A Five Year Analysis of Autumn Hawk Migration at Chimney Rock, Martinsville, N.J.

by CHRISTOPHER D. AQUILA & STEVEN B. BYLAND

Introduction

1994 marked the fifth consecutive year of the Chimney Rock Hawk Watch. It was organized in 1990 by Christopher Aquila and is currently maintained by Aquila and a highly competent team of 5 individuals including co-author Steve Byland. The mass of hawk migration data we have accumulated over the last 5 years, results from the most consistent and formal hawk watch effort so far attempted at this location. However, it is by no means the first or only hawk counting that has taken place at Chimney Rock. The location has been a known hawk lookout for decades, with occasional counts conducted for at least the last 45 years. It is in fact mentioned in print as far back as 1951 by Olin Pettingill in his classic book A Guide to Bird Finding East of the Mississippi, as one of the best lookouts for watching hawk flights in the Watchung Mountains.

As with most hawk counts, our main purpose in conducting the Chimney Rock Hawk Watch is to gain knowledge and insight on long-term population trends of migrant Raptors. The data we collect may prove to be invaluable in their regional protection and conservation. It could also play an integral role in the future establishment of local land management practices.

The objective of this paper is to present a clear, concise layout of the migration data we have recorded at the watch during the last 5 years. It is hoped that the reader will not only come away with a better understanding of the statistical aspects of the data, but also of the regional significance of the Chimney Rock/Watchung Ridge Corridor as a flight path for migrating hawks.

Location

The Chimney Rock Hawk Watch is conducted from a single fixed location on the First Watchung Ridge, near its western terminus in Martinsville, New Jersey. The count site can best be described as a rocky basaltic outcrop, approximately 250' above Chimney Rock Road and the adjacent Middle Brook. The overall elevation at the count site is approximately 350' above sea level. The property is owned by the Somerset County Park Commission and is officially known as the Washington Valley Park Tract

Methods and Procedures

The hawk watch is conducted September 1st-December 1st of each year. Through the season, the count is maintained by 5-6 skilled hawk counters. Each count day is assigned one hawk counter who is responsible for recording all migrant hawks by species, that pass through the general airspace of the count site. It is important for the counter to be able to differentiate between migrant hawks and "resident" birds that might be in the vicinity. This is generally accomplished by observing the flight behavior of the bird. Most migrants maintain a steady point-to-point flight over the watch, and are rarely in view for more than a minute before vanishing into the southwestern sky. On the other hand, resident birds such as Red-tailed Hawks circle the count site all day at low altitudes, never really leaving the area. After one visit, the observer becomes well aware of this pattern and considers it in making future decisions. The only modification related to this topic was the exclusion of Turkey Vultures from the daily count, due to the sheer number of resident birds regularly observed at the count site. As pointed out, it is clearly possible to distinguish between migrant and resident birds, when you are dealing with 3-5 resident Red-tailed Hawks, as is the case at Chimney Rock. However, accuracy is all but lost when you attempt to single out migrant Turkey Vultures among the 15-18 resident vultures regularly observed throughout the airspace of the count site. After taking our count accuracy into consideration, Turkey Vultures have not been logged in the daily count since 1991, our second season.

The counter is not only responsible for maintaining a consistent and accurate daily record of the hawk flight, but an hourly record of weather conditions as well. Although the counter may be assisted and advised by any number of other qualified individuals present at the watch, all final decisions are recorded by the assigned hawk counter

When the season is completed, the cumulative totals are compiled and sent off to the hawk Migration Association of North America (HMANA), an organization responsible for standardiz ing and coordinating hawk watches across the continent. HMANA will register and record the totals for all the hawkwatches, then publish the results in their bi-annual journal, Hawk Migration Studies.

Coverage at Chimney Rock has ranged from a low of 44 days in 1992, to a high of 88 days in 1994. As with most hawk watches, the consistency of coverage is not only weather dependent, but subject to the availability of human resources. To deal with this problem, a research assistant program was developed in cooperation with faculty members at Cook College-Rutgers University. Prospective students are field trained in the necessary skills and techniques they will need to help conduct the watch. Each student is then assigned a day to assist with the count. To maintain identification skills, consistency, and accuracy, members of the team work closely with each student, regularly monitoring and field testing them throughout the season. From 1-3 college credits are earned depending on the number of hours the student has logged at the watch. An evaluation of each student's overall performance is conducted at the end of the season.

TABLE A
Annual Totals - Chimney Rock Hawk Watch

                       |      1990      |      1991      |      1992      |      1993      |      1994      |     Grand Total
 Species               | Totals       % | Totals       % | Totals       % | Totals       % | Totals       % | Totals       %
-----------------------+----------------+----------------+----------------+----------------+----------------+----------------
 Turkey Vulture        |   N/A*    N/A* |     63    1.1% |   N/A*    N/A* |    N/A*   N/A* |    N/A    N/A* |     63    0.1%
 Osprey                |    147    3.0% |    198    3.4% |    229    3.4% |    536    2.6% |    644    3.7% |  1,754    3.2%
 Bald Eagle            |      7    0.1% |     10    0.2% |     14    0.2% |     60    0.3% |     39    0.2% |    130    0.2%
 Northern Harrier      |     38    0.8% |     46    0.8% |     82    1.2% |    174    0.8% |    268    1.6% |    608    1.1%
 Sharp-shinned Hawk    |  1,122   23.2% |  1,495   26.0% |  1,703   25.6% |  3,554   17.1% |  4,042   23.5% | 11,916   21.6%
 Cooper's Hawk         |     26    0.5% |     32    0.6% |     85    1.3. |     129   0 6. |     282   1.6% |    554    1.0%
 Northern Goshawk      |      0    0.0% |      0    0.0% |      0    0.0% |      3    0.0% |      3    0.0% |      6    0.0%
 Red-shouldered Hawk   |     18    0.4% |     15    0.3% |     32    0.5% |    165    0.8% |    189    1.1% |    419    0.8%
 Broad-winged Hawk     |  2,789   57.7% |  3,059   53.3% |  3,423   51.5% | 14,012   67.6% |  8,555   49.8% | 31,838   57.7%
 Red-tailed Hawk       |    151    3.1% |    187    3.3% |    196    2.9% |    476    2.3% |    850    4.9% |  1,860    3.4%
 Rough-legged Hawk     |      0    0.0% |      0    0.0% |      0    0.0% |      1    0.0% |      3    0.0% |      4    0.0%
 Golden Eagle          |      2    0.0% |      4    0.1% |      3    0.0% |      9    0.0% |      8    0.0% |     26    0.0%
 American Kestrel      |    442    9.1% |    525    9.1% |    734   11.0% |  1,219    5.9% |  1,797   10.5% |  4,717    8.6%
 Merlin                |     36    0.7% |     51    0.9% |     59    0.9% |    186    0.9% |    205    1.2% |    537    1.0%
 Peregrine Falcon      |      7    0.1% |     10    0.2% |     23    0.3% |     60    0.3% |     40    0.2% |    140    0.3%
 Unidentified Raptor   |     49    1.0% |     45    0.8% |     66    1.0% |    143    0.7% |    259    1.5% |    562    1.0%
-----------------------+----------------+----------------+----------------+----------------+----------------+----------------
   Total Raptors       |  4,834  100.0% |  5,740  100.0% |  6,649  100.0% | 20,727  100.0% | 17,184  100.0% | 55,134  100.0%
-----------------------+----------------+----------------+----------------+----------------+----------------+----------------

 Total Days                     68               55               44               75               88              330
 Total Hours                   340              275              264              400              658            1,937

 * Not Included In Daily Counts

TABLE B
Peak Flight Days - Chimney Rock Hawk Watch


                          |               1991               |               1992               |               1993               |               1994               |
 Species                  | Number     Date(s)               | Number     Date(s)               | Number     Date(s)               | Number     Date(s)               |
--------------------------+----------------------------------+----------------------------------+----------------------------------+----------------------------------+
 Osprey                   |     18     9/29                  |     30     9/13                  |     66     9/19                  |     91     9/15 *                |
 Bald Eagle               |      2     9/27 & 10/7           |      4     9/13                  |     18     9/19 *                |      7     9/15                  |
 Northern Harrier         |      7     10/12 & 10/19         |     11     9/12                  |     15     11/2                  |     24     9/15 *                |
 Sharp-shinned Hawk       |    168     10/12                 |    182     10/12                 |    294     9/24                  |    352     10/2 *                |
 Cooper's Hawk            |      7     9/27 & 10/19          |      7     9/20 & 10/1           |     16     10/10                 |     42     10/ *                 |
 Northern Goshawk         |      -     -                     |      -     -                     |      1     10/29, 11/7 & 11/16 * |      1     11/16, 11/26 & 11/29 *|
 Red-shouldered Hawk      |      2     10/12, 20, 25 & 28    |      8     11/1 & 11/7           |     19     11/16 *               |     18     11/12                 |
 Broad-winged Hawk        |  1,325     9/20                  |  1,922     9/12                  |  8,425     9/20 *                |  3,962     9/18                  |
 Red-tailed Hawk          |     36     10/13                 |     35     11/1                  |    121     11/7                  |    240     11/10 *               |
 Rough-legged Hawk        |      -     -                     |      -     -                     |      1     11/7 *                |      1     11/10, 11/17 & 11/19 *|
 Golden Eagle             |      2     10/26                 |      1     10/24, 10/25 & 11/7   |      2     10/25                 |      3     11/10 *               |
 American Kestrel         |     52     10/7                  |     95     9/19                  |    194     9/19                  |    224     9/18 *                |
 Merlin                   |      8     10/7                  |     12     10/12 & 10/17         |     26     9/19 *                |     24     9/15                  |
 Peregrine Falcon         |      5     10/5                  |     13     10/3 *                |     11     10/8                  |      4     10/10                 |
--------------------------+----------------------------------+----------------------------------+----------------------------------+----------------------------------+
 Peak Flight Date         |                                  |                                  |                                  |                                  |
   (All Species Combined) |  1,600     9/20                  |  2,157     9/12                  |  8,893     9/19 *                |  4,557     9/18                  |

 * Represents All-Time Peak Flight Day

TABLE C
1994 Hawk Watch Totals For Regional Inland Sites


---------------------------------------------------------------------------------------------------------------------------------------------------
                             Chimney                  Racoon     Militia      Hawk       Central      Quaker                   Mount
 Species                       Rock     Boontoon       Ridge       Hill     Mountain       Park        Ridge      Butler       Peter   Montclair
---------------------------------------------------------------------------------------------------------------------------------------------------
 Black Vulture                   N/A *        23         N/A *        70          56           2           0           2           4           1
 Turkey Vulture                  N/A *       386         N/A *       381         196         161         354         223          72         774
 Osprey                          644         237         159         222         472         690         393         234         127         430
 Bald Eagle                       39          28          91          19          80          48          29          17          11          38
 Northern Harrier                268          88         143          83         296          54         166          99          55         156
 Sharp-shinned Hawk            4,042         633       1,779       1,116       4,931         916       2,128       1,383       1,078       2,567
 Cooper's Hawk                   282          44         113         155         573          94         165         198         134          83
 Northern Goshawk                  3           0          24           4          31           7           5           7           1           1
 Red-shouldered Hawk             189          33         154          52         264         228         136          28          37         208
 Broad-winged Hawk             8,555      12,160       7,321       3,056       3,513       9,028      18,180      10,377       3,381      20,893
 Red-tailed Hawk                 850         554       3,364         787       4,424         610         289         259         577       1,446
 Swainson's Hawk                   0           1           1           1           0           0           0           1           0           0
 Rough-legged Hawk                 3           0           2           2           9           3           0           1           0           1
 Golden Eagle                      8           3          38           3          85           1           7           4          12           4
 American Kestrel              1,797         863         280         279         688         488         842         461         321         662
 Merlin                          205           5          17          25          54          52          31          22          15          29
 Peregrine Falcon                 40           3          10          20          24          37           9           7           7          11
 Unidentified Raptor             259           6          39         101         250          70          79          32         100         103
---------------------------------------------------------------------------------------------------------------------------------------------------
   Total Raptors              17,184      15,067      13,535       6,376      15,946      12,489      22,813      13,355       5,932      27,407
---------------------------------------------------------------------------------------------------------------------------------------------------
   Total Days                     88         104          64          92         129         114          76          68          70          97
---------------------------------------------------------------------------------------------------------------------------------------------------
   Total Hours                   658         542       385.5         668       1,004         647         583         504         427         672
---------------------------------------------------------------------------------------------------------------------------------------------------
   Hawks Per Hour                 26          28          35          10          16          19          39          26          14           41
---------------------------------------------------------------------------------------------------------------------------------------------------

 * Not Included In Daily Counts At This Location

Results

In the first five years of the Chimney Rock Hawk Watch, 55,134 hawks of 15 different species have been recorded. The count during this period covered 330 days, spanning 1,937 total hours. Table A contains all significant cumulative totals recorded for each year the watch has been in operation. Table B is a cumulative breakdown of peak flight days for all species recorded at the watch. Of particular interest are the 18 Bald Eagles and 8,425 Broad-winged Hawks recorded on 9/19 & 9/20/93, respectively. These figures are obviously impressive by themselves, but they only alert the reader to a portion of the overall hawk flight recorded during that two day period. When the final numbers were calculated, it turned out to be the greatest single period of migration that we ever recorded at the watch. In 22 hours (11 hours logged each day), we counted 88 Ospreys, 28 Bald Eagles, 20 Northern Harriers, 440 Sharp-shinned Hawks, 11 Cooper's Hawks, 6 Red-shouldered Hawks, 12,712Broad-winged Hawks, 5 Red-tailed Hawks, 1 very early Golden Eagle, 352 American Kestrels, 32 Merlins, 7 Peregrine Falcons, and 10 unidentified birds for a grand total of 13,712 birds, approximately 66% of the 1993 season total of 2O,727 hawks recorded in 22 hours of hawkwatching. While greater individual totals have occurred since, it is unlikely that another movement of this magnitude will occur again in the near future.

Table C compares 1994 season totals at Chimney Rock to those of other regional inland hawk watches. Although all of the individual species totals logged at Chimney Rock compare very well to other established sites, it is the overall falcon totals that make Chimney Rock unique in the region. With 1,797 kestrels and 205 Merlins counted in 1994, we logged more than twice the number of kestrels and nearly 4 times as many Merlins as any other inland hawk watch in the region. The 40 Peregrines we tallied was also substantially more than any other regional watch, although the Central Park count site did come close with a respectable 37 for the season. In fact, for two consecutive years Chimney Rock has ranked as one of the top 10 inland hawk watches in North America (north of Mexico) for combined kestrel, Merlin, and Peregrine totals, (Hawk Migration Studies, 1993 & 94). This is a rather impressive statistic when you consider that there are approximately 160 inland hawk watches throughout the continent. As to where they are migrating from enroute to Chimney Rock, it is believed that the majority of these falcons are those which are migrating either southwest along the shore of Connecticut or west along both the north and south shores of Long Island. When these birds reach the greater New York City Metropolitan Area (as most of them will do), they can apparently see the First Watchung Ridge out ahead of them. At this point, instead of flying south along coastal New Jersey, some decide to fly westward (inland), utilizing the Watchung Ridge. This eventually brings these birds over Chimney Rock, making it an alternate inland flight path for a large number of falcons typically associated with coastal migration.

Conclusion

Based on the 5 years of cumulative information presented in this paper, Chimney Rock has shown itself to be a rather significant hawk migration corridor. Table C emphasizes this by showing where Chimney Rock stands in comparison to other hawk watches in the region. The extraordinary number of falcons logged each year at the watch make Chimney Rock one of the top inland locations for falcon migration, not only for the region, but for all of North America as well. Our goal is to continue to lead the hawkwatch on what we feel is a very consistent positive path into the future.

References

Hawk Migration Association of North America. 1993.
Continental Summary.
Hawk Migration Studies, 20, No. 1: 15-64.

Hawk Migration Association of North America. 1994.
Continental Summary.
Hawk Migration Studies, 19, No. 1: 19-69.

Pettingill, 0. 1951.
A Guide to Bird Finding East of the Mississippi.
Oxford University Press, New York

Acknowledgments

We wish to thank the following individuals and organizations who have been instrumental in the success of the Chimney Rock Hawk Watch. They are: Rose MacConnell and the rest of the Somerset County Freeholders; Ray Brown and Jane Butts as well as the entire Somerset County Park Commission for their overall support and permission to conduct the watch at Chimney Rock, Mike Anderson and the New Jersey Audubon Society; Dr. James Applegate of Cook College; and Wayne and Else Greenstone of the Montclair Hawk Watch.

The following people deserve special recognition and thanks for their direct participation in the count. Without their assistance and know-how, the count could not be conducted. Anne Blessing, Linda Byland, David Dendler, Patty Dexter, Linda Federico, Don Freiday, Sharon Fullagr, Darryl Gibson, George Hall, Gary Himber, Henry Kielblock, Paul Lauber, Doug Max, Al Pochek, Anne Purcell, Kerry Robinson, Bob Sanders, David Shealer, Todd Watts, Libby Wolf, David Womer, and Joe Zurovchak.

We would also like to thank all the Cook College students who have assisted with the count: Jill Hoffman, Chris Jennelle, Cindy Loveland, Sherry Meyer, Bill Morris, Kelly Volansky, James Vollozi, and Maritza Zuleta. And, to the many other hawk enthusiasts who visit Chimney Rock each fall and help us scan the horizons.

This article originally appeared in the Summer 1995 issue of Records of New Jersey Birds. It is reproduced here with the permission of the authors.

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