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Habitat Associations of Migrating and Overwintering
Grassland Birds in Southern Texas

Tables


Table 1.  Dominant upland habitats (physiognomic classes) found within the Coastal Sand Plains in southern Texas, during fall, winter, and spring, 1991-1992 and 1992-1993, based on McMahon et al. (1984).
Physiognomic class Description
Grassland Dominated by grasses and forbs, lacks woody vegetation (or with <10% woody canopy coverage).
Shrub-grassland Grass-woody plant interspersion with woody plants generally <3 m tall and comprising <30% woody canopy coverage.
Parkland Grassland-woodland interspersion, with woody plants ≥3 m tall, and comprising <50% woody canopy coverage.
Brushland Dominated by woody plants <3 m tall and comprising ≥30% woody canopy coverage.
Woodland Dominated by trees ≥3 m tall and generally having a closed canopy.

 

Table 2.  Proportion of total bird species that are grassland birds (total number of bird species) and proportion of total bird density that are grassland birds (total number of birds per 10 ha) observed within five habitat types during three portions of the nonbreeding season in southern Texas, 1991-1992 and 1992-1993.
  Grassland Shrub-grass Parkland Brushland Woodland
Species richness
Fall
0.28 (18) 0.26 (47) 0.16 (67) 0.18 (61) 0.12 (74)
Winter
0.48 (25) 0.30 (46) 0.16 (74) 0.13 (88) 0.13 (93)
Spring
0.39 (23) 0.41 (37) 0.29 (52) 0.31 (48) 0.26 (54)
Overall
0.35 (40) 0.25 (67) 0.17 (104) 0.16 (114) 0.12 (122)
Density
Fall
0.23 (36.2) 0.18 (108.5) 0.09 (131.3) 0.11 (95.9) 0.02 (156.0)
Winter
0.73 (87.3) 0.57 (157.6) 0.28 (145.5) 0.36 (114.9) 0.22 (87.2)
Spring
0.49 (80.0) 0.50 (123.3) 0.36 (133.4) 0.39 (96.5) 0.16 (100.0)
Overall
0.55 (67.8) 0.43 (129.8) 0.25 (136.7) 0.27 (102.4) 0.11 (114.4)

 

Table 3.  North American Breeding Bird Survey (BBS; surveywide, 1966-1993) and Christmas Bird Count (CBC; Texas, 1959-1988) trends of 21 grassland birds that breed in temperate North America and winter in or migrate through southern Texas.
Species Residency status
in Texas
a
Range
juxtaposition
b
Trendc
BBS CBC
Grassland Specialists
Long-billed Curlew
(Numenius americanus)
TW C -1.3 -2.1
Upland Sandpiper
(Bartramia longicauda)
T D 2.4↑↑↑ NA
Northern Harrier
(Circus cyaneus)
TW O -0.9↓ -0.7
Short-eared Owl
(Asio flammeus)
TW O -2.4 -0.4
Horned Lark
(Eremophila alpestris)
TWB O -0.8↓↓ 5.4
Sedge Wren
(Cistothorus platensis)
TW D 1.7↑ 4.3↑↑↑
Sprague's Pipit
(Anthus spragueii)
TW D -4.3↓↓↓ 2.1
Grasshopper Sparrow
(Ammodramus savannarum)
TWB C -3.8↓↓↓ 0.5
Le Conte's Sparrow
(Ammodramus leconteii)
TW D -0.7 1.4
Savannah Sparrow
(Passerculus sanwichensis)
TW C -0.8↓↓↓ 0.6
Vesper Sparrow
(Pooecetes gramineus)
TW C -0.8↓↓ -2.6↓↓
Dickcissel
(Spiza americana)
TB D -1.8↓↓↓ -0.3
Lark Bunting
(Calamospiza melanocorys)
TW C -1.3 -3.7
Eastern Meadowlark
(Sturnella magna)
TWB O -2.5↓↓↓ 0.4
Shrub-grassland Specialists
Loggerhead Shrike
(Lanius ludovicianus)
TWB O -3.5↓↓↓ -1.3↓↓
Common Yellowthroat
(Geothlypis trichas)
TWB O -0.5↓↓↓ -2.1↓
Lark Sparrow
(Chondestes grammacus)
TWB O -3.4↓↓↓ -5.1↓↓↓
Cassin's Sparrow
(Aimophila cassinii)
TWB O -2.5↓↓↓ -0.1
Field Sparrow
(Spizella pusilla)
TW O -3.3↓↓↓ -1.3
Clay-colored Sparrow
(Spizella pallida)
TW D -1.2↓↓↓ -2.1
Brown-headed Cowbird
(Molothrus ater)
TWB O -0.8↓↓↓ -5.3↓
a South Texas residency: T = transient, W = winter resident, B = breeding-season resident.
b Juxtaposition of wintering and breeding ranges: O = markedly overlap, D = markedly disjunct, C = contiguous or slight overlap.
c Trends in abundance from the BBS and the CBC were obtained from Sauer et al. (1997) and Sauer et al. (1996), respectively. BBS and CBC trends are based on statistical methods reported by Geissler and Sauer (1990), and are presented as the average percent annual change during the survey interval: ↓ (decreasing) at P < 0.10, ↓↓ at P < 0.05, ↓↓↓ at P < 0.01; ↑ (increasing) at P < 0.10, ↑↑↑ at P < 0.01.

 

Table 4.  Mean ± SE densities (birds per 10 ha) in five habitat types and seasonal distributions (%) of 21 grassland bird species during the nonbreeding season (fall, winter, and spring) in southern Texas, 1991-1992 and 1992-1993.
Species Density Season
Grassland Shrub-grass Parkland Brushland Woodland F W S
Grassland Specialists
Long-billed Curlew
0.04 ± 0.03 0 0 0.02 ± 0.02 0 0 75 25
Upland Sandpiper
0.06 ± 0.01 0.38 ± 0.20 0.07 ± 0.07 0 0 3 0 97
Northern Harrier
0.08 ± 0.04 0.08 ± 0.03 0.11 ± 0.40 0.06 ± 0.02 0 11 70 19
Short-eared Owl
0 0.92 ± 0.48 0 0 0 0 100 0
Horned Lark
0 0.08 ± 0.06 0.42 ± 0.42 0.17 ± 0.16 0 92 8 0
Sprague's Pipit
0.10 ± 0.10 0.17 ± 0.10 1.88 ± 1.67 0 0 0 98 2
Sedge Wren
0.33 ± 0.23 0.43 ± 0.21 0.28 ± 0.28 0.66 ± 0.24 0.19 ± 0.13 6 40 54
Grasshopper Sparrow
8.33 ± 2.11 7.38 ± 1.77 5.11 ± 1.44 4.57 ± 1.70 1.30 ± 0.44 2 41 57
Le Conte's Sparrow
3.61 ± 1.34 4.89 ± 1.51 2.57 ± 1.09 1.25 ± 0.62 0.12 ± 0.08 0 74 26
Savannah Sparrow
10.04 ± 2.15 11.72 ± 2.44 3.39 ± 1.32 7.25 ± 1.94 2.50 ± 1.27 7 72 21
Vesper Sparrow
1.88 ± 8.85 5.14 ± 1.76 6.07 ± 2.10 3.59 ± 1.25 1.78 ± 0.78 1 65 34
Dickcissel
0.21 ± 0.21 4.91 ± 1.83 4.45 ± 1.90 1.92 ± 0.78 0.61 ± 0.31 12 0 88
Lark Bunting
0 0.05 ± 0.32 0 0.08 ± 0.06 0.05 ± 0.05 0 71 29
Eastern Meadowlark
11.50 ± 2.06 17.52 ± 2.60 4.94 ± 1.31 3.28 ± 0.70 0.97 ± 0.49 21 51 28
Shrub-grassland Specialists
Loggerhead Shrike
0.29 ± 0.09 0.67 ± 0.14 0.59 ± 0.12 0.45 ± 0.08 0.28 ± 0.12 56 31 13
Common Yellowthroat
0 0 0.31 ± 0.15 0.28 ± 0.15 0.56 ± 0.41 13 0 87
Lark Sparrow
0.14 ± 0.14 0.23 ± 0.17 1.32 ± 0.61 0.29 ± 0.12 0.59 ± 0.25 24 38 38
Cassin's Sparrow
0.46 ± 0.33 0.99 ± 0.38 0.59 ± 0.31 0.49 ± 0.22 0.65 ± 0.30 18 15 67
Field Sparrow
0 0 0.50 ± 0.35 0.54 ± 0.39 0.93 ± 0.76 22 66 12
Clay-colored Sparrow
0 0 0.04 ± 0.04 0.06 ± 0.06 0.14 ± 0.10 0 16 84
Brown-headed Cowbird
0 1.36 ± 0.90 1.09 ± 0.46 3.16 ± 2.36 2.19 ± 1.24 17 4 79
Totals
Grassland specialists
36.18 ± 5.12 53.68 ± 7.58 29.27 ± 5.17 22.81 ± 4.80 7.52 ± 2.12 10 53 37
Shrub-grass specialists
0.89 ± 0.36 3.24 ± 1.07 4.44 ± 0.99 5.27 ± 2.47 5.34 ± 1.88 21 18 61
All grassland birds
37.08 ± 4.58 56.92 ± 6.97 33.71 ± 5.31 28.08 ± 5.13 12.86 ± 2.93 10 51 39

 

Table 5. Significant (P ≤ 0.05) habitat associations, by season or by season and year, of grassland birds wintering or migrating through southern Texas, 1991-1992 and 1992-1993.
Species/group
Season
Average densities (birds per 10 ha)a
Grassland Shrub-grass Parkland Brushland Woodland
Grasshopper Sparrow
Spring (Yr 2) 24.5A 18.9A 18.8A 0.0B 0.6B
Le Conte's Sparrow
Winter 9.2AB 11.6A 2.7B 3.7AB 0.4B
Spring 1.7A 3.1AB 5.0A 0.0B 0.0B
Savannah Sparrow
Winter 23.2AB 26.4A 8.5AB 10.2AB 6.8B
Eastern Meadowlark
  11.5AB 17.5A 4.9B 3.3B 1.0B
Grassland specialist
Fall 7.3AB 15.1A 8.2AB 7.6AB 1.4B
Winter 53.0AB 77.1A 34.2AB 34.4AB 16.1B
Spring 37.3AB 54.2A 37.6A 22.7AB 4.7B
All grassland birds
Fall 8.2AB 19.6A 11.1AB 10.6AB 3.1B
Winter 63.7AB 89.8A 41.4AB 40.0AB 19.1B
a Densities within a row followed by similar letters are not significantly (P > 0.05) different.

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