HawkWatch Update Archive - 2009
Below are the weekly Riding the Winds updates from the 2009 Hawk Watch season on Cadillac Mountain, written by Jenna Dodge, the 2009 Raptor Intern. Earliest reports are at the bottom and later reports are at the top.
October 13, 2009. Migration season is coming to an end here in Acadia National Park, and as of Monday we had surpassed our yearly average with 2,660 passing raptors. Overall, the number of species we saw heading south for the winter was in accordance with our average, so we might assume that raptor populations are stable and healthy. However, various weather conditions can send birds past us in areas where we can’t spot them. Therefore, when scientists determine the stability of populations, they look at a many hawk-watch sites across New England for trends. Overall, we have noticed that certain species have either fallen short or exceeded our average numbers: the American kestrel and peregrine falcon, respectively.
This was a low year for American kestrels, with 497 individuals out of an average of 705. Once considered to be the most numerous falcon in North America, this exquisite raptor has been suffering a significant decline for the past 10 years, which has been documented in various hawk-watch sites along the Northeast Coast. There are a variety of theories to explain this alarming trend. American kestrels are obligate secondary cavity nesters, meaning that they must nest in tree cavities, crevices, abandoned building, or nest boxes that have been already excavated, and they will live at the cusp of forests and open fields. In the early 20th century, the common land practice was agriculture, which provided an ideal habitat for kestrels—clear, open fields with strips of woodland. Since humans have shifted their relationship to the land and urban sprawl is common, many of the fallow fields are becoming reforested. Loss of habitat, a strong determining factor in population health, could be a reason why American kestrels are becoming less abundant. Another factor is an increase in predators; both northern goshawk and peregrine falcon populations have increased since the 1970s, which would cause a correlating decrease in the smaller kestrel. Furthermore, it is possible that DDT, a slow-degrading insecticide, is still prevalent in the ecosystem and inhibiting reproduction for many raptors, including kestrels. There has also been a parallel between regions with a high incidence of West Nile virus (WNV) and low American kestrel populations. These birds become infected with this deadly disease by eating insects, including WNV-contaminated mosquitoes. This theory is still not quite fully understood; however, there are many ongoing research studies hoping to solve the link between WNV and kestrel decline.
On a much lighter note, we saw 31 peregrine falcons fly through on their migratory path—more than double the average number. This is especially great to witness because it means that this once highly endangered raptor is now doing well along the East Coast. In the 1960s, the eastern subspecies actually went extinct east of the Mississippi River due to DDT preventing successful reproduction. Intensive restoration efforts were made throughout the East during the 1980s and were very successful at reinstating peregrine populations in natural cliff habitats; this achievement is clearly demonstrated through various hawk-watch sites.
To get a more information on raptors and migration, visit the Hawk Migration Association of North America (HMANA) website. Park rangers will be on Cadillac Mountain until Wednesday, October 14, so please come to HawkWatch from 9 a.m. to 2 p.m. We are located 200 yards down the Cadillac North Ridge Trail. Bring your binoculars (the park may provide some if you do not own any) and an eager curiosity for raptors and their splendor.
October 6, 2009. The somber drone of a motor cuts the stillness on top of Cadillac Mountain like a chainsaw tearing through finely woven silk: a gas-hawk, or airplane, has taken to the sky. To the majority of the world this image is brazenly normal; however, when given a more careful eye, this standard mode of transportation transforms into a flying contraption that deviates from the natural world. For centuries, humans have been transfixed by the lyrical movements of birds in flight. Prior to the first successful machine flight in1903 in Kitty Hawk, North Carolina, humans had attempted to mimic birds’ natural abilities.
Many technological advances have been inspired by the natural world: the use of echolocation by whales and bats to find food helped model sonar equipment, and birds have contributed endlessly to the study of aviation. Perhaps the first person to truly attempt to recreate a bird’s aerial triumphs was Leonardo da Vinci. As a Renaissance man in all facets of the term, his time as scientist, observer, and inventor was partially devoted to examining the behavior and flight patterns of birds and bats, after which he modeled many flying machines. In 1505, he released the Codex on the Flight of Birds, which was comprised of 18 different designs for flying contraptions, including a helicopter and a glider. When put to the test, many failed and plummeted to the ground; the glider, however, was constructed and executed with success, and its design is still pertinent to modern-day flight.
This long-lived fascination with avian creatures has enlightened artists, philosophers, scientists, and even the United States military. With names like the F-16 Fighting Falcon and A-4 Skyhawk, images of cunning and high speed maneuverability come to mind, not to mention the ferocity of a raptor in pursuit. In-depth examinations of the fastest creature on earth, the peregrine falcon, specifically the shape and use of its wings, provided inspiration for military aircrafts. It leaves me to wonder that without birds to inspire our creations, would they have ever been constructed? So the next time you step aboard an airplane destined for a far off place, imagine the efforts it took to create such a machine and give thanks to its muse.
HawkWatch will continue until October 14, and with little time remaining in our migration season, please join us from 9 a.m. to 2 p.m. (weather permitting), 200 yards down the Cadillac North Ridge Trail to welcome the rest of our travelling raptors. Bring your binoculars (the park may provide some if you do not have any) and an eager curiosity for raptors and their splendor.
September 29, 2009. Since the HawkWatch season began, we have seen 2,194 passing migrants; with three weeks left, we expect to reach our yearly average of 2,560. So far we have discussed birds belonging to the falcon, accipiter, and buteo groups, but the last three migrants cannot be lumped into a single group: the osprey, northern harrier, and the bald eagle are characteristically unique from the rest and require individual attention.
The osprey (Pandion haliaetus) is widely dispersed throughout the world, inhabiting regions near bodies of water—streams, oceans, rivers, lakes, marshes, and mangroves—due to its primarily exclusive diet of fish. The osprey, or fish hawk, has several key adaptations that provide it with ample equipment to forage for fish. In flight, they have an interesting silhouette; their 5–6-foot wingspan is crooked and appears to have a droopy “M” shape, a peculiar shape suggested to make the osprey more streamlined as it plunges up to depths of one meter below the surface of the water. Dense, oily feathers prevent the bird from getting waterlogged, and spiky pads on their feet, called spicules, help grip slippery fish. To date, we have seen 130 individuals of this intriguing species as they move to the southeastern United States and parts of Central America for their winter grounds.
The northern harrier (Circus cyaneus), once commonly referred to as marsh hawk, is found in wetlands, grasslands, and meadows of North America, Europe, and Asia. This hawk has a diverse diet and will fly low towards the ground as it hunts for small mammals, birds, reptiles, or even carrion. Atypical from most hawk species, the northern harrier relies much on hearing to locate and catch prey—owl-like facial discs are used to manipulate sound direction, and their feathers are even soft, much like owls. In flight their 42–54 inch wingspan is held in a slight dihedral, and a large white rump on their dorsal side is a strong identifying characteristic. Similar to the American kestrel, the northern harrier exhibits sexual dimorphism in plumage; the male has a blue-gray coloration whereas the female favors a more modest reddish brown. We have seen 72 individuals of this remarkable bird as they travel to their winter grounds ranging from the mid-Atlantic coast all the way to Central America.
The bald eagle (Haliaeetus leucocephalus) is unique to coastal regions and other bodies of water in North America and upper Central America, perhaps making it a fitting emblem for our nation. This immense bird has an average wingspan of 6–7 feet and can live in the wild up to 30 years. Once considered to be the American fish eagle, the bald eagle has developed a more opportunistic approach to its diet as natural fish populations have decreased and will also prey upon mammals, birds, and reptiles. Their foraging technique is to first scavenge; then, if that fails, the bald eagle will pirate, or steal, food from others. It will hunt for itself as a last resort. We have seen 13 individuals migrate through, many of which have been juvenile birds. Acadia is home to a stable population of bald eagles that seems to increase during the winter months—as fresh bodies of water freeze, inland bald eagles will migrate to the open coast where food is plentiful.
With only a couple of weeks remaining in our migration season, please join us at HawkWatch from 9 a.m. to 2 p.m. (weather permitting) 200 yards down the Cadillac North Ridge Trail to welcome the rest of our traveling raptors. Bring your binoculars (the park may provide some if you do not have any) and an eager curiosity for raptors and their splendor.
September 22, 2009. Calm winds from the northeast pushed another 153 raptor migrants past HawkWatch on Monday; three of these belonged to our third most abundant species seen heading south for the winter—the broad-winged hawk. To date we have seen less than expected numbers for this species, at 191 individuals out of an average of 300. The broad-winged hawk is a member of the buteo group along with the red-tailed hawk, which we have seen flying along the Atlantic Coast migratory path this year.
Birds of prey belonging to the buteo group are similar in their broad, rounded wings and short, rounded tail that are designed to expertly soar in the air. They are particularly well made for catching and rising high up on thermals, columns of warm air. By feeding low on the food chain, both the broad-winged and red-tailed hawks escaped the seemingly ubiquitous demise of raptors in the mid-1960s as the result of pesticides, and their populations have generally stayed stable throughout the years.
Broad-winged hawks (Buteo platypterus) are the smallest and most numerous North American buteos, with an average wingspan of 36 inches. They inhabit deciduous and mixed woodlands of the eastern United States and Canada. Their typical diet is small mammals, snakes, and lizards that they hunt from a perched position or while soaring through the sky over a clearing. Their consistent presence in nature has captured the awe of many hawkwatch site participants, as the most frequent migrant seen heading towards Central and South America for their wintering grounds. A dark-outlined wing on the ventral side is the classic characteristic of broad-winged hawks, along with their wing silhouette, for identifying them in flight.
Red-tailed hawks (Buteo jamaicensis) are the most widely distributed buteo, with fourteen different subspecies spanning deserts, open fields, forests, bluffs, and urban areas of North and Central America. This common hawk has a very large wingspan of 42–54 inches that they use to fly in a slight dihedral and kite, or hover, in mid-air. The red-tailed hawk not only varies in appearance—its breast color can range from pure white to stark black—but in behavior and ecology as well. They can hunt small to medium mammals either from a high soaring position in the sky, a perched branch, or a fast pursuit near the ground and will also employ a pirating strategy in which they will steal food from others. Perhaps the raptor species most adaptable to human development, the red-tail can live in most habitats and withstand a variety of climates—hence their increasing presence in human-altered arenas. Individuals of this species living in the northern ranges will be expected to migrate south as far as they need to in accordance with prey availability. To date, at 16 individuals we have seen less than half of expected red-tail migrants , although they tend to migrate a little later in the season.
As peak migration continues through mid-September, we have seen nearly 1,800 migrants and are sure to see more! Please join us from 9 a.m. to 2 p.m. (weather permitting) 200 yards down the Cadillac North Ridge Trail at HawkWatch to welcome the rest of our traveling raptors. Bring your binoculars (the park may provide some if you do not have any) and an eager curiosity for raptors and their splendor.
September 15, 2009. The northerly winds at HawkWatch Monday provided an ample viewing of 56 migrating raptor species; there was a strong push of sharp-shinned hawks and American kestrels as they passed directly over Cadillac on their way to southern wintering grounds. Typically, American kestrels are the second most abundant migrant we expect to see; we have seen 194 so far this season. American kestrels belong to the falcon family along with the merlin and peregrine falcon, which we have seen on their migratory path as well.
Species belonging to the falcon family are linked by their sharp, sickle-shaped wings and a long, narrow tail which enable them to employ high speeds and execute unparalleled aerial maneuvers. Their role as chief predators popularized the art of falconry—hunting with a bird of prey, wherein their impeccable predatory instincts were harnessed by humans. This modern practice dates back all the way to 2000 B.C. where it originated in the Orient and, prior to recent times, was exclusive to those of noble bearing; a falcon on your wrist was a mark of wealth—a peregrine for an earl, a merlin for a lady, and a kestrel for a servant.
American kestrels (Falco sparverius) are the smallest of the falcon family with an average wingspan of 20–24 inches and thought to be the most abundant of falcons with a range spanning North, Central, and South America. Within their range, they prefer to nest in cavities of dead trees in developed open fields and tropical lowlands and even are found in urban areas. While hunting for small rodents, insects, and reptiles they will often perch on an overlook and are one of the few raptor species that can kite or hover in air. Kestrels can be considered an anomaly in the raptor world because they exhibit sexual dimorphism—males appear different from females in plumage. Male kestrels have slate blue wings and a deep rust body on their dorsal side, whereas females tend to favor a more drab brown coloration. This species is the most abundant falcon we see at HawkWatch, with an average of 705 individuals, as they migrate to the southeastern United States for the winter.
Merlins (Falco columbarius) are slightly larger than kestrels with an average wingspan of 20–26 inches, but they are drastically darker in appearance and have a much heavier wing beat. This species hunts small to medium birds, bats, insects, and small rodents in prairies and boreal and coastal forests of North America and Eurasia. To date we have seen a fraction of the expected number of merlins crossing over Cadillac (17 out of an average of 62) as they also head to the southeastern U.S. for the winter months.
Peregrine falcons (Falco peregrinus) are the largest falcon we see at HawkWatch and are a spectacular specimen with an average wingspan of 36–42 inches. This widely distributed bird, found on every continent except Antarctica, can dive at speeds from 100 to 200 mph, which is typically performed while hunting other birds. Up until 1999, peregrines were federally endangered due to their population decline in the late 1960s due to the pesticide DDT, which caused reproductive failure as a result of thinned eggshells. Since the banning of DDT in 1972 and intensive restoration efforts, peregrine numbers are on the rise. Acadia National Park and its conservation easements are home to five nesting territories. This season we have seen four peregrine migrants on their way to South and Central America, a decent number compared to the season average of 14 individuals.
As peak migration inches closer (mid-September), we have seen nearly half of our expected migrants and are sure to see more! Please join us from 9 a.m. to 2 p.m. (weather permitting) 200 yards down the Cadillac North Ridge Trail at HawkWatch to welcome the rest of our travelling raptors. Bring your binoculars (the park may provide some if you do not have any) and an eager curiosity for raptors and their splendor.
September 9, 2009. The past couple of northerly wind days have helped push more than 400 migrating raptors right over our heads on top of Cadillac Mountain, providing HawkWatch participants with great views and memories of these passing birds of prey. The most common migrant we have seen is the sharp-shinned hawk; to date we have counted 347 individuals of this species. The sharp-shinned hawk belongs to the accipiter group along with two other species, Cooper’s hawk and northern goshawk, that we expect to see fly south.
Species deemed accipiters, or true hawks, dwell in dense woodland habitats where their short, rounded wings and long tails help them dart in and around trees whilst they are in pursuit of food. Due to a general lack of awareness and use of the pesticide DDT, accipiter populations became threatened in the 1960s and 1970s. Thankfully, times have changed, and their numbers appear to be healthy again. This has been partly deduced from the annual migration count; a motivating factor for HawkWatch is to help determine population trends of these birds.
Sharp-shinned hawks (Accipiter striatus) are the smallest of the accipiters, with an average wingspan of 20–27 inches, and range throughout North and Central America. Their diet consists mainly of other birds (such as songbirds) but can include lizards, insects, and small mammals as well. In flight, the classic sharp-shinned wing beat is very quick and described as a “flappity-flappity-glide.” Once they depart from their northern breeding grounds, this blue jay-sized raptor will journey hundreds of miles down to the southeastern United States, where they will stay for the winter. This is a very common species at HawkWatch; we tend to see about 1,000 individuals migrating through annually.
Cooper’s hawks (Accipiter cooperii), or chicken hawks, are very similar in appearance to the sharp-shinned hawk and vary only slightly in size and in flight; they have a wingspan of 24–36 inches and a more pronounced head while in flight. Cooper’s hawks also tend to glide more and have a slower wing beat than the quicker sharp-shinned hawk. They hunt other birds, often game fowl, and also take other prey items such as mammals, lizards, and amphibians. Their preference for hunting poultry ironically made them targets for hunting by farmers, which contributed to their population downfall. They travel to parts of the southeastern U.S. as well as the Caribbean Islands and parts of Central America. Thus far we have seen just nine individuals migrating over Cadillac Mountain. Acadia sits towards the northern end of their range, so we only average about 33 birds per season.
Northern goshawks (Accipiter gentilis) are the largest accipiter, with an average wingspan of 36–48 inches, and can weigh between 1 and 3 pounds. Their range is limited to thick forests of the northern hemisphere, where conifer-dominated habitats are prevalent. They are formidable predators that can hunt more challenging prey: small- and medium-sized mammals like a quick snowshoe hare, as well as other birds. To date we have seen no northern goshawks begin their migration south, which is normal since they tend to migrate a little later in the season when the lack of prey forces them south. This is a fairly rare species for us to encounter at HawkWatch; we only average seven birds per season.
To spot the more common sharp-shinned hawk, catch a glimpse of the infrequent Cooper’s hawk, or search for the rare northern goshawk, please join us from 9 a.m. to 2 p.m. (weather permitting) 200 yards down the Cadillac North Ridge Trail. Bring your binoculars (the park may provide some if you do not have any) and an eager curiosity for raptors and their splendor.
September 1, 2009. Wings are to birds as opposable thumbs are to humans: indispensable and a defining characteristic. These feathered appendages are responsible for giving birds flight and the ability to soar, dive, glide, and, in the case of raptors, the ability to hunt and overcome prey. A lot of information about a raptor can be gleaned from the size, shape, and beat of wings including species identification and type of habitat it lives in. Learning to identify raptors based on these field marks is crucial, which I have come to realize in the past two weeks of HawkWatch.
The majority of the species of migrating raptors that are expected to fly overhead Cadillac Mountain this season can be broken down in three major groupings based upon similarities in wing morphology: buteos, accipiters, and falcons.
The classic buteo wing is long and broad and is accompanied by a short, wide tail that is designed for soaring. Buteos are experts at exploiting thermals (warm air bubbles) and rising up in circles high in the sky typically found near the edge of open fields and forested areas. They employ this type of flight while scanning below for small mammals that comprise a portion of their diet. On top of Cadillac, we can see many broad-winged hawks (Buteo platypterus) and red-tailed hawks (Buteo jamaicensis), the uncommon red-shouldered hawk (Buteo lineatus), and the rare rough-legged hawk (Buteo lagopus).
Accipiters have short, rounded wings and a relatively long tail that are well suited to their dense woodland habitat. These specially designed wings are highly effective in making rapid changes in direction as accipiters dart in and out of trees whilst in pursuit of their desired prey item, a small bird. Our most common accipiter seen at HawkWatch is the sharp-shinned hawk (Accipiter striatus). We may also see the Cooper’s hawk (Accipiter cooperii) and the northern goshawk (Accipiter gentillis).
The standard falcon wing is long and sharp with a long and narrow tail that was expertly crafted to execute great speeds in a dive while hunting in open habitats. As a peregrine falcon draws its wings close to its body, it can employ speeds of 100–200 mph as it chases other birds. American kestrels (Falco sparverius) are the most frequent falcon sighting on Cadillac with the merlin (Falco columbarius) and peregrine falcon (Falco peregrinus) making appearances as well.
Hopefully by studying the typical silhouette of these three groups you may become a pro at identifying raptors in flight. To put your knowledge to the test and to practice with actual birds in flight, please join us from 9 a.m. to 2 p.m. (weather permitting) 200 yards down the Cadillac North Ridge Trail at HawkWatch. Bring your binoculars (the park may provide some if you do not) and an eager curiosity for raptors and their splendor.
August 26, 2009. As summer fades into autumn, it is accompanied by many important changes like the shortening of available daylight and a drop in temperature. These two key features of seasonal shift are a strong cue for many animals; it may trigger the return to school for humans or the preparation for hibernation for black bears, but for raptors or birds of prey, it means migration.
This annual southward movement is initiated by an abundance of food, temperature, and, predominately, the amount of available daylight. A decrease in the photoperiod plays a key role in prompting certain hormones that signal raptors it is time to get ready for their seasonal journey. To prepare, raptors will consume ample amounts of food to bulk up their fat, or fuel, reserves needed to fly great distances. They can often be observed acting in a very restless manner as if they were itching to get on the “road,” or, in their case, the wind.
Strong gusts of wind from the north help push raptors to their desired destination along the eastern coast; this jagged North American boundary acts as a map for migrating birds and provides key landmarks to keep them on course. Furthermore, updrafts, vertical movements of warm air, form along mountainsides and are very favorable to birds that exploit them for a free ride. Due to this, each year raptors by the thousands fly over Cadillac Mountain, the highest peak on the eastern seaboard, which makes it an excellent site to view their journey. Since 1995, employees of Acadia National Park have watched the sky; recorded the particular raptor species and correlating abundance as the birds soar overhead; and related information to the public. HawkWatch is a vital component in assessing raptor populations throughout the nation, and there are many sites where hawk-watching is performed. Data are submitted to the nonprofit organization Hawk Migration Association of North America (HMANA) and provide researchers with a notion of the health of the population.
Since its inception in Acadia, HawkWatch has entertained numerous visitors with about eleven different species of raptors, averaging about 2,600 sightings per season. We can expect to see a variety of birds of prey atop Cadillac—falcons, accipters, buteos, eagles, osprey, and harriers, which all possess unique physical characteristics, as well as the ecological and intrinsic importance that we will discuss in later issues of Riding the Winds.
Over the next couple of months, the fall sky will become heavily spotted with migrating raptors, and with your help we may contribute to the pool of knowledge surrounding migration. Please join us from 9 a.m. to 2 p.m. (weather permitting) ~200 yards down the Cadillac North Ridge Trail to take part in HawkWatch. Bring your binoculars (the park may provide some if you do not have any) and an eager curiosity for raptors and their splendor.