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Archive for September, 2009

Read about the flurry of hawk activity (this season nearly 1.800 hawks have already been spotted!) in Jenna Dodge’s most recent report:

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 hawk

Broad-winged hawk (NPS photo).

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 hawk (NPS photo).

Red-tailed hawk (NPS photo).

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. At 16 individuals to
date, 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 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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The weekly HawkWatch updates from Jenna Dodge:

The past couple of northerly wind days have helped push over 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 different individuals of this particular 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, are found to dwell in dense woodland habitats wherein 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 an infamous pesticide, DDT, accipiter populations became very threatened in the 1960s and 1970s. Thankfully, the times have changed and their numbers appear to be healthy again. This has been partly surmised from the annual migration count and is a motivating factor for HawkWatch, to determine population trends of these very important birds and to ensure that they continue to thrive.

Sharp-shinned hawks (Accipiter striatus) are the smallest of the accipiters with an average wingspan of 20-27 inches and ranges throughout North and Central America. Their diet comprises mainly of other birds (such as songbirds) but can take 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 over hundreds of miles down to the southeastern United States where the will stay for the winter. This is a very common species and we tend to see about 1,000 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; it has a wingspan of 24-36 inches and a more pronounced head while in flight. While in flight, Cooper’s hawks tend to glide more and have a slower wing beat than the quicker sharp-shinned. They like to hunt other birds, often game fowl, as well with the occurrence of taking other prey items such as mammals, lizards and amphibians. Their preference for hunting poultry ironically made them very popular to be hunted; farmers persecuted these birds with bullets that contributed to their population downfall. Thus far we have seen just nine individuals migrating over Cadillac Mountain and can travel to parts of the southeastern U.S. as well as Caribbean Islands and parts of Central America. Acadia sits at 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 to 48 inches and can weigh between 1 and 3 pounds. Its range is limited to thick forests of the northern hemisphere wherein conifer dominated habitats are much more preferred. 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 amount of prey forces them south. This is a fairly rare species for us to encounter migrating through since we only average 7 per season.

To spot the more common sharp-shinned hawk, catch a glimpse of the infrequent Cooper’s hawk or awe at the rarity of a 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) and an eager curiosity for raptors and their splendor.

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Learn how to identify the major raptor groups in Acadia National Park in Jenna Dodge’s latest HawkWatch report:

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.

Acciptor, buteo, and falcon wing silhouettes (NPS photo).

Acciptor, buteo, and falcon wing silhouettes (NPS photo).

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.

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