 |
 |
 |
 |
 |
 |
 |
|
ABUNDANCE OF WHITE-TAILED DEER
(ODOCOILEUS VIRGINIANUS) WITHIN
VALLEY FORGE NATIONAL HISTORICAL PARK AND MOVEMENTS RELATED TO SURROUNDING
PRIVATE LANDS
Technical Report NPS/NERCHAL/NRTR-03/091
M. J. Lovallo1 and Walter M. Tzilkowski
School of Forest Resources
The Pennsylvania State University
University Park, PA 16802
1current address:
Pennsylvania Game Commission
2001 Elmerton Avenue
Harrisburg, PA 17110
February 2003
U.S. Department of the Interior
National Park Service
Northeast Region
Philadelphia, Pennsylvania
_______________________________________________________
Executive Summary
In the metropolitan
and suburban landscape of southeastern Pennsylvania, the abundance of
white-tailed deer (Odocoileus virginianus) is of considerable public
interest and debate. The population of white-tailed deer at Valley Forge
National Historical Park (VAFO) is perhaps the most well known regional
example. To provide information for the planning and management of VAFO,
a study of white-tailed deer within the park and adjacent suburban lands
was conducted during 1997, 1998, and 1999. Objectives were to determine
1) the abundance of deer within the current (1997) park boundary, 2)
the home range and movements of deer inside the park and on adjacent
land, and 3) the type of vegetative cover used more or less than expected
by deer at various times.
A complete census of all individuals in a large free-roaming deer population
is not feasible, therefore, a mark-resight technique was employed to
estimate the number of white-tailed deer within the park. One hundred
twenty deer were captured and marked during the three years. Ninety-four
females and 19 males were equipped with radio-collars or ear-tag transmitters.
Seven females wore vinyl collars with no transmitter attached. In 1997,
45 deer were captured and marked, 36 within the park and 9 on private
land. Fifty-five deer were captured and marked in 1998, 37 within the
park and 18 on private land. And in 1999, 20 deer were captured and
marked, 12 within the park and 8 on private land.
Eight geographic sampling units, called compartments, were defined and
used to count deer. A sighting index was derived from the ratio of marked
individuals seen to the number of marked individuals known from radio
telemetry to be in the area. Using the sighting index, a population
estimate of deer within the park was computed. Population estimates
could not be computed for adjacent lands primarily because buildings
hindered the sighting of deer. Deer were counted three times in April-May
of each year of the three-year study. The mean of these counts was 557
deer in 1997, 536 in 1998, and 577 in 1999. When the sighting index
was applied, estimates of the deer population in the park were 772 in
1997, 913 in 1998, and 1,016 in 1999. The mean annual density was 70/km2
(181 deer/mile2).
Annual home ranges for 90 females and 15 males were determined. Individual
locations of deer were determined using a hand-held or vehicle-based
telemetry unit that received a signal from transmitters on deer collars
and ear tags. The 100% minimum convex polygon and the 95% adaptive kernel
home range estimators were used to determine annual home ranges. Most
annual home ranges were less than 200 hectares (498 acres), with the
largest being those of juvenile males. Average female annual home range
area was 100.7 hectares (249 acres), based on the minimum convex polygon
method.
Average distance traveled beyond the park boundary was 122 meters (401
feet) for the 71 females that had greater than 50% home range within
the park. The maximum distance that one of these females traveled beyond
the park boundary was 1,094 meters (3,589 feet). Locational data for
males were limited because of the small number equipped with radio transmitters.
Of 15 annual home ranges calculated for males, 13 were almost completely
inside the park (98%-100%). The remaining two annual home ranges were
greater than 50% outside the park.
Vegetative cover preferred by monitored deer was investigated. Average
forest cover within home ranges of females was 49, 43, and 43% for 1997,
1998, and 1999, respectively. Home range meadow cover averaged 37, 41,
and 41%, respectively, for those same years. The remaining cover was
residential and agricultural. Home ranges of males averaged 54, 52,
and 51% forest cover and 28, 31, and 25% meadow cover, respectively,
for the three years. Both males and females spent more time in meadows
during the night and in forest cover during the day.
Spatial distribution, or landscape use, of deer that had greater than
50% of their home range within the park indicated high use in the central
and southwestern portion of the park. In the southwestern corner of
the park, daily movements of deer occurred primarily from the area of
Stirling’s Headquarters to the residential neighborhood to the
west, where deer would spend the night. In the western portion of the
park, south of the river, deer moved infrequently between the park and
private property. North of the river in the northwestern section of
the park there was nocturnal movement of deer into the adjacent residential
area. Deer that occupied the area adjacent to the agricultural fields
of Saint Gabriel’s Hall foraged in and around those fields at night
and spent the day in the park woodlot. There was little or no movement
of deer into the mobile home development on the northeastern boundary
of the park. In the southeastern portion of the park there was movement
of deer into the Glen Hardie neighborhood at night. The Pennsylvania
turnpike is a significant barrier to deer along the southern park boundary.
However, deer did occasionally cross that highway.
Of the 120 deer that were captured and marked, 39 mortalities were observed.
Vehicle collisions were the most common cause of mortality, accounting
for 69% (27 of 39) of all mortalities. This result is consistent with
previous results from 1984 to 1995 that indicated an average of 78 deer
per year killed on park roads. Vehicle-deer collisions accounted for
84% of known deer mortalities during that time.
Earlier studies in Pennsylvania reported deer density at Gettysburg
National Military Park increased from 37/km2 (95/mile2) to 53/km2 (136/mile2)
during 1990-93, and deer density averaged 58/km2 (150 deer/mile2) during
1992-94 at Letterkenny Army Depot near Chambersburg. The PA Game Commission
reported that Pennsylvania supported 1.5 million white-tailed deer at
an average density of 12.8/km2 (33.2 deer/mile2) state-wide in 2000.
For comparison, estimates of white-tailed deer numbers in VAFO increased
from 772 to 1,106 from 1997 to 1999, an average annual density of 70
deer/km2 (181 deer/mi2). Continued growth of the deer herd is probable.
_____________________________________________
The entire report is available to view or download in PDF file format. Using PDF files requires the free Adobe Acrobat Reader. If you do not already have it installed on your computer, you may download it now. Download Reader.
To download
a pdf file, click on this icon in the toolbar of the pdf window: 
.
This will allow you to save the file on your computer. If you want to
copy or print only a small part of the saved file, click on this icon
to select the desired text: 
.