Testing VHF/GPS Collar Design and Safety in the Study of Free-Roaming Horses
Citation: Collins GH, Petersen SL, Carr CA, Pielstick L (
Testing VHF/GPS Collar Design and Safety in the Study of Free-Roaming Horses
Gail H. Collins 0
Steven L. Petersen 0
Craig A. Carr 0
Leon Pielstick 0
Elissa Z. Cameron, University of Tasmania, Australia
0 1 U. S. Fish and Wildlife Service, Sheldon-Hart Mountain National Wildlife Refuge Complex , Lakeview, Oregon , United States of America, 2 Department of Plant and Wildlife Services, Brigham Young University , Provo , Utah, United States of America, 3 Department of Animal and Range Sciences, Montana State University , Bozeman , Montana, United States of America, 4 Doctor of Veterinary Medicine , Burns, Oregon , United States of America
Effective and safe monitoring techniques are needed by U.S. land managers to understand free-roaming horse behavior and habitat use and to aid in making informed management decisions. Global positioning system (GPS) and very high frequency (VHF) radio collars can be used to provide high spatial and temporal resolution information for detecting free-roaming horse movement. GPS and VHF collars are a common tool used in wildlife management, but have rarely been used for freeroaming horse research and monitoring in the United States. The purpose of this study was to evaluate the design, safety, and detachment device on GPS/VHF collars used to collect free-roaming horse location and movement data. Between 2009 and 2010, 28 domestic and feral horses were marked with commercial and custom designed VHF/GPS collars. Individual horses were evaluated for damage caused by the collar placement, and following initial observations, collar design was modified to reduce the potential for injury. After collar modifications, which included the addition of collar length adjustments to both sides of the collar allowing for better alignment of collar and neck shapes, adding foam padding to the custom collars to replicate the commercial collar foam padding, and repositioning the detachment device to reduce wear along the jowl, we observed little to no evidence of collar wear on horses. Neither custom-built nor commercial collars caused injury to study horses, however, most of the custom-built collars failed to collect data. During the evaluation of collar detachment devices, we had an 89% success rate of collar devices detaching correctly. This study showed that free-roaming horses can be safely marked with GPS and/or VHF collars with minimal risk of injury, and that these collars can be a useful tool for monitoring horses without creating a risk to horse health and wellness.
Funding: Research was funded and supported by the United States Fish and Wildlife Service, the United States Bureau of Land Management (BLM), the Roaring
Springs Ranch, Oregon State University, and Brigham Young University. The Fish and Wildlife Service and BLM did provide funds for the purchase of the GPS
collars. These funds were allocated through budgets for the purchase of this equipment. Those who provided the funds to Gail Collins were not involved in this
study. Funding sources at Brigham Young University and Oregon State University had no role in study design, data collection, and analysis, decision to publish, or
preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Free-roaming horse (Equus caballus) management is a complex
issue incorporating social, economic, emotional, political, and
environmental factors. The complexity associated with developing
appropriate free-roaming horse management practices has
highlighted the need for an improved understanding of free-roaming
horse behavior, habitat use, resource impacts, and movement
patterns across the landscape. Global positioning system (GPS)
collars offer a robust tool to track horse activity with high spatial
and temporal resolution. In 1994, Lotek Engineering introduced
the first animal-based GPS tracking device . Since its initial
development, GPS collar technology has been widely adopted and
significantly improved through reduced collar and receiver size,
lowered collar weight, increased longevity (battery life), lowered
costs, and increased data storage and retrieval capacity .
Very high frequency radio (VHF) and GPS collar technologies
are commonly used by wildlife managers and researchers to track
and monitor a diversity of wildlife species, ranging from migratory
birds  and small mammals to large herbivores and carnivores
. World-wide, over the past 30 years, thousands of individuals of
a variety of species have been captured and collared to study
ecological dynamics and behavior . Examples of studies
involving large numbers of collared ungulates include moose
(Alces alces; ), elk (Cervus canadensis; , bison (Bison
bison; , white-tailed deer (Odocoileus virginianus; ,
mule deer (O. hemionus;  and barren-ground caribou
(Rangifer tarandus; . Collars have also been used to track
a variety of livestock species, in particular cattle (Bos primigenius;
In contrast, few studies report the use of VHF or GPS collar
technology in the study of wild Equids, however, those that have
incorporated this technology have successfully generated data for
the study of animal movement, behavior, and habitat use. For
example, Siniff et al.  deployed 89 collars with and without
VHF transmitters on free-roaming horses in western Nevada to
monitor foaling and mortality rates. Kaczensky et al. 
successfully deployed 16 VHF/GPS collars with pre-programmed
timed-release detachment devices on nine Przewalksis horses
(Equus ferus przewalskii) and seven Asiatic wild asses (Equus
hemionus onager) in the Mongolian Gobi. In the Australian
outback, Hampson et al.  placed VHF/GPS collars on 12
feral horses to track travel patterns between feeding grounds and
water holes. Eight collars were placed on adult female plains
Zebras (Equus burchelli antiquorum) to test the influence of collar
weight on animal behavior and location error .
Despite the technologys widespread application, in the United
States collars have been barred from use on free-roaming horses
that are under the jurisdiction of the Bureau of Land Management
(BLM) because of previous incidents of collar-related injuries to
horses fitted with VHF collars. The BLM is responsible for
management of the majority of free-roaming horses in the United
States. Problems included ill-fitting collars and, more importantly,
a lack of collar removal that resulted in horses wearing collars for
extended periods causing significant injury (personal
communication Wild Horse and Burro Research Committee, 2010). Horse
necks increase in width from the base of the head (lower
mandible/axis) to the point of neck attachment above the
shoulders and withers. Collars that are attached too low on the
neck towards the withers have high potential for significant
movement and associated injury. This is primarily due to slippage
that occurs as collars slide up and down the neck while feeding,
walking, and running. This rubbing motion can create hair wear
and if excessive, open wounds and sores.
In the United States, free-roaming horse welfare and safety is a
paramount management issue and because of safety concerns,
there has been a limited use of VHF/GPS collar technology for
improving our understanding of free-roaming horse ecology and
management. The purpose of this study was to evaluate VHF/
GPS collars and assess their potential to cause injury to
freeroaming horses. This includes an assessment of collar design,
degree of injury, and collar detachment reliability. Note that the
terms free-roaming, free-ranging, feral, and wild horse are used
interchangeable by horse management agencies and in scientific
literature, however, these terms all refer to horses that live in an
untamed state but have ancestors that were once domesticated. In
this paper, we refer to these animals as free-roaming horses.
We used two separate study locations to evaluate the utility and
safety of VHF/GPS collars in characterizing free-roaming horse
movement and habitat use patterns: the Roaring Springs Ranch
(RSR) in southeast Oregon and the Sheldon National Wildlife
Refuge (SNWR) in northwest Nevada (Figure 1). The RSR served
as our initial pilot study, testing collar design on domestic,
freeroaming horses while the SNWR provided an opportunity to
evaluate collars on feral, free-roaming horses.
Pilot Study Roaring Springs Ranch. The RSR is located
on the western side of Steens Mountain (42.36108u N 118.78923u
W) in the northernmost extent of the Great Basin, High Desert
Ecological Province  (Figure 1). The privately owned ranch
covers approximately 171,991 hectares, ranging in elevation
between 1,3862,324 m. The area receives approximately 32 cm
of precipitation annually, primarily during winter and early spring
months. The sagebrush-steppe vegetation is dominated by
mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana
(Rydb.) Beetle), bottlebrush squirreltail (Elymus elymoides (Raf.)
Swezey), Idaho fescue (Festuca idahoensis Elmer), bluebunch
wheatgrass (Pseudoroegneria spicata (Pursh) A. Love), and
Sandbergs bluegrass (Poa secunda J. Presl).
In-Field Study Sheldon National Wildlife Refuge. The
SNWR is located along the southern Oregon border to the north
and near the California border to the west (41.72079uN latitude,
119.39703uW). The SNWR covers approximately 232,694
hectares of sagebrush-steppe habitat with elevations that range
between 1,2002,100 m. Average annual precipitation ranges
between 18 and 33 cm. Plant communities in this region are
dominated by big sagebrush (A. tridentata ssp. vaseyana and ssp.
wyomingensis Beetle and Young), little sagebrush (A. arbuscula
Nutt.), antelope bitterbrush (Purshia tridentata (Pursh) DC.),
bottlebrush squirreltail, Idaho fescue, and bluebunch wheatgrass.
Several tree species such as quaking aspen (Populus tremuloides
Michx), western juniper (Juniperus occidentalis Hook.), and
curlleaf mountain mahogany (Cercocarpus ledifolius Nutt.) are found
in scattered stands throughout the SNWR.
Field data collection
Pilot study Roaring Springs Ranch. Between March and
August 2009, we deployed six commercial (Lotek GPS3300;
Figure 2) and 11 custom-built (Figure 3) VHF/GPS collars on 12
privately-owned domestic horses. Five individuals were collared
twice during this portion of our study (Table 1). Two weeks after
the initial collar deployment in March 2009, six custom collars
were removed in order to recover the data. A second deployment
of five custom collars which were constructed with breakaway
detachment devices occurred in June 2009 (Table 1). Six horses
were mares and 6 were geldings, ranging in age from 617 years
old. Two of the mares also had foals in attendance. The design and
construction of the custom-built collars followed Clark et al. 
and were used because they were more cost effective than
commercial collars and because this design has experienced
increased use in the field. These horses were allowed to range
freely as a group within a 12,140 hectare fenced pasture, and
rounded-up by ranch personnel every two to four weeks in order
to evaluate each horse for potential injuries as a result of the
collars. For the purposes of this study, these animals were assumed
to provide a fair representation of free-roaming horses, including
the presence of a dominant male horse, while the ability to
regularly and safely handle these individuals afforded us the
opportunity to evaluate the potential for injury associated with
collar placement and fit.
Collar detachment or drop-off devices are designed to break
open the collar band and allow it to fall free from the animals neck
without direct human contact. Proper deployment of the
detachment device prevents the need to recapture and further
handle the animal. Two of the most common types of collar
detachment devices are either a remotely-detonated device which
uses a remote trigger to activate a small explosive to separate the
collar band or a remote timed-release device which mechanically
separates the collar band within a pre-programmed time period.
Occasionally these types of collar detachment devices fail to
function correctly, thus a common alternative is to use breakaway
or rot-away detachment devices such as rubber tubing or leather
or cotton spacers. As the material is exposed to the sun and other
environmental elements, it becomes brittle and breaks apart
allowing the collar to fall from the animals neck. For this study, we
selected to use a breakaway device constructed of K cm diameter
rubber tubing. The collar band was cut in half and two holes
drilled into each cut end. Two pieces of tubing were then threaded
in parallel through each pair of holes and tied into a knot to close
the cut collar band ends (Figure 3).
During the pilot study, we tested the efficacy of two types of
collar detachment devices. Five of the custom-built collars were
outfitted with a breakaway collar detachment device constructed
of rubber tubing (Figure 3) and all six of the commercial collars
were outfitted with a commercial remotely-detonated device
Figure 1. Pilot and in-field study site locations. The Roaring Springs Ranch (pilot study) is located in southeast Oregon. The Sheldon National
Wildlife Refuge (in-field study) is located in northwestern Nevada.
Commercial (with breakaway1)
Custom-built (no breakaway)
Custom-built (with breakaway2)
1Remotely-detonated breakaway detachment device.
2Breakaway detachment device constructed of rubber tubing.
(Figure 2). The original six custom collars did not have
detachment devices (Table 1).
In-field study Sheldon National Wildlife Refuge. Using
modifications to the collar design developed during the pilot study
we attached six commercial (Lotek GPS3300) and eight custom
collars VHF/GPS collars to free-roaming horses within the
Sheldon National Wildlife Refuge in August 2009 (Table 2).
Horses were gathered as a group and herded into corrals via
helicopter and fourteen adult mares were collared and released at
the site of capture. All collared mares were also implanted with a
unique micro-chip prior to release for future identification. In
October 2010, horses were again gathered by helicopter. We
attached commercial collars (Lotek GPS3300) to six adult mares,
four of which were collared previously in August 2009, and all
were released at the site of capture (Table 2).
All collars were deployed on adult mares ranging in age from
four to 24 years old and ten of the mares were attended by foals at
the time of collaring. During the initial collar deployment in
August 2009, all collars were outfitted with both a breakaway
device (i.e., rubber tubing, K cm diameter) and a commercially
available remote timed-release device (Lotek mini drop off) set to
detach with a delay of approximately 53 weeks (Figure 4).
Following the initial deployment in August 2009, all of the
breakaway devices installed on the six commercial collars activated
prior to the pre-programmed date for the timed-release devices.
The commercial collars were retrieved from the field, and were
refurbished by the manufacturer for re-deployment in October
2010 on SNWR. Because the timed-release devices were still intact
and operating when retrieved, they were not replaced during
refurbishment and instead reset in the field according to the
manufacturers instructions. The refurbished commercial collars
deployed in October 2010 were outfitted with only the reset
timedrelease detachment devices.
This study was carried out in strict accordance with the protocol
approved by the Brigham Young University Institutional Animal
Care and Use Committee (USDA Permit Number: 27-2956, BYU
Protocol number 08-081). No permits were required to perform
this research. The pilot study was performed on private land under
the authority of the landowner while the field study was performed
with permission and guidance of the USFWS on the Sheldon
National Wildlife Refuge. Our research did not involve
Federallyor State-listed endangered species or species of concern. The
owners of the domestic horses granted permission for their animals
to be use in this study.
Pilot study Roaring Springs Ranch
Hair wear includes thinning and breakage of hair where friction
is enough to provide visible evidence of contact with the collar. In
approximately 30% of the cases, hair wear at the RSR pilot study
was sufficient enough to expose the skin, however, as this took
place over an extended period, the underlying skin adapted by
thickening and strengthening the epidermal structure and the skin
remained pliable with no evidence of callus formation or loss of
elasticity. In no case was the skin integrity compromised. Collars
were placed high on the neck to reduce collar movement while
also limiting the potential for collar damage associated with horse
to horse interactions (e.g., kicking), or getting the collar caught in
vegetation or on fences. Moreover, collaring only mature animals
prevented the possibility of an immature animal outgrowing the
collar and causing injury. During the pilot study, one of our main
goals was to evaluate study horses for potential issues or injury
attributed to the collar. The collars were installed behind the head
and ears (Figure 2) and initially adjusted in tightness to
approximately 2.5-5 cm spacing between the neck and the collar.
Observations over the first 4 weeks following deployment
included: 1) slight to moderate abrasions or callus on the jowl at
Table 2. Type of collar, type of detachment device, and date dropped for VHF/GPS collars deployed on free-roaming horses in
2009 and 2010, Sheldon National Wildlife Refuge, NV.
August 2009 Deployment
October 2010 Deployment
Activated detachment device
1Individual captured at a later date without the collar, it is unknown which detachment device activated first.
2Timed-release detachment devices failed, collars were manually removed during subsequent captures.
the jugular furrow; and 2) slight to moderate wearing in the hair at
the widest point of the neck and on the mane. We also found that
the remote collar detachment device was causing skin irritation by
rubbing along the jowl (Figure 2). As a result, we made the
following modifications to the collar design: 1) to reduce swinging,
side-to-side collar movement, the collar shape was narrowed by
adding collar length adjustments to both sides of the collar which
created a more natural oval shape (as opposed to round or
offcentered) in alignment with the shape of a horses neck; 2) to
augment the oval shape in the custom collars we added foam
padding to the upper portion of the VHF/GPS box; 3)
repositioning the remote collar detachment device higher on the
neck to avoid contact with the jowl; and 4) tightening the collar to
1.3 cm spacing on a flexed neck to reduce collar movement up
and down along the neck. Following these modifications we
observed only slight wear in the hair along the neck and mane of
the horses with no abrasions or calluses even after several months
of wear. It is important to note that all of the domestic horses
gained substantial weight during the course of the study owing to
naturally improving range conditions through the spring and
summer, and there were no associated issues with the tightness of
During the pilot study, two of the breakaway devices detached
before 40 days while the remaining three collars with breakaway
detachments were intact when the study ended and the collars
removed in August 2009. Six of the seven (87%) remote-detonated
collar detachment devices detached as expected after 93 days
deployed. The reason for the single failure is unknown.
In-field study Sheldon National Wildlife Refuge
During the pilot study, we documented that several of the
domestic geldings were able to slip the upper portion of the collar
band over one or both ears; we did not see this occur with any of
the mares. The exact reason for this is unknown, but to reduce the
potential for harm to free-roaming male horses, the decision was
made to only collar mares during the in-field portion of the study.
In addition, we suspected that intrasexual fighting among male
horses would likely result in substantial collar damage .
For the custom-built collars deployed in August 2009, the VHF
malfunctioned almost immediately and stopped transmitting from
seven of the eight collars making the collars irretrievable from the
field. The remaining collar was successfully retrieved field via a
functioning VHF transmitter and a second collar was found by
chance and recovered by a member of the public. All eight horses
who received custom-built collars were recaptured during
subsequent helicopter gathers between 2010 and 2012. None of
these individuals were wearing a collar when recaptured and
under examination showed no evidence of lasting injury as a result
of the collar (e.g., calluses, scars). Because the collars were
irretrievable from the field due to the VHF malfunction, it is
unknown exactly when and which collar detachment device
activated first (the breakaway or timed-release), but the end result
was the same with all collars detaching successfully.
The VHF transmitters in the commercial collars transmitted a
signal throughout the study. For the commercial collars deployed
in August 2009, all six had their breakaway device detach before
the set remote timed-release date of approximately 370 days since
deployment, ranging from 122 to 254 days (Table 2). The
commercial collars were then refurbished by the manufacturer
and redeployed with only the field-reset timed-release detachment
device in October 2010. For those redeployments, four of the six
remote timed-release devices functioned properly although at
roughly two different time intervals (386 days and 703717 days;
Table 2). The remaining two remote timed-release devices failed
to activate altogether.
Collar wear during the in-field study was as expected from that
observed following the collar modifications during the pilot study.
During the course of the in-field study, we located the bands with
marked individuals via VHF by air or ground every 1 to 2 months,
and all of the mares appeared from a distance to be in good health
and wearing the collars without issue. These observations included
individuals wearing collars that had stopped transmitting a VHF
signal, but were able to be located due to their association with
mares whose collars were transmitting correctly. Fourteen mares
were incidentally captured during subsequent gather efforts and
under direct examination showed very little to no evidence of
effects related to the collar regardless of type of collar deployed. If
evidence of the collar was present, we observed only a small callus
or a slight wearing of the hair along the neck and mane. Of the
two individuals whose timed-release detachment device did not
function properly, one was recaptured in 2013 still wearing the
collar and showed no injury or damage as a result of the collar
even after 3 years of continuous wear (Figure 4).
Ill-fitting collars and problems associated with them clearly
influence research results and have implications for ethics within
the wildlife profession . With that in mind, we set out to test the
efficacy and safety of collar deployment on a high profile species,
the free-roaming horse in the United States. This work
demonstrated that free-roaming horses can be safely collared using an
appropriately modified design with minimal to no detectable
physical impact to the horse.
We tested the custom-built collars due to the greater cost savings
however, we experienced issues with their functionality, likely due
to inexperience with the construction and potentially rougher
handling by horses than other species. We observed several
instances where a commercial collar took a direct kick from
another horse and continued to function normally. For those
custom-built collars we could recover, in several locations soldered
joints in the electronics were broken leading us to suspect there
were flaws in the construction. Collars built following the Clark et
al.  design are effective in monitoring animal movement ,
however based on our experiences, these collars should be
constructed by experienced technicians.
In evaluating the collar detachment devices, the collars
detached successfully in 89% of the cases. We suspect issues
related to failure in the second deployment of the timed-release
devices were related to our attempts to field-reset them, where two
detached at the expected time, two detached at twice the expected
time, and two failed to detach. For those collars that were not
removed by either a remote-detonated or a timed-release device,
the fail-safe breakaway devices were 100% effective. The downside
of the breakaway devices is a lack of control over when the collar
will detach, which in our environment ranged roughly between 4
and 8 months. This timing would be expected to be variable
depending on the thickness of the rubber tubing used, climate
(temperature, sun intensity) of the study area, and time of year
(winter vs. summer). We expect that thicker tubing, would last
longer, however, tubing thicker than the diameter tested in this
study would be difficult to tie into the collar and may subsequently
The potential exists for horses to be injured when collars get
caught in trees or fencing. Although we did not specifically
monitor for these events, we saw no evidence of any injuries that
could be attributed to horses being trapped in fencing or trees
because of collars. Moreover, breakaway devices may provide
protection against this type of injury, however more research
specifically on the strength of the rubber tubing is required to fully
address this question.
Based on our experience in this study, collar fit is an important
consideration when using VHF/GPS collar on free-roaming
horses. By maintaining a natural oval shape and fitting the collar
high on the neck, collar movement and subsequent wear was
significantly reduced. In addition, collar detachment devices
should be installed along the collar in locations to ensure they
do not cause excessive wear along the horses jowl.
Injury to study animals can occur when using GPS/VHF
collars. Krausman et al.  observed collar related injuries on wild
sheep and mule deer and indicated that, as in our study, injuries
were related to ill-fitting collars. Once collars were properly
aligned with the shape of the neck and protruding fasteners made
flush with the collar straps, injury rates were substantially reduced,
however wild sheep were apparently more susceptible to collar
wear injury . Moreover, many collar related injuries appear
associated with changing neck size, either from juvenile growth or
physiological changes including periods of hibernation  or
breeding . Designs with expandable collar straps or
breakaway devices have been proposed to address neck size changes
. For horses, there is a risk of collar-related injury
associated with increased neck size when juveniles are collared
or if neck size expands as body condition improves with high
quality and abundant spring and summer forage. In our case, we
chose not to collar juveniles and saw no evidence of collar related
injuries associated with improved body condition. However,
break-away devices should be considered on collars as a way to
prevent potential neck size issues, particularly if collars are being
deployed on juvenile animals. In most cases, it does appear that
with properly fitted collars, GPS/VHF collars can be effectively
and safely used in free ranging animal studies without significant
collar related injury to study animals. In our review of collar-based
wild Equid studies, none reported observations of significant
collar-related injuries to study animals [2627,30,36] and both
Brooks et al.  and Gerard et al.  indicated that there was
no evidence negative impacts associated with collars on either
zebras or feral horses.
Although not reported in this paper, the data collected by our
GPS collars provided useful information with respect to the
effectiveness of geospatial data in evaluating free-roaming horse
ecology including landscape-level movement patterns  and
habitat selection . These results, along with other GPS collar
based studies of horse behavior in Canada  and Australia 
and other wide-ranging ungulates [1113,1920], demonstrate the
effectiveness and utility of the data generated by collars in the
study of wild and free-roaming horses.
The use of VHF/GPS collar technology is critical to
understanding how free-roaming horses, particularly in the Western
United States, move across the larger landscape and use
increasingly scarce resources. Lack of this information has
contributed to the management complexity of this species .
Applying this technology to the study of free-roaming horses will
provide the opportunity to better understand horse resource use,
habitat preference, home range, and movement patterns and can
be incorporated into investigations of social structure and herd or
band dynamics as well as behavioral modifications associated with
reproductive management including contraceptive use and
sterilization. Moreover, an improved understanding of horse ecology is
critical to the appropriate management of natural resources in the
western US and is needed to address questions related to predator
relationships, competition for habitat, and interactions among and
between horses, wildlife, and livestock. Our study indicates that
VHF/GPS collar technology can be safely used as a tool in the
development the body of knowledge required to effectively
manage wild and free-roaming horses.
Support was provided by the U.S. Fish and Wildlife Service, Brigham
Young University, Oregon State University. We would like to thank Stacy
Davies and the staff at Roaring Springs Ranch for allowing us to test collar
design on their saddle horses. The Bureau of Land Management provided
collars used during the pilot effort. Doug Johnson donated collars to use in
the pilot study. Pat Clark helped train in non-commercial collar
development. Amy Johnson-Gooch and Leah Knighton spent many hours
building collars, and Megan Nordquist assisted with collar deployment.
Cattors Livestock, Limited was invaluable in safely gathering horses. Brian
Day and Paul Steblien assisted with logistics and other support. Thoughtful
reviews by the associate editor and anonymous reviewers were greatly
The findings and conclusions in this article are those of the author(s) and
do not necessarily represent the views of the U.S. Fish and Wildlife Service.
Conceived and designed the experiments: GHC SLP CAC LP. Performed
the experiments: GHC SLP CAC LP. Analyzed the data: GHC SLP CAC
LP. Contributed reagents/materials/analysis tools: GHC SLP LP. Wrote
the paper: GHC SLP CAC.
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