Annual counts | Distribution (time of day, week) | Changes (last 8 yrs) | Links | Articles | Sources

The Chimney Rock Hawk Watch accessible via a paved trail from the parking lot at the end of Miller Ln. off of Vosseller Ave. just north of Rt. 22 in Martinsville was started in 1990 by Christopher Aquila. Chris is the director of the hawk watch maintained by the Foundation for Avian Research and Education of NJ (FARE of NJ) Avian Migration Project. a group of birders which staff the site from September 1st to November 1st. You can learn a lot by just standing around and listening to them call out sightings.
John Kee compiles the data at chimneyrock.s5.com which is the basis for the analysis below.
There is older historical data at www.rci.rutgers.edu/~magarell/chimney_rock/
Maps: Martinsville, Washington Valley Park

These raptors (Hawks, Falcons and Eagles) are migrating from Canada and the Northern U.S. to destinations from Mexico to South America for the winter. See map at HawkMountain.org.

Many head south along the coast over Cape May NJ. Others turn west and fly over the Watchung Mountains where favorable wind currents assist them, then turn south when they get to eastern Pennsylvania. See migration below.

You will usually get 2-5 days between September 12th and 25th, where Large kettles of broad winged hawks form over Chimney Rock, occasionally with 1,000 or more birds and more than 7,000 in a day.
Hawks form "kettles" (called "boils" in NY) in thermal updrafts during migration. When they find a column of warm, rising air they stretch out their wings to rise with it. Other hawks see the kettle forming and join the crowd. The kettle grows and grows.
  As each hawk reaches altitude at the top of the thermal he sets his wings and glides away toward his destination.

There are local groups of turkey vultures which just circle around the area; Novices frequently mistake them for hawks. The vultures are just hanging around, while the hawks and eagles are moving NE to SW.

There are several resident red tail hawks, a coopers hawk and peregrine falcon that over winter here. You may see them occasionally.

 
See other pictures in hobbies/bird_watching

Totals Excluding Vultures. (see yearly totals below)

Cumulative Total Sightings

2012 as of 11/16 22,274
Year Total*  Year Total*
2013 22,309
2012 22,274 2000 28,379
2011 13,012 1999 23,075
2010 14,979 1998 18,727
2009 15,007 1997 18,127
2008 12,275 1996 31,564
2007 9,411 1995 19,545
2006 10,060 1994 17,184
2005 8,693 1993 20,727
2004 10,635
2003 6,214
2002 13,241
2001 9,763
(Including Vultures 2005-2010)
2012 appears to be another banner year. Comparisons after the large broad wing flights toward the end of Sept.
Year as of 9/25 Total for
year
Broad
winged
All
Others
Total Broad
winged
All
Others
Total Broad
winged
% of Total
1996 24,509 2,182 26,691 24,648 6,822 31,47078%
2000 20,140 2,299 22,439 21,558 6,821 28,37976%
2010 8,041 1,950 9,991 8,337 6,755 15,092 55%
2011 7,403 1,304 8,708 7,639 5,373 13,012 59%
2012 16,130 1,950 18,080 16,392 5,882 22,274 74%

Totals * thru 1996 1998 2000 2002 2003 2006 2007 2008 2009 2010 2011 2012 2013 2014
Sep 08 108 550 289 178 178 119 148 112 248 170 7696 412 286
Sep 15 1,574 4,354 1,542 874 357 754 1,269 990 4,609 3,165 634 4,408 7,696 2,541
Sep 25 26,691 11,859 22,439 8,810 1,438 5,176 5,769 8,955 11,534 10,000 8,708 18,080 19,141 7,960
Sep 30 27,399 12,909 24,711 10,125 2,768 6,843 6,486 9,405 11,850 10,379 9,246 18,646 19,737 8,160
Oct 15 29,623 15,416 27,075 11,603 5,320 8,101 8,291 10,826 14,032 13,104 11,050 20,110 20,691 9,113
Oct 31 30,984 18,195 28,175 13,107 9,110 11,424 14,474 14,544 12,791 21,337 21,664
Nov 15 31,470 18,632 28,368 13,241 6,585 9,835 9,366 11,824 14,943 15,092 13,01222,274 22,309
Nov 30 § 31,564 18,727  
Highest two days 1996 1998 2000 2002 2003 2006 2007 2008 2009 2010 2011 2012 2013
Day Sep 20Sep 24Sep 22Sep 179/309/219/16Sep 18Sep 19Sep 20Sept 17Sep 16 Sep 16
Count 17,923 5,353 7,450 4,128 1,151 1,619 3,703 4,484 3,674 4,029 4,584 7,346 8,738
Day Sep 19 Sep 10Sep 25Sep 2410/019/259/15Sep 16Sep 15Sep 14Sep 16Sep 19 Sep 15
Count 5,018 990 6,163 1,453 562 1,301 770 1,818 2,876 1,809 2,961 3,201 4,449
* less vultures
§ Count stoped on Nov. 15 in recent years

Counts for the big 12 days in September
Year 09-14 09-15 09-16 09-17 09-18 09-19 09-20 09-21 09-22 09-23 09-24 09-25
2014 1,958 155 320 550 2,344 170 8 2 1,068 906 51 0
2013 2,370 4,449 8,738 1,095 34 42 20 44 584 275 218 395
2012 9 1,404 7,346 423 13 3,201 187 33 23 1,454 902 90
2011 41 64 2,961 4,584 265 21 28 6 26 0 36 147
2010 681 1,809 36 1,045 350 281 4,029 764 26 69 33 113
2009 1,266 2876 58 111 1,626 3,674 210 10 34 27 309 866
2008 10 613 1,818 703 4,484 377 35 39 83 105 302 19
2007 13 167 140 17 770 3,703 83 135 18 20
2006 158 363 42 13 858 1,619 156 11 59 1,301
2000 287 469 1,421 1,314 68 16 803 2,633 7,450 5 1,024 6,163
Most of the variability comes from Sept 15-25 which usually accounts for 40-70% of the total; The number of sightings from Sept 25 to Nov 15 on the lowest year, 2003, was 1,800 and on the highest year, 1996, was 24,500.

Sitings on any given day will vary considerably (from only a few to 7,000 or more) depending on wind direction. See wind below.

Median hawks per day (1997-2001)

Distribution by time of day

(For a day with 100 sightings)

5 Year average sightings per day (1997-2001)
WeekMedian/
Day
LowHigh
Sep. Wk1 26 2 203
Sep. Wk2 126 1 1933
Sep. Wk3 213 8 7450
Sep. Wk4 194 0 6163
Oct. Wk1 145 3 566
Oct. Wk2 77 1 448
Oct. Wk3 106 0 492
Oct. Wk4 44 0 419
Nov. Wk1 29 0 156
Nov. Wk2 7 0 354
Numbers vary widely depending on
weather. see table to right.
Counts by Wind Direction (Birds/Hr.)
W 65
WNW 92
NW 103
NNW 146
N 19
NNE 16
NE 159
E 285
SE 4
SSE 4
S 4
SSW 2
SW 6
WSW 34

(Weather)
* Total includes vultures starting in 2005.

Wind:
Typically winds will be favorable the day after a front moves thru.
The stronger the wind, the closer the hawks will fly to the treetops where substantially less air turbulence occurs, and the more easily the hawks will be seen.
A textbook viewing day for hawk watching will occur in Pennsylvania, New York, and New Jersey under the following conditions: the passage of a low pressure system to the north over the New England states; an advancing cold front moving south from Canada; the northwest winds for a few consecutive days. Under these conditions migration would occur along northerly facing slopes along the ridges.
When a high pressure system is positioned in the area, hawks disperse over large areas often resting and hunting while awaiting an increase in windspeed and thermals. As the high moves eastward, a southerly airflow moves in and hawks return using updrafts along south facing slopes.
Note: At Chimney rock even with the south facing first range of the Watchung mountains, the counts are low with a south wind.
Source: Autumn Raptor Migration by Bill Streeter
Falcons (Peregrine, Kestrel, Merlin), with their sleek profile are not adapted for soaring flight, so are not affected by wind direction.

Counts by Species: (thru 2005) (see changes below)

Species Highest 2000 Peak Dates Peak Hrs.
Broad-winged 24656 21588 9/14-9/25 9-5
Sharp-shinned 4597 3303 9/24-10/19 10-6
Am. Kestrel 2000 1514 9/23-10/19 10-6
Red-tailed 908 127 10/29-11/10 10-4
Osprey 945 598 9/15-9/28 9-6
Cooper's 564 395 10/10-10/19 10-5
N. Harrier 474 199 9/13-10/10 10-5
Red-shouldered 401 109 10/10-11/2 10-3
Merlin 338 277 9/13-10/11 11-7
Bald Eagle 110 94 9/13-9/20 9-6
Peregrine Falcon 113 64 10/3-10/10 10-5
Golden Eagle 18 9 10-19-22 12-5
N. Goshawk 15 1 10/20-11/7
Rough-legged 3
One day count distribuition for
Sep. 15-30
(Av. 1997-2001)
Count Days
1-19 1
20-49 2
50-99 2
100-199 3
200-499 2
500-999 3
1000-1999 2
2000-7500 1
Probabliliy
1-99 1/3
100-499 1/3
500+ 1/3
Sources:
- Species Records thru 2005 by John Kee
- A Five Year Analysis of Autumn Hawk Migration at Chimney Rock, Martinsville, N.J. (1990-1994) , by Christopher D. Aquila & Steven B. Byland
- Species Records Page and Flight Distribution
Pictures in Bird Watching.

Decline

Species
Chimney Rock (Average birds per year)
Cape May *
1996-20002004-2008 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).
See:
"Using Autumn Hawk Watch to Track Raptor Migration and to Monitor Populations of North American Birds of Prey" - Article on Sharp Shinned migration decline - USDA Forest Service Gen. Tech. Rep. PSW-GTR-191. 2005

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-stopping—perhaps the result of increased use of bird feeders as hunting habitat by sharp-shins—and 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 50,00035,267
Hawk Mountain Kempton, PA 20,00021,708
Chimney Rock Martinsville, NJ 19,00013,241
Montclair Montclair, NJ 12,00011,340
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






Migration:
Typical Broad winged hawks migration:
Sept. 10 - Lake Ontario
Sept. 15 - Mass.
Sept. 17 - NJ and PA
Oct. -1   - Texas
They may not fly on some days because of weather or the need to refuel so the average from above is 65-90 miles per day.
Red-Tails and others tend to be later.

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.

In some species of raptors, every individual migrates. In other species, only part of the population migrates and some individuals remain on the breeding grounds. Other species are completely sedentary. Overall, about 45 percent of all raptor populations migrate.

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.
See also Migration Path | Hawk Mountain Sanctuary

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
Ospreys, Peregrine falcons Pacific coast of S. America & Bolivia
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/

See also:
Chimney Rock Quarry
25 Nature Spectacles in New Jersey, by Joanna Burger and Michael Gochfeld


Return to: Martinsville Information

last updated 27 Sept 2014