the birds naturally dispersed westward or if they were introduced by humans. They continued to spread westward in Europe, reaching Yugoslavia by 1912, Hungary by 1930, Germany by 1945, Norway by 1954, Britain in by 1955 and Portugal by 1974.
The expansion of Eurasian Collared-Doves into Europe has been described as explosive. As long as birds have access to food from bird feeders or from gleaned seeds from pastures and grain fields, they can tolerate fairly cold weather. Areas where the annual average low temperature is below 32 degrees are too harsh for these birds.
These doves occur now in the Western Hemisphere as well, although in a patchwork pattern. The introduction into our hemisphere can be traced back to two events. In the mid-1970’s, a breeder brought Eurasian Collared-Doves to New Providence, Bahamas. A few birds were released during a burglary and the breeder subsequently released the rest of his breeding stock of 50 birds.
A second release occurred on Guadaloupe in 1976. It is clear that the populations now established elsewhere in the Caribbean and in much of North America stemmed from these two introductions.
The first of these doves to reach North America arrived in south Florida. Confirmed records were obtained in 1986 although there were reports of collared doves of some ilk in south Florida over a decade earlier.
By the late 1980’s, Eurasian Collared-Doves were reported from several Florida counties in the northern part of that state, Georgia and Arkansas. From that point onward, the expansion has been explosive, similar to the colonization of Europe.
Breeding populations are now established in all the southeastern states along with California, Colorado, Illinois, Kansas, Missouri, Montana, Nebraska and Texas. Records of stragglers have been reported as far north as Montana, North Dakota and Saskatchewan. The Maine bird falls into this category.
As with the European invaders, North American Eurasian Collared-Doves are strongly associated with humans. Suburban gardens, town parks and areas with mixed shrubs and trees provide favored habitat. They tend to avoid urban centers and woodlands. Coastal areas, particularly with mixed habitats of scrubland, pastures, and grain fields, host the largest populations. These doves avoid areas of intensive farming.
The patchy distribution of established populations results from a phenomenon called jump-dispersal. Collard-doves will disperse long distances, establish a new breeding population, and then fill in the area between. We can expect a more continuous distribution of these birds as jump-dispersal continues. The cold temperatures in Maine may keep the species from becoming an established member of our avifauna. We’ll have to wait and see.
[First published on June 9, 2013]
Categories: Species Accounts
The wonderful spectacle of spring migration is coming to an end with the arrival of the last warblers, thrushes and cuckoos. As usual, it’s been a delightful three months of arrivals and departures.
Species arrive on their own schedules. We know that Red-winged Blackbirds and Common Grackles will be among the first spring migrants in early March, the first Eastern Phoebes will arrive in early April and early May will bring Ruby-throated Hummingbirds.
Why do our various species of migratory breeding birds arrive at different times of the spring? Ultimately, food is the answer.
Migratory breeding birds, especially males, are anxious to arrive on the breeding grounds as soon as possible to stake out a nice territory and attract a mate. But arriving before there is food to eat can be fatal.
Red-winged Blackbirds and Common Grackles do fine in early March because they can subsist on seeds. Common Loons, Ospreys, and Belted Kingfishers must have fish so arriving after ice-out is a must. Phoebes and Tree Swallows depend on flying insects that only emerge in April. Warblers and vireos rely on caterpillars and other leaf-eating insects that only emerge after the deciduous trees leaf out in early to mid-May.
The explanatory power of food availability can be applied to the eight species of woodpeckers that commonly occur in Maine. Six of these species do not migrate at all. The most common of these are Downy Woodpecker, Hairy Woodpecker, Red-bellied Woodpecker and Pileated Woodpecker. All feed in the stereotypical woodpecker way of drilling into wood to expose the galleries of insects. Using their ridiculously long, barbed tongues, these woodpeckers harpoon the insects. Carpenter ants are a favorite of Pileated Woodpeckers.
The Black-backed Woodpecker and American Three-toed Woodpecker are resident but uncommon woodpeckers in Maine. They favor burned-over areas, concentrating on the beetles that attack newly burned wood. These two woodpeckers tend to forage just beneath the bark scales for their meals.
The food of all of these species is available year-round. These woodpeckers have no need to undertake arduous migratory journeys.
We do have two species of woodpeckers, the Northern Flicker and Yellow-bellied Sapsucker, that depart in the fall and return back to us in April. Their dietary preferences necessitate a departure for more moderate winter climates.
Flickers do much of their foraging on their ground, particularly hunting for ants. Nearly half of a flicker’s diet comes from ants. Flickers also catch insects like butterflies and beetles on the wing. A dense snow pack, hibernating ants and a lack of flying insects force Northern Flickers to withdraw from Maine each fall.
Yellow-bellied Sapsuckers feed by creating shallow holes, called sap wells, in the bark of trees. The sap that oozes into the wells provides food for the sapsuckers. The sap is a fluid carried in phloem cells of the tree, just beneath the bark. This fluid is rich in carbohydrates, particularly sucrose (table sugar) sapsucker is not unlike a vampire, exposing the phloem cells and drinking the sucrose that oozes out. Unlike most woodpeckers, a sapsucker has a tongue that is brush-tipped, perfectly adapted for lapping up sap.
The sap wells in the phloem are usually rectangular in shape. I am sure that you have seen these sap wells before, arranged in neat rows parallel to the ground. A sapsucker tends its sap wells daily, making sure they continue to ooze sugar by enlarging the area of the well.
Sapsuckers do supplement their diet with insects. Foraging for insects is especially important when parents are feeding nestlings. The young sapsuckers need protein to grow.
In the winter, the phloem freezes solid, depriving sapsuckers of their favored food. Once again, the lack of available food in the winter forces sapsuckders to migrate south.
[First published on May 26, 2013]
Categories: Migration · Species Accounts
This column continues the discussion of Osprey biology from the last column. I wrote about the dependence of Osprey on live fish for food.
Ospreys are not picky about the fish they prey upon in either marine or freshwater environments. As long as the fish are in shallow water or within three feet of the surface of deeper water, they are at risk from an attack from above by a feathered menace.
Ospreys are effective fishers. They succeed in getting a fish on 24% of their dives. The average hunting time to catch a fish is 11.8 minutes.
Ospreys may nest in loose colonies. A critical feature for a nest site is proximity to fishing habitat; Ospreys don’t mind commuting 10 miles to fish. They also like nest sites that are open.
A study in Nova Scotia demonstrated the cleverness and even cooperation of Ospreys that were nesting close together. At that site, Ospreys were feeding on marine fish. Sometimes they fed on fish that tend to concentrate in shoals: alewives, pollock and smelt. At other times, they took fish like winter flounder that tend to be more randomly distributed.
Ospreys at their nests watched other Ospreys returning to their nest with food. If the returnee had an alewife or pollock, other Ospreys would immediately head off in the direction from which the successful forager came. A fish shoal had been found and there should be plenty of fish for all!
If the forager came back with a flounder, the Ospreys did not respond in the same way. Information on the location of a non-schooling fish like a flounder has little value for later foragers.
One might think that Ospreys taking a cue from other Ospreys with prey is a form of parasitism. However, there is evidence that an Osprey returning with a smelt or other shoaling fish gives a distinctive flight display to alert other Ospreys to the fish shoal. This behavior seems to be a cooperative behavior, reminiscent of the bee waggle dance where bees communicate the presence of nectar-rich plants to other bees.
Ospreys have had a mixed relationship with humans. Persecution caused the demise of Ospreys in Scotland and southern and central California in the early part of the 20th century. This persecution came in the form of egg collecting for private collectors, hunting to obtain stuffed specimens for people’s parlors and irrational killing of birds of prey by ignorant shooters.
The removal of large trees along the shores of Lake Huron to create space for housing developments led to a precipitous decline of Ospreys in that area of Minnesota.
Of course, the greatest human-related scourge on Ospreys was the widespread use of DDT over 20 years beginning around 1950. This “wonder insecticide” found its way into our marine and freshwater systems. The DDT was absorbed by small animals and was difficult to eliminate. As a result, DDT biomagnified as it passed up the food chain, becoming more concentrated as it passed from prey to intermediate predators to top predators like the Osprey.
The major effect on the Osprey was to cause eggshell thinning; the eggs were easily broken by an incubating parent. Some adult mortality from exposure also occurred. Over 90% of the Ospreys between New York and Massachusetts perished.
Fortunately, the banning of DDT has led to a recovery. By 2000, most Osprey populations had recovered to pre-DDT levels.
On a happier side, the provision of nesting poles has led to dramatic increases in local Osprey populations.
[Originally published on May 12, 2013]
Categories: Species Accounts
For birders, one of the joys of April is the arrival of the Ospreys. We’ll look at this remarkable raptor today and in the next post.
Let’s start with the scientific name of Osprey, Pandion haliaetus. The genus name Pandion comes from a king of Athens in Greek mythology. Unfortunately, the scientist, Savigny, who established the genus name did not know his mythology very well. Pandion had two daughters. A man named Tereus married one of the daughters and later forsook her for her sister. The Greek gods transformed the sisters into a nightingale and a swallow and Tereus into a hawk. Tereus spent eternity chasing the swallow and the nightingale. So, Tereus would be a much better genus name for the Osprey.
But Pandion does have the prefix Pan- meaning all, an appropriate meaning here. Ospreys have a nearly worldwide distribution. They occur on all of the major continents with the exception of Antarctica as well as many oceanic islands, including such far-flung islands the Lesser Sunda Islands in the South Pacific.
The specific name haliaetus is the genus of the Bald Eagle, so there is a bit of similarity there.
The common name turns out to be a misnomer as well. This word comes from Latin roots, meaning bone-breaker. This name is appropriate for the Lammergeier, an Old World vulture that drops bones onto rocks to crack them and expose the marrow. Oops!
I think Fish Hawk would be a much more appropriate common name for the Osprey. Fish make up at least 99% of the diet. Other animals that are rarely taken are salamanders, birds, snakes, voles, squirrels and even a small alligator. Finally, it must be have been mind-boggling for observers to see an Osprey tearing flesh from the carcass of a White-tailed Deer and another competing with Turkey Vultures for access to a road-killed opossum.
Access to fish is a strong determinant of the distribution of Ospreys. In North America, a look at the distribution map of breeding sites reveals they nest broadly in Florida but are restricted to the coastal plain along the rest of the east coast until they reach Maine. As you know, Ospreys nest commonly throughout most of our state. They also breed across Canada, extending south into many of the northern-most states with breeding populations extending along the Pacific coast to central California.
Over much of their breeding range, winters are cold enough to cause lakes and rivers to freeze, denying Ospreys access to fish. Hence, the majority of Ospreys breeding in North America are migratory, spending the winter either along the coast or rivers in Central and South America. Unlike many migratory hawks, Ospreys readily migrate over broad expanses of water.
We have all thrilled at the sight of an Osprey diving for fish. An Osprey may fly as high as 200 yards above the water to seek a fish near the surface. Sometimes they hover as they scope the scene. The dive is made feet first and is usually no deeper than three feet.
The feet of an Osprey are marvelous tools. The talons are long and razor sharp. The base of the foot pad and toes are covered with short spines that aid in gripping a slippery fish. The outer toe is flexible and can reverse its orientation so that the foot of an osprey can have two toes pointing forward and two backward to grip a fish firmly.
An Osprey can fly with a fish weighing half its body weight. Their long wings and powerful wing muscles allow them to generate enough lift to rise off the water with their load. Once aloft, the Osprey will orient the fish parallel to its own body to reduce air resistance.
[Originally published on April 28, 2013]
Categories: Species Accounts
In today’s column, I want to alert you to a couple of recently published bird books from Princeton University Press. The first is The Crossley ID Guide to Raptors. This book follows the format of Crossley’s well-received Crossley ID Guide to Eastern Birds. The Crossley guides use photographs rather than paintings or drawings to illustrate the birds. For each species, a composite plate with many images superimposed on an appropriate landscape is presented. This new guide contains 101 photographic scenes with 35 double-facing. Brief, dense text on identification is provided at the bottom of each plate.
The new raptor guide is co-authored by Jerry Ligouri and Brian Sullivan. Ligouri has published a raptor field guide of his own and both men are expert in raptor identification.
To really develop confidence in identifying a bird species, you need to master five views: from above, from below, from head on, from tail on, and from a lateral view (left or right). Crossley and colleagues make sure that views of all of all these perspectives are provided for each raptor. Of course, the plumage of young raptors differs from adults; these different plumages are well covered along with geographic differences. They devote five plates to the Red-tailed Hawk and three to the Rough-legged Hawk.
The book contains 81 photographic plates. The last third of the book provides an account of each species, including a large map of the distribution of each species. Each account follows a consistent format with sections called Overview, Flight Style, Size and Shape, Geographic Variation, Molt, Similar Species, Hybrids, Status and Distribution, Migration, and Vocalizations.
An extremely useful feature of the book is a collection of mystery photos. The authors provide a number of composite plates to test the reader’s identification skill. For instance, one plate gives a number of eagles in flight; a reader needs to decide if each is a Golden Eagle or a Bald Eagle. Similarly, one plate pictures 21 accipiters at all different angles. The challenge is to decide if each is a Sharp-shinned Hawk or a Cooper’s Hawk. A key is provided for each plate, giving the species, age and sex of each mystery photo and a brief explanation. These plates are powerful learning tools. From my experience, they will also give you a generous piece of humble pie!
Thirty-four species are covered including two species of New World vultures, six falcons, and 24 hawks, eagles and kites. The book measures 10×7.5 inches so is really not convenient to carry in the field. Use it as a learning resource and refer to it often.
The second newly published book is The World’s Rarest Birds by Erik Hirschfield, Andy Swash and Robert Still. The scope of the book is based on the Red List of Birds maintained by the International Union for the Conservation of Nature (IUCN). The IUCN Red List is considered to be the most scientifically objective system for classifying species in terms of their risk of extinction. The Red List incorporates six different levels of concern and this new book covers the 197 species listed as Critically Endangered and the 389 listed as Endangered.
The book begins with a description of the types of threats on Red-listed birds. These threats include geological events, fishing, damming, pollution, energy production and mining, climate change, logging, and agriculture/aquaculture.
The coverage of the species accounts is geographic with the world divided into Europe and the Middle East; Africa and Madagascar; Asia; Australasia; Oceanic Islands; the Caribbean, North and Central America; and South America.
Four species are covered on each page with a color photograph, a distribution map, an estimate of population size, a listing of threats to the species and a short paragraph on the biology and population changes. Scattered throughout are descriptions of threatened species hotspots. This fine book is simultaneously fascinating and saddening.
[Originally published on April 27, 2013]
Categories: Book Reviews · Field Guides