We collected data at a privately-owned farm in northeast Mississippi, USA, which consisted of 2,104 ha, 486 ha of which were used for row crop production and 587 ha that were used for a cattle operation (Fig. 1). In spring 2005, 79 ha of this property were enrolled in the Conservation Reserve Program’s Conservation Practice 33 (CP33: Habitat Buffers for Upland Birds). Based on the enrollment criteria for this practice, agricultural conservation buffers 9.1-36.5 m wide are established around the perimeter of crop production fields with native warm-season grasses and forbs. Producers implementing CP33 on their land receive a cost-share to offset establishment costs, as well as monetary incentives and annual rental payments to compensate for lost opportunity costs [29Burger LW Jr, McKenzie D, Thackston R, Demaso SJ. The role of farm policy in achieving large-scale conservation: Bobwhite and buffers. Wildl Soc Bull 2006; 34: 986-93.
[http://dx.doi.org/10.2193/0091-7648(2006)34[986:TROFPI]2.0.CO;2] ]. Buffers enrolled in CP33 are required to be disturbed to maintain them as early-successional habitat specifically for Northern Bobwhite and potentially other grassland birds [29Burger LW Jr, McKenzie D, Thackston R, Demaso SJ. The role of farm policy in achieving large-scale conservation: Bobwhite and buffers. Wildl Soc Bull 2006; 34: 986-93.
[http://dx.doi.org/10.2193/0091-7648(2006)34[986:TROFPI]2.0.CO;2] ].

Fig. (1) Aerial photograph of agricultural land enrolled in Conservation Reserve Program practice CP33: Habitat Buffers for Upland Birds at a privately-owned farm in northeast Mississippi, USA. Disturbance schedule of buffers indicated by red (prescribed burn), blue (control), and yellow (light disking) polygons, 2007-2009.

After CP33 enrollment, buffers measuring 18.2 or 36.5 m wide were then established, surrounding the perimeter of 14 crop production fields at the farm. These buffers included a mix of native warm-season grasses [e.g., big bluestem (Andropogon gerardi), little bluestem (Schizachyrium scoparium), indiangrass (Sorghastrum nutans)] and forbs [e.g., partridge pea (Chamaecrista fasciculata), black-eyed susan (Rudbeckia hirta), maximilian sunflower (Helianthus maximiliani)].

We investigated 3 different disturbance treatments in agricultural conservation buffers at the study site: (1) Light disking in the fall (September-October), (2) Prescribed burning in the spring (March-April), and (3) No disturbance (control). Because data collection occurred during the avian breeding season (May-early August), confounding between disturbance type and breeding season did not influence the data. We randomly assigned 1 of the 3 disturbance treatments to each group of buffers surrounding the same field, with only 1 buffer/field group disturbed each year (14 buffer-bordered fields, 51 total buffers). Planted crops in the fields included a corn-soybean rotation or Bermuda grass (Cynodon dactylon) established for cattle forage. Data we collected during 2007 provided pre-disturbance information. We documented vegetation and bird responses to disturbance during the first (2008 and 2009) and second (2009) growing seasons post-disturbance. Because this study concluded prior to 2010, we considered buffers disturbed after the 2009 breeding season in-field controls.

We used distance sampling techniques to estimate breeding bird density as it incorporates a decreasing detection probability with increasing distance from an observer [30Buckland ST, Anderson DR, Burnham KP, Laake JL, Borchers DL, Thomas L. Introduction to distance sampling 2001.]. We established 200-m long line transects that ran parallel to a buffer’s long axis in 46 of the agricultural conservation buffers at the study site [5 buffers were too short to accommodate a 200-m line transect; (Fig. 2)]. Strip transect surveys were conducted by a single observer (HLA) 0530-1000 (central standard time) on mornings with no precipitation and wind speeds less than 24 km/hour [31Smith MD, Barbour PJ, Burger LW Jr, Dinsmore SJ. Breeding bird abundance and diversity in agricultural field borders in the Black Belt Prairie of Mississippi. Proc Annu Conf Southeast Assoc Fish Wildl Agencies 2005; 43-56.]. Fixed-width transect surveys were conducted at a travel rate of 10 m/min, during which the observer recorded bird detections in 1 of 4 distance bands that together covered the width of the buffers: 0-5 m, 5-10 m, 10-15 m, and 15-20 m. Temperature, percent cloud coverage, and wind speed were recorded at the start of each transect survey. The observer visited each transect 6 times during each breeding season (twice monthly, May-early August), 2007-2009.

Fig. (2) Diagram of a 200-m transect used to estimate diversity and density of breeding birds in agricultural conservation buffers at a privately-owned farm in northeast Mississippi, USA, 2007-2009.

We estimated avian diversity in the agricultural conservation buffers using Shannon’s Diversity Index [32Shannon CE, Weaver W. The mathematical theory of communication 1963.], which is calculated as:

(1)

where H’ is the Shannon’s Diversity Index value, n is the number of detected species, and P_i is the fraction of the observed sample composed of the i^th species. We calculated diversity indices for the type of and time since disturbance using mean detections/ha for all birds detected during line-transect surveys.

To determine if disturbance influenced avian diversity at the buffer level, we compared mean avian diversity in buffers based upon variables reflecting year (2007, 2008, 2009) by treatment (burn, disk, control) using general linear models in SAS PROC MIXED [33SAS 9.4 product documentation. 2013.]. Because individual buffers of the same field were physically connected and adjacent to the same crop field, we included field as a random variable. To determine if disturbance influenced avian density at the field level, we compared the mean avian diversity of fields based on year by treatment variables using general linear models in SAS PROC MIXED, including year as a repeated measure [33SAS 9.4 product documentation. 2013.]. At both the buffer and field level, we further evaluated significant results using a Welch t-test. For all these statistical analyses, we used a significance level of α = 0.05.

We used conventional distance sampling techniques in Program Distance to estimate the detection function of all birds of any species in the agricultural conservation buffers based on the type of and time since disturbance [34Thomas L, Buckland ST, Rexstad EA, et al. Distance software: design and analysis of distance sampling surveys for estimating population size. J Appl Ecol 2010; 47(1): 5-14.
[http://dx.doi.org/10.1111/j.1365-2664.2009.01737.x] [PMID: 20383262] ]. Additionally, we estimated detection functions for species with more than 100 detections in the buffers (i.e., Dickcissel, Red-winged Black- bird, Indigo Bunting). Species with less than 100 detections provided insufficient data to generate a robust estimate of a detection function [30Buckland ST, Anderson DR, Burnham KP, Laake JL, Borchers DL, Thomas L. Introduction to distance sampling 2001.].

It is recommended that approximately 5-10% of distance data be right-truncated to increase model precision [30Buckland ST, Anderson DR, Burnham KP, Laake JL, Borchers DL, Thomas L. Introduction to distance sampling 2001.]. Because we recorded detections in 5-m distance bands rather than exact distances, truncation required censoring all or none of the detections in a given band. The 15-20 m band terminated at the buffer-crop ecotone at a transect’s crop side (i.e., field interior) and the buffer-field margin ecotone at a transect’s non-crop side (i.e., field exterior). Vegetation discontinuities associated with edges attracted birds, resulting in more detections in the outer distance bands (15-20 m) and a non-monotonically declining detection function with distance (Fig. 3). This violated an assumption of distance sampling, which states the probability of detecting an object; in this case, a bird, decreases with increasing distance from an observer [30Buckland ST, Anderson DR, Burnham KP, Laake JL, Borchers DL, Thomas L. Introduction to distance sampling 2001.]. Thus, we truncated detections in this band and estimated detection functions using detections in the first 3 distance bands (0-15 m). We used Akaike’s Information Criterion (AIC) to determine the best fit detection function from appropriate key functions (half-normal or uniform) with possible cosine or simple polynomial adjustment terms. Model selection was based on the least AIC value, goodness-of-fit, and detection probability.

Given that model selection results most frequently supported uniform detection probabilities at or near 1.0 and a relatively narrow detection width, we estimated bufferand year-specific avian density in the agricultural conservation buffers with respect to type of and time since disturbance by calculating mean number of avian detections/ha for each buffer during 2008 and 2009. We made these estimations using all avian detection data and not just the truncated data used in Program Distance analyses. We evaluated potential differences in avian density between control and disturbed buffers at the buffer and field level using general linear models in SAS PROC MIXED [33SAS 9.4 product documentation. 2013.]. Procedures for these analyses were similar to diversity analyses, again with α = 0.05.

There were no pre-treatment differences in mean avian diversity in 2007 among the agricultural conservation buffers (F_4,34.9 = 0.65, P = 0.630). There was still no difference in diversity at the buffer level regardless of type of or time since disturbance in 2008 (F_2,36 = 1.34, P = 0.274) and 2009 (F_4,37.4 = 0.32, P = 0.864). In 2008, although relative effect sizes were large, -29% for burned buffers and -92% for disked buffers compared to control buffers suggesting a short-term reduction in avian diversity the first growing season post-disturbance, confidence intervals included zero (Fig. 4). In 2009, effect sizes on diversity were 70% in burned buffers in their second growing season and 42% for disked buffers in their first growing season relative to controls, suggesting a positive response to disturbance, although confidence intervals again included 0.

At the field level in 2007, there were no pre-treatment differences in avian diversity (F_2,11 = 0.69, P = 0.523). Implementation of disturbance treatments did not affect avian diversity in 2008 (F_2,11 = 0.62, P = 0.557) and 2009 (F_2,11 = 1.37, P = 0.294). Estimates of effect sizes (relative to control fields) were relatively large and in opposite directions for prescribed burning (2008, 69% increase in diversity; 2009, 124%) and light strip-disking (2008, 25% decrease in diversity; 2009, 5%).

All model selection results generated in Program Distance supported the uniform key function with a cosine adjustment to estimate detection functions regardless of the type of or time since disturbance (Table 2). Detection probabilities were also all 1.00 ± 0.00 for Dickcissels (Table 3) and Indigo Buntings (Table 4); Red-winged Blackbird detection probabilities were all 1.00 ± 0.00 except for buffers during the second growing season post-disking (0.50 ± 0.12; Table 5).

Fig. (4) Shannon’s Diversity Indices (mean ±1 standard error) at the buffer (left) and field (right) levels for all bird species detected in control and disturbed agricultural conservation buffers at a privately-owned farm in northeast Mississippi, USA, 2008-2009.

Table 2
Results of Akaike's information criterion (AIC), detection function [f(0)], probability of detection (p), and percent coefficient of variation (%CV) for all birds detected in control and disturbed agricultural conservation buffers at a privately-owned farm in northeast Mississippi, USA, 2007-2009.

Table 3
Results of Akaike's information criterion (AIC), detection function [f(0)], probability of detection (p), and percent coefficient of variation (%CV) for Dickcissels (Spiza americana) detected in control and disturbed agricultural conservation buffers at a privately-owned farm in northeast Mississippi, USA, 2007-2009.

Table 4
Results of Akaike's information criterion (AIC), detection function [f(0)], probability of detection (p), and percent coefficient of variation (%CV) for Indigo Buntings (Passerina cyanea) detected in control and disturbed agricultural conservation buffers at a privately-owned farm in northeast Mississippi, USA, 2007-2009.

Table 5
Results of Akaike's information criterion (AIC), detection function [f(0)], probability of detection (p), and percent coefficient of variation (%CV) for Red-winged Blackbirds (Agelaius phoeniceus) detected in control and disturbed agricultural conservation buffers at a privately-owned farm in northeast Mississippi, USA, 2007–2009.

At the buffer level in 2007, there was no difference in avian density among buffers prior to disturbance (F_4,35.1 = 1.76, P = 0.160). Avian density in control and disturbed buffers did not differ in 2008 (F_2,35.4 = 0.99, P = 0.383) and 2009 (F_4,37.4 = 0.58, P = 0.680). In 2008, relative effect sizes on avian density were -26% for burned buffers in the first growing season and -68% for disked buffers in the first growing season (Fig. 5), reflecting a short-term decline in density. However, confidence intervals included 0. In 2009, relative effect sizes on total avian density were -10% for buffer the first growing season post-burn and -2% the second season post-burn. Again, confidence intervals on effect sizes included 0.

At the field level, prior to disturbance, there was no difference in avian density among fields bordered by agricultural conservation buffers (F_2,11 = 0.59, P = 0.572). After disturbance regimes had been implemented, total avian density did not differ among treatments in 2008 (F_2,11 = 0.80, P = 0.475) and 2009 (F_2,11 = 0.28, P = 0.752). Relative effect sizes for avian density were positive for prescribed burning (2008, 112%; 2009, 15%), whereas effect sizes on avian density were mixed for disked fields (2008, 10%; 2009, -29%). However, field level confidence intervals on effect sizes included 0 for years and treatments.

Fig. (5) Least squares mean density estimates (mean ±1 standard error) at the buffer (left) and field (right) levels for all bird species detected in control and disturbed agricultural conservation buffers at a privately-owned farm in northeast Mississippi, USA, 2008-2009.

Fig. (6) Dickcissel (DICK), Red-winged Blackbird (RWBL), and Indigo Bunting (INBU) densities (mean ±1 standard error) at the buffer level in control and disturbed agricultural conservation buffers at a privately-owned farm in northeast Mississippi, USA, 2008-2009.

In 2007, there was no difference in Dickcissel density prior to disturbance (F_4,38 = 0.98, P = 0.428). Furthermore, neither type of nor time since disturbance influenced Dickcissel density in buffers during 2008 (F_2,37.7 = 0.81, P = 0.454) and 2009 (F_4,38.9 = 0.50, P = 0.735). In 2008, Dickcissel density in buffers the first growing season post-burn was -33% relative to control buffers (Fig. 6). In 2009, relative effect size in Dickcissel density between these same buffers their second growing season post-burn and controls was 19%. Confidence intervals on effect sizes, however, included 0 for years and treatments.

At the field level in 2007, there was no difference in Dickcissel density (F_2,11 = 0.01, P = 0.989). Post-disturbance Dickcissel density still did not differ among fields bordered by agricultural conservation buffers in 2008 (F_2,11 = 0.09, P = 0.911) and 2009 (F_2,11 = 0.54, P = 0.599). Effect sizes on mean Dickcissel density in fields with disking as the assigned treatment were -6% in 2008 and -3% in 2009 relative to control fields (Fig. 7). Conversely, the relative effect size in Dickcissel density between burned and control fields was 19% in 2008 and 27% in 2009. Though these results suggest a positive response to prescribed burning, confidence intervals included 0.

Fig. (7) Dickcissel (DICK), Red-winged Blackbird (RWBL), and Indigo Bunting (INBU) densities (mean ±1 standard error) at the field level in control and disturbed agricultural conservation buffers at a privately-owned farm in northeast Mississippi, USA, 2008-2009.

In 2007, there was no difference in Red-winged Blackbird density in agricultural conservation buffers prior to disturbance (F_4,34.7 = 1.43, P = 0.246). Blackbird density did not differ between disturbed and control buffers in 2008 (F_2,34.8 = 0.40, P = 0.675) and 2009 (F_4,36.5 = 0.21, P = 0.931). In 2008, there was a 73% difference in relative effect size between blackbird densities in buffers the first growing season post-disk and control buffers. Based on relative effect sizes in 2009, blackbird density in disked buffers compared to control buffers was -33% during the first growing season post-disk, and -61% the second growing season. Confidence intervals of these effect sizes, however, included 0.

At the field level, there was no difference in Red-winged Blackbird density in buffer-bordered fields prior to disturbance (F_2,11 = 1.50, P = 0.267). After disturbance had occurred, there was still no difference in blackbird density among the fields in 2008 (F_2,11 = 1.42, P = 0.283) and 2009 (F_2,11 = 0.58, P = 0.575). In 2008, relative effect sizes in blackbird density were 659% for burned fields and 108% for disked fields compared to control fields. In 2009, this difference was reduced to 17% for burned fields. At this time, the relative effect size between disked and control fields was -63%. Despite these large relative effect sizes, though, their respective confidence intervals included 0.

Indigo Bunting density did not differ among agricultural conservation buffers prior to disturbance in 2007 (F_4,38 = 1.12, P = 0.362). Based on relative effect sizes in 2008, bunting density in burned and disked buffers during their first growing season post-disturbance was greater than in control buffers (burned, 88%; disked, 118%). In 2009, bunting density in buffers during their first growing season post-burn was 12% greater relative to controls. Bunting density in disked buffers during their second growing season was 46% greater compared to controls. Despite these large effect sizes, however, there was no difference in bunting density regardless of type of or time since disturbance (2008, F_2,36 = 3.18, P = 0.053; 2009, F_4,41 = 1.49, P = 0.224).

Indigo Bunting density did not differ among buffer-bordered fields prior to disturbance in 2007 (F_2,11 = 1.22, P = 0.331). Indigo Bunting density still did not differ among buffer-bordered fields after disturbance had occurred (2008, F_2,11 = 0.77, P = 0.486; 2009, F_2,11 = 1.38, P = 0.292). In 2008, relative effect sizes for bunting density between disturbed and control fields were -46% for burned fields and -17% for disked fields. These differences increased to -53% for burned fields and -23% for disked fields in 2009. Confidence intervals for these effects sizes, however, did include 0.

Our results most frequently supported uniform detection functions, thus it is likely all birds present in the agricultural conservation buffers during transect surveys were detected. Similarly, based on a review of 75 published papers from 1985 to 2001 that conducted transect surveys of grassland birds, the probability of detection of Henslow’s (Ammodramus henslowii), Grasshopper, and Savannah Sparrows ranged from 0.93 to 1.0 when a bird was within 25 m of an observer [35Diefenbach DR, Brauning DW, Mattice JA. Variability in grassland bird counts related to observer differences and species detection rates. Auk 2003; 120: 1168-79.
[http://dx.doi.org/10.1642/0004-8038(2003)120[1168:VIGBCR]2.0.CO;2] ]. Due to uniform detection in the 0-15 m distance range, followed by an increase in detections in the 15-20 m distance range, avian behavior was likely not negatively influenced by observer presence and birds were attracted to the buffer edge where there was alternative vegetative cover (i.e., crop or non-crop habitat). If birds had been negatively influenced by observer presence, detections would have increased with increasing distance from the observer. Therefore, vegetation differences among buffers (e.g., vegetation height, vegetation density) and aversion behavior exhibited by birds in response to the observer did not influence the probability of detection during transect surveys.

Prescribed fire and light disking did not affect breeding bird diversity and density at either the buffer or field level during the first and second growing seasons post-disturbance. However, direction and magnitude of relative effect sizes on diversity and density for burned and disked buffers indicate the possibility of a type two error (i.e., failing to reject a false null hypothesis). If indeed our alternate hypothesis was true, this would be consistent with previous studies reporting differences in avian diversity and density between disturbed and undisturbed habitats. In northeast Nebraska, grassland bird abundance and diversity were greater in disked CRP fields than those that were unmanaged [36Negus LP, Davis CA, Wessel SE. Avian response to mid-contract management of conservation reserve program fields. Am Midl Nat 2010; 14: 296-310.
[http://dx.doi.org/10.1674/0003-0031-164.2.296] ]. In northwestern North Dakota, avian species richness and abundance of Bobolink, Grasshopper Sparrow, and Western Meadowlark were greater in burned than in unburned mixed-grass prairie sites [21Madden EM, Hansen AJ, Murphy RK. Influence of prescribed fire history on habitat and abundance of passerine birds in northern mixed-grass prairie. Can Field Nat 1999; 113: 627-40.]. These studies, however, occurred in large blocks of grassland habitat. Many grassland bird species, including Dickcissels, are area-sensitive species that prefer large habitat patches [37Bakker KK, Naugle DE, Higgins KF. Incorporating landscape attributes into models for migratory grassland bird conservation. Conserv Biol 2002; 16: 1638-46.
[http://dx.doi.org/10.1046/j.1523-1739.2002.01328.x] ]. Because agricultural conservation buffers only provide strip grassland habitat and cover a small area (0.17-3.49 ha in this study), disturbance methods used to maintain the early-successional state of buffers may not be an important factor in avian habitat selection at the field level. When applied in a rotational fashion, only ¼-⅓ of buffers is disturbed within any single year, leaving the remainder undisturbed, creating a mosaic of successional stages at the whole-field scale.

Although disturbance did not statistically affect diversity or density of breeding birds in our agricultural conservation buffers, disturbance does alter vegetation structure (e.g., vegetation height and density), which may influence a bird’s choice of habitat [38Best LB. The value of buffer habitats for birds in agricultural landscapes. In: Hohman WL, Halloum DJ, Eds. A comprehensive review of Farm Bill contributions to wildlife conservation, 1985-2000 Tech Rep 2000; 75-94.]. Burned mixed-grass prairies in north-central North Dakota had minimal vegetation coverage with little standing dead vegetation 1-year post-burn, but this increased and stabilized following the second growing season [39Grant TA, Madden E, Berkey GB. Tree and shrub invasion in northern-mixed-grass prairie: implications for breeding grassland birds. Wildl Soc Bull 2004; 32: 807-18.
[http://dx.doi.org/10.2193/0091-7648(2004)032[0807:TASIIN]2.0.CO;2] ]. In the agricultural conservation buffers at our study site, nest densities of Dickcissels and Red-winged Blackbirds were greater in burned buffers than in disked buffers [40Adams HL, Burger LW Jr, Riffell S. Disturbance and landscape effects on avian nests in agricultural conservation buffers. J Wildl Manage 2013; 77: 1213-20.
[http://dx.doi.org/10.1002/jwmg.568] ]. Alternatively, disking encourages the germination of forbs by disrupting grass-root structures and setting succession back further than burning [41Jones J, Coggin DS, Cummins JL, Hill J. Restoring and managing native prairies: A handbook for Mississippi landowners. Stoneville: Wildlife Mississippi 2007.]. In buffers used during this study, forb species richness in disked buffers was greater than in control and burned buffers during summer 2008 (P = 0.009-0.039) [42Dollar JG. Responses of butterfly and forb communities to management of semi-natural grassland buffers. Thesis 2011.]. In May 2009, these same buffers had a greater number of forb species than control and burned buffers (P = 0.009) [42Dollar JG. Responses of butterfly and forb communities to management of semi-natural grassland buffers. Thesis 2011.]. A greater presence of forbs in disked buffers can create suitable habitat for pollinating insects [17Dollar JG, Riffell SK, Burger LW Jr. Effects of managing semi-natural grassland buffers on butterflies. J Insect Conserv 2013; 7: 577-90.
[http://dx.doi.org/10.1007/s10841-012-9543-7] ], or other insect species that could serve as a food source for breeding grassland birds and their nestlings [43Mitchell KL, Riffell SK, Burger LW Jr, Vilella FJ. Nestling provisioning of Dickcissels in native warm-season grass field buffers. Wilson J Ornithol 2012; 124: 198-209.
[http://dx.doi.org/10.1676/11-152.1] ].

Dickcissels are grassland specialists and a species of concern. From 1966 to 1979, Dickcissel populations in the Southeastern United States were declining at a rate of 6.1% every year [44Sauer JR, Hines JE, Fallon J. The North American breeding bird survey, results and analysis 1966-2007, version 515 2008. http://www. mbr-pwrc.usgs.gov/bbs/]. In recent years, however, Dickcissel populations have begun to increase. For instance, in the Mississippi Alluvial Valley; the physiographic region where our study site is located; the 2005-2015 Dickcissel population increased at a rate of 2.42% per year [45Sauer JR, Niven DK, Hines JE, et al. The North American breeding bird survey, results and analysis 1966–2015, version 207 2017. http:// www.mbr-pwrc.usgs.gov/bbs/]. Dickcissels likely do not require as large of early successional areas during the breeding season compared to other grassland birds (e.g., Eastern Meadowlark, Savannah Sparrow) [46Herkert JR. The effects of habitat fragmentation on Midwestern grassland bird communities. Ecol Appl 1994; 4: 461-71.
[http://dx.doi.org/10.2307/1941950] ]. Thus, Dickcissels may respond positively to conservation practices in fragmented areas, like those of the CRP in agricultural landscapes.

Dickcissels prefer grassland habitat with tall, dense vegetation structure [47Delisle JM, Savidge JA. Avian use and vegetation characteristics of conservation reserve program fields. J Wildl Manage 1997; 61: 318-25.
[http://dx.doi.org/10.2307/3802587] , 48Hughes JP, Robel RJ, Kemp KE, Zimmerman JL. Effects of habitat on Dickcissel abundance and nest success in conservation reserve program fields in Kansas. J Wildl Manage 1999; 63: 523-9.
[http://dx.doi.org/10.2307/3802638] ]. This may be one reason why Dickcissels were detected frequently in control buffers during this study. Because of the absence of disturbance, vegetation in these buffers provided many perching, singing, and foraging sites for birds. Disturbance temporarily alters this vegetation structure by reducing ground cover and vertical density. Time since disturbance can determine how quickly buffers can recover and once again accommodate Dickcissels during the breeding season. Dickcissels at our study site, for instance, had greater nest densities in burned buffers than those that were disked [40Adams HL, Burger LW Jr, Riffell S. Disturbance and landscape effects on avian nests in agricultural conservation buffers. J Wildl Manage 2013; 77: 1213-20.
[http://dx.doi.org/10.1002/jwmg.568] ].

Prescribed burning in agricultural conservation buffers did not significantly reduce Dickcissel density relative to the control buffer regardless of time since disturbance. Frequently, though, Dickcissel densities in grassland habitats decline immediately following a prescribed burn because of a lack of vegetative cover [23Fuhlendorf SD, Harrell WC, Engle DM, Hamilton RG, Davis CA, Leslie DM Jr. Should heterogeneity be the basis for conservation? Grassland bird response to fire and grazing. Ecol Appl 2006; 16(5): 1706-16.
[http://dx.doi.org/10.1890/1051-0761(2006)016[1706:SHBTBF]2.0.CO;2] [PMID: 17069365] ]. Given time, vegetation in burned buffers can recover quickly from disturbance because of warmer soil temperatures and greater availability of soil nutrients [49Harper CA, Bates GE, Hansbrough MP, Gudlin MJ, Gruchy JP, Keyser PD. Native warm-season grasses: Identification, establishment and management for wildlife and forage production in the mid-south. Knoxville: University of Tennessee Extension, PB1752 2007.]. This quick recovery may provide Dickcissels cover later in the breeding season. In central South Dakota, Dickcissel densities increased from early to late seral stages of a mixed-grass prairie [50Fritcher SC, Rumble MA, Flake LD. Grassland bird densities in seral stages of mixed-grass prairie. J Range Manage 2004; 57: 351-7.
[http://dx.doi.org/10.2307/4003858] ]. Additionally, Dickcissel abundance in Oklahoma grasslands increased with time since burning [18Olson DM, Wäckers FL. Management of field margins to maximize multiple ecological services. J Appl Ecol 2007; 44: 13-21.
[http://dx.doi.org/10.1111/j.1365-2664.2006.01241.x] ].

Alternatively, vegetation in disked buffers did not recover from disturbance as quickly as vegetation in burned buffers [41Jones J, Coggin DS, Cummins JL, Hill J. Restoring and managing native prairies: A handbook for Mississippi landowners. Stoneville: Wildlife Mississippi 2007.]. Because of this, Dickcissel density was greater in control and burned buffers than in disked buffers with respect to relative effect sizes. Though a greater abundance of forbs in disked buffers can provide Dickcissels foraging sites, these plants may not be able to provide optimal breeding and nesting sites for this species. Thus, Dickcissels occur in reduced abundance due to the lack of perching, singing, and nesting sites.

Red-winged Blackbirds, though commonly known as a wetland species, will breed in several habitat types throughout Mississippi, such as lowlands, weedy fields, roadways, and ditch banks [51Turcotte WH, Watts DL. Birds of Mississippi 1999.]. Blackbirds are also a facultative grassland species and will benefit from management practices used to promote grassland birds [52Patterson MP, Best LB. Bird abundance and nesting success in Iowa CRP fields: The importance of vegetation structure and composition. Am Midl Nat 1996; 135: 153-67.
[http://dx.doi.org/10.2307/2426881] , 53Vickery PD, Tubaro PL, Cardoso da Silva JM, Peterjohn BG, Herkert JR, Cavalcanti RB. Conservation of grassland birds in the western hemisphere. Stud Avian Biol 1999; 19: 2-26.]. Furthermore, this species is known commonly as a crop pest and their presence in agricultural conservation buffers may be viewed as a drawback to this conservation practice by land managers. For instance, the flocking and foraging behavior of Red-winged Blackbirds in the northern Great Plains causes extensive damage to sunflower (Helianthus annuus) [54Linz GM, Klug PE, Dolbeer RA. Ecology and management of red-winged blackbirds. In: Linz GM, Avery ML, Dolbeer RA, Eds. Ecology and management of blackbirds (Icteridae) in North America 2017; 17-41.
[http://dx.doi.org/10.4324/9781315156439-2] ]. However, in the southeastern United States, cultivated rice may make up a large portion of the birds’ diet [54Linz GM, Klug PE, Dolbeer RA. Ecology and management of red-winged blackbirds. In: Linz GM, Avery ML, Dolbeer RA, Eds. Ecology and management of blackbirds (Icteridae) in North America 2017; 17-41.
[http://dx.doi.org/10.4324/9781315156439-2] ], which is a crop not typically grown in upland areas where buffers are more commonly established.

Red-winged Blackbird density in burned buffers did not differ from control buffers in 2008 and 2009. In a Kansas study, Red-winged Blackbird density was greater in unburned than burned sites, but this difference was not significant [55Robel RJ, Hughes JP, Hull SD, Kemp KE, Klute DS. Spring burning: resulting avian abundance and nesting in Kansas CRP. J Range Manage 1998; 51: 132-8.
[http://dx.doi.org/10.2307/4003197] ]. Red-winged Blackbird densities in an east-central North Dakota mixed-grass prairie increased 2 to 5 years post-burn [28Johnson DH. Effects of fire on bird populations in mixed-grass prairie. In: Knopf FL, Samson FB, Eds. Ecology and conservation of Great Plains vertebrates 1997; 181-206.
[http://dx.doi.org/10.1007/978-1-4757-2703-6_8] ]. Though there was no significant difference in blackbird densities between burned and unburned buffers in this study, we did not collect data past the second growing season post-disturbance. Thus, it is possible a difference in blackbird density between these 2 disturbance types may have been detected had the study continued during subsequent years [28Johnson DH. Effects of fire on bird populations in mixed-grass prairie. In: Knopf FL, Samson FB, Eds. Ecology and conservation of Great Plains vertebrates 1997; 181-206.
[http://dx.doi.org/10.1007/978-1-4757-2703-6_8] ].

Though there were no significant differences found in this study, Red-winged Blackbird density in 2008 was greater in control buffers than in disked buffers based on relative effect sizes. In 2009, this difference was still existent in these same buffers during their second growing season after disking. Like Dickcissels, Red-winged Blackbirds are associated positively with vertical vegetation density [52Patterson MP, Best LB. Bird abundance and nesting success in Iowa CRP fields: The importance of vegetation structure and composition. Am Midl Nat 1996; 135: 153-67.
[http://dx.doi.org/10.2307/2426881] ]. Thus, these birds may avoid disked buffers because of a lack of foraging and breeding habitat.

Red-winged blackbirds are known for causing excessive crop damage. In North Dakota, South Dakota, and Nebraska, for instance, the average annual impacts of Red-winged Blackbirds, along with Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) and Common Grackles (Quiscalus quiscula), on sunflower production from 2009 to 2013 were US $18.7 million, US $7.3 million, and US $2.6 million, respectively [56Ernst K, Elser J, Linz G, et al. The economic impacts of blackbird (Icteridae) damage to sunflower in the USA. Pest Manag Sci 2019; 75(11): 2910-5.
[http://dx.doi.org/10.1002/ps.5486] [PMID: 31087456] ]. In regards to our study, planted crops included soybean, corn, and Bermudagrass. We did not observe any occurrences of crop damage by Red-winged Blackbirds to these crops while performing transect surveys. Furthermore, in a concurrent study, we determined Red-winged Blackbird nest success was only 12.9% at the peak of their breeding season (early August), thus buffers may serve only as sink habitat for this species [40Adams HL, Burger LW Jr, Riffell S. Disturbance and landscape effects on avian nests in agricultural conservation buffers. J Wildl Manage 2013; 77: 1213-20.
[http://dx.doi.org/10.1002/jwmg.568] ]. However, land managers should be attentive to potential crop damage by Red-winged Blackbirds or similar species.

Indigo Buntings are a common forest-field edge species that will utilize woodland and grassland habitat in close proximity [57Weldon AJ, Haddad NM. The effects of patch shape on Indigo Buntings: Evidence for an ecological trap. Ecology 2005; 86: 1422-31.
[http://dx.doi.org/10.1890/04-0913] ]. These birds may also be found in shrubby areas and weedy fields [58Payne RB. Indigo bunting (Passerina cyanea), version 2.0. In: Poole AF, Ed. Birds of North America 2006.]. Indigo Buntings may also prefer edge habitat more irregular in shape than linear habitat [57Weldon AJ, Haddad NM. The effects of patch shape on Indigo Buntings: Evidence for an ecological trap. Ecology 2005; 86: 1422-31.
[http://dx.doi.org/10.1890/04-0913] , 59Brennan SP, Schnell GD. Relationship between bird abundances and landscape characteristics: The influence of scale. Environ Monit Assess 2005; 105(1-3): 209-28.
[http://dx.doi.org/10.1007/s10661-005-3694-x] [PMID: 15952521] ], such as that commonly provided by agricultural conservation buffers.

As with Dickcissels and Red-winged Blackbirds, Indigo Bunting density did not vary significantly between disturbed and undisturbed buffers during this study. Several studies, however, have shown Indigo Buntings respond positively to disturbance. In North American oak (Quercus spp.) savannahs, for instance, bunting densities increased following prescribed burns [60Brawn JD, Robinson SK, Thompson FR III. The role of disturbance in the ecology and conservation of birds. Annu Rev Ecol Syst 2001; 32: 251-76.
[http://dx.doi.org/10.1146/annurev.ecolsys.32.081501.114031] ]. Indigo Buntings have also been frequently observed in New Hampshire clear-cut forest sites [61Costello CA, Yamasaki M, Pekins PJ, Leak WB, Neefus CD. Songbirds response to group selection harvests and clearcuts in a New Hampshire northern hardwood forest. For Ecol Manage 2000; 127: 41-54.
[http://dx.doi.org/10.1016/S0378-1127(99)00131-0] ]. However, Indigo Bunting density can be least immediately following disturbance due to lack of vegetative cover. Frequent burning, for instance, can reduce shrub density and, in turn, Indigo Bunting density [62Brennan LA, Engstrom RT, Palmer WE, et al. Whither wildlife without fire? Trans North Am Wildl Nat Resour Conf 1998; 63: 402-14.]. Also, Indigo Buntings preferred areas with dense herbaceous ground cover when white-tailed deer (Odocoileus virginianus) were excluded from forested sites in Virginia-Indigo Bunting density increased with time since exclusion [63McShea WJ, Rappole JH. Managing the abundance and diversity of breeding bird populations through manipulation of deer populations. Conserv Biol 2000; 14: 1161-70.
[http://dx.doi.org/10.1046/j.1523-1739.2000.99210.x] ].

Unmanaged agricultural conservation buffers may be able to provide more cover for Indigo Buntings than those that have recently been disturbed. With time, however, disturbed buffers could be preferred Indigo Bunting habitat as vegetation density in unmanaged buffers increases.