Table Of ContentWilson Bulletin 117(1):15-22, 2005
MINIMUM POPULATION SIZE OF MOUNTAIN PLOVERS
BREEDING IN WYOMING
REGAN E. PLUMB, ERITZ L. KNOPF,^^ AND STANLEY H. ANDERSON'
1
—
ABSTRACT. As human disturbance of natural landscapes increases, so does the need for information on
declining, threatened, and potentially threatened native species. Proposed listing ofthe Mountain Plover (Char-
adriusmontanus) as threatened underthe U.S. Endangered Species Act in 1999 was found unwarranted in 2003,
but this species remains of special concern to management agencies and conservation groups. Whereas large
concentrations of breeding Mountain Plovers occur in Montana and Colorado, estimates of the numbers of
Mountain Plovers in Wyoming have ranged from only 500 to 1,500 individuals and are based largely on
conjecture. In 2002, we visited all known breeding locales in the state to define areas ofconcentrated sightings
in the Laramie, Shirley, Washakie, Great Divide, and Big Horn basins. In 2003, we used distance sampling to
estimate breeding bird densities in these five areas. We pooled these estimates and applied the resulting density
to a minimum occupied range for the Mountain Plover based on the documented sightings and a previously
derived home-range size of 56.6 ha ± 21.5 (SD) to generate a minimum population estimate for the state.
Average Mountain Ploverdensity was4.47 ± 0.55 (SE)birds/km-. Wecalculatedaminimumpopulationestimate
of 3,393 birds for Wyoming. The Mountain Plover population breeding in Wyoming appears to contribute
substantially to a revised continental population estimate of 11,000 to 14,000 birds. Our approach may have
applications to quantifying minimum population status of other uncommon species or species of special con-
servation concern using current database records, such as those compiled in Natural Heritage Programs at the
state level. Received 28 January 2004, accepted 10 December 2004.
The Mountain Plover (Charadrius montan- ing range is restricted to east-central Montana
us) is one of 12 avian species endemic to the (Skaar 2003), the tablelands of Wyoming
grasslands of North America (Mengel 1970). (Oakleaf et al. 1992), and eastern Colorado
Plovers nest on the shortgrass prairie and (Andrews and Righter 1992, Kingery 1998).
shrub-steppe of the western Great Plains and The North American population was recently
Colorado Plateau, especially in areas used his- estimated at 8,000 to 10,000 birds (Knopf
torically by large assemblages of herbivores, 1996a).
such as prairie dogs (Cynomys spp.), bison In response to evidence of the species'
{Bison bison), and pronghorns (Antilocapra widespread decline, in 1999 the U.S. Fish and
aniericana; Knopf 1996a). The species win- Wildlife Service (USFWS) proposed listing
ters from north-central California to Arizona, the Mountain Plover as threatened under the
Texas, and northern Mexico. U.S. Endangered Species Act (ESA) (U.S.
Once numerous in Colorado and Wyoming Fish and Wildlife Service 1999). The USFWS
and common in western Kansas, South Da- recently determined that threats to Mountain
kota, and Nebraska, Mountain Plovers began Plovers and their habitat are not likely to en-
to decline throughout their range early in the danger the species in the foreseeable future:
20th century (Laun 1957). They have contin- thus, the proposed listing ofthe bird was with-
ued to do so over the past 30 years at a rate drawn (U.S. Fish and Wildlife Service 2003).
approximating 3% per year (Knopf 1996a). As Regardless, the Mountain Plover remains as a
a result, the species’ continental breeding species of special concern to wildlife and laiul
range has been significantly reduced. Today managers throughout its range.
the majority of the Mountain Plover's breed- Although significant breeding po|')ulations
occur in Montana and C'olorado, there is e\i-
' Wyoming Coop. I'ish und Wildlife Research Ihiil, dcnce that Wyoming may provide habitats for
Univ. ol Wyoming, liox 3166 Uuiv. .Station. I.aramie. many brcctling Mountain ldo\ers as well. Sur-
WY
8207I-3166, USA. vey efforts for plovers in Wyoming. cs|X'cially
ter.‘2Ul.5.S(.)-G('eo(l’oegnitrcealAv.eS.u,rvfeoyr,tl(-o'rotllCionsl,liCnsO.8S0ci5e2n6c-e8(1'e1n8-. in the wake of the recent I-2SA proposal, ha\e
USA. rcN’calcd i-HK'kcts of breeding birds throughout
’Corresponding author; e-mail; the state, particularly in south-central and
t’rit/_knopr(«fiisgs.gov eastern Wyoming. I'hc contribution of Moun-
16 THE WILSON BULLETIN • Vol. 117, No. I, March 2005
tain Plovers in Wyoming to the continental Between 12 May and 18 July 2002, we vis-
breeding population is poorly understood, as ited all locations in Wyoming with one or
no reliable statewide population estimate ex- more pre-2002 plover sightings and surveyed
ists. Rough estimates, based largely on con- for presence of Mountain Plovers. We mod-
jecture, have ranged from 500 to 1,500 indi- eled survey protocol after Mountain Plover
viduals (FLK). survey guidelines set forth by the USFWS
Wunder et al. (2003) recently estimated the (U.S. Pish and Wildlife Service 2002). We
size of a similarly undefined population of drove transects along established roads and
Mountain Plovers in South Park, (Park Coun- two-track roads, stopping at 0.4-km intervals
ty), Colorado. Distance sampling was used to to conduct visual scans for plovers. We con-
estimate density of breeding plovers, from ducted these scans outside of the vehicle to
which a population estimate was extrapolated prompt movement of nesting or resting plo-
based on an estimate ofoccupied habitat. Plo- vers and maximize their detectability. There
vers in South Park occurred at an average den- was no predetermined length of time for each
sity of 7.9 ± 0.9 (SE) birds/km^ across sam- visual scan; rather, each lasted as long as nec-
pled portions of >80,000 ha of potential hab- essary to covera 360-degree panoramaaround
itat. Wunder et al. (2003) concluded that the vehicle. Surveys were conducted in the
South Park, with an estimated population of morning between local sunrise and 1 1:00
>2,300 Mountain Plovers, contributes 15- MST, and in the afternoon between 16:30 and
20% of breeding plovers to the continental local sunset to take advantage of horizontal
population. lighting that facilitates detection of plovers.
Following the success of Wunder et al. Playback calls were not used. GPS coordi-
(2003) in generating a population estimate in nates were taken at the site where each Moun-
South Park, Colorado, we used distance sam- tain Plover was first observed. As time al-
pling to generate density estimates ofbreeding lowed, we also surveyed surrounding areas of
plovers in Wyoming. Although we used dis- acceptable habitat from which there were no
tance sampling following Wunder et al. prior records of plovers; these new sightings
(2003), plovers are much more widely scat- were added to the pre-2002 database.
—
tered in fragmented habitats across Wyoming Mountain plover study areas. We identi-
compared with their single-county study in fied five Mountain Plover breeding areas for
Colorado. Our objectives were to (1) compile our study. We stratified these areas into two
all documented sightings ofMountain Plovers grassland landscapes and three desert-shrub
in Wyoming, (2) visit all locals ofdocumented landscapes. The two grassland landscapes
sightings in 2002 to confirm presence of were located in the Laramie and Shirley ba-
breeding plovers, (3) conduct surveys ofadult sins, and the desert-shrub areas were in the
plovers at selected areas in 2003, and (4) ex- Big Horn, Great Divide, and Washakie basins.
trapolate ploverdensities overthe documented The five areas were selected based upon ac-
breeding range to obtain a minimum popula- cessibility for field personnel and the avail-
tion estimate for Mountain Plovers in Wyo- ability of adequate potential habitat to find a
ming. minimum of40 plovers in a 5-day survey pe-
METHODS riod. Accessibility was limited on many pri-
vately owned lands and occasionally vehicle
Documentedsightings andstatewide recon- access was limited on public lands.
—
naissance. We collected information about Study areas in the Laramie and Shirley ba-
documented locations of Mountain Plovers sins included a portion of the Laramie Plains
from state and federal agencies, non-profit and that extends north and west from Laramie to
consulting firms, and individuals in Wyoming. Medicine Bow and Foote Creek Rim, and the
We mapped these locations using a Geograph- central portion of Shirley Basin, roughly de-
ic Information System (GIS; ESRI ArcMap lineated by the two intersections of Wyoming
8.3). More than 40 agencies, firms, and indi- highways 77 and 487 in northeastern Carbon
viduals contributed to the compiled database County. These basins represent the highest-el-
representing the documented distribution of evation grasslands in Wyoming (Knight 1994)
Mountain Plovers throughout the state. and are characterized by interspersed short-
Plumb et al. • MOUNTAIN PLOVERS IN WYOMING 17
and mixed-grass prairie. Shortgrass species in- when most breeding birds were on nests. This
clude blue grama (Bouteloua gracilis) and survey was designed to detect all adult plo-
buffalograss (Buchloe dactyloides). Common- vers, but especially those that ultimately might
ly occurring mixed-grass species include nee- nest unsuccessfully and leave the area before
dle-and-thread grass {Stipa comata), western the second survey. The second survey oc-
wheatgrass (Agropyron smithii), Sandberg curred in late June to coincide with the chick-
bluegrass (Poa sandbergii), threadleaf sedge rearing phase. The courtship phase in late
{Carexfilifolia), and Indian ricegrass (Oryzop- April and early May was avoided, as survey
sis hymenoides). Several shrub species, in- estimates from that period would be subject
cluding pricklypearcactus {Opiintiapolyacan- to error incurred by detections of migrating
tha), big sagebrush {Artemisia tridentata), birds.
budsage {A. spinescens), and fourwing salt- Using an ATV driven at <15 km/hr, two
bush (Atriplex canescens) are present. Vege- observers conducted surveys in each study
tation communities vary with topography, area along transects with a minimum of 400-
which ranges from basins and saltpans to el- m spacing between lines. Plovers move eva-
evated plateaus. White-tailed prairie dog {Cy- sively in response to observers on foot, but
nomys leucurus) colonies are common and are more tolerant of slow-moving vehicles;
grazing by domestic cattle and pronghorn an- thus, we used an ATV to help ensure detection
telope is pervasive. of birds at their initial location. Each transect
The desert-shrub study areas included the began on a road or two-track that ran along-
Mexican Flats, located west of Dad between side (narrow strips) or through (large patches)
Wamsutter and Baggs in the Washakie Basin potential plover habitat. We used a random
(Carbon County); a portion of the Great Di- numbers table to determine the distance (from
vide Basin of the Red Desert located south of the access road or two-track) driven into each
Cyclone Rim in northern Sweetwater County; survey area before beginning the transect per-
and parts of the Big Horn Basin near Cody pendicular to the access road. We stopped at
and Powell (Park County) and Greybull (Big 0.4-km intervals while surveying and stepped
Horn County), particularly Polecat and Chap- off the ATV. This approach encouraged plo-
man benches. These shrubland areas are typ- vers to stand from their nests, and thus be-
ified by saline soils and are dominated by come more visible. All transects were con-
greasewood {Sarcohatus vermiculatus), shad- ducted simultaneously by two observers (the
scale {Atriplex confertifolia), fourwing salt- double-observer method). Playback calls were
bush, and Gardner’s saltbush {A. gardneri), not used. We used a laser range hnder (Bush-
with winterfat {Ceratoides lanata) and prick- nell Yardage Pro Sport, rated to 450 m) to
lypear cactus interspersed. A mosaic is often measure the distance to each bird detected and
formed with stands ofbig sagebrush, saltbush, a standard compass to establish the sighting
and greasewood. Mixed-grass species such as angle from the transect line. We look GPS co-
western wheatgrass, prairiejunegrass {Koeler- ordinates on the transect line for each detec-
ia macrantha), saltgrass {DistichIis stricta), tion. We conducted all sampling between local
and ncedle-and-thread grass also occur. Com- sunrise and 1:00 and between 16:30 and lo-
1
munity composition is highly dependent on cal sunset to take advantage of horizontal
topography, moisture availability, and soil lighting (reducing the effects of plumage
type. Oil and gas development is common, counter-shading) and peak activity levels of
particularly in the Mexican Flats area. The the birds. We further reduced the sampling
landscape is grazed by domestic sheep and window on exceptionally warm days (>30
cattle, and by pronghorn. Wild horses are also C) when heat may have reduced activity le\els
present in the Washakie and Great Divide ba- and heat waves may ha\e reduced detectabil-
sins to the south. White-tailed prairie dog col- ity. Sampling was not conducted when in-
onies are common throughout. clement weather or poor lighting threatenctl to
—
Population sampling. During two lO-day bias probability of detection.
surveys in 2003, we surveyed tor adult Moun- Occupied range. Jo define the known oc-
tain Plovers at the five study areas delined in cupietl range for Mountain Plovers in Wyo-
2002. riie initial survey occurred in late May, ming. we combined Mountain Plover loca-
18 THE WILSON BULLETIN • Vol. 117, No. 1, March 2005
tions from the reconnaissance phase in 2002, cess, whereas the hazard-rate key function is
the distance-sampling phase in 2003, and the a derived model. We pooled plover sightings
locations documented elsewhere. We then recorded from the two 2003 surveys and trun-
overlaid onto the GIS map a lattice with grid cated the largest 10% of sampled distances to
size equal to the average home range of the reduce error incurred by outliers, as recom-
Mountain Plover during brood rearing (56.6 mended by Buckland et al. (2001). Histo-
ha). The average home-range size of 56.6 ha grams of the probability of detection were in-
was first determined from a study in Weld spected for violation of statistical assump-
County, Colorado, by affixing radio transmit- tions. We also considered the six suggested
ters to adult plovers that were attending models with stratification by habitat, but strat-
chicks, and recording daily movements ified models were inferior to unstratified mod-
(Knopf and Rupert 1996). Comparable home- els. Comprehensive explanations of sampling
range sizes have since been found in other procedure and model selection are given in
Mountain Plover habitats (Dreitz et al. 2005). Buckland et al. (2001) and Burnham and An-
We calculated the minimum breeding range of derson (2002). Our analytic approach was
Mountain Plovers in Wyoming by summing similar to that used by Wunder et al. (2003)
the area ofthe grids in the overlaid lattice that for estimating Mountain Plover densities in
intersected at least one Mountain Plover lo- Park County, Colorado.
cation. A minimum estimate of population We used Akaike’s Information Criterion
size for Wyoming was based on the 2003 den- (AIC) to evaluate the relative strength ofeach
sity estimates extrapolated across this mini- of the 12 models. Because AIC identifies the
mum breeding range. best of a set of competing models but does
—
Distance analyses. Using program DIS- not reflect the quality offit, goodness-of-fit P-
TANCE 3.5 (Thomas et al. 1998), we esti- values were also considered to identify poorly
mated overall Mountain Plover densities, as fitting models {P < 0.05), should any exist.
well as densities for subsets of grassland and To avoid bias incurred by basing parameter
desert-shrub habitats. Distance sampling estimates on a single model from a set of
(Buckland et al. 2001) uses a set of robust closely competing models, we used model av-
models to estimate densities on the basis of eraging based on weighted AIC contributions
measured distances between detected objects from all 12 models to generate overall density
and a central point or transect from which the estimates. We estimated density, detection
objects were detected. With regard to under- probability, and detection strip half-width for
lying assumptions, methodological self-as- grassland and desert-shrub habitat subsets us-
sessment, and efficiency in the field, DIS- ing model averaging across a set of unstrati-
TANCE is superior to relative-abundance es- fied models for each habitat.
timates generated using point counts (Norvell
RESULTS
et al. 2003). We treated the distance data as —
continuous estimates and considered each of Inventory and occupied range. We com-
six models suggested by Buckland et al. piled and mapped >2,000 sightings ofMoun-
(2001). These models were each composed of tain Plovers representing input from >40
a key function or general shape proposed to sources. These records included 1,347 sight-
fit the detection function, and a nonparametric ings from the Wyoming Natural History Di-
flexible form called a “series expansion” that versity Database, —93% and —57% of which
adjusted the key function. The six models were reported in the last 20 and 10 years, re-
used were the uniform key function with co- spectively. Virtually all documented sightings
sine and simple polynomial expansion series, from other sources were made within the last
the half-normal key function with cosine and 10 years. In 2002, we detected 171 Mountain
hermite polynomial expansion series, and the Plovers on 1,416 km of roads and two-tracks
hazard-rate key function with cosine and sim- during reconnaissance visits to previously
ple polynomial expansion series. The uniform documented sites. We added these 2002 plo-
and half-normal key functions are proposed ver locations and 449 new locations recorded
shapes for the detection function, based on a during distance sampling in 2003 to the da-
priori assumptions about the detection pro- tabase of documented sightings to map the
5
Plumb et al. • MOUNTAIN PLOVERS IN WYOMING 19
TABLE 1. Estimates (SE) ofMountain Ploverdensity, probability ofdetection, and effective detection strip
half-width in grassland and desert-shrub habitats in Wyoming for 2003. Estimates (SE) are derived from DIS-
TANCE 3.5 (Thomas et al. 1998).
Grassland Desert-shrub
Birds detected 113 190
Density (plovers/km^) 5.17 (1.06) 4.23 (0.67)
Detection probability 0.82 (0.13) 0.73 (0.06)
Effective strip half-width (m) 114.70 (18.68) 111.50 (8.6)
known occupied range ofMountain Plovers in Although the hazard-rate key function with
Wyoming. The resulting 2,695 compiled ob- cosine and simple polynomial expansion se-
servations intersected 1,341 cells in the over- ries provided the best fit to the detection func-
laid 56.6-ha “home range” grid. Therefore, tion for the unstratified data, all 12 models
the known occupied range of Mountain Plo- (six unstratified, six stratified) had AAIC <
vers in Wyoming included at least75,901 (i.e., 5.0 and goodness-of-fit P-values >0.1. The
1,341 X 56.6) ha ofpotential habitat. The five overall density estimate, averaged over 12
study areas for the randomized distance sam- models, was 4.47 ± 0.55 birds/km^ (Table 2).
pling in 2003 overlapped 44% of the known In general, the unstratified models showed
plover locations in Wyoming. lower AIC values than the stratified models.
Density and minimum population esti- Although the poorest fitting unstratified model
—
mates. We detected 303 Mountain Plovers was as likely as the best stratified model
during distance sampling along 276 km of (AAIC = 2.2, w, = 0.07 for both), the unstrat-
transects, roughly divided among the five ified models contributed 78% of the weighted
study areas in 2002. Pooled data across the estimates. All of the models fit the data well:
two 2003 sampling efforts yielded a minimum goodness-of-fit test statistics for the unstrati-
of40 detections for each study area. Estimates fied models (from lowest to highest P-value)
of density, detection probability, and effective ranged from = 3.56 {P = 0.17) to -
strip half-width were similar for grassland and 2.12 {P = 0.35).
desert-shrub habitats (Table 1). Assuming an average home-range size of
TABLE 2. Models used to generate density estimates for Mountain Plovers in five breeding areas in Wyo-
ming for 2003. Both pooled and stratified models are included. Models were run using 303 detections and 10%
truncation. Models are ordered by increasing AAIC. The AIC weight (vr,), density estimate, and coefficient of
variation (CV) are provided for each model.
AICweight Density
Model AAIC (ve,) (birds/kn4) cv
Unstratified
Hazard rate + cosine ().(P 0.20 4.37 0.12
Hazard rate + simple polynomial ().(P 0.20 4.37 0.12
Uniform simple polynomial 0.6 0.1 4.60 0.1 1
Half normal + hermite polynomial 1.7 0.09 4.45 0.15
Half normal -f cosine 2.2 0.07 4.53 0.15
Uniform + cosine 2.2 0.07 4.52 0.14
Stratified^
Uniform -I- simple polynomial 2.2 0.07 4.59 0.10
Hazard rate + simple polynomial 3.0 0.05 4.37 0.12
Hazard rate -f cosine 3.0 0.05 4.37 0.12
Half normal + hermite polynomial 4.2 0.02 4.80 0.1 1
1lalf normal + cosine 4.2 0.02 4.80 0.1 1
Uniform -1- cosine 5.0 0.02 4.55 0.1 1
•AIC IWIJ.
Stralilicilbyhabiialtype.
20 THE WILSON BULLETIN • Vol. 117, No. 1, March 2005
56.6 ha (Knopf and Rupert 1996) for Moun- Mountain Plovers. It is likely that many
tain Plovers, the overall density estimate can breeding locales are still unknown and un-
be applied to the 75,901 ha of geographic surveyed, thus affirming the minimum nature
range documented in Wyoming to generate a of our estimates. The second assumption, that
population estimate of 3,393 birds (75,901 ha the home-range size from Weld County, Col-
X 4.47 birds/km-). The lower confidence limit orado, can be applied to other areas, has re-
for average Mountain Plover home range cently been confirmed by studies that revealed
(35.1 ha) can be used to generate a more con- comparable home-range size in dissimilar
servative estimate of 2,270 birds. Because the habitats at various locales (Dreitz et al. 2005).
occupied range for Mountain Plovers in Wy- Finally, we assumed that densities in sampled
oming is surely underestimated, the upper areas are representative of densities through-
confidence limit for home range (78.1 ha) may out the species’ occupied range. This latter as-
be a better approximation, yielding a popula- sumption was supported by the similar plover
tion estimate of 4,427 birds. densities calculated in grassland versus desert-
shrub habitats.
DISCUSSION We did not need to assume plover occupan-
Generating reasonable population estimates cy of all pre-2003 grid cells in our extrapo-
is particularly challenging for low-density lation of calculated plover density across the
species of conservation concern, such as the pre-2003 sightings template. Distance sam-
Mountain Plover. Distance sampling is a pow- pling in the 2003 survey areas was indepen-
erful tool for developing such estimates given dent ofboth the pre-2003 cell distribution and
the time and resources to collect adequate any knowledge of statewide plover-density
data. Buckland et al. (2001) recommend a patterns. The 2003 distance-sampling tran-
sample size of at least 60-80 detections, but sects (covering 44% of the pre-2003 area)
admit that suitable precision may require sev- would have been as likely to sample 2003-
eral hundred detections. Reasonable sample occupied as 2003-unoccupied cells in the pre-
sizes were only achieved in this study by fo- 2003 database. Thus, the distance sampling
cusing sampling efforts on areas with rela- effort in 2003 included “occupancy” infor-
tively high concentrations of recent (<20 mation relative to the earlier sightings.
years) Mountain Plover sightings. Those areas Plover densities were comparable across
occur either where plovers are most visible or habitat types. The overall density in grassland
where people look for plovers. Much (perhaps habitats was slightly higher (5.17 birds/km-)
most) of the potential plover habitat in Wyo- than in desert-shrub habitats (4.23 birds/km-),
ming has never been surveyed for the species. with considerable overlap between confidence
The validity of the extrapolated minimum intervals. Eighty-six percent of the desert-
population estimates described here largely shrub confidence interval was contained by
rests on the accuracy ofestimates ofoccupied the grassland confidence interval. The congru-
range and average home-range size for Moun- ence of density estimates across habitats sup-
tain Plovers. Given the impracticality (scale of ports the calculation of a pooled density esti-
effort, access to private lands) ofsurveying all mate to represent plover habitats statewide.
potential Mountain Plover habitat in Wyo- The average density ofMountain Plovers in
ming, we initially considered a habitat-based documented breeding areas in Wyoming (4.47
model that employed satellite imagery for es- ± 0.55 birds/km-) is somewhat lower than
timating the occupied range of the species. most density estimates within the species’
This model was deemed unsuitable because breeding range. Finzel (1964) reported 6.2
Mountain Plovers in Wyoming frequently oc- birds/km- near Laramie and 12.3 birds/km^
cupy habitat patches ofsuch small size or sub- near Cheyenne, Wyoming. Wunder et al.
tle distinction, relative to the dominant cover (2003) reported densities of6.0-9.0 birds/km^
type, that suitable patches cannot be distin- for South Park, Colorado, and Knopf (1996a)
guished remotely. Therefore, we compiled reported densities of up to 4.7 birds/km- on
documented sightings of plovers collected by Pawnee National Grassland in Colorado and
field biologists to represent a best-available 1.3-6.8 bird/km“ on prairie dog towns in
approximation of a statewide survey for Montana. Graul and Webster (1976) estimated
Plumb et al. • MOUNTAIN PLOVERS IN WYOMING 21
plover densities at 8.0 birds/km^ in areas of Mountain Plovers, like many species of
Wyoming and Montana. conservation interest, occur in low densities
Our calculated potential habitat of 759 km^ and in a variety of landscapes. Plovers often
for Mountain Plovers in Wyoming is an un- are not detected in general biotic surveys due
derestimation. Most private lands have never to their relative inconspicuousness. Our study
been surveyed for plovers. These lands are took advantage of an existing database of
primarily used for grazing, a majorcomponent mostly casual observations to focus intensive
of plover habitats throughout the year (Knopf surveys for estimating population status in
1996a, Wunder and Knopf 2003). The only Wyoming. This approach may be useful for
desert regions of Wyoming being surveyed quantifying minimum population size ofother
consistently at present are those targeted for species of conservation concern. Existing da-
011 and gas leasing or development. We also tabase records, such as those available from
note that whereas the most productive grazing state Natural Heritage Programs, may be par-
lands in Wyoming are in private ownership, ticularly useful.
our surveys were conducted on publicly
ACKNOWLEDGMENTS
owned, less productive landscapes. Mountain
Plover densities are likely higher in the pri- We are especially grateful to V. L. Sepulveda for
vately owned and more productive land- invaluable field assistance spanning two seasons.
scapes, and those landscapes are under-repre- Thanks to M. B. Wunder for assistance with program
sented in our potential-habitat database. DISTANCE, andtotheU.S. FishandWildlifeService,
U.S. Geological Survey, U.S. Bureau of Land Man-
Considering that the recent global popula- agement, and the Wyoming Game and Fish Depart-
tion estimate for Mountain Plovers is 8,000 to mentforfunding assistance. B. A. Banulis, S. R. Moh-
10,000 individuals (Knopf 1996a), and that ren, N. P. Nibbelink, J. C. Oakleaf, and S. J. Slater
Wyoming’s conservative estimate of 3,393 provided critical GIS support. Field biologists G. P.
plovers may not include birds that (1) occupy Beauvais,T. W. Byer, L. D. Hayden-Wing, L. G. Keith,
large expanses at low densities, (2) occur in T. Maechtle, S. H. Nicholoff, R. J. Oakleaf,M. S. Reid,
isolated small patches of habitat (e.g., historic D. F. Saville, and L. Van Fleet deserve recognition. S.
buffalo wallows; FLK pers. obs.), or (3) breed Ju.scDriipnts.mWoerearperoivniddeebdtehdeltpofullancdoowmnmeernstsinotnhetLhearmaamni-e
at undiscovered spots, Wyoming’s Mountain and Shirley basins forproviding access to theirprivate
Plovers appear to contribute substantially to a lands. We acknowledge R. L. Leachman forhistireless
revised continental population estimate of years of effort to secure the future of Mountain Plo-
1 1,000 to 14,0()0 birds. Furthermore, manage- vers.
ment strategies for Mountain Plover habitat in LITERATURE CITED
Wyoming often emulate the historical ecolog-
ical drivers (e.g., drought and grazing; Knopf Andrews, R. and R. Richter. 1992. Colorado birds:
and Samson 1997) to a greater extent than do a reference to their distribution and habitat. Den-
practices in neighboring states where cultiva- ver Museum of Natural History, Denver. Colora-
do.
tion and urbanization are more widespread.
When rangeland conversion to row cropping BuckiL..aLnada,keS.,TD,. DL.. BRo.rAcnhderesr,soann,dKL..PT.hBolmarsn.ha.2m0,01J..
does occur in Wyoming, it is generally to a Introduction to distance sampling. O.xfcnd Uni-
lesser extent than in other states within the versity Press. New York.
plover’s range. Between 1982 and 1997, more Burnham, K. P. and D. R. Ander.son. 2002. Model
than three times as much rangeland within the .selection and multi-model inference: a practical
information-theoretic approach. Springer-Verlag.
occupied breeding range of Mountain Plovers
New York.
w1a2sticmoensvearstemduicnhMopontteantniaalthhaanbitinatWwyaosmicnogn;- DrEITM/o,vVe.meL.n.tsM.anBd. hWolmNeDIraRn.gAesNDof1.MoL.unKtnaoiint.PI2o0\0e.rSs.
verted in Colorado (U.S. Fish and Wildlife raising broods in three C'olorado landscapes. Wil-
Service 2003). Wyoming’s population of son Bulletin, in press.
Mountain Plovers and relatively intact ex- l iN/i I , .1. F. 1904. Avian populations of four herba-
panses of grazed rangeland may become in- ceous communities in southeastern Wyoming,
(’ondor 00:490 510.
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and agricultural development continues in status of the Mountain Plover, (’ondor 78:205
contiguous states. 207.
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and movements of Mountain Plovers breeding in Register: 64(30):7587-7601
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Knopf, E L. and E B. Samson. 1997. Conservation of ver survey guidelines, http://montanafieldoffice.
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Mengtehfes,is.R.UniMv.ers1i9t7y0.ofTWhyeomNiorntgh, ALmarearmiicea.n central the proposed rule to list the Mountain Plover as
plainsasanisolatingagentinbirdspeciation. Pag- threatened. Federal Register 68(174):53083-
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Norvell, R. E., E P. Howe, and J. R. Parrish. 2003. 80.
A seven-year comparison of relative-abundance WuNDER, M. B., F. L. Knopf, and C. A. Pague. 2003.
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