P.(Paul) Hendricks.

Surveys for grassland birds of the Malta Field Office-BLM, including a seven-year study in north Valley County (Volume 2008) online

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Surveys for Grassland Birds

of the Malta Field Office -
BLM, including a Seven-year
Study in North Valley County

Prepared for:

USDI Bureau of Land Management
Glasgow Field Station

Prepared by:

Paul Hendricks, Susan Lenard, Cobum Currier,
Bryce A. Maxell and John Carlson

Montana Natural Heritage Program

a cooperative program of the
Montana State Library and the University of Montana

April 2008


__^^ Natural Heritage

Surveys for Grassland Birds

of the Malta Field Office -
BLM, including a Seven-year
Study in North Valley County

Prepared for:

USDI Bureau of Land Management
Glasgow Field Station

P.O. Box 871
Glasgow, MT 59230

Agreement Number:

ESAO 10009, Task order #16

Prepared by:

Paul Hendricks, Susan Lenard, Cobum Currier,
Bryce A. Maxell and John Carlson


Natural Heritage

^^ QfatK S-'-mS The University of

^MSrary %J^ Montana

© 2008 Montana Natural Heritage Program

PO. Box 201800 • 1515 East Sixth Avenue • Helena, MT 59620-1800 • 406-444-5354

This document should be cited as follows:

Hendricks, P., S. Lenard, C. Currier, B. A. Maxell, and J. Carlson. 2008. Surveys for Grassland
Birds of the Malta Field Ofl&ce - BLM, including a Seven-year Study in North Valley County.
Report to the Bureau of Land Management. Montana Natural Heritage Program, Helena, MT.
26 pp. plus appendices.


Executive Summary

Grassland-associated birds have exhibited the
steepest population declines of any suite of bird
species in North America over the past several
decades, primarily due to loss of habitat resulting
from conversion of native prairie to agricultural
production. To better understand the relationships
of prairie vegetation structure with presence and
relative abundance of native prairie bird species,
fixed-radius point counts were randomly placed
across BLM lands in north Valley County in
areas with native grassland cover. Our objective
was to gather habitat information to help guide
management of grasslands for a variety of species,
including a suite of grassland birds that are of
conservation concern. The project evolved into
a multi-year inventory (2001-2007). No other
project focused on grassland birds in Montana has
gathered consistent data at the same locations for
this length of time.

More than 75 species of birds were recorded
on 1410 point-counts (189 - 207 points each
year) in north Valley County. Twenty species
were recorded on at least one point count every
year, nine of which are Montana Species of
Concern (SOC): Long-billed Curlew (Numenius
americanus), Sprague's Pipit (Anthus spragueii).
Brewer's Sparrow (Spizella breweri). Lark Bunting
(Calamospiza melanocorys). Grasshopper Sparrow
(Ammodramus savannarum), Baird's Sparrow
(Ammodramus bairdii), McCown's Longspur
(Calcarius mccownii). Chestnut-collared Longspur
(Calcarius ornatus), and Bobolink (Dolichonyx
oryzivorous). Chestnut-collared Longspur occurred
on the greatest percentage (79.7-89.9%) of our
point counts. Next in order of relative abundance
were Horned Lark, Western Meadowlark,
Sprague's Pipit, and Baird's Sparrow. Each of
these species was detected every year on at least
30% of our count points.

The results of our seven-year study revealed
considerable variation in precipitation and
vegetation conditions in north Valley County
that influenced where birds settled during the
breeding season. For the seven years combined.
Long -billed Curlew and McCown's Longspur

occupied sites with shorter and less dense
grasslands, while Grasshopper Sparrow, Baird's
Sparrow, and Bobolink favored taller and denser
grassland patches. Chestnut-collared Longspur and
Sprague's Pipit occupied points with intermediate
vegetation height and density near-the ground.
Lark Bunting tended to occur on sites where
vegetation was moderately taller but of equally low
near-ground density as Long-billed Curlew and
McCown's Longspur. Brewer's Sparrow was most
dissimilar from the other species, occupying points
with tall vegetation but relatively low near-ground

April-May precipitation varied among the seven
years nearly five-fold, with extremes in 2002 and
2007, respectively, and mean vegetation height
and density tended to correspond accordingly.
April-May precipitation accounted for 11% of
variation in mean vegetation height among years
on our points. Likewise, we found April and May
precipitation a good predictor of the percentage
of point counts on which some SOC birds would
occur. Greater numbers of Baird's Sparrow,
Chestnut-collared Longspur, and Bobolink tended
to occur in years with greater spring precipitation,
while Long-billed Curlew showed a negative
response to increased spring precipitation, an
expected pattern because this species selects sites
with low-stature grass for nesting.

Within-year differences in vegetation structure
between occupied and unoccupied points were not
consistently strong across years for any species
except Baird's Sparrow, which occupied points
with taller and denser near-ground vegetation than
was available where it was absent. Grasshopper
Sparrow occupied points each year with taller or
denser vegetation, but not always both. Each of
the other SOC birds occupied points in some years
that did not differ from unoccupied points in either
measure of vegetation structure. That all of these
bird species co-occurred every year, sometimes in
substantial numbers and despite large differences in
preferred vegetation structure, indicates that current
management is maintaining a mosaic of vegetation
conditions at large enough landscape scales to


retain what appears to be a complete or nearly
complete mixed-grass prairie bird community.

Surveys conducted during 2007 in nearby northern
Blaine and Phillips counties found the same SOC
birds in roughly the same proportions, with the
exception of Baird's Sparrow, which was less
abundant, and McCown's Longspur, which was
more abundant (reflecting shorter and less-dense
vegetation in Blaine and Phillips counties). This

suggests that a large region of north-central
Montana continues to support a diverse grassland
bird community. To better understand the extent
of this community, which has not been well
surveyed, we developed predicted distribution
models for 11 grassland SOC birds which should
help focus surveys. Outputs from these models
highlight the importance of Valley, Phillips, and
Blaine Counties to the conservation of these
grassland bird Species of Concern in Montana.



Considerable thanks and appreciation to Dave
Waller, former Glasgow BLM Field Office wildlife
biologist, and Roxanne Falise, former BLM State
Wildlife Program Director, for recognizing the
importance of this project and providing the funds
to make it possible. Thanks also to Sue Crispin,
Director of the Montana Natural Heritage Program,
for her editorial comments on this report.

This project was supported by an agreement
between the Bureau of Land Management and the
Montana Natural Heritage Program (BLM AFA
- ESA010009, Task order #16).

Table of Contents

Introduction 1

Study Area 2

Methods 4

Point Selection and Project Design 4

Survey Timing 5

Avian Point-Count Methodology 5

Vegetation Measurement Protocols 6

Precipitation 6

Statistical Analyses 6

Results 8

Overview 8

Precipitation and Vegetation 9

Precipitation and Annual Abundance of Species of Concern Birds 10

Vegetation Structure and Annual Abundance of Species of Concern Birds 11

Vegetation Structure and the Presence of Species of Concern Birds on Point Counts 12

Discussion 20

Conclusions 22

Summary and Recommendations 23

Literature Cited 24

Appendix A: Global and State Rank Definitions

Appendix B: Summary of point-count surveys in northern Blaine and Phillips counties

during 2007.
Appendix C: Predictive distribution models for grassland birds.

List of Figures

Point count locations in the north Valley County, Montana study area 3

Occurrence of nine Montana bird Species of Concern on point counts in

north Valley County during 200 1-2007 9

June vegetation on three count points (68.3, 90. 1, 93.3) in north Valley

County, contrasting 2006 and 2007 10

April-May precipitation and June vegetation height on count points,

2001-2007, in north Valley County 10

April-May precipitation in north Valley County during 2001-2007 (Opheim

station) and the relative abundance of nine Montana bird Species of Concern 1 1

Ordination of nine Species of Concern birds on vegetation structure in north

Valley County, Montana, based on mean values for 2001-2007 combined 13

Vegetation height and vegetation density (number of rod contacts) for sites
occupied by nine Montana bird Species of Concern in north Valley County

during 200 1-2007 16

Figure B 1 . Point count locations in northern Blaine and Phillips counties,

Montana in 2007 Appendix B - 1
















List of Figures (Con't)

Figure B2. McCown's Longspur nests Appendix B - 4

Figure B3. June 2007 vegetation on three count points in north Phillips

County Appendix B - 4

Figure CI. Composite Image of Predicted Distributions for 11 Grassland Bird

Species of Concern Appendix C - 8

Figure C2. Greater Sage-Grouse Predicted Distribution Outputs Appendix C - 9

Figure C7. Mountain Plover Predicted Distribution Outputs Appendix C - 14

Figure C 1 2 . Long-billed Curlew Predicted Distribution Outputs Appendix C - 1 9

Figure C17. Sprague's Pipit Predicted Distribution Outputs Appendix C - 24

Figure C22. Brewer's Sparrow Predicted Distribution Outputs Appendix C - 29

Figure C27. Lark Bunting Predicted Distribution Outputs Appendix C - 34

Figure C32. Grasshopper Sparrow Predicted Distribution Outputs Appendix C - 39

Figure C37. Baird's Sparrow Predicted Distribution Outputs Appendix C - 44

Figure C42. McCown's Longspur Predicted Distribution Outputs Appendix C - 49

Figure C47. Chestnut-collared Longspur Predicted Distribution Outputs Appendix C - 54

Figure C52. Bobolink Predicted Distribution Outputs Appendix C - 59

List of Tables

Table 1. Summary of observers, number of transects, and number of point counts

each year 5

Table 2. Bird species of conservation interest occurring on point counts in north

Valley County during 2001-2007 7

Table 3. Bird species detected every year (2001-2007) within north Valley County,

Montana point-count circles 8

Table 4. April and May precipitation (cm) measured at the Opheim station (0PMM8),

north Valley County 9

Table 5. Descriptive statistics (mean [SD]) for vegetation measurements at North

Valley County point counts, 2001-2007 9

Table 6. Spearman correlations between percent occurrence on point counts for nine

SOC birds and vegetation height and vegetation density index (contacts),

2001-2007 12

Table 7. Vegetation height and vegetation density index (contacts) comparing points

where nine SOC birds were detected and not detected, 2001-2007 12

Table 8. Mean vegetation height and near-ground vegetation density (contacts 0-1 dm)

for points occupied by nine Montana SOC birds 14

Table 9. Mean vegetation height and density index (contacts 0-1 dm) comparisons

for points where nine Montana SOC birds were detected and not detected 19

Table B 1 . Bird species detected on point counts in north Blaine and Phillips

counties in June 2007 AppendixB - 3


List of Tables (Con't)

Table B2. Comparison of the relative abundances (percent of point counts) for
eight Montana Species of Concern birds in north Blaine and Phillips
counties and north Valley County that were detected on point counts
in 2007 AppendixB-3

Table C 1 . Overview of Bird Observations Used in Modeling Effort Appendix C - 3



In recent decades, grassland bird populations
have exhibited range-wide declines (Knopf 1994,
Peterjohn and Sauer 1999, Vickery et al. 1999,
Askins et al. 2007). Historical conversion of the
landscape to agricultural cropland is clearly the
greatest contributing factor to loss of suitable
habitat (Samson and Knopf 1994, Fitzgerald et al.
1999, Knapp et al. 1999, Blann 2006). Habitat
loss resulting from fragmentation and conversion
for agricultural, industrial, and human habitation
uses continues, contributing further to grassland
bird population declines. Additionally, a variety of
land management practices in areas of remaining
intact prairie can negatively impact prairie bird
populations (Saab et al. 1995). Worldwide,
grasslands are recognized as the most imperiled of
terrestrial landscapes (Samson and Knopf 1996).

Individual grassland bird species choose where
to settle for breeding and nesting from a matrix
of habitats available across the prairie landscape.
Historically, each species probably exhibited
pronounced fluctuations in local abundance as
vegetation conditions changed in response to
drought, fire, and grazing by bison and locust.
The extermination of bison, the extinction of
Rocky Mountain locust, and aggressive control
of fire during the settlement of the Great Plains
profoundly altered the composition of grasslands
(Knapp etal. 1999). Grassland associated species
favoring vegetation structure and composition
promoted by human activities (managed grazing,
fire suppression, and annual mowing) have
generally benefited, while species requiring a
more natural disturbance regime (periodic fire
and historic grazing patterns) have generally
experienced declines (Sauer et al. 2005). Because
of the widespread loss of native grasslands,
remaining tracts of prairie grassland vegetation are
increasingly valuable for native bird species.

Understanding how grassland birds respond to
different vegetation conditions can contribute to
the range-wide conservation of prairie bird species,
because this permits managers to manipulate
vegetation in ways that can promote or inhibit
settlement and nesting. Unlike other areas in the
Northern Great Plains, populations of many native
grassland bird species have been relatively stable
in northeastern Montana over the last 40 years
(Sauer et al. 2005). Thus, north Valley County is
ideal for understanding the ways in which a suite
of grassland birds responds to "natural" variation
in grassland conditions, because it appears the
impacts of livestock grazing on vegetation structure
of public rangelands throughout much of the region
are relatively minor.

The purpose of this report is to provide a
summary of project activities during 2001 - 2007,
supplementing Lenard et al. (2006) and Hendricks
et al. (2007). In this report we 1) identify the
regular grassland-breeding bird community in
north Valley County (revised from earlier reports),
2) provide an assessment of the status of a suite of
Montana bird Species of Concern (SOC) that are
members of this community, 3) identify the role
spring precipitation plays in fluctuations of these
species through its effects on vegetation structure,
and 4) describe the range of vegetation conditions
where each species settled during the nesting
period. In addition, we provide the results of a
one-year survey of grassland birds conducted in
adjacent northern Blaine and Phillips counties (on
lands administered by the Malta Field Office-BLM)
in 2007 and contrast these with results of the north
Valley County project. Finally, we present and
discuss predicted distribution models for the nine
grassland SOC birds we discuss more fully in this
report. We anticipate these models will be useful
for guiding future survey and monitoring efforts.

Study Area

Located on the Northern Glaciated Plains, the study
area lies in the northern half of Valley County
in northeastern Montana (Figure 1). The county
lies adjacent to the border with Saskatchewan,
Canada and is bounded by the Missouri River to
the south, Phillips County to the west and Daniels
and Roosevelt Counties to the east. The project
area includes BLM lands north of Glasgow, east
of Opheim and west of Valleytown, in an area
roughly 45 x 30 miles (1350 square miles). Bitter
Creek, Frenchman Creek, Crow Creek, Rock
Creek, Willow Creek, and Buggy Creek, all located
generally within the project boundaries, drain
to the Milk River. The Bitter Creek Wilderness
Study Area, nearly 60,000 acres of highly eroded
badlands recognized for its unique, isolated and
unspoiled nature, is situated approximately at the
project center. To the east and adjacent to the
project area is Dry Fork Creek, primarily contained
within a large block of Montana Department of
Natural Resources Conservation lands. Cooper et
al. (2001) describe this area as possibly the best
intact site of a rare mid-grass prairie (northern
porcupine grass-thickspike wheatgrass) remaining
in the United States.

The physical characteristics of this area are
similar to the surrounding lands. Glacial till and

outwash cover the terrain as the area's gently
rolling landscape was scoured by at least two
glacial events. The most common substrate in
the project area is clay shale, marine in origin and
dark grey in color (Cooper et al. 2001). The local
climate is considered semi-arid with precipitation
of approximately 10-14 inches (25.4-35.6 cm) per
year, much of it falling as early summer rains in
late May and early June. Winters are generally
frigid while the summers can be hot, punctuated
by hail-producing thunderstorms that can result in
flash floods. The greatest topographic variation
in the county occurs at its eastern half; the highest
elevation of approximately 3,300 feet (1006 m)
occurs near Opheim to the north, while the lowest
elevation of approximately 2,000 feet (610 m)
occurs where the Missouri River leaves the county
to the south. Specific point locations on the project
ranged from 2,448-3,049 feet (746-930 m) in
elevation. While the primary landcover within the
project boundary is native mixed-grass prairie, the
majority of the surrounding land has been cropped
for agricultural production. This area is significant
as it encompasses the most extensive remaining
piece of intact prairie land in Montana. For a more
detailed description of vegetative communities and
distinguishing attributes specific to the study area
see Cooper et al. (2001).


^ Point Ceqrfit Loeatsan

Bur#aucfLand Managfl^mfri
^^ M^KmaSdwOtTmn Lands

I j Pitvsltlmi

Sin am

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Figure 1. Point count locations in the north Valley County, Montana study area.


Point Selection and Project

The long-term project (2001-2007) focused on
BLM lands in north Valley County, supplemented
by similar work in northern Blaine and Phillips
counties in 2007. Initial steps for identifying where
to sample for birds involved using a Geographic
Information System (GIS) to stratify the area under
consideration by soil type using the University of
Montana Satellite Image Land Cover Classification
(SILC) soil data. Areas classified as having silty
soils, those that support growth of native grass
species important to grassland birds, were used to
delineate the area within which inferences were
to be made (i.e., the target population). Areas
classified as high clay content soils were eliminated
from survey, because the vegetation associated
with clay soils does not generally support a broad
diversity of grassland birds. Eliminating high-
clay soils effectively eliminated the badlands area
surrounding Bitter Creek located at the center
of the study area. However, some areas on the
western portion of the project ended up being
located in areas with high-clay soil.

Within the area targeted for sampling, 120 bird
survey point locations were randomly generated
from which we originated transects for the
project. Originally, each point-count transect
was to consist of four points. However, since the
original point locations were random, it would
have been difficult, if not impossible, to generate
a line of four points within one pasture (generally
a quarter-section) given the 300 meter minimal
distance required between points for standard
point-count protocol (Hutto et al. 1986, Drapeau
et al. 1999). Thus, the scope of the project was
changed to accommodate transect lines consisting
of three points. After locating the randomly-
generated point on the ground via a GPS unit, the
second and third points were identified by field
personnel walking no less than 300 meters from
each previous point, resulting in a total straight line
transect length of approximately 600 meters. Each
of the three points defined the spot at which each
point-count survey was conducted. Coordinates

for all points were recorded on GPS units for
finding survey locations in subsequent years. The
second and third points in each transect were
generally established to the northeast if there was
room to do so and remain in the same pasture as
the original point. If this was not the case, then
the points were oriented to the southwest of the
original point. Efforts were made to keep all three
points within the same pasture/grazing treatment.
This sometimes necessitated placing the second
and third points on opposite sides of the first point
(one to the northeast and one to the southwest). If
a northeast-southwest placement was not possible,
then a northwest-southeast orientation was
followed, in whichever direction allowed the points
to be contained within one pasture. Inadvertently,
and due to time constraints at the start of the
project, nine transects ended up with points not
wholly contained within one pasture. One transect
includes one point-count circle entirely in a
different pasture; 7 transects include all center
points in the same pasture, but one of the 100 m
radius point-count circles overlapping an adjacent
pasture; and 2 transects include one point with the
center in an adjacent pasture but a portion of the
100 m point-count circle within the first pasture.

During the first field season (2001) the points
were divided among two field personnel such
that points west of the Willow Creek/Bitter Creek
area were assigned to one observer while those
on the east were assigned to the second observer.
The points ultimately surveyed were selected
across each region based upon accessibility and
distribution. Points were generally considered
accessible if they could be reached by vehicle (on
existing two-tracks) to within a walking distance
of approximately one mile. Effort was also made
to survey both the eastern and western points
such that the maximum north-south distribution
was accomplished. Field personnel attempted to
maximize the number of point counts conducted in
a day; 3-4 transects (9-12 points) were targeted
each morning.

Point counts were conducted by Paul Hendricks
and John Carlson during the first three years

(2001-2003) of survey (Table 1). In 2004, the
point counts were conducted by four individuals:
Paul Hendricks, John Carlson, Susan Lenard,
and Coburn Currier. In 2005 - 2007, Hendricks,
Lenard, and Currier conducted the counts. During
the initial year (2001), 69 of the 120 original
random points were surveyed, with three points
per transect for a total of 207 point counts. These
original 69 transects became the targeted transects
for survey each subsequent year through 2007.
Although we attempted to conduct point-count
surveys on all points every year, weather conditions
and time restrictions prevented this from occurring
some years.

Survey Timing

Across all years, point-count survey work
commenced on or after 21 May (usually after 1
June) and was completed on or before 12 July;
effort was made each year to complete all counts

by the end of June. Except for two transects during
2001, point counts began as early as sunrise and
were completed by 10:37. During the start of
the project, Paul Hendricks observed the level of
vocalization of prairie birds in the evening hours
appeared comparable to the early morning hours
and conducted six point counts (two transects)
in the evening hours, between 19:00 and 19:40.
Subsequently, the decision was made to restrict
surveys to the morning hours, although studies in
grasslands elsewhere (Swengel and Swengel 2000)
indicated no single period of the day was optimal
for detecting all bird species.

Avian Point-Count Methodology

All point counts were ten minutes in duration
and conducted within approximately five hours
following sunrise (and generally not earlier
than 05:50). During each point count, birds
observed during time intervals of - 3 minutes.

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