Decline

Species	Chimney Rock (Average birds per year)					Cape May *
	1996-2000		2004-2008		Decline/ Increase		% of total (2004-8)	Decline/ Increase
	Average #	% of total	Average #	% of total
Broad-winged	15,688	65.6%	5,980	53.5%	-62%		3%	-54%
Sharp-shinned	3,876	16.2%	2,458	22.0%	-37%		45%	-47%
Am. Kestrel	1,724	7.2%	779	7.0%	-55%		13%	-48%
Osprey	733	3.1%	468	4.2%	-36%		6%	-49%
Cooper's	475	2.0%	467	4.2%	-2%		15%	32%
N. Harrier	278	1.2%	213	1.9%	-23%		3%	-40%
Merlin	276	1.2%	197	1.8%	-29%		5%	-25%
Red-shouldered	242	1.0%	184	1.6%	-24%		1%	4%
Red-tailed	271	1.1%	155	1.4%	-43%		5%	-48%
Bald Eagle	90	0.4%	129	1.2%	44%		0.8%	46%
Peregrine Falcon	77	0.3%	98	0.9%	27%		4%	0%
Golden Eagle	11	0.05%	14	0.13%	31%		0.05%	-19%
N. Goshawk	7.0	0.03%	2.4	0.02%	-66%		0.1%	-48%
Rough-legged	1.2	0.01%	0.6	0.01%	-50%		0.002%	-82%
Unidentified
Raptor	86	0.4%	16	0.1%	-82%
Acciptor	42	0.2%	11	0.1%	-75%
Buteo	19	0.1%	5	0.0%	-72%
Falcon	12	0.1%	5	0.0%	-58%
Total	23,909		11,182		-53%		33,511	-39%

* Cape May % of total: 2004-2008; Decline: 1996-2000 vs 2004-2008. See Cape May page
Sources: chimneyrock.s5.com by John Kee
      Hawk Migration Assiciation of North America's (HMANA) hawkcount.org

Decline:
The declines vary by species.
Broad winged hawks, Sharp-shinned hawks, American Kestrels, Osprey and Red-tailed hawks had the largest declines of 44-60%.
Cooper's hawks increased. Bald eagles have increased by about 45% as they continue to recover from their decline due to DDT (1946-1972), loss of habitat and hunting.
Most others declined in the 25-25% range.

There are a variety of factors which more experienced birders have proposed to account for the decline. I couldn't find any definitive studies.

• Weather patterns - From 1995 to 2000 Chimney Rock counts were down in years when Hawk Mountain counts were up. Could weather be pushing the birds further west?
• More backyard feeders and loss of neotropical prey has been proposed as reason for sharp-shin migratory short-stopping (Wintering at more northerly latitudes). See articles below.
• Reduction of habitat in the north.
• Regional drought in the late 1990s resulted in reduced stream flows and water levels, which in turn affected fish populations in the southwest.
• Bird flu and West Nile Virus. An October, 2009 USGS report "North American Raptors Susceptible to Avian Influenza" says Kestrels are extremely susceptible to highly pathogenic avian influenza (H5N1). Other endangered and threatened raptors may also be at risk if the virus reaches North America. However it does not indicate there is currently a problem.
  Between August and October 2002, The U. of Minn. Raptor Center admitted 70 birds suspected of having the West Nile virus. About 60 of those died. More birds are dying in the Midwest than in the East
  See "West Nile Virus: The Latest Threat To Raptors", May 2003, from the Delaware Valley Raptor Center.
• Climate change has been suggested as a factor, but that is probably based on Feb. 2009 Audubon Society study showing many birds wintering an average of 35 miles farther north because of a 5° F rise in the average January temperature in the US over the last 40 years. This does not account for birds wintering more than 1,000 miles farther north where where the winter low averages 40° F cooler (0° in southern NY vs 40° in northern Mexico).

Demography and Populations -- Sharp-shinned Hawk -- Birds of North America Online at Cornell says:. (Requires subscription: $5/mo, $42/yr)
"Sharp-shinned hawks are the most difficult accipiter and among the most difficult birds to census in North America."
"Declines in counts at migration watchsites in e. North America from 1940s to early 1970s almost certainly due to widespread use of DDT."
"Declines in the 1980s and early 1990s initially were attributed to various factors acting singly or in concert: environmental contaminants (mainly organochlorines), migratory short-stopping, natural population cycles, depressed populations of Neotropical migratory prey species, and the aging of eastern forests. Recent analyses of concurrent Christmas Bird Count data from the region, however, have revealed significant increases in numbers of Sharp-shinned Hawks overwintering in areas north of the watchsites in question (i.e., e. Canada and the ne. U.S.), strongly suggesting that the declines are due to migratory short-stoppingÑperhaps the result of increased use of bird feeders as hunting habitat by sharp-shinsÑand not to an overall decline in eastern populations (Dunn and Tessaglia 1994, Duncan 1996, Viverette et al. 1996)."
Viverette, C. B., S. Struve, L. J. Goodrich, and K. L. Bildstein. 1996. Decreases in migrating Sharp-shinned Hawks at traditional raptor-migration watchsites in eastern North America. The Auk 113:32-40.

Conservation Status Report - Sharp-shinned Hawk, 2007 at HawkMountain.org states:
"From 1974 to 2004, migration counts declined a statistically significant 1.1 % per year at Hawk Mountain Sanctuary, Pennsylvania and 4.5 % per year at Cape May Bird Observatory, New Jersey."
"The decline in numbers at Cape May might indicate declined reproductive success, as most individuals counted at Cape May Point are juveniles."
"The discrepancy between migration trends (lower) and those from CBCs (Christmas Bird Counts) (higher) may be due to migratory short-stopping."

Fall Raptor Migration over Lake Erie Metro Park (increasing)
State of the Birds - The 2009 Report from the Interior Dept. shows that Wetland birds are increasing while Grasland and Aridland birds are declining.

Saving Migratory Birds for Future Generations: The Success of the Neotropical Migratory Bird Conservation Act, Compiled by American Bird Conservancy, May 2009

A Feb. 2009 Audubon Society study found that more than half of 305 birds species in North America, a hodgepodge that includes robins, gulls, chickadees and owls, are spending the winter about 35 miles farther north than they did 40 years ago.
Over the 40 years covered by the study, the average January temperature in the United States climbed by about 5 degrees Fahrenheit, which they speculate may be the reason. (Hawks were not mentioned in the summary I saw.)

Potential Impacts of Global Climate Change on Bird Communities of the Southwest by Charles van Riper III, Mark K. Sogge, and David W. Willey Biological Resources Division U.S. Geological Survey

Species mix Chimney Rock vs Cape May:
Buteos (Broad Winged hawks in particular) like to exploit updrafts off of ridges, hence the large numbers at Chimney Rock on the first range of the Watchung Mountains.
Falcons (Peregrine, Kestrel, Merlin) rely more on their own powers of flight and do not need mountain updrafts.
Accipiters (Sharp-shinned, Coopers Hawks, ...) and falcons tend to follow the shorelines, hence higher counts at Cape May.

Other Hawk Watch Sites:
Counts are for Fall only.
See map at: www.rci.rutgers.edu/~magarell/chimney_rock/about_cr.html

Site	Location	Median Fall Totals	2002 Total
Cape May	Cape May, NJ	50,000	35,267
Hawk Mountain	Kempton, PA	20,000	21,708
Chimney Rock	Martinsville, NJ	19,000	13,241
Monclair	Monclair, NJ	12,000	11,340
Militia Hill	Fort Washington State Park, PA	9,000
Wildcat Ridge	Hibernia, NJ	9,000	7,011
Racoon Ridge	Blairstown (Hemlock Glen), NJ	15,000	* 4,238
Scotts Mountain, Merrill Creek	Washington, NJ	9,000	8,737
Sunrise Mountain	Stokes State Forest, Branchville, NJ		* 4,678
Bake Oven Knob	Germansville, PA		20,778

(Median 1998-2002)
* Racoon Ridge only counted for 9 days in Sept. 2002
* Sunrise Mountain only had counts for 13 days in Sept. 2002
Some sites keep Spring totals also (Feb-May) which are about 1/3 of Fall totals.
Other New Jersey sites at: New Jersey Sites, Hawk Migration Assiciation of North America (HMANA)
and the JerseyBirds mail list.

Scherman-Hoffman Wildlife Sanctuary (New Jersey Audubon Society)
Bernardsville, (908) 766-5787

Hawks will fly around 10 hours per day and travel from 100 to 250 miles. Ducks and geese might travel as much as 400 to 500 miles per day.
Many species of wading and swimming birds are able to feed at all hours, they migrate either by day or night. Soaring birds such as broad winged hawks only migrate during the day to take advantage of thermals.

Raptors fly from 29-40 MPH at an elevation of 700 - 4,000 ft.

Migration may have as much to do with availability of food as weather.

Wintering locations:

Broad-wings	Central America and N. South America
Sharp-shinned	Southern US, Central America
Coopers	Gulf coast, Mexico to Honduras
Kestrel	Coastal Mexico, Central America

See:
Flyways And Byways at 10000birds.com
New Jersey Osprey Project
Tails of Birding: Where Do the Hawks Go?
Random House Atlas of Bird Migration: Tracing the Journey's of the World's Birds, 1995

Terms:
BBS - Breeding Bird Survey
CBC - Christmas Bird Count

Articles
- John Kee - Species Records thru 2005
- Christopher D. Aquila & Steven B. Byland - A Five Year Analysis of Autumn Hawk Migration at Chimney Rock, Martinsville, N.J. (1990-1994)
- Kyle McCarty and Keith L. Bildstein - "Using Autumn Hawk Watch to Track Raptor Migration and to Monitor Populations of North American Birds of Prey", USDA Forest Service Gen. Tech. Rep. PSW-GTR-191. 2005
- Robyn Worcester, Ron Ydenberg - Cross-Continental Patterns In The Timing Of Southward Peregrine Falcon Migration In North America, 2008,
- Johnd Elong, Stephen W. Hoffman - Differential Autumn Migration Of Sharp-Shinned And Cooper's Hawks In Western North America

Links
Other Links:
Current Counts at Hawk Migration Assiciation of North America's (HMANA) hawkcount.org (NJWMP at Chimney Rock)

Bird Watching Here
Cornell Lab of Ornithology
  Cornell's All About Birds
The Hawk Conservancy Trust
Chimney Rock Hawk Watch: Other Birding Sites
Data entry overload? Learn eBird tricks and tips! - eBird.org
Binoculars,
Birding and Raptors in Northwest New Jersey at www.njskylands.com
Links at main Hawk Watch Page
Bird Watching in hobbies
Squirl Proof Bird feeders
Autumn Raptor Migration
NPWRC :: Migration of Birds

Sources:
chimneyrock.s5.com John Kee.
www.rci.rutgers.edu/~magarell/chimney_rock/