wintering and breeding bird population response to on-going...
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A N T H O N Y K . H E N E H A N 1 , F I D E LH E R N Á N D E Z 1 , E R I C D . G R A H M A N N 1 , T I M O T H Y E . F U L B R I G H T 1 , A N D R E W N . T R I 3 , D A V I D B . W E S T E R 1 , A N D M I C H A E L H E H M A N 2
Wintering and Breeding Bird Population Response to On-going Large-scale Grassland Restoration
1 C A E S A R K L E B E R G W I L D L I F E R E S E A R C H I N S T I T U T E , T E X A SA & M U N I V E R S I T Y - K I N G S V I L L E , K I N G S V I L L E T X 7 8 3 6 3
2 H I X O N R A N C H , C O T U L L A T X 7 8 0 1 4
3 M I N N E S O T A D N R , S T . P A U L M N 5 5 1 5 5
Non-native grasses
� Mixed effects on birds:
� Vegetation structure is more important than species for wintering grassland birds1
� For some species of grassland bird, non-native grasses can substitute for nesting cover when native grasses are lacking2
Photo: Anthony Henehan
� Spread throughout the United States
1Block and Morrison 2010, Macías-Duerte and Panjabi 2013, Ruth et al. 20142 Jones and Bock 2005
Buffelgrass
� Buffelgrass (Pennisetum ciliare) is a bunch-forming grass native to Africa
� Creates dense monotypic stands, reducing diversity and structure of grasslands
� Presently found throughout the southwestern United States limited to areas without freezing
Photos: Matt Wojda
Buffelgrass: South Texas “Wondergrass”
� Planted in southern Texas in the early 1900s. Failed to establish until the 1940s
� Hailed as a solution to drought-related forage problems
� Increased stocking rates from 12 ha/animal unit to 4 ha/animal unit (Hanselka 1988)
Photos: Matt Wojda
Buffelgrass and Birds
� Little is known regarding effects of buffelgrass on birds
� Flanders et al. (2006) found decreased densities of birds on buffelgrass-dominated grasslands
� Dealt only with breeding birds; wintering bird response to buffelgrass unknown
Photos: Anthony Henehan
Habitat Restoration
� Prior research on grassland restoration dealt with small-scale (<5 ha) studies
� Large-scale (>50 ha) restoration projects may offer insight into population-wide responses of grassland birds to these efforts
� Our study: 118 ha restoration project
Photo: Matt Wojda
Restoration Timeline
Photo: Matt Wojda
2013 2014 2015 2016 2017
Pre-restoration Restoration Activities Post-restoration monitoring
Winter Bird
Breeding Bird
Hypotheses and Objective
� H1: Buffelgrass decreases the density of wintering and breeding grassland birds
� H2: Maintaining brush mottes will maintain an avian presence during restoration
� Estimate density of these groups and compare among study areas over time
Photos: Anthony Henehan
Study Areas
NA
RE
NN
3 Study Areas in La Salle County, TX• Non-native Area (109-ha): dominated by buffelgrass and mesquite (Prosopsis
glandulosa)• Native Area (117-ha): thorn-scrub dominated by species such as granjeno (Celtis
ehrenbergiana) and huisache (Acacia farnesiana)• Restoration Area (118-ha): pre-restoration similar to non-native area. During
restoration, site devoid of grass. Some mesquite mottes left
Restoration Area Pre- and During Restoration
Pre-restoration During restoration
Study Areas
Non-native Area Native Area
Bird Survey Methods
� Point-transect distance sampling
� Winter (Dec–Jan 2013–2014)
� Summer (Jun–Jul 2014–2015)
� Start at sunrise, end 3 hours after sunrise
� 100-m radius, 3 minutes of silence, 5 minutes of surveying
� Record distance to every bird from point with laser rangefinder
� Non-native control: 15 points
� Native control: 23 points
� Restoration: 23 points
Data Analysis
� Analyzed data in Distance 6.2
� 2 Analyses:
� Study area and year
� Grassland and Shrubland Birds
� Tested 6 different models for each dataset
� Chose best model based on AIC values
� Bootstrapped 999 iterations
� Reporting bootstrapped densities with 95% CI
Rainfall
4.83
11.38
7.79
17.79
0
2
4
6
8
10
12
14
16
18
20
Winter Summer
Ra
infa
ll (
cm)
Season
Total Rainfall
2013/2014
2014/2015
Winter Bird Richness
18 18
24
16
19
10
0
5
10
15
20
25
30
Non-native Native Restoration
Nu
mb
er
of
Sp
eci
es
Study Area
Winter Bird Richness
2013
2014
Winter Total Density
Reporting bootstrapped densities with 95% CI
15.93
7.12
19.7
13.07 12.56
4.08
0
5
10
15
20
25
30
35
NN NA RE
Bir
ds
pe
r h
a
Study Area
Total Winter Bird Densities
Pre-restoration
During Restoration
Winter Group Densities
Reporting bootstrapped densities with 95% CI
15.73
3.38
20.04
11.9
2.49 2.190
5
10
15
20
25
30
35
NN NA RE
Bir
ds
pe
ha
Study Area
Winter Grassland Bird Densities
Pre-restoration
During Restoration
0.9
6.07
1.351.36
10.53
2.13
0
5
10
15
NN NA RE
Bir
ds
pe
r h
a
Study Area
Winter Shrubland Bird Densities
Pre-restoration
During Restoration
Summer Bird Richness
16
1819
13
20
7
0
5
10
15
20
25
NN NA RE
Nu
mb
er
of
Sp
eci
es
Study Area
Summer Bird Richness During Restoration
2014
2015
Summer Total Density
Reporting bootstrapped densities with 95% CI
10.48
18.63
5.98
9.01
12.4
2.72
0
5
10
15
20
25
30
NN NA RE*
Bir
ds
pe
r h
a
Study Area
Total Summer Bird Densities During Restoration
2014
2015
*n < 15
Summer Group Densities
Reporting bootstrapped densities with 95% CI
2.611.37 1.17
7.01
1.43
0
2
4
6
8
10
12
14
NN NA RE*
Bir
ds
pe
r h
a
Study Area
Summer Grassland Bird Densities During Restoration
2014
2015
7.96
17.15
4.973.94
11.38
0
5
10
15
20
25
NN NA RE
Bir
ds
pe
r h
a
Study Area
Summer Shrubland Bird Densities During Restoration
2014
2015
*n < 15
Discussion- Restoration Area
� Large decrease in wintering birds on restoration area to be expected� Hope to document an increase in wintering and breeding bird densities
post-restoration
� Still maintained an avian presence during winter
� Breeding birds appear to be mainly shrubland birds
� Even during heavy rainfall year (2015), did not obtain sufficient observations to estimate density
Photos: Anthony Henehan
Other insights
� Non-native grasslands utilized heavily by grassland birds in winter
� Depending on rainfall, non-native grassland breeding bird assemblage changes from shrubland to grassland birds � Mostly Dickcissel (Rappole and Blacklock 1985)
Photos: Anthony Henehan
Management Implications
� Brush mottes appear to act as refugia for maintaining an avian presence during winter
� Not as effective for breeding birds
� Buffelgrass stands may not be as adverse environments as initially thought for wintering birds
Literature Cited
� Block, G., and M. L. Morrison. 2010. Large-scale effects on bird assemblages in desert grasslands. Western North American Naturalist 70:19–25.
� Flanders, A. A., W. P. Kuvlesky, Jr., D. C. Ruthven III, R. E. Zaiglin, R. L. Bingham, T. E. Fulbright, F. Hernández, and L. A. Brennan. 2006. Effects of invasive exotic grasses on South Texas rangeland breeding birds. The Auk 123:171–182.
� Hanselka C. W. 1988. Buffelgrass: South Texas wonder grass. Rangelands 10:279–281.
� Jones, Z. F., and C. E. Bock. 2005. The Botteri’s Sparrow and exotic Arizona grasslands: An ecological trap or habitat regained? The Condor 107:731-741.
� Macías-Duerte, A., and A. O. Panjabi. 2013. Association of habitat characteristics with winter survival of a declining grassland bird in Chihuahuan desert grasslands of Mexico. The Auk 130:141–149.
� Rappole, J. H., and G. W. Blacklock. 1985. Birds of the Texas Coastal Bend. Texas A&M University, College Station, Texas, USA.
� Ruth, J. M., T. R. Stanley, and C. E. Gordon. 2014. Associations of wintering birds with habitat in semidesert and plains grasslands in Arizona. The Southwestern Naturalist 59:199–211.
� Fidel Hernández� Timothy Fulbright� Eric Grahmann� David Wester� Andrew Tri� John Edwards� Michael Hehman� Danielle Belleny� Matt Wojda� Monika Burchette� Andrea Bruno
� The Hixon Ranch
� Tim and Karen Hixon
� Rene Barrientos
� Coastal Bend Audubon Society
� South Texas Quail Coalition
� Texas Parks & Wildlife
� Exxon Mobile
Contributors
Questions