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Relative Effects of Litter and Management on Grassland Bird Abundance in Missouri, USA

Tables

Table 1.  Summary of study and survey effort for Henslow's and Grasshopper Sparrows and Dickcissels management type in southwestern Missouri prairies in June during to 1999. Some sites contained multiple management types. 
  All Hay Hay + burn Burn
Number of sites 43 24 27 7
Mean patch size per site (ha) 137 149 118 244
Median patch size per site (ha) 65 69 68 68
Minimum-maximum patch sizes (ha) 6 - 855 16 - 593 10 - 571 6 - 855
Total unit surveys 535 242 256 37
Total survey distance (km) 224.3 96.8 114.3 13.1
Mean (±SD) unit survey distance (m) 419 ± 220 400 ± 197 447 ± 235 353 ± 229
No. individuals recorded
    Henslow's Sparrow 1,874 1,192 627 55
    Grasshopper Sparrow 678 375 285 18
    Dickcissel 2,174 1,043 995 136

 

Table 2.  Forward stepwise linear regression of log-transformed relative bird abundance (individuals/km per unit survey) at southwestern Missouri prairies during June 1994-1999 versus environmental variables, with P < 0.05 to add/remove variables. Step (step-rank in regression) and standardized coefficients (r) are provided only for statistically significant litter and management results. From left to right columns, multiple r statistics: 0.616, 0.530, 0.442, and 0.567, n = 519 unit surveys and P < 0.00005 for each regression. 1995, 1999, crepuscularity, time of day, percent sunshine, and wind speed never had P < 0.05.
  Henslow's Grasshopper Dickcissel Combined birds
Step r Step r Step r Step r
Management
  Hay 2 + 0.276 d 5 + 0.192 d   10    
  H + B last hay 5 + 0.142 b         10 − 0.101 a
  H + B last burn     8 − 0.152 c     7 − 0.213 d
  Burn 8 − 0.100 a     5 − 0.150 c 5 − 0.295 d
  Years since treatment     1 − 0.126 a        
Litter
  1 + 0.367 d 9 − 0.207 b     2 + 0.183 d
Habitat
  Diversity 6 − 0.199 d 6 + 0.098 a 6 − 0.156 c 6 − 0.147 c
  Prairie size 4 + 0.232 d     4 + 0.220 d 4 + 0.306 d
  Quality 7 + 0.117 b 7 + 0.111 b 9 + 0.083 a 3 + 0.180 d
  Type 9 + 0.082 a 2 + 0.167 d        
Geography
  Latitude         3 − 0.168 d 8 − 0.266 d
  Longitude     4 − 0.226 d     8 − 0.209 d
Timing
  Date in June         2 − 0.222 d    
  Trend 1994 - 1999     3 − 0.096 a        
  1994         8 + 0.119 a    
  1996         1 + 0.276 d 1 + 0.193 d
  1997         7 − 0.100 a    
  1998     10 − 0.128 b        
Weather
  Temperature 3 − 0.114 b            

In all tables:   a P < 0.05,   b P < 0.01,   c P < 0.001,   d P < 0.0001

 

Table 3.  Forward stepwise linear regressions of log-transformed relative bird abundance (individuals/km per unit survey), at southwestern Missouri prairies during June, (1994 to 1999) versus environmental variables, analysed separately for each year, with P < 0.05 to add/remove variables. Step (step-rank in regression), and standardized coefficients (r) are provided only for statistically significant litter and management results, as well as the number of significant steps in each regression.
  1994 1995 1996 1997 1998 1999
Step r Step r Step r Step r Step r Step r
Henslow's Sparrow
  Hay 3 + 0.270 c 1 + 0.265 b                
  H + B last hayed             3 − 0.292 b        
  H + B last burned                        
  Burn     5 − 0.355 c     2 − 0.255 b 2 − 0.380    
  Years since treatment                        
  Litter 1 + 0.570 d 3 + 0.489 d 1 + 0.466 d 1 + 0.397 d 1 + 0.601 d 1 + 0.443 d
  n steps 4   5   3   5   4   1  
Grasshopper Sparrow
  Hay     4 + 0.285 b 4 + 0.226 a 3 + 0.444 c        
  H + B last hayed                        
  H + B last burned         2 − 0.235 a            
  Burn                          
  Years since treatment     2 − 0.429 d 3 − 0.358     1 − 0.380 c    
  Litter             2 − 0.422 c        
  n steps 1   5   4   4   2   1  
Dickcissel
  Hay             2 + 0.273 a        
  H + B last hayed                        
  H + B                        
  Burn     3 − 0.263 b         1 − 0.497 c    
  Years since treatment                        
  Litter                 2 + 0.275 b    
  n steps 3   5   0   2   3   1  
Combined birds
  Hay     1 + 0.303 c     1 + 0.338 b        
  H + B last hayed                        
  H + B last burned         2 − 0.346            
  Burn 3 − 0.202 a 3 − 0.437 d 3 − 0.467 c 2 − 0.289 b 1 − 0.709 c    
  Years since treatment                        
  Litter 1 + 0.435 d            3 + 0.240 a 2 + 0.525 1 + 0.308 b
  n steps 3   5    5    3    6    1  
Multiple r statistics ranged from 0.468 to 0.782, 0.275 to 0.615, 0.219 to 0.574, and 0.308 to 0.748, for Henslow's Sparrow, Grasshopper, Sparrow, Dickcissel, and combined birds, respectively. N = 96, 91, 81, 82, 86, and 83 unit surveys for each year respectively. P values for the regressions ranged from 0.0000 to 0.0000, 0.000 to 0.009, 0.0000 to 0.046, and 0.0000 to 0.005 respectively.

 

Table 4.  Percentage of unit surveys for Henslow's and Grasshopper Sparrows and Dickcissels in June, 1994 to 1999 which began in each of six time periods (Central Standard Time), by management type. The earliest survey began at 07h07 and the latest ended at 18h25.
  Hay
(n = 242)		 Hay + Burn
last hayed
(n = 130)		 Hay + Burn
last burned
(n = 126)		 Burn
(n = 37)		 Total
07h00 to < 09h00 5.8 23.8 19.8 32.4 15.3
09h00 to < 11h00 23.1 26.9 22.2 21.6 23.7
11h00 to < 13h00 24.0 13.1 19.0 18.9 19.8
13h00 to < 15h00 21.0 16.9 22.2 10.8 19.6
15h00 to < 17h00 20.2 16.9 12.7 13.5 17.2
17h00 to < 19h00 5.8 2.3 4.0 2.7 4.3

 

Table 5.  Mean (± SD) relative bird abundance (individuals/km per unit survey) at southwestern Missouri prairies during June 1994 to 1999, by individual species and all species combined, for each management type and litter category. N = number of unit surveys in each sample. Means within a litter × species cell (testing for differences among management types, down a column) not followed by any similar capital letters are significantly different (Duncan's post-hoc test of log-transformed abundances, P < 0.05). Means within a management type × species cell (testing for differences among litter categories, across a line) not followed by any similar lower case letters are significantly different (Duncan's post-hoc test of log-transformed abundances, P < 0.05).
  Light litter a Medium litter b Heavy litter c
n       mean ± SD n       mean ± SD n       mean ± SD
Henslow's Sparrow
 Hay d 17 6.82 ± 6.59 A  b 126 10.74 ± 11.87 A  b 99 15.78 ± 10.58 A  a
 Hay + burn  
    Last hay e 20 2.14 ± 2.81 B  c 90 7.62 ± 10.60 AB  b 20 13.35 ± 9.20 A  a
    Last burn f 84 1.04 ± 2.31 B  c 15 2.77 ± 2.69 BC  b 27 13.88 ± 8.82 A  a
 Burn g 13 2.49 ± 3.28 B  a 15 2.72 ± 4.94 C  a 9 4.27 ± 8.93 B  a
Grasshopper Sparrow
 Hay 17 4.98 ± 5.33 A  a 126 5.46 ± 5.59 A  a 99 1.56 ± 2.60 A  b
 Hay + burn  
    Last hay 20 2.74 ± 2.73 AB  a 90 3.73 ± 5.46 AB  a 20 3.03 ± 4.62 A  a
    Last burn 84 1.75 ± 2.31 B  a 15 1.40 ± 2.36 BC  a 27 1.36 ± 2.37 A  a
 Burn 13 2.02 ± 2.06 AB  a 15 0.21 ± 0.80 C  b 9 0.00 ± 0.00 A  b
Dickcissel
 Hay 17 12.64 ± 6.59 A  a 126 10.48 ± 7.44 A  a 99 11.55 ± 7.16 A  a
 Hay + burn  
    Last hay 20 5.96 ± 5.49 B  b 90 9.44 ± 6.66 A  a 20 8.58 ± 6.27 A  ab
    Last burn 84 9.16 ± 4.99 A  a 15 6.63 ± 4.13 A  a 27 9.94 ± 7.04 A  a
 Burn 13 11.58 ± 5.00 A  a 15 7.68 ± 7.11 A  a 9 9.83 ± 6.39 A  a
Combined birds
 Hay 17 24.44 ± 10.10 AB  a 126 26.67 ± 15.63 A  a 99 28.89 ± 13.53 A  a
 Hay + burn  
    Last hay 20 10.84 ± 7.88 C  b 90 20.80 ± 15.62 A  a 20 24.97 ± 12.20 A  a
    Last burn 84 11.95 ± 6.35 C  b 15 10.80 ± 5.38 B  b 27 25.07 ± 13.16 A  a
 Burn 13 16.08 &plusm; 8.49 BC  a 15 10.60 ± 8.47 B  a 9 11.99 ± 11.19 B  a
a F tests for light litter × species cells: 11.61, 3.41, 6.47 and 5.98 for Henslow's Sparrow, Grasshopper Sparrow, Dickcissel, and combined birds, respectively, with P (rounded to the fourth decimal place) = 0.0000, 0.0195, 0.0004, and 0.0008.
b F tests for medium litter × species cells: 7.48, 10.96, 1.97 and 15.22, respectively, with P = 0.0000, 0.0000, 0.1193, and 0.0000.
c F tests for heavy litter × species cells: 8.58, 2.27, 1.80 and 8.66, respectively, with P = 0.0000, 0.0825, 0.1493, and 0.0000.
d F tests for hay × species cells: 9.35, 22,42, 1.31 and 1.51, respectively, with P = 0.0001, 0.0000, 0.2729, and 0.2220, respectively.
e F tests for hay + burn last hay × species cells: 7.95, 0.18, 3.90, and 7.50, respectively, with P = 0.006, 0.8315, 0.0227, and 0.0000, respectively.
f F tests for hay + burn last burn × species cells: 70.28, 0.64, 1.81, and 10.36, respectively, with P = 0.000, 0.5283, 0.1682, and 0.0000, respectively.
g F tests for burn × species cells: 0.19, 10.42, 2.35, and 1.78, respectively, with P = 0.8281, 0.0003, 0.1106, and 0.1850, respectively.