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Archive for October, 2009

The final HawkWatch report of the year from Jenna Dodge:

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.

American Kestrel (NPS photo)

American Kestrel (NPS photo)

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.

a more information on raptors and migration, visit the Hawk Migration Association of North America (HMANA) website at http://www.hmana.org. 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.

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Jenna Dodge’s latest HawkWatch report:

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.

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Read Jenna Dodge’s most recent HawkWatch report:

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 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.

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