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Third Year Report: The Effects of Prescribed Fire and Shrub-layer
Mastication on Bird Communities in Ponderosa Pine Forests of the San Juan
Mountains, CO
A Citizen Science Project conducted by members of the
Weminuche Audubon Society
and
Audubon Rockies
In cooperation with
The San Juan Headwaters Forest Health Partnership
and
Mountain Studies Institute
Report Prepared By:
Herb Grover, and Jean Zirnhelt, Weminuche Audubon Society, Pagosa Springs, CO,
and
Keith Bruno, SW Colorado Community Naturalist for Audubon Rockies, Pagosa Springs,
CO.
December, 2021
2
Abstract:
The use of prescribed fire and mechanical thinning to reduce wildland fuels is a common practice in the Ponderosa
Pine-dominated forests of the American Southwest. The effects of these treatment methodologies on bird
communities has received a great deal of attention across Arizona and New Mexico, but very little work has been
done in southcentral or southwestern Colorado. Working through the San Juan Headwaters Forest Health
Partnership, a collaborative of local, state, and federal agencies and organizations, we assembled a team of
volunteers associated with the local Weminuche Audubon Society in 2019, 2020, and 2021 to monitor bird
community composition in three sites dominated by Ponderosa Pine that were subject to prescribed fire in 2019,
coincident with the initiation of the study (Turkey Springs site); mechanically thinned in 2017 (Fawn Gulch); and a
mature Ponderosa Pine forested site that has not been burned or thinned for more than 75 years (Jackson Mountain).
As documented in our first-year report, tree density at the Fawn Gulch (FG) site (85 trees/ha) was less than at either
the Turkey Springs (TS) (128 trees/ha) or Jackson Mountain (JM) (132 trees/ha) sites. Gambel Oak dominated the
shrub layer at all three sites, which was largely absent at the TS site after prescribed fire in 2019, but recovered by
2020; widely dispersed at FG; and notably most dense at JM. Data on bird species presence and individual bird
counts by species were collected at 15 monitoring points at each site a minimum of ten times across a seven-week
period beginning in late May of 2019, 2020 and 2021. Looking across the three years of the study, 82 bird species
have been documented, with 37 species, common to all years, representing over 90% of sightings. Twelve species
were observed at all three sites in all three years of the study, accounting for about 67% of all birds counted. There
were 9 species unique to the 2019 season, 10 species found only in our 2020 sample season, and 10 species found
only in 2021. The TS site, which had the fewest species and birds counted in 2019, showed noticeable recovery to
37 species and 688 individual birds in 2020, and 35 species accounting for 609 birds in 2021. The FG site, which
had the greatest number of species of the three sites in 2019 (34 species), was surpassed in number of species by the
JM site in 2020 (45 species and), but had more birds counted in 2020 compared to JM (856 vs. 683, respectively).
In 2021, JM had slightly more bird species and birds counted compared to the other two sites. Summing across
years, FG had a greater number of species observed (63 vs. 58 at JM and 49 at TS), and a greater number of birds
counted (1936 vs. 1613 at JM and 1482 at TS). Grouping bird species into feeding guilds, and the application to
our data of simple measures of species diversity, species evenness, and community similarity provide further
insights that are discussed. We analyzed nesting behaviors with a focus on cavity nesters. Species-level responses
to wildland fuel reduction treatments indicate that several species benefited from the effects of shrub-layer thinning
treatments, including several species that have exhibited marked population declines over the past 50 years or so.
These findings suggest that treatments contributing to forest heterogeneity have a short-term negative impacts on
bird communities, with relatively quick recovery within a year or so, followed by a net positive impact on bird
communities over the long-term and at a regional/landscape scale.
Acknowledgments:
The data and information generated by this study is the work of many dedicated volunteers who collectively
contributed more than 600 hours to the completion of this project in each of the three years of the study. Their
names (in alphabetical order) are: (Note: a = 2019 participant; b = 2020 participant; c = 2021 participant)
Carol Ashmorea, b
Bob Endresa, b, c
Gary Hopkinsb
Joan Rohwerb, c
Ben Baileya, c
Karissa Fosterb
Donna Huffmanc
Darryl Saffera
Bill Bredinga, b
Savannah Fosterc
Kurt Huffmanc
Anna Schneiderc
Brenda Bredinga, b
Gloria Godob
Liz Jamisonb, c
Marie Smithb
Pat Bremera, b, c
Byron Grecoa, b, c
Charles Martineza, b, c
Loyette Stewarta, b, c
Keith Brunoa, b, c
Herb Grovera, b, c
Holly Mathewsc
Anne Stevensa, b, c
Tricia Byersa, b, c
Linda Groverb
Kim Mathewsc
Jim Stevensa, b, c
Diane Cirksenaa
Jaqueline Hagberga
Susan McAdamsa, b
Kathy Strangb
Suzanne Coea
Rob Hagberga, b
Randy McCormicka, b, c
Tom Strangb
Maureen Collinsa, b, c
Dana Haywardb, c
Kitty Nealc
Alyce Walkerc
John Duvalla, b
Deb Haywardc
Rita Peckb
Jean Zirnhelta, b, c
Becky Endresa, c
We also appreciate the assistance of USFS personnel Anthony Garcia, Mat Tuten and Fred Elliot in locating
prospective study sites, and Anthony Culpepper of Mountain Studies Institute for providing treatment and vegetation
data used to characterize the sites chosen for our study. Thanks also go to several unnamed reviewers who
commented on earlier drafts of this report.
3
Third Year Report – A Citizen Science Project:
The Effects of Prescribed Fire and Shrub-layer Mastication on Bird Communities in Ponderosa Pine Forests
of the San Juan Mountains, CO
Introduction:
In 2019, members of the Weminuche Audubon Society (WAS - http://www.weminucheaudubon.org ), partnering
with Audubon Rockies (https://rockies.audubon.org), the San Juan Headwaters Forest Health Partnership (SJHFHP -
http://sanjuanheadwaters.org ) and its member organizations and agencies (e.g., Mountain Studies Institute -
https://www.mountainstudies.org), United States Forest Service (USFS) Pagosa Ranger District -
https://www.fs.usda.gov/detail/sanjuan/about-forest/districts/?cid=stelprdb5154746 ), initiated a study of how bird
community species composition and structure in Ponderosa Pine forests in the San Juan Mountains of southwestern
Colorado might be affected by mastication and/or prescribed fire treatments designed to reduce wildland fuel loads.
The report for the first and second years of the study (Grover et. al., 2019; Grover et. al., 2020) can be downloaded
from the Weminuche Audubon Society website at http://www.weminucheaudubon.org/bird-community-monitoring/.
First and second year findings are also summarized in YouTube videos posted at
https://www.youtube.com/watch?v=mfBiFN0gR6A and https://youtu.be/zI1QNo7qZBU, respectively. The results
from the 2021 sample season for this project are the primary focus of this report, along with comparisons to earlier
years of the study.
There is a vast literature detailing the consequences of livestock grazing and forest management practices on the
buildup of wildland fuel loads and increased densities of woody understory growth in dry and moist mixed-conifer
forests across the western United States (e.g., Baker, 2018; Block and Conner, 2016; Covington, 1994; Harrington
and Sackett, 1990; Korb et. al., 2013; McWethy et. al. 2019; and Romme et. al. 2009). As evidenced by the record
expanse of wildland fires in western states over the past several years, and the catastrophic consequences of these
fires for residential communities located in the wildland-urban interface (WUI) (e.g., Ager et. al., 2019), moderating
the buildup of wildland fuel loads is receiving much greater emphasis by managers of forested landscapes. Notably,
current forest management practices emphasize various approaches to reducing wildland fuel loads, including
selective harvesting and/or thinning; prescribed fires; and understory removal by mastication (i.e., mowing). These
management practices have the potential of impacting wildlife in affected areas, including forest bird communities
(see Block and Conner, 2016; and Lowe et. al., 1978) by modifying forest composition and structure, thereby
affecting habitat quality and food resources for a wide range of species.
USFS personnel with the Pagosa Ranger District in the San Juan National Forest, in collaboration with the SJHFHP,
have been proactive in implementing understory mastication and prescribed fire treatments to establish strategically
defensible areas in the dry and moist mixed-conifer forests surrounding Pagosa Springs, CO. This led some local
residents interested in bird conservation to wonder how fire mitigation practices implemented in these forests might
affect the distribution and abundance of bird species in and around the treatment areas, resulting in a citizen science
bird monitoring project initiated in 2019 (Grover et. al., 2019) that has continued with data collection in 2020
(Grover et. al. 2020), and 2021.
As a citizen science project, this study incorporates several objectives complementary to the scientific question that
is being investigated. For example, volunteers participating in this study have become better informed regarding:
• the ecology of fire and its importance to our surrounding forest ecosystems;
• how and why catastrophic wildfires have become more common and destructive;
• what agencies charged with forest management are doing to mitigate wildfire occurrence and severity; and
• why the residents living in the WUI should be interested in this issue.
Added benefits of the study also include opportunities for participants to:
• improve their birding skills by learning from one another;
• gain a better understanding of how scientific field studies are conducted; and,
• strengthen the community of conservation-minded birders in our area.
Study Areas:
Detailed descriptions of the three study areas included in this project, and methodologies for characterizing these
sites – Turkey Springs (TS); Fawn Gulch (FG); and Jackson Mountain (JM) – are found in the first-year report
4
(Grover et. al., 2019; http://www.weminucheaudubon.org/bird-community-monitoring/). Table 1 from the first-year
report, summarizing site characteristics, is included below. Note that all three sites are located within approximately
16 km (~10 miles) of Pagosa Springs, CO, and are comparable in elevation and slope characteristics. The sites
differ, however, in overstory tree densities and shrub-layer characteristics, due in large part to the timing and types
of fire mitigation measures aimed at reducing wildland fuel loads at TS and FG, while no such measures have been
implemented for many decades at JM. The TS site was subject to prescribed fire at the outset of the 2019 sample
season in early June; the FG site was subject to shrub-layer mastication treatment in 2017; while there is no record
of the JM site ever having been subject to intentional management to reduce wildland fuel loads.
Table 1. General site characteristics of Turkey Springs (TS), Fawn Gulch (FG), and Jackson Mountain (JM)
study areas. (from Grover et. al. 2019)
Turkey Springs (TS)
Fawn Gulch (FG)
Jackson Mountain (JM)
Approximate Study Area (ha)
23
26
16
Lat/Long Approx. Center Point:
37.29036; -107.15552
37.31866; -106.93801
37.34598; -106.94378
Elevational Range:
~ 2400 m to ~ 2470 m
(~ 8000 ft to ~ 8100 ft)
~ 2380 m to ~ 2400 m
(~ 7800 ft to ~ 7900 ft)
~ 2340 m to ~ 2400 m
(~ 7675 to ~ 7875 ft)
Aspect:
E to ENE (gentle slope)
NW (gentle slope)
SSW (moderate slope)
*Tree Density (# trees/ha):
128a
85a
132a
Tree Density (# trees/ha) – Ponderosa Pine Only
128
79
110
*Mean Inter-tree distance (m) [SE]
8.8 [0.52]a
10.9 [0.82]b
8.7 [0.79]ab
*Mean DBH (cm) [SE]
41.1 [2.33]
42.8 [1.54]
36.6 [1.99]
*Mean Area/Tree (m2)
77.9
118.2
75.94
*Basal Area (m2/ha)
20.26
13.1
16.26
Bird Community Sampling Methodology: (see also Grover et. al. 2019, and 2020)
The bird community sampling design employed in this study is a modification of established methodologies used by
the Bird Conservancy of the Rockies to study riparian areas in southwestern Colorado (see van Boer et. al., 2018)
and other similar studies of bird community response to wildland fuel reduction treatments or wildland fires (e.g.,
Hurteau et al., 2008; Jentsch et al., 2008). We identified areas within each study site where three “loops” of five
monitoring points each were established. Monitoring points were located at least 75 m away from forest roads, and
at distances of approximately 75 m from one another (Figs. 2, 3, and 4). By arranging monitoring points in “loops”,
monitoring teams would end their session closer to the starting point of their transect, minimizing “downtime”
walking back to their starting point.
For the second and third seasons of this study, special precautions were taken to adhere to established CDC
guidelines with regard to COVID-19 transmission. However, the majority of volunteers in 2021 were vaccinated,
which minimized risk of infection. Regardless, volunteers were advised to refrain from participation if they felt ill;
they were discouraged from carpooling to the sites; and distancing guidelines and wearing masks was also
encouraged, even while in the field. Otherwise, the sampling protocols established in 2019 were followed in 2020
and 2021 for collecting data from each loop of monitoring points as follows:
• Teams of at least two volunteers each were identified and assigned responsibility to collect data for two
loops per team at a particular study site over a period of seven weeks, beginning on or about the third week
of May, and ending on or about the second week of July 11.
• Each team was asked to visit their assigned loops at least four times over the period of the study. In
addition, each team was asked to visit 2 loops at each of the other two sites. Team members were also
encouraged to visit additional sites with other teams to gain from, or contribute to the birding experience of
co-participants.
• Data collection consisted of visiting each point on each assigned loop for 6 minutes, and recording and
counting birds identified by sight or song during that 6-minute sampling interval.
• Only birds within approximately 35 m of the monitoring point, or halfway between points, were to be
recorded.
• All sampling at the monitoring points was to be completed between the hours of 6 am and 10 am.
• Incidental bird identifications during the walk from one point to the next could be recorded separately;
• Incidental bird identifications in areas separate from established study loops (i.e., at or near where vehicles
were parked) could also be recorded separately.
5
Figure 1. Map showing locations of Turkey Springs, Fawn Gulch, and Jackson Mountain study areas.
Figure 2. Map showing locations of monitoring points within Turkey Springs study area. TS = Turkey
Springs; L # = Loop number; P # = Monitoring point number.
Fawn Gulch
Turkey Springs
Pagosa Springs
Jackson Mountain
6
Figure 3. Map showing locations of monitoring points within Fawn Gulch study area. FG = Fawn Gulch; L #
= Loop number; P # = Monitoring point number.
Figure 4. Map showing locations of monitoring points within Jackson Mountain study area. JM = Jackson
Mountain; L # = Loop number; P # = Monitoring point number.
7
The overall study design consisted of 3 loops at each of the 3 sites previously described – TS; FG; and JM. A
sufficient number of birders volunteered for the study in 2021 to assign 3 teams to each site, with one additional
team “floating” across all three sites. The experience of the team members varied from accomplished birders to
those self-identified as being at an intermediate or beginner skill level. Each site had at least one team of
accomplished birders assigned. This design provided redundancy in loop coverage, and allowed for each site to be
visited on a regular basis by a team of accomplished birders. Teams were encouraged to visit sites or loops other
than those assigned to them as well, and accomplished birders were encouraged to assist the teams of
intermediate/beginner birders as much as possible.
Over the course of the study, there have been 42 different volunteer observers involved, with about 25 observers
actively participating in the study each year (see Acknowledgements). Table 2 summarizes the number of loop
visits per site by year. In the total dataset for 2019, FG received more site visits than TS and JM. To make the data
comparable across sites in that year, 4 FG site visits were selectively removed to re-balance the project dataset. The
details of that process are explained in our first-year project report (Grover et. al. 2019). Greater care was exercised
in 2020 and 2021 to coordinate site visits to yield a dataset that was balanced across sites in terms of number of loop
visits. In the process of analyzing our 2020 dataset, we determined that 10 visits to each loop was the most efficient
strategy for our study – i.e., a greater number of loop visits did not yield additional information critical to our
analysis.
Table 2. Summary of number of loops visited per site and total number of volunteer observers visiting each
site by year. (see also Grover et. al. 2019 and 2020)
Site
Turkey Springs
Fawn Gulch*
Jackson Mountain
Loop Visits
Observers
Loop Visits
Observers
Loop Visits
Observers
2019
22
44
19
42
18
42
2020
34
108
35
114
36
100
2021
31
105
31
84
30
98
* 2019 data shown for FG are re-balanced. (See Grover et. al. 2019 for detailed explanation)
Multiplying the number of team members per visit times the number of visits and loops per visit reveals for 2020,
108 observer-visits at TS; 114 observer-visits at FG; and 100 observer-visits at JM, and 105 vs. 84, vs. 98 observer-
visits, respectively, in 2021. With the benefit of the experience from the 2019 and 2020 field seasons, the bird
identification skills of many of our observers were also markedly improved. It is worth noting that across all three
years, between 50% and 75% of bird identifications were by sight; the remainder being by song. This is in contrast
to other similar studies in which identification by song is more common than by sight.
We conservatively estimate that each observer-visit entails a minimum of 2.5 hours of volunteer time. Add to this
estimated time involved in orientation sessions; site preparation; tree sampling visits (2019 only); and data analysis
and report preparation yields estimates of over 500 volunteer hours in 2019; over 900 hours in 2020; and over 800
hours in 2021.
Results and Discussion:
Table 3 summarizes the bird species documented for 2021 that were common to all
three sites; unique to each of the three sites; or documented at two of the three sites.
Of the 60 total species recorded for 2021, 22 were found at all three sites this year.
Comparing sites in 2021, 35 total species were recorded at TS, with 6 species unique
to that site; 40 total species were recorded at FG, with 7 species unique to that site;
and 43 total species were recorded at JM, with 11 species unique to that site.
In 2021, the number of birds counted across all three sites, totaling 1855, were evenly
distributed across the three sites, with 33% at TS; 32% at FG; and 35% at JM (Tables
3 and 4). Corresponding data tables from our first- and second-year reports are
included as Appendix A to this report (see also Grover et al., 2019, and 2020).
Definitions:
Common – bird species that have been
reported at more than one study site or
in more than one year, including those
37 species observed in all three years of
the study, or those species ranked in the
top 15 species by relative abundance.
Uncommon or rare – bird species
observed in small numbers, typically
fewer than 10, and observed at only one
or two sites or in only one or two years
of the study.
Unique – bird species observed at only
one site or in only one year; typically, in
small numbers (fewer than 5 birds).
8
Table 3. Summary of the 60 different bird species observed across the three study areas in 2021. Data shown
are the number of sample points at which respective bird species were recorded (i.e., frequency); and the
number of birds of the respective species observed (i.e., abundance). Species lists represent those found at all
three sites, sorted by abundance within the respective sites; those unique at any one of the three sites, sorted
by abundance within the respective sites; and those found at two of the three sites, unsorted
The cumulative relative abundance for the 22 species common to all three sites totaled 87.4% of all sightings (Table
3; calculations not shown). At TS, the common bird species accounted for 84.6% of the birds documented at that
site, with slightly greater cumulative relative abundances of 89.1% at FG, and 88.7% at JM.
Each of the species unique to a particular site were observed in small numbers (i.e., 1, 2, or 3 individuals), with
cumulative relative abundances for unique species ranging from 9% at JM, to 5% at FG, and 3% at TS. For those
species found at any two sites, the cumulative relative abundances were between 1.7% and 5.8%. This indicates that
species common to all three sites represented the majority of bird sightings recorded, and that those common bird
species were more-or-less evenly distributed across all three sites.
As shown in Table 4, 82 different species of birds have been recorded across the three years of this study, with a
total of 5031 birds counted. The number of species unique to a site varied from 4 at TS in 2019, to 11 at FG in 2019
9
and JM in 2020 and 2021. These numbers are also summarized in detail in Table 3, and Appendix A. Note that the
Hermit Thrush, a species unique to JM, was the only species observed at a single site across all three years of the
study, as shown in Table 4 in the “All Years” column.
The number of species common to all sites within years is also shown in Table 4, ranging from 15 in 2019, to 26 in
2020. Twelve species were seen at all three sites in all three years (see also Table 6 below).
Table 4. Summary of total number of bird species and birds counted across years at all three sites. The
heading “All Years” represents summations across all years of the study. Unique bird species refers to
species observed only at a respective site in a given year or across multiple years. (see also Grover et al. 2019,
and 2020)
Year
2019
2020
2021
All Years
Total # Different Species
54
58
60
82
Total # Birds Counted
949
2227
1855
5031
# Unique Bird Species by
Site:
Turkey Springs
4
4
6
0
Fawn Gulch
11
7
7
0
Jackson Mountain
8
11
11
1
Species Common to All Sites
15
26
22
12
Figure 5 further illustrates how the numbers of bird species identified per site differed across years. In particular,
the number of bird species recorded for TS increased from 26 in 2019, to 37 and 35 species in 2020 and 2021,
respectively. This likely reflects the response of the bird community to recovery of the understory following the
prescribed fire treatment that was implemented on this site concurrent with the initiation of the study in 2019. At
FG, the number of bird species ranged from 33 in 2019 to 40 species in 2021. However, referring back to the un-
balanced data provided in our first-year report (Grover et. al. 2019) reveals that 39 species were identified at FG in
2019. This would suggest that, with increased sample density, the number of bird species at FG has been fairly
uniform across years.
There was a notable increase in numbers of bird species observed at JM, from 33 in 2019, to 45, and 43 species in
2020 and 2021, respectively (Fig. 5). As noted previously, JM differs substantially from the other two sites in terms
of shrub-layer height and density. This makes bird identification more challenging in that identification by song
becomes more important as shrub-layer foliage density impairs sight identification. It is likely that, over the course
of this study, the observers visiting JM on a regular basis improved their skills at identification by song, which, in
addition to year-to-year variability, could account for the trend observed in numbers of species documented at JM.
Another contributing factor to greater number of birds and bird species observed at JM in 2020 and 2021 is the
continued thinning and logging activity taking place in the areas surrounding our study sites, which could make our
study site a refuge area for some birds.
The numbers of birds counted at each site in each year of the study is summarized in Table 4, and illustrated by site
in Figure 6. The lower number of birds counted in 2019 likely reflects fewer loop visits in 2019 compared to 2020
and 2021 (see Table 5). The inexperience of volunteers with data collection protocols in the first year of the study
may have been a contributing factor as well. Notably, the number of monitoring points at which no birds were
sighted (Table 5) is much higher in 2019 compared to the other years of the study across all three sites.
Table 5. Summary of total points monitored at each site (# loop visits x 5 points/loop), along with number
points with no birds observed in each year. Note that percentages are rounded to the nearest whole number.
Points Monitored
Points with no Birds
Site
2019
2020
2021
2019
2020
2021
Turkey Springs
110
170
155
18 (16%)
10 (6%)
13 (8%)
Fawn Gulch
95
175
155
14 (15%)
3 (2%)
4 (3%)
Jackson Mountain
90
180
150
15 (17%)
12 (2%)
4 (3%)
10
Figure 5. Summary of number of bird species observed by site and by year.
Figure 6. Summary of number of birds counted at each site by year.
The impacts of the 2019 prescribed fire on the TS bird community likely accounts for the lower number of bird
species and lower number of birds observed there compared to other sites as well (Table 4). Bird counts at TS
increased substantially in 2020 and 2021, corresponding to recovery of the understory shrub-layer (Fig. 6), but the
number of points lacking bird sightings remains high at TS relative to the other sites across all years (Table 5),
49
26
37 35
63
34
39 40
58
33
45 43
0
10
20
30
40
50
60
70
3-Yr Total 2019 2020 2021
Number of Different Species
Bird Species by Year and by Site
Turkey Springs Fawn Gulch Jackson Moutain
1482
185
688 609
1936
486
856
594
1613
278
683 652
0
500
1000
1500
2000
2500
3-Yr Total 2019 2020 2021
Tota l Nu mber of Bird s by Site a nd by Ye ar
Turkey Springs Fawn Gulch Jackson Mountain
11
suggesting that habitat quality (e.g., shrub layer density) remains less favorable for the bird community compared to
the other sites.
At FG, there were substantially more birds counted in 2020 than in 2019 (a difference of 370 birds), or 2021 (a
difference of 262 birds) (Fig. 6). Sample density may account for some proportion of this increase as the number of
loops and points visited in 2020 (see Table 2 and Table 5) was greater at FG than in other years or at other sites, and
the number of observer-visits (114; Table 2) was also greatest at FG in 2020 compared to the other sites.
Table 6 summarizes the distribution of the number of common or unique bird species observed at each site within
and across years. For example, of the 82 total bird species recorded over the first three years of this study, 49 were
recorded at TS; 63 at FG; and 58 at JM (see also Fig. 5). At TS and FG, 18 species were observed in all three years
of the study (i.e., common), with 26 species common to all three years at JM. At TS and JM, the species common to
all three years accounted for 85% and 86% of the birds counted at those sites, respectively. FG stands out as having
76% of the birds observed accounted for by species common to all three years, and a much higher proportion of
birds unique to each year of the study (~ 9% at FG) compared to TS (~5%) and JM (~3%).
Table 6. Summary of bird species numbers and relative abundances grouped across or within years by site.
Turkey Springs
Fawn Gulch
Jackson Mountain
# Species
Cum Rel
Abund (%)
# Species
Cum Rel
Abund (%)
# Species
Cum Rel
Abund (%)
TOTAL Species
49
63
58
All Years
18
85.3
18
76.3
26
86.1
2019+2020
2
0.3
2
0.8
3
2.4
2020+2021
11
10.5
8
12.3
7
7.9
2019+2021
0
0
4
1.4
1
0.5
2019
4
2.2
10
2.7
3
0.9
2020
4
1.1
11
4.9
9
1.3
2021
6
1.4
10
1.6
9
0.9
Tables 7, 8, 9, and Figure 7 contain summaries of the species-specific data across years for the TS, FG, and JM sites,
respectively. As shown in the tables and in Figure 7, with one exception, the cumulative relative abundance of bird
species shared across all years ranged from about 80% to a high of 95% (TS in 2019). The noted exception is a low
of 69% reported for FG in 2020 (Table 8 and Fig. 7). The abundance of several species account for this disparity –
sightings of House Wrens, Mourning Doves, Plumbeous Vireos, and Warbling Vireos, which were also reported at
FG in 2021; and Band-tailed Pigeons, Black-capped Chickadees, and Grace’s Warblers, which were reported at FG
only in 2020, were all recorded in relatively high numbers in 2020 (Table 8 and Fig. 7). Although some other
species were observed in lesser numbers at FG in 2020 compared to other years (e.g., Green-tailed towhee; Stellar’s
Jay; Northern Flicker), the number of species observed in greater numbers in 2020, and their abundances, exceeded
those for species whose numbers were smaller across years. These results, coupled with the fact that FG had the
highest number of different species observed across all three years (63 vs. 49 at TS, and 58 at JM; Table 6), and
slightly higher numbers of bird species recorded in individual years compared to the other two sites (10 or more at
FG vs. 9 or fewer at TS and JM; Table 6), suggests that a significant component of the bird community at FG varies
more from year-to-year than has been observed for the other two sites.
Table 10 contains a listing of the 37 bird species observed in all three years. Within each year, the birds listed in
Table 10 accounted for 92.6%; 94.7%; and 96.5% of birds counted in 2019, 2020, and 2021, respectively. Summing
across years, there were a total of 5031 birds counted by observers in this study, with 4779 birds represented by the
37 common species listed in Table 10. Notably, the birds counted in the 37 species observed in all three years
constitute 95% of all birds counted.
Of the 37 bird species common to all three years, 12 species were seen at all three sites in all three years (shaded
rows in Table 10). Not surprisingly, 8 of those species were the top 8 ranked species by relative abundance.
12
Summing relative abundances of these 12 species reveals that about 67% of the birds counted were among those
species found at all three sites in all three years of the study.
Table 7. Summary of bird species observed at Turkey Springs site across the three years of this study.
13
Table 8. Summary of bird species observed at Fawn Gulch site across the three years of this study.
14
Table 9. Summary of bird species observed at Jackson Mountain site across the three years of this study.
15
Figure 7. Summary of cumulative relative abundances for the bird species recorded in respective years at
each site. Numbers in parentheses are the number of species common to all three sites in that respective year.
(see also Tables 4, 6, 7, 8, and 9)
Table 11 contains a summary of the 15 top-ranked bird species by year according to relative abundance. In 2019,
the top 15 species accounted for 82% of all birds counted; almost 79% in 2020; and 87.4% in 2021. Of the 15 top-
ranked species shown for each year, 9 species were observed in all three years, to include the American Robin,
Chipping Sparrow, Green-tailed Towhee, Northern Flicker, Pygmy Nuthatch, Violet-green Swallow, Western
Wood-Pewee, White-breasted Nuthatch, and Yellow-rumped Warbler. Comparing this list to information in Table 7
reveals that the American Robin, Northern Flicker, Pygmy Nuthatch, Violet-green Swallow, Western Wood-Pewee,
White-breasted Nuthatch, and Yellow-rumped Warbler were observed at all three sites in all three years of the study.
Note also that the American Robin is ranked first in all three years; and that the Pygmy Nuthatch, Violet-green
Swallow, and Western Wood-Pewee are all in the top 4 species by relative abundance in all three years of the study.
The majority of bird species observed in any single year of the study, or across two years of the study, were recorded
as single bird sightings, or as three or fewer birds (Table 12). Sixteen bird species were observed in two of the three
years of the study (Table 12). Notable among those species for their abundance were the Band-tailed Pigeon and
Grace’s Warbler, both observed in 2020 and 2021. All sightings of the Band-tailed Pigeon occurred at FG, with
Grace’s Warbler observed at FG and JM in 2020, and at TS and JM in 2021 (see Table 3, and Appendix A).
As shown in Table 12, nine species were seen only in 2019; 10 species only in 2020; and 10 species only in 2021.
The most numerous species recorded only in 2019 were Canada Geese (17 birds) observed at FG and JM, and
Northern Rough-winged Swallows (25 birds) observed at FG (see Table 3, and Appendix A). In 2020, a total of five
Red- breasted Nuthatches were observed at TS and JM. In 2021, 3 birds each were observed for the Three-toed
Woodpecker and the Wild Turkey. Notably, the Three-toed Woodpecker was documented as an incidental at TS in
2020, but was observed at our monitoring points at FG in 2021. Wild Turkeys were observed at both FG (2 birds)
and JM (1 bird) in 2021 (see Table 3, and Appendix A).
Table 13 lists the bird species observed as “incidentals only” in the respective years of this study. For example, the
American Kestrel was noted as an incidental in 2019, but was not observed at any of the established monitoring sites
in that year, or in 2020 or 2021 either. Similarly, at least one Western Meadowlark was noted as an incidental in
85.3
95.1
80.5
87.7
76.3
81.6
69.2
83.5
86.1 84.5 82.1
91.0
0.0
20.0
40.0
60.0
80.0
100.0
All Years (12) 2019 (15) 2020 (26) 2021 (22)
Cumulative Relative Abundances for
Species Observed in Respective Years
Turkey Springs Fawn Gulch Jackson Moutain
16
Table 10. Summary of bird species observed in all three years sorted by total relative abundance. (Notes:
shading indicates bird species observed at all three sites in all three years; * a total of 82 different species
were observed across all three years)
Table 11. Comparison of top 15 ranked bird species among the 37 bird species common to all three years of
the study.
17
Table 12. Summary of bird species abundances recorded in any two years, or any single year of the study.
18
Table 13. List of bird species identified as incidental in respective years that were not observed at monitoring
points in those years. INC ONLY = incidental only that year; none = no sightings; TS = Turkey Springs site;
FG = Fawn Gulch site; JM = Jackson Mountain site.
Species
2019
2020
2021
American Kestrel
INC ONLY
none
none
Dark-eyed Junco
INC ONLY
TS, FG, JM
TS, FG, JM
Mountain Bluebird
INC ONLY
none
TS
Western Meadowlark
none
INC ONLY
JM
Sharp-shinned Hawk
none
INC ONLY
TS
Wild Turkey
none
INC ONLY
FG, JM
Canada Goose
FG, JM
none
INC ONLY
Pine Siskin
FG
TS
INC ONLY
Red Crossbill
FG
TS, FG, JM
INC ONLY
Red-naped Sapsucker
none
none
INC ONLY
2020, was not seen in 2019, but was observed at JM monitoring points in 2021. Pine Siskins and Red Crossbills
were observed at monitoring points in 2019 and 2020, but recorded only as incidentals in 2021. Wild Turkeys were
encountered during routine monitoring in 2021, but only noted as incidentals in 2020. Canada Geese were also
observed from monitoring points in 2019, but were not seen in 2020, and were documented as incidentals in 2021.
The small number of birds noted as “incidentals only” compared to the total number of bird species documented in
this study reinforces our confidence that our sampling protocol was effective in representing the composition of the
bird communities in our three study areas.
Community -level observations-
The fields of population and community ecology have, for over a century of field research, addressed questions
concerning the causes and consequences of the distribution and abundance of various species’ populations or groups
of species. Regardless of the taxonomic group of interest, one uniform outcome of these studies is that a relatively
small number of species tend to be very common, with a greater number of species found to be uncommon or rare in
a region surveyed (e.g., Flather and Sieg, 2007; Gaston, 2011). The results of our study are consistent with this
general pattern. As already noted, of the 82 different bird species observed over the three years of this study, 37
species, representing about 95% of the birds counted, were observed in all three years. Moreover, 12 of those
species were observed at all three sites over the course of the study, representing about 67% of the birds counted
(Tables 4 and 6; Figs. 5 and 6). This means that about 7% of the birds counted, or about 352 birds, were distributed
across 45 species of birds observed infrequently or in small numbers in only one or two years of the study. This
raises an important question – should conservationists be more concerned about patterns in the distribution and
abundance of common species, or focus their attention on the uncommon or rare species? We will address this issue
further in the Summary and Conclusions section of this report.
Because the TS site was subject to prescribed fire at the outset of this study in 2019, data from this site offered an
ideal opportunity to document potential impacts of wildland fuel reduction treatments on the bird community, which
is the central scientific question of this study. From 2019 to 2021, the number of bird species at TS increased from
26 in the 2019 dataset, to 37 in 2020, and 35 in 2021 (Fig. 5). Interestingly, the number of species recorded at FG
ranged from 34 in 2019, to 39 in 2020, and 40 in 2021. The number of species at JM increased from 33 in 2019 to
45 in 2020, and 43 species in 2021 (Fig. 5). Of the 82 different bird species observed across the three years of this
study, 49 species were documented at TS, 63 species at FG, and 58 species at JM (see Fig. 5). We also counted a
greater number of birds at FG and JM compared to TS over the course of the study (Fig. 6). FG emerges as not only
having the greatest proportion of bird species (Fig. 5), but also the largest proportion of birds observed, with about
38% of the total number of birds counted, compared to 29% at TS and 32 % at JM, (Fig. 6).
These results point to recovery of the TS site from prescribed fire, even by the second year of the study. Although
the number of bird species encountered at FG appears stable across years, the distribution of birds across species
varies more at FG than at either of the other two sites (see discussion of species diversity and species evenness
19
below). The greater year-to-year variability at FG is also indicated by the lower cumulative relative abundance
among the 18 species recorded at FG in all three years (76.3%; Table 6) compared to the other two sites.
Species Diversity-
Ecologists for many decades have debated the proper application of diversity indices to compare two or more
ecological communities. The Shannon Index (H`), also known as the Shannon-Weaver or Shannon-Wiener Index, is
derived from information theory and describes the degree of uncertainty in predicting the species of the next
individual picked at random from a community (see Morris et al., 2014). The Shannon Index increases as the
number of species increases (species richness), and is also increases as individuals are distributed more evenly
across species (species evenness).
The equation for the Shannon Index is: H` = -åpi ln pi., where pi is the relative abundance of individuals of the ith
species, (see Cox, 2002; Jost, 2006; Jost, 2009). Note that ln (natural logarithm) is typically used in calculating H`,
although some researchers have used log2 or log10.. In our 2019 report, we used log10, then recalculated H` using log2
in 2020. For this report, all H` values have been recalculated using ln.
Figure 8 illustrates H` values calculated for each site by year. Higher values are obtained for JM in each year of the
study, followed by FG, then TS in 2021 and 2019, with FG and TS very similar in 2020. As noted by many authors
(e.g., Jost 2006, 2009; Morris et al., 2014), interpretation of H` is complicated by the fact that it is a unitless index
that convolves both species richness (number of different species recorded), and species evenness (numbers of
individual birds distributed to each species).
The Simpson Index (Ds) is used to represent species evenness (Cox, 2002), and is calculated by the equation:
!"# = !
(
!#$
)
S
&
(
&#$
) ; where N = the total number of individuals of all species; and n = the number of individuals of each
species. Higher values of Ds indicate that individuals are more evenly distributed among species; lower values
indicate greater dominance by a subset of species.
As shown in Fig 9, Ds values were uniformly higher for JM compared to FG or TS in all three years of the study.
Species evenness increased and stabilized for TS from 2019 to 2020 and 2021; and was substantially higher for FG
in 2020 compared to 2019 or 2021. Referring to species abundance values shown in Tables 7, 8, and 9, and Fig. 7,
helps explain these patterns in Ds. For example, FG has the lowest cumulative relative abundances for species
observed across sites in all three years (Fig. 7). This indicates that a greater number of birds at FG were observed
for species not seen in at least one of the sample years (e.g., see data in Table 8 for House Wren; Mourning Dove;
Plumbeous Vireo; and Warbling Vireo).
As pointed out in several reviews (e.g., Jost 2006, 2009), H` is a measure of entropy or uncertainty in a system,
which is a representation of diversity in a system, but the index as calculated is non-linear. Jost (2009) illustrates
this point by comparing two hypothetical communities in which individuals were evenly distributed across 5
species, yielding an H` of 1.609 in case 1, compared to case 2 in which a community of 10 species yielded an H` of
2.305. In his model, doubling the number of species did not result in a doubling of the value for H`, illustrating the
difficulties in using H` to draw comparisons between ecological communities.
In his synthesis of the mathematical basis for diversity indices, Jost (2006, 2009) proposes a new index – Effective
Number of Species (ENS), which is calculated as: exp(H`). Jost shows that ENS varies proportionally to the number
of species in his demonstration model, offering a more intuitive index for comparing ecological communities.
Several other authors have proposed indices of diversity that purportedly represent species diversity more effectively
than H` or Ds, or similar indices reported in the literature (e.g., Morris et. al., 2014; Augousti 2021), most of which
are mathematically more complicated than ENS. We, therefore, opted to use ENS in our analysis.
Figure 10 illustrates the ENS indices we calculated from H` values for our dataset. Not surprisingly, the patterns
shown parallel those observed for H` in Fig. 8, but the ENS index allows quantitative comparisons that are not
applicable using H`. For example, based on ENS values, we can infer that in 2020 the bird community at JM was
almost 24% more diverse than for TS in that year, but only about 12% more diverse compared to FG. Remember,
because ENS is based on H`, both species richness and species evenness affect this result as well.
20
Figure 8. Comparison of the Shannon Index, H’, between sites and across years. The equation for H’ is:
H’ = -
å
pi ln pi.; where pi = the relative abundance of individuals of the ith species. TS = Turkey Springs; FG =
Fawn Gulch; and JM = Jackson Mountain.
Figure 9. Comparison of Simpson’s Index (Ds) by site and by year. The equation for Ds is discussed in the
text. TS = Turkey Springs; FG = Fawn Gulch; and JM = Jackson Mountain.
Looking further at ENS values reveals that index values for species diversity increased to their highest values in
2020 for all sites, from their lowest values in 2019, and intermediate values in 2021. JM exhibits the highest ENS
values for all three sites across all three years. FG shows the greatest inter-annual variability in bird species
diversity, nearly doubling from 2019 to 2020, then falling by about 20% from 2020 to 2021.
These findings corroborate and extend inferences made from our analysis of numbers of bird species and numbers of
birds distributed across species at our three sites across the term of this study. For example, increasing ENS values
2.5
2.86 2.8
2.4
32.8
2.9 3.1 3
0
1
2
3
4
2019 2020 2021
Shannon Index (H') by Site and by Year
Turkey Springs Fawn Gulch Jackson Mountain
8.9
12.7 12.5
8.2
13.6
9.6
10
16.3
14.3
0
5
10
15
20
2019 2020 2021
Simpson's Index (Ds) by Site and by Year
Turkey Springs Fawn Gulch Jackson Mountain
21
for TS are consistent with recovery of that site following prescribed fire in 2019 (see also Table 3 and 4; and Figs 5
and 6). Lower values for FG in 2019, followed by increased numbers in 2020 and 2021 reflect lower species
evenness (i.e., Ds; see Fig. 9), even though FG had the highest or second highest number of species in each year of
the study (see also Table 4; and Figs. 5 and 6), a likely consequence of inter-annual variability in bird community
composition. Finally, JM had consistently higher Ds values than the other two sites (Fig. 9), and also had the
highest or second highest species richness values in each year of the study (see also Table 4; and Figs. 5 and 6). As
noted earlier, these results may reflect improved bird identification skills of observers, but may also be a
consequence of bird movement into the area of the JM study site in response to nearby thinning and logging
activities.
Figure 10. Comparison of Effective Number of Species (ENS) by site and by year. The equation for ENS is
exp (H’) as developed by L. Jost (2006 and 2009). TS = Turkey Springs; FG = Fawn Gulch; and JM =
Jackson Mountain.
Community Similarity-
A simplified index for comparing ecological communities when relative abundance values (in percent) are available
is the Coefficient of Communities (C%): where C% = å (lower % relative abundance values for shared species
between two sites) (Cox, 2002). Values for this index range from 0 for communities with the least similarity, to 1
for communities that are identical to one another.
Year-by-year calculations of C% shown in Fig. 11 reveal that JM and FG are least similar across the course of this
study, with C% values ranging from 58% to 72%. TS, by comparison, is 64% similar in 2019 vs. 2020 and vs.
2021, but is 77% similar between 2020 vs. 2021. These patterns reflect the proportions of shared vs. unique species
by year shown for each site in Table 6. The data shown in Table 6 reveals that JM had 26 species common to all
three years, out of a total of 58 different species observed at that site; TS had 18 shared species out of a total of 49
different species observed across all three years; and FG also had 18 shared species out of a total of 63 different
species observed. Using C%, we can infer that year-to-year differences across 2019 vs. 2020 is less at JM; with
similar year-to-year differences at TS; and greatest year-to-year differences at FG for 2019 vs. 2021. At both JM
and TS, there were greater similarities in bird community composition in 2020 vs. 2021 (77% and 72%,
respectively) than observed in any other year-by-year comparisons.
A similar approach was used within years to reveal site-by-site similarities, as shown in Fig. 12. These calculations
indicate notably less similarity across sites in the 2019 dataset compared to 2020. For example, C% values ranged
12.2
17.5 16.4
10.9
20.1
15.8
17.5
22.9
19.9
0
5
10
15
20
25
2019 2020 2021
Effective Number of Species (ENS)
by Site and by Year
Turkey Springs Fawn Gulch Jackson Mountain
22
Figure 11. Year by year comparison of Community Coefficient (C%) values calculated based on bird relative
abundances across species. TS = Turkey Springs; FG = Fawn Gulch; and JM = Jackson Mountain.
Figure 12. Community Coefficient (C%) values calculated based on bird relative abundances within years
and across sites for 2019 vs. 2020. TS = Turkey Springs; FG = Fawn Gulch; and JM = Jackson Mountain.
from 69% for TS compared to JM in 2019; to 47% for FG compared to JM in that year. The range of values in the
2020 dataset was much narrower – 60% for TS x FG, to 52% for TS x JM, while JM is equally similar to TS and FG
in 2021. These differences between years are driven in part by the greater diversity of bird species observed at FG
0.64 0.58 0.66
0.64 0.70
0.58
0.77
0.66 0.72
0
0.5
1
TS x TS FG x FG JM x JM
Community Coefficient (C%) for Sites
2019 v 2020 2019 v 2021 2020 v 2021
0.47
0.69
0.51
0.60
0.52
0.59
0.50
0.62 0.63
0
0.2
0.4
0.6
0.8
TS x FG TS x JM FG x JM
Community Coefficient (C%) SIte vs. Site by
Yea r
2019 2020 2021
23
in 2019 compared to either TS or JM. In 2020, JM had a greater number of species, but many of those new species
were observed in very low numbers (see Table 3).
Looking across years, there was greater similarity across sites in 2021 and 2020 compared to 2019 (Fig. 12). This
pattern seems to be driven by the TS site bird community recovering to numbers more similar to FG from 2019 to
2020. The increasing trend in C% shown for FG x JM comparisons across years may reflect improved bird
identification skills among observers at JM, resulting in a more accurate representation of the bird community at that
site through time.
Tropic-level Impacts: Effects of Bird Predation on Herbivorous Invertebrates-
Studies elucidating the role of birds in controlling foliovorous arthropod populations consistently find a reduction in
herbivorous invertebrates in many different ecosystem types (e.g., Atlegrim, 1992; Holmes, 1990, Heyman and
Gunnarsson, 2011). In view of the difficulties associated with quantifying bird predation on arthropods (see
Dahlsten et. al., 1990), the most compelling findings come from studies in which various methods are used to
exclude bird predation from vegetation (i.e., netting exclosures; Bridgeland et al. 2010; Heyman and Gunnarsson,
2010), coupled in some cases with insecticide applications to additionally suppress arthropod populations (e.g.,
Marquis and Whelan, 1994). The general consensus from these and other studies is that bird predation may
effectively limit prey population densities when at endemic levels, especially during bird breeding season, but insect
outbreaks often overwhelm the ability of bird populations to control such irruptions (Holmes, 1990). Venier and
others (2009), however, were able to quantify enhanced breeding success in several warbler species common to the
eastern boreal forests when spruce budworm outbreaks occurred.
The indirect consequences of bird predation on plant growth has also been demonstrated for sugar maple seedlings
in the eastern deciduous forest (Strong et. al., 2000), and white oak in hardwood forests of Missouri (Marquis and
Whelan, 1994). Finally, experimental work by Heyman and Gunnarsson (2010) in suburban deciduous forests in
Sweden confirms that removal of the forest understory, through impacts on various arthropod populations,
significantly reduces bird population densities as well.
The results of our study are consistent with research showing that understory removal reduces bird densities (e.g.,
Heyman and Gunnarsson 2010). Simplifying forest understory structure, as was accomplished with prescribed fire
at the TS site at the onset of our study, resulted in at least a short-term reduction in bird abundance (see Figs. 5 and
6). and bird community diversity (see Figs. 8, 9, and 10). Mastication at FG, however, which occurred at least 2
years before our study began, did not have prolonged impacts on bird species richness (Fig. 5); apparent abundance
(Fig. 6); evenness (Fig. 9); or diversity (Figs. 8 and 10). Spruce budworm and bark beetle infestations that have
significantly impacted forests across the western states, and in particular in higher elevation forests surrounding our
area, do not seem to be a problem in the vicinity of our study sites. Although difficult to confirm, bird predation
may be a contributing factor to the apparent absence of insect outbreaks in dry-mixed conifer forests in our area.
Species-level response – Feeding Guilds-
Table 14 summarizes the categorization of bird species encountered in our study according to their feeding habits
using lists contained in Lowe et al., (1978); Bock and Lynch (1970); and life history characteristics published by the
Cornell Laboratory of Ornithology (www.allaboutbirds.org; see also Grover et. al., 2019, and 2020). The relative
abundances of species in the most common of these feeding guilds are illustrated in Fig. 13. Bird species
categorized as ground-brush foraging (GBF) (e.g., American Robin, Green-tailed Towhee; Northern Flicker; see
Table 14) are most common at all three sites, with timber-foliage searching (TFS) (e.g., Plumbeous Vireo, Warbling
Vireo, Yellow-rumped Warbler; see Table 14) second most common at JM. Aerial flycatchers (AF) (e.g., Violet-
green Swallow; see Table 14)) and timber-drilling/gleaning species (TDG) (e.g., Hairy Woodpecker, Pygmy
Nuthatch, White-breasted Nuthatch; see Table 14) were notably abundant at TS, with TDG species demonstrating
modest increasing trends across years at both TS and JM. The relative abundance of aerial flycatchers (AF) at TS
remained notably consistent across years, due largely to the presence of Violet-green Swallows (Table 14; Fig. 13).
Notably, the increase in TFS species (led by increases in Plumbeous Vireos; Western Tanagers; and Yellow-rumped
Warblers) and TDG species (led by Pygmy Nuthatches and White-breasted Nuthatches) at TS from 2019 to 2021 is
consistent with the recovery of the shrub layer following the prescribed fire at that site in 2019 (Table 14; and Fig.
13). The number of species in the GBF guild at TS increased from 7 to 18 species across years, led largely by the
return of Dark-eyed Juncos, Mourning Doves, Western Bluebirds, House Wrens, and Red Crossbills. American
24
Robins, Chipping Sparrows, Mourning Doves, and Western Bluebirds were observed at TS in 2019, but were
recorded in substantially higher numbers at that site in 2020 and 2021, due in part to increased sample density, but
the scale of response in these species exceeds the increase in sample density, indicating a substantial contribution of
shrub layer recovery to this finding.
At JM, the decreasing trend in the relative abundance of GBF species shown in Fig. 13 does not reflect a decrease in
numbers of birds representing species in this category, which actually increased, but rather a concurrent increase in
abundance and relative abundance of TDG species (Table 14). Indeed, numbers of American Robins, Chipping
Sparrows, Green-tailed Towhees, and Northern Flickers (all GBF species) increased substantially across years at
JM, with a concurrent increase in numbers of Hairy Woodpeckers, Pygmy Nuthatches, and White-breasted
Nuthatches (all TDG species) at that site. This result may reflect, at least in part, year-to-year variability, but as
discussed earlier, improved birding skills of observers may partially account for this result as well.
Species-level response – Nesting Behaviors-
The availability of nesting sites is expected to have a significant influence on bird species present at a site (see Coe,
2014). Using information from the Cornell Lab (www.allaboutbirds.org; see also Coe, 2014), we categorized birds
as tree/shrub nesters; ground/cliff, or “other,” nesters (where “other” refers to use of crevices or ledges on buildings
or other structures); and cavity nesters. Using these information resources, we categorized cavity nesters into
primary (species that excavate or enlarge nest cavities each breeding season); secondary (species that use existing
cavities from primary excavators); or primary or secondary nesters (species that may be weak excavators and may
use existing cavities if available).
Cavity nesting species are of great interest in the conservation community because of potentially limited availability
of sites amenable to cavity excavation (e.g., standing dead trees or “snags”, or living trees with soft or decaying
areas on branches or boles); important interdependencies that exist between primary and secondary cavity nesters;
and the implications of this group to ecosystem function (Bednarz et. al., 2004; Coe, 2004; Ibarra et. al., 2017;
Martin and Li, 1992). In this context, the concept of “nest-webs” and the role of primary nest cavity excavators as
“keystone” species (see Bednarz et. al., 2004; Coe, 2014; and Ibarra et. al., 2017) has particular relevance for forest
managers. Primary cavity excavators (e.g., Hairy Woodpecker, Northern Flicker) are keystone species in the sense
that they are essential to the reproductive success of weak nest excavator species (e.g., Lewis’s Woodpeckers; many
Chickadee species) and bird species that rely exclusively on pre-existing cavities for reproduction. Cavity nest
excavators also play a role in other ecosystem functions, in particular wood decomposition, through the dispersal of
fungal spores during nest excavation and foraging (Farris et. al., 2004). The work of Ibarra et. al., (2017) provides
compelling evidence that cavity nesters are also important determinants of forest ecosystem resilience in the context
of forest management practices.
Looking across all 82 species encountered through the three years of our study, we identified 42 tree/shrub nesting
species; 19 ground/cliff/other species; and 20 cavity nesting species (see Table 15; only data for cavity nesters is
shown). Among the 20 cavity nesting species, 5 are categorized as primary nesting species (Downy Woodpecker,
Hairy Woodpecker, Northern Flicker, Three-toed Woodpecker, and Williamson’s Sapsucker); 10 species fall into
the secondary nesting category (American Kestrel, Ash-throated Flycatcher, European Starling, House Wren,
Mountain Bluebird, Mountain Chickadee, Tree Swallow, Violet-green Swallow, Western Bluebird, White-breasted
Nuthatch); with 5 species capable of either excavating new cavities or using existing cavities for their nests (Table
15). Notably, cavity nesting species made up about 30% of bird sightings in each year of the study (35% in 2019;
27% in 2020; and 31% in 2021). In terms of relative abundance across all years, 45% of birds counted at TS were
cavity nesters, predominantly Violet-green Swallows and Pygmy Nuthatches; with 21% of birds counted at FG; and
29% of birds counted at JM falling into this category. Northern Flickers, White-breasted Nuthatches, and Pygmy
Nuthatches were the most widespread cavity nesting species at all three sites, with House Wrens observed most
frequently at JM.
In our study, Hairy Woodpeckers and Northern Flickers were the most abundant primary cavity nesters seen at all
three sites in each year of the study, along with Violet-green Swallows and White-breasted Nuthatches as abundant
secondary cavity nesters, and Pygmy Nuthatches the most common species fulfilling either category (Table 15). It
is notable that each of these species increased in numbers, some markedly, from 2019 to 2021. These increases are
consistent with recovery of the TS site from prescribed fire, as well as year-to-year variability in bird species
abundance, with an increase in sample density across years a potential contributing factor to this outcome as well.
25
Table 14. Summary of bird species by feeding habit (i.e., feeding guilds) across sites. Categorization of bird
species based on Lowe et al., 1978; Bock and Lynch, 1970; and Cornell Lab of Ornithology
(www.allaboutbirds.org )
26
Figure 13. Relative abundances of bird species feeding guilds at Turkey Springs; Fawn Gulch; and Jackson
Mountain study sites. GBF = Ground/Brush Foraging; TFS = Timber Foliage Searching; AF = Aerial
Flycatcher; F = Flycatcher; and TDG = Timber Drilling/Gleaning.
0
10
20
30
40
50
GBF TFS AF FTDG
Relative Abundance (%)
Turkey Springs
2019 2020 2021
0
20
40
60
GBF TFS AF FTDG
Relative Abundance (%)
Fawn Gulch
2019 2020 2021
0.0
10.0
20.0
30.0
40.0
50.0
GBF TFS AF FTDG
Relative Abundance (%)
Jackson Mountain
2019 2020 2021
27
Table 15. Summary of cavity nesting species identified across all three years of the study. Primary cavity
nesters are those species that actively excavate new cavities in each breeding season; secondary cavity nesters
occupy existing cavities left by primary excavators. (categorizations based on data obtained from
www.allaboutbirds.org; and Coe, 2014) (Conservation Scores are from Tables 16 and 17)
Other less common species that increased across years were Black-capped Chickadees, House Wrens, Mountain
Chickadees, and Western Bluebirds. Williamson’s Sapsuckers and Tree Swallows were uncommon in our study and
were present in very low numbers, along with Downy Woodpeckers and Lewis’s Woodpeckers. The observation
that these uncommon species decreased from 2019 to 2021, or were observed only in one or two of the three years
of study, suggests that their presence or absence was a consequence of year-to-year variability in bird community
composition and was not affected by sample density.
Most notable among the cavity nester are those exhibiting conservation scores of 12 or higher, indicating some
concern for the sustainability of their populations. These include Williamson’s Sapsucker, Lewis’s Woodpecker,
and the Mountain Bluebird. Regardless of conservation status, cavity nesting bird species fulfill a critical role in
forest ecosystems through their consumption of insects and other invertebrates that, if their population numbers are
left unchecked, can have significant impacts on other measures of ecosystem function.
Comparative Studies:
Previous studies in Ponderosa Pine forests across the American southwest reported increases in populations of GBF
and AF species, and decreases in TFS species in recently burned sites, consistent with the trends observed in this
study (Blake, 1982; Lowe et al., 1978). Kalies et al., (2010) in their meta-analysis of 25 studies on fire and thinning
effects on Ponderosa Pine forests across Arizona noted that thinning and fuel reduction treatments favored passerine
bird populations in general, with neutral impacts on GBF bird species and neutral to positive impacts on AF and
TDG species.
Western Bluebirds are reported to respond positively to prescribed fire (Hurteau et al., 2008). This is consistent with
our observations, with Western Bluebirds sighted at the recently burned TS site and FG site, but absent from the
non-treated JM site. Notably, Western Bluebirds increased in numbers at TS and FG from 2019 to 2020, and at TS
through 2021 (see Tables 7 and 8). In the same study by Hurteau et al., (2008), Mountain Chickadee populations
were noted to decline in thinned areas. While not a decisive trend in our study, Mountain Chickadees were absent
from TS in 2019, but returned in 2020 and 2021 (see Tables 7 and 8). Their numbers also increased at FG and JM in
2020 compared to 2019, but decreased at these two sites in 2021.
28
Brawn and Balda (1988) noted a positive impact of increased tree density and canopy cover on the Western Wood-
Pewee and Black-headed Grosbeak. Dickson et al., (2009) also noted a short-term decline in Western Wood-Pewee
in response to prescribed fire across several Ponderosa Pine sites in Arizona and New Mexico. These patterns are
not consistent with our findings, in which the Western Wood-Pewee is among the 5 most abundant species at TS and
FG in both 2019 and 2020 (Tables 2 and 4), but drops to the third most abundant species at JM in 2019, and the
ninth most abundant species at that site in 2020, where tree density and canopy cover is greatest (Tables 2 and 4).
The length of time since fire disturbance has an influence on bird species found at a site. Lowe et al., (1978) studied
bird community composition across several Ponderosa Pine sites in Arizona subject to wildfires at intervals of 1, 3,
7, and 20 years before monitoring. They identified a pattern of increasing total bird densities in the early years after
a burn, then decreasing total bird population numbers as the forest recovered, as demonstrated by the Western
Bluebird, a member of the GBF feeding guild. A similar pattern was particularly evident in their data for birds in
the TFS feeding guild (e.g., Yellow-rumped Warbler and Steller’s Jay). Timber-Drilling/Gleaning (TDG) species,
in particular the Pygmy Nuthatch, showed a decreasing trend across years. Dickson et al., (2009), reported similar
findings with a positive response to prescribed fire for Steller’s Jay, Plumbeous Vireo, and Hairy Woodpeckers. A
temporal gradient is not as well represented in our study compared to findings reported by Lowe et al., (1978), and
our sample size is small compared to many other studies reported in the literature, but comparing FG to the other
sites in our study yields similar patterns in total bird counts and species richness to their results, suggesting that FG
represents a forest community in which feeding habitat is more productive for a wider range of bird species than
provided by either the TS (recently burned) or JM (untreated) sites (see Table 14). Gillihan (1997) also noted a
positive response of several bird species to the presence of Gambel Oak, including the Brown-headed Cowbird,
Green-tailed Towhee, and Virginia’s Warbler, all of which were found at both our FG and JM sites, where the oak
shrub layer was well developed, and at TS in 2020 and 2021 as the oak shrub layer recovered from prescribed fire.
Consistent with the findings of Lowe et al., (1978), TDG species show a pattern of decline in relative abundance
across our study sites within years with TS > JM > FG (see Fig. 13). One reason reported in the literature for TDG
bird species increasing in response to recent prescribed fire has to do with a concurrent increase in bark beetles
following a burn over the following seasons (Pope et al., 2009). A parallel finding regarding the abundance of Hairy
Woodpeckers in recently burned Ponderosa Pine stands subject to wildfire indicates an increase in this species in the
first few years following burning in response to elevated populations of bark beetles and wood borers (Covert-
Bratland et al., 2006). Findings reported in the literature regarding TDG bird species is consistent with the
increasing trend in relative abundance of TDG species noted for the TS site in our study from 2019 to 2021.
Conservation Notes: The Cornell University Laboratory of Ornithology provides a summary of findings included in
the 2016 State of North America’s Birds (SONAB) report on their “All About Birds” website (Cornell, 2019). The
conservation status of over eleven-hundred birds in North America is summarized with a score reflecting the level of
concern for each species (Tables 16, 17, and 18). Factors included in the SONAB assessment include population
size, breeding distribution, nonbreeding distribution, threats to breeding, threats to nonbreeding, and population
trends (see www.stateofthebirds.org). The resulting conservation concern (CC) scores range from 4 for common,
widespread bird species that are thriving, to 20 for species of greatest concern for the sustainability of that species.
Of the 82 bird species documented over the course of this study, 29 species have shown population declines since
the late 1960’s, and 32 species have CC scores of 10 or greater (Tables 16, 17, and 18). Six of the species we
recorded over the three years of our study – Lewis’s Woodpecker, Virginia’s Warbler, Cassin’s Finch, Band-tailed
pigeon, Grace’s Warbler, and Olive-sided Flycatcher – are included on the bird conservation watch list because of
steep declines in population numbers, resulting in their “near-threatened” status. Although Lewis’s Woodpecker is
commonly observed in several areas surrounding Pagosa Springs, it was recorded as a single bird at the TS site in
our study in 2019, noted as an incidental in 2020, with three Lewis’s Woodpecker sightings at JM in 2021.
Similarly, Virginia’s Warbler was documented only at the JM site in 2019 and 2020, but recorded at FG and JM in
2021. Cassin’s Finch was one of the unique species at the FG site in 2019, but occurred at the TS site in 2020, and
was seen at both TS and FG in 2021. The recurring sightings of Band-tailed Pigeons at the FG site was one of the
most exciting observations of 2020, complemented by a single siting at JM in 2021. Grace’s Warbler was noted as
an incidental in 2019, but was sighted much more commonly at both FG and JM in 2020 and at TS and JM in 2021.
Finally, an Olive-sided Flycatcher was recorded at FG in 2021.
29
Of the remaining bird species with CC scores > 10, four were found at all three of our study sites in 2019 (Tables
16, 17, and 18). These include the Broad-tailed Hummingbird, Pygmy Nuthatch, Steller’s Jay, Western Wood-
Pewee, and Northern Flicker. The Western Wood-Pewee, Northern Flicker, and Steller’s Jay were relatively
common in our dataset. In 2020 we documented the presence of single individuals of Dusky Grouse and Northern
Goshawk at FG; and Dusky Flycatcher and Black-chinned Hummingbird at JM, each of which has conservation
scores of 10 and 11. Overall, FG stands out as the site with the greatest number of sightings of bird species with CC
scores > 10, with 14 species in 2019, 4 in 2020, and 3 in 2021, and is the site where most of the species with the
highest CC scores were observed.
One of the most exhilarating sightings across all three years of our study was that of a nesting pair of Common
Nighthawks at the TS site in 2019 (Grover et. al., 2019), and another siting at FG in 2021. The Common Nighthawk
is a reclusive species typically observed foraging for flying insects at dawn or dusk (Conservancy, 2019) and has
been documented as a component of Ponderosa Pine bird communities in our region (Gillihan, 1997). It is estimated
that Common Nighthawk populations have declined by more that 60% since the late 1960’s (Ornithology, 2019), for
reasons that are not well understood. Volunteers at the TS site observed a ground nest with 2 eggs in early June,
2019, which may have been destroyed when the area was burned at that time. Subsequent site visits confirmed that
the nest was re-occupied after the initial prescribed fire and the parents were apparently successful in hatching either
the original or a second brood consisting of two eggs. In 2021, a Common Nighthawk nest was identified at both
the FG and TS sites, and we were able to document fledgling success for both nests.
The Pine Siskin, another species in steep decline, was observed at the FG site in 2019 (Table 14). In 2020, Pine
Siskins were observed in small numbers at TS (see Appendix A), but were not recorded at any of our study sites in
2021. The estimated 80% decline in this species over the past 50 years has been attributed to predation and disease,
particularly in suburban habitats (Cornell, 2019). Its presence in forested sites dominated by White Fir and along
forest roads, has been reported in our region (Gillihan, 1997). As discussed earlier in this report, the FG site had the
lowest tree density and greatest inter-tree distances (Table 1), representing conditions consistent with Gillihan’s
observations regarding the preferred habitat for Pine Siskin.
Equally notable was the discovery of Plumbeous Vireo, Warbling Vireo, Williamson’s Sapsucker, and House Wren
nests at the JM site, and the cavity nest for Northern Flickers at the TS, FG, and JM sites in 2019, 2020, and 2021.
All of these species were observed in earlier studies in Ponderosa Pine forests in our region by Gillihan (1997).
Because of its relatively low estimated global population estimate (300k; see Table 6), the Williamson’s Sapsucker
has a CC score of 12. CC scores for the Northern Flicker and Plumbeous Vireo species reflect less concern (CC
scores of 10; see Table 17), but both of these species are estimated to have declined by 49% and 56%, respectively,
since the late 1960’s (Cornell, 2019). The House Wren has a very stable or increasing population status and is not of
particular concern with regard to its conservation status. It was particularly rewarding that volunteers were able to
track the successful hatching of young from the nests of each of these species. Violet-green Swallow nests were
present in several standing dead trees at both the TS and JM sites in 2020. These same “snags” also housed House
Wrens at the same time, underscoring the significance of preserving standing dead trees as critical nesting habitat for
several bird species.
Scanning the conservation notes from SONAB (Cornell, 2019) regarding the species encountered in our study
(Tables 17, 18, and19) reveals several species that could benefit from the prescribed fire and shrub-layer thinning
treatments applied to the TS and FG sites included in our study. For example, Lewis’s Woodpecker, Cassin’s Finch,
MacGillvary’s Warbler, Warbling Vireo, and Downy Woodpecker respond negatively to over-mature forest
conditions. Other species, cavity nesters in particular, benefit from dead trees common in mature forest stands
intergrading with patches of younger forested areas recovering from fire, and the presence of a well-developed shrub
layer (e.g., Mountain Bluebird, Williamson’s Sapsucker, Pygmy Nuthatch, Green-tailed Towhee, etc.). This leads
us to the conclusion that forest heterogeneity, resulting from the prescribed fire and thinning treatments encountered
in our study areas, represents a net benefit to the extended bird community in the forests of the San Juan Mountains.
30
Table 16. Summary of conservation status of bird species recorded in this study in 2019 (from Grover et. al., 2019). Conservation status categories,
concern scores, and estimates of population status are taken from Cornell Laboratory of Ornithology website – www.allaboutbirds.org. = common
to all sites; = unique to one site; = found at two sites.
31
Table 17. Summary of conservation status of bird species recorded in this study in 2020. Conservation status categories, concern scores, and estimates
of population status are taken from Cornell Laboratory of Ornithology website – www.allaboutbirds.org. = common to all sites; = unique to
one site; = found at two sites.
Table 18. Summary of conservation status of bird species recorded in this study in 2021. Conservation status categories, concern scores, and estimates
of population status are taken from Cornell Laboratory of Ornithology website – www.allaboutbirds.org. = unique to one site.
32
Summary and Conclusions:
The scientific question examined by this study concerned the potential effects of wildland fuel reduction treatments
(i.e., prescribed fire or shrub layer mastication) on bird community composition in the dry, mixed-conifer forests of
southwestern Colorado. As a citizen science project, other complementary objectives of the study included raising
awareness among participants regarding the principles of fire ecology and forest management, particularly with
regard to wildland fuel management practices; engaging participants in the planning and conduct of field studies;
improving the birding skills of participants through interactions of novice birders with skilled birders; and
strengthening the sense of community among conservation-minded birders in our area. We viewed the achievement
of these complementary objectives as equally important to investigating the scientific question we posed, and
consequently some confounding variables (e.g., bird species mis-identification, uneven sampling frequencies, etc.)
are embedded in the study, as may be the case with any citizen science project. Nonetheless, the dataset we have
generated by returning to the same sites and monitoring points at the same time of year over a three-year period
represents an invaluable resource for understanding year-to-year variability in bird community composition in our
area; the response of the bird community to wildland fuel reduction treatments; and other factors that should be
accounted for when considering alternative forest management practices.
Bird Community Response to Prescribed Fire and Mastication-
The primary objective of this project was to identify possible differences in bird community composition and
structure between Ponderosa Pine forested sites recently subjected to wildland fuel reduction treatments compared to
an untreated, old-growth site. Our data revealed a reduction in bird species richness, abundance, and overall
diversity at the TS site immediately following prescribed fire treatments in early June, 2019. Recovery of the shrub
layer at the TS site was clearly evident by 2021, with subsequent changes in the bird community to render this site
more like FG and JM in species composition and feeding guilds.
Comparing 2019, 2020 and 2021 datasets reveal that increased sampling frequency and involvement of more
observers per site visitation (i.e., sampling density; see Tables 2 and 5) in 2020 and 2021 contributed to a substantial
increase in the number of birds recorded, but had a marginal impact on the increased number of species recorded.
Regardless, patterns in the increased number of birds within species at TS were interpreted to indicate recovery of
that site from prescribed fire in 2019. Although the numbers of birds counted at FG increased from 2019 to 2020,
there was not a substantial change in numbers of species observed. Increased sampling density at JM, however,
yielded both an increase in bird numbers and a notable increase in the number of bird species documented for that
site. We attribute that finding to improved birding skills by observers assigned to that site, particularly with regard
to identification by song.
Commonness vs. Rarity of Bird Species-
Patterns in commonness vs. rarity that have been noted in ecological studies over the past century of ecological
research was revealed by the findings of our study. Of the 82 bird species observed across the three years of this
study, 37 were observed in all three years, and 12 of those bird species were observed at all three sites in all three
years (Tables 10, 11, and 12). Notably, 8 of the 12 species observed at all three sites across years were among the
most abundant species counted (Table 10). The 37 bird species observed in all three years accounted for over 95%
of all birds counted, and 67% of the 5031 birds observed in this study were accounted for by the 12 species seen at
all three sites in all three years.
The commonness vs rarity issue begs the question: Which species are more important to focus on when considering
management options or when monitoring forest health – common species, or uncommon/rare species? Certainly, the
most common and most abundant bird species are likely to have the greatest quantitative impact on populations of
insects and other invertebrates that they feed upon, and which could potentially impair forest health through
defoliation, tree death, or spread of disease. But the absence of uncommon or apparently rare species may have
inordinate consequences for ecosystem functionality as well (e.g., Leitao et. al., 2016). Flather and Sieg (2007), and
Gaston (2011) provide a thorough analysis of issues concerning uncommon/rare species contributions to ecosystem
function (e.g., functional complementarity, redundancy, and asynchrony), concluding that protection of uncommon
species deserves our full attention in order to enhance ecosystem resilience in response to changing environments.
Certainly, issues surrounding the ecological roles of uncommon/rare species are superseded by the ethical precept
that all species possess intrinsic value and that protecting biodiversity has value in and of itself (e.g., Sandler, 2012;
Palmer et. al., 2014). Many writers, citing the life’s work of icons such as Aldo Leopold; Stephen J. Gould; E.O.
33
Wilson; and others, underscore the significance of the intrinsic value of species as foundational to the field of
conservation biology (e.g., Piccolo, 2017; Schweiger, 2009). There is also a substantial literature produced by
accomplished scientists invoking a theological basis for protecting species based on intrinsic value (e.g., DeWitt,
2000; Van Dyke, 2010). Hence, we conclude that evaluating and categorizing forest management practices based on
potential impacts on common vs. uncommon/rare species is a false dichotomy – the potential impacts of
management practices on all species must be carefully considered, regardless of their relative abundances.
Nesting vs. Feeding Behaviors and Ecosystem Resilience-
Ibarra et al. (2017) address complementary issues to the commonness/rarity topic in the context of forest resilience,
with a focus on forest management practices that interfere with the success of tree cavity nesting bird species (e.g.,
logging; thinning; and fire). Indeed, the cavity nesting species identified across the three years of this study
accounted for almost 30% of all birds counted, with the 6 most common cavity nesting species (Hairy Woodpecker,
Northern Flicker, Pygmy Nuthatch, Violet-green Swallow, Western Bluebird, and White-breasted Nuthatch)
accounting for about 27.5% of all birds counted (see Tables 14 and 15). Moreover, looking across the range of
cavity nesting species found at our sites, several feeding guilds are represented. Of the 20 cavity nesting species
observed in our study (see Table 15), 7 belong to the TDG feeding guild; 6 to the GBF guild; 2 to the TFS guild; 3
to the AF guild; 1 to the F guild; and 1 is a raptor (American Kestrel) (see Table 14). Of the 6 most common cavity
nesting species, 3 belong to the TDG guild (Hairy Woodpecker, Pygmy Nuthatch, and White-breasted Nuthatch); 2
to the GBF guild (Northern Flicker, Western bluebird); and 1 belongs to the AF guild (Violet-green Swallow). The
distribution of cavity nesting bird species across feeding guilds, along with their numerical importance in this study,
affirms that forest management practices that are protective of potential cavity nesting sites (e.g., dead snags) are
critical to enhancing forest resilience to changing environmental conditions that might promote population growth in
potentially harmful insect or invertebrate species.
Secondary Objectives-
The secondary objectives of this study concerned raising the awareness of participants regarding the importance of
fire in Ponderosa Pine forest ecosystems; the role of wildland fuel management in protecting residential
communities in the WUI; and improving their understanding of how field studies are conducted. The feedback
participants provided to project coordinators in each year of the study affirms that we have been very successful in
accomplishing these objectives.
Finally, through the conduct of this project we anticipated that participants would benefit from improving their bird
identification skills and, by working as teams to accomplish the goals of our study, they would also form a more
cohesive group of citizen scientists concerned with conservation issues. In these regards, feedback from participants
in both years of this study affirm that our study has been overwhelmingly successful. Certainly, among the most
rewarding and somewhat surprising outcomes of this project was the dedication participants exhibited toward the
success of this study, and their enthusiasm for continuing the project in coming years.
Recommendations for Future Work:
In response to the enthusiasm shared by participants in the 2019 and 2020 field seasons, we continued the project
into 2021 with increased participation by first and second-year observers and the addition of several new volunteers.
A fourth year of data would be helpful in understanding year-to-year variability in bird community composition in
our region, and would also improve our understanding of successional recovery from wildland fuel reduction
treatments.
What we have learned from continuation of this study is that 10 visits to each loop would provide adequate data for
our analysis. Continued engagement of participants in bird identification workshops, particularly identification by
song, would also prove valuable.
As noted in our 2019 and 2020 reports (Grover et. al., 2019, and 2020), the need for more detailed data on plant
community structure is essential for understanding the response of the bird community to wildland fuel reduction
treatments. In particular, tree heights and the size and distribution of Gambel Oak clusters have significant
influences on bird communities. While we have some data regarding these habitat characteristics, we need to
standardize how we characterize measures of forest structure across sites and expand our dataset to more effectively
represent the shrub layer.
34
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Appendix A
Data Summaries from First and Second Year Reports:
Table 3 (from Grover et. al., 2019). Summary of all bird species observed across the three study areas
monitored, including the FG Re-balanced data. Data shown are the number of birds counted (abundance)
and number of monitoring points where the species were reported (frequency). Species lists represent those
found at all three sites sorted by abundance; those unique to the sites shown sorted by abundance; or those
found at two respective sites (unsorted).
38
Table 2 (from Grover et. al., 2020). Summary of all bird species observed across the three study areas in
2020. Data shown are the number of sample points at which respective bird species were recorded (i.e.,
frequency); and the number of birds of the respective species observed (i.e., abundance). Species lists
represent those found at all three sites, sorted by abundance within the respective sites; those unique at one of
the three sites, sorted by abundance within the respective sites; and those found at two of the three sites,
unsorted