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2012 SOUTHEASTERN NATURALIST 11(3):423–436
Summer use of Rice Fields by Secretive Marsh Birds in the
Mississippi Alluvial Valley of Northeast Louisiana
Jonathon J. Valente1,2,*, Sammy L. King3, and R. Randy Wilson4
Abstract - Many secretive marsh bird (SMB) species nest within rice fields, yet in most
regions we do not understand the extent to which these birds use such habitats. In the
summers of 2007 and 2008, we investigated summer use of rice fields by SMBs in northeast
Louisiana and evaluated the local (within 100 m) and landscape (within 1 km) habitat
characteristics influencing site selection. We did not encounter any SMB species in 2007,
but we encountered low densities of Ixobrychus exilis (Least Bitterns), Rallus elegans
(King Rails), and Fulica americana (American Coots) in mid-July of 2008. It is unclear
whether or not the birds we detected were actually breeding in the rice fields, or merely
using them as late summer foraging areas. When we combined detections of all species,
we found that probability of occupancy was positively influenced by the proportion of the
local habitat dominated by flooded ditches containing herbaceous emergent vegetation.
Ditches likely provide refuge and resource alternatives that may be particularly important
to these birds in the late summer when rice fields are drained and harvested. However,
given that SMBs were detected at less than 10% of the 72 rice fields we surveyed, it
appears as though Mississippi Alluvial Valley rice fields contribute very little toward
supporting SMB populations.
Greater than 50% of the wetlands in the lower 48 US states have been destroyed
over the past two centuries (Dahl 1990), and conversion of wetlands
for agricultural purposes has been implicated as one of the leading causes of
this destruction (Tiner 1984). The connection between global wetland loss and
rice agriculture is particularly evident; annually, rice occupies 1,500,000 km2 of
land worldwide, more than any other agricultural crop (Forĕs and Comín 1992),
and an estimated 57% of global rice fields occupy former natural wetland areas
(Lawler 2001). However, virtually all rice production involves field inundation
at some point during the year (Chang and Luh 1991), and consequently these
“agricultural wetlands” can provide habitat and resources for many of the same
bird species that use natural wetlands (Lawler 2001).
Rice fields provide important foraging habitat for diverse and abundant avian
communities in many of the most important rice-growing territories of the world,
including Japan (Maeda 2001), the Mediterranean region of Europe (Fasola and
1School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA
70803. 2Current address - US Army Engineer Research and Development Center, Environmental
Laboratory, 3909 Halls Ferry Road, Vicksburg, MS 39180. 3US Geological
Survey Louisiana Cooperative Fish and Wildlife Research Unit, 124 School of Renewable
Natural Resources, Louisiana State University, Baton Rouge, LA 70803. 4US Fish
and Wildlife Service, 6578 Dogwood View Parkway Suite B, Jackson, MS 39213. *Corresponding
author - Jonathon.J.Valente@gmail.com.
424 Southeastern Naturalist Vol. 11, No. 3
Ruiz 1996, Fasola et al. 1996), the Central Valley of California (Day and Colwell
1998, Elphick and Oring 1998, Shuford et al. 1998), and the US Gulf Coastal
Plain (Huner et al. 2002, Remsen et al. 1991). In fact, rice agriculture may be
vital in maintaining bird populations in some places; rice fields support approximately
75% of wintering shorebirds in the Sacramento Valley of California
(Shuford et al. 1998) and 50–100% of wading birds in the Mediterranean region
during the peak of the breeding season (Fasola et al. 1996). The quality of these
habitats is often comparable to more natural wetland systems (Elphick 2000,
Helm et al. 1987), and as a result, some species select nesting locations based on
their proximity to rice complexes (Tourenq et al. 2004).
For other species, such as secretive marsh birds (SMBs), rice fields can actually
provide critical nesting habitat. SMBs are a group of wetland-obligate
breeders that includes all rails, bitterns, moorhens, and gallinules (Conway
2009). Evidence suggests that many SMB species have suffered drastic population
declines over the past 30 years (Eddleman et al. 1988, Timmermans et al.
2008), which may be primarily attributable to wetland loss (Conway et al. 1994,
Eddleman et al. 1988). During the breeding season, rice fields exhibit many of the
attributes commonly required by these species, including shallow water, dense
emergent vegetation, and food resources like rice seeds, aquatic invertebrates,
amphibians, and fish (Czech and Parsons 2002). Thus, maintaining rice fields
with habitat features utilized by SMBs may be extremely important for conservation
of these species in the future. The majority of the research on breeding SMB
use of agricultural wetlands in the US has taken place on the Gulf Coastal Plain
(GCP), where several species have been recorded nesting successfully in rice
fields (Helm et al. 1987, Hohman et al. 1994, Pierluissi 2006, Pierluissi and King
2008), including Rallus elegans Audubon (King Rail), Porphyrula martinica
L. (Purple Gallinule), Gallinula chloropus L. (Common Moorhen), and Ixobrychus
exilis Gmelin (Least Bittern). These birds tend to prefer fields surrounded
by ditches and landscapes with little tree cover (Pierluissi 2006) and can even
achieve greater reproductive success in rice fields than in more natural systems
(Helm et al. 1987). However, SMB habitat preferences may differ among regions
because of differences in agricultural practices and available habitat features.
Five SMB species are known to breed in natural wetlands of the Mississippi
Alluvial Valley (MAV), including Common Moorhens, Least Bitterns, Purple
Gallinules, Fulica Americana Gmelin (American Coot), and King Rails (Valente
et al. 2011). However, little is known about how these birds use regional
rice fields. In the MAV of Louisiana, rice fields tend to be located in landscapes
dominated by non-flooded agriculture and remnant tracts of dense bottomland
hardwood forest, whereas the GCP is comprised largely of rice, fallow rice fields,
and coastal marsh. Farmers in the MAV also tend to use later planting dates, and
different rice varieties and flooding regimes than those of the GCP. Moreover,
the structure provided by ditch vegetation may be especially crucial for breeding
SMBs in the MAV, where breeding can begin in early March (Meanley 1953),
but rice does not mature until early May or June. To further our understanding of
the role agricultural systems play in SMB conservation, we investigated breeding
2012 J.J. Valente, S.L. King, and R.R. Wilson 425
SMB use of rice fields in the MAV of northeast Louisiana. The goals of our study
were to determine which SMB species breed in rice fields and to identify the local
and landscape-level habitat characteristics that attract those species.
Our study area encompassed most of the MAV in Louisiana north of 31°1'2"
north latitude and east of 92°10'15" west longitude (Fig. 1). The region is located
in the historic floodplain of the Mississippi River and was once dominated
by dense bottomland hardwood forest, though an extensive levee system now
isolates this area from floodwaters. In the past 200 years, more than 80% of this
habitat has been altered (The Nature Conservancy 2009), and now the region is
predominantly comprised of agricultural fields and remnant forest patches. Rice
is not one of the primary crops grown in the MAV, so most of the fields surrounding
our survey areas were cultivated in corn and soybeans.
We were granted access to approximately 4000 ha of rice fields on seven private
farms and approximately 140 ha on Grand Cote National Wildlife Refuge
(NWR). In the spring of 2007, we digitized all rice fields on those properties
using ESRI® ArcMap™ 9.1 (ESRI, Inc.). To reduce the probability of detecting
the same bird at 2 different sites, we randomly placed 1 point on the perimeter of
each rice field with the stipulation that all points had to be at least 700 m apart, a
more conservative distance than the 400 m recommended by Conway (2009). We
eliminated about one third of the resulting 113 rice fields for logistical reasons
(e.g., location relative to other sites, distance from nearest lodging) and we randomly
selected 37 from the remaining to be used as our study sites in 2007. These
fields were distributed across four farms and one NWR. In 2008, we selected all
new sites (n = 35) on four farms using the same procedure.
Bird sampling protocol
Four trained observers (three unique to each year) conducted morning and
evening callback surveys between 20 March and 24 June 2007 and between 19
May and 22 August 2008. Pierluissi (2006) found that rice needed to be both
flooded and approximately 65–70 cm tall before SMBs would begin nesting
in it, and none of our sample fields had even been planted when we started our
surveys in 2007. Yet, Meanley (1953) noted that King Rails utilized overgrown
ditches around rice fields early in the breeding season in Arkansas, and thus the
survey period in 2007 was designed to coincide with the approximate breeding
phenology of target species (Valente et al. 2011) in order to detect birds that
might be using those ditches; surveying was delayed in 2008 due to a lack of detections
in 2007. In both years, we attempted to survey sites once or twice every
15 days (sampling period), although approximately 1 month elapsed between
the last two sampling periods in 2008 due to personnel constraints. Survey
426 Southeastern Naturalist Vol. 11, No. 3
procedures followed those outlined by the Standardized North American Marsh
Bird Monitoring Protocols (Conway 2009); each survey included a 1-minute
“settling” period, a 5-minute silent period, and a 6-minute callback period. The
callback period consisted of playing 30 seconds of calls from 6 SMB species
(Least Bittern, King Rail, Botaurus lentiginosus Rackett [American Bittern],
Figure 1. Locations of rice farms situated in Louisiana’s Mississippi Alluvial Valley
which were sampled for secretive marsh birds during the breeding seasons of 2007 and
2008. White stars represent farms sampled in 2007 only, black stars represent farms
sampled in 2008 only, and gray stars represent farms sampled in both years.
2012 J.J. Valente, S.L. King, and R.R. Wilson 427
Common Moorhen, Purple Gallinule, and American Coot, sequentially) followed
by 30 seconds of silence. Pierluissi (2006) found that the American
Bittern call elicits responses from King Rails, so we incorporated it into the
study design despite the fact that Louisiana is outside its breeding range. Calls
were played from an RP2700A portable CD player (RCA, Paris, France) and
broadcast through 40-1434 portable folding speakers (RadioShack, Fort Worth,
TX). Observers measured the distance from the sampling point to the approximate
(because many detections were aural) location of each individual bird
using Yardage Pro Sport 450 range finders (Bushnell, Overland Park, KS).
Local- and landscape-scale habitat
Each time we visited a rice field to conduct a bird survey, we recorded the
mean rice height for the target field and whether or not the field was flooded.
Local habitat surveys were conducted once at each site between 1 June and 7
June 2007, and between 19 August and 22 August 2008. For these surveys, we
recorded the proportion of a 100-m radius circular plot around each sampling
point covered by rice, flooded ditches, agriculture, grass and weeds, young trees
(<3 m tall), and mature trees (≥3 m tall). These values summed to 1 for each
plot. Ditches that did not contain any standing water were considered uplands
(ditch flooding status remained fairly consistent throughout the duration of the
bird survey period). Because ditch vegetation may be particularly important to
breeding SMBs around rice fields, we further characterized the vegetation within
the associated flooded ditches by recording each plant species present, and the
proportion of the flooded ditch it covered. Submerged ditch areas that were not
covered by vegetation, or were dominated by structurally insignificant floating
plants such as Lemna minor L. (Lesser Duckweed) were considered open water.
We collected landscape-scale habitat information by centering a 1-km radius
circular plot (Pierluissi and King 2008) on each sampling point, and overlaying
that on digital orthophotos taken in 2007 as part of the US Department of Agriculture’s
National Agriculture Imagery Program. We printed the image of each
plot and classified all parts of the landscape into one of five categories in the field:
1) agriculture (including rice); 2) residential, grassland, or pasture; 3) wetland
or permanent water; 4) young trees (<3 m); or 5) mature trees (≥3 m). We then
digitized these 1-km landscapes using ArcMap™ and calculated the proportion
of each that was comprised of those habitat features.
Initial review of our data indicated that no SMB individuals were ever detected
in our study fields (or surrounding ditches) when the rice was <65 cm tall,
a finding that has been echoed in previous studies (Pierluissi 2006). Thus, we assumed
that fields in which the rice never reached 65 cm during our survey period
(n = 30) were not even available for use by SMBs, and those were eliminated
from our habitat analyses. It should be noted that the rice in all of these fields
probably reached a height of >65 cm at some point after our surveys concluded,
and if we had included them in our habitat models then they would have been
428 Southeastern Naturalist Vol. 11, No. 3
considered “unoccupied,” when in fact they may have become occupied once the
rice was tall enough.
We initially planned to use a likelihood-based approach to model site occupancy
for each species separately as a function of measured habitat variables
while simultaneously accounting for detection probability (MacKenzie et al.
2002). However, because occupancy appeared to be highly dependent on rice
height, which varied greatly over the course of our survey period, our data
almost certainly violated the “closure” assumption (i.e., if a site is occupied
during any survey then it is assumed to be occupied during all surveys) that
is fundamental to this modeling technique. Additionally, the extremely low
number of bird detections forced us to combine all species into a single habitat
analysis. Thus, each of the sites that were surveyed after the rice reached 65 cm
were deemed “occupied” if any SMB individual was ever detected within 250 m
of the survey point; all other sites were deemed “unoccupied”. Because there
was no site replication between years, we pooled all data for habitat models in
order to augment sample size.
We combined the habitat information we recorded into 9 local-scale variables
and 4 landscape-scale variables that we thought could plausibly influence
SMB site occupancy based on previously published accounts and our own
field observations (Table 1). Rather than model occupancy as a function of all
possible combinations of these 13 variables (8192 models), we chose to first
reduce the number of variables to be included in a global model. To do this, we
constructed models (PROC LOGISTIC, SAS v. 9.2, SAS Institute, Cary, NC)
that included each of the habitat variables individually (models of interest), and
then compared them to an intercept-only model (null) using Akaike’s information
criterion corrected for small sample sizes (AICC; Burnham and Anderson
2002:66). If there was no reduction in the AICC value associated with a model
of interest (i.e., not an improvement over the reduced model), then the habitat
variable was eliminated from further consideration. When 2 of the retained variables
were highly correlated (i.e., Pearson correlation coefficient |r| ≥ 0.7), we
compared the models of interest containing those 2 variables and eliminated the
one that had the larger AICC value. We then constructed a global habitat model
that included all retained habitat variables, and compared it to models containing
all possible combinations of those retained variables using AICC and Akaike
weights (ωi; Burnham and Anderson 2002:75); we also performed a Hosmer
and Lemeshow goodness-of-fit test (Hosmer and Lemeshow 2000) on each of
these models to ensure they fit the data (α = 0.05). We accepted the variables in
the most parsimonious model (i.e., the model with the lowest AICC value) as the
best predictors of SMB occupancy.
In 2007, we conducted 259 bird surveys (7.0 surveys/site) and detected 16
total SMB individuals. Fifteen of these birds (8 American Coots and 7 Common
Moorhens) were actually located in natural wetlands adjacent to the target rice
2012 J.J. Valente, S.L. King, and R.R. Wilson 429
fields. The only SMB individual we actually detected using one of our surveyed
agricultural areas in 2007 was an American Bittern detected on 3 April. Because
our study area is outside of the breeding region for this species, we assumed it
was a transient migrant. Thus, no breeding SMBs were detected using our rice
sites in 2007. In 2008, we conducted 248 surveys (7.1 surveys/site) and detected
13 total SMB individuals, including 1 American Coot, 3 King Rails, and 9 Least
Bitterns. These birds were detected at 7 different sites, and all were located
within the agricultural matrix we were surveying. Interestingly, all of these individuals
were encountered between 11 July and 17 July, which is approximately
2.5 months after breeding behavior had been documented in the region (Valente
et al. 2011).
In both years, farmers began planting rice in early April and continued until
the first week of May. Fields planted earliest began to germinate during the first
2 weeks of May, and fields with emergent rice were flooded anywhere from the
second week of May to the last week of June. Draining the fields for harvest began
in early August. Rice was generally not tall enough to support nesting (≈65
cm) until early to late June in either year. Thus, rice reached a height of ≥65 cm
during our sampling period in only 7 of the 37 sites in 2007 but in all 35 sites in
2008. Data collected at these 42 combined sites (7 occupied) were used in our
Only 3 models containing individual habitat variables showed improvement
over the null model (Table 1). NR_HERB_DITCH was eliminated from further
consideration due to high correlation (r = 0.996) with HERB_DITCH. This extremely
high correlation stems from the fact that HERB_DITCH was calculated
as the sum of NR_HERB_DITCH and ROBUST_DITCH, and only 1 site had
a value >0 zero for ROBUST_DITCH. Thus, only 2 habitat variables were included
in our global habitat model.
We constructed four models containing all possible combinations of these
retained variables (Table 2). The best model based on AICC included only one
variable, HERB_DITCH; no other model had substantial support (Burnham and
Anderson 2002:70). HERB_DITCH had a significant (α = 0.05) positive effect on
probability of occupancy in both models in which it was included. DITCH100M
had a positive effect when included as the only explanatory variable and a negative
effect in the global model, but the parameter estimate was not significantly
different from 0 (α = 0.05) in either case. There was no evidence for lack of fit in
any of the models tested.
The most significant finding from our study is that we only recorded potentially
breeding SMBs at less than 10% of the rice fields we surveyed over 2 years.
MAV rice fields appear to support extremely low densities of SMBs during this
time period when compared with other rice-growing regions in the Southeast.
Pierluissi (2006) searched fields for breeding SMBs on the Gulf Coastal Plain and
found that a large percentage of them contained Purple Gallinule (≥50%), King
430 Southeastern Naturalist Vol. 11, No. 3
Table 1. The change in AICC values resulting from individually adding local (within 100 m) and landscape (within 1 km) habitat variables to an interceptonly
logistic model of secretive marsh bird occupancy of rice fields surveyed in northeast Louisiana in 2007 and 2008. Values in bold indicate variables
that improved the model when included. An asterisk indicates that the variable was not included in the global occupancy model due to high correlation with
another variable that was included.
Variables Dominant land cover Description of habitat ΔAICC
RICE100M Rice agriculture All active, planted rice fields 2.14
TREES100M All trees Predominantly mature forest 2.21
AG100M Agriculture All active and fallow agricultural fields, including rice 0.99
DITCH100M Ditches Irrigation ditches containing standing water -1.50
ROBUST_DITCH Ditch supporting robust herbaceous emergent vegetation Typha spp. -
NR_HERB_DITCH Ditch supporting non-robust herbaceous emergent vegetation Echinodora spp., Sagittaria spp., Alternanthera -7.67*
philoxeroides Grisebach, etc.
HERB_DITCH Ditch supporting all herbaceous emergent vegetation Sum of ROBUST_DITCH and NR_HERB_DITCH -7.68
WOODY_DITCH Ditch supporting woody emergent vegetation Brunnichia spp., Salix nigra Marshall, Cephalanthus 2.19
occidentalis L., etc.
OPEN_DITCH Open water ditches Open water, Lemna minor L., etc. 2.15
WATER1KM Water Lakes, rivers, streams, and wetlands 1.66
TALLTREES1KM Trees ≥3 m Predominantly mature forest 1.15
TREES1KM All trees Mature forest and young reforested areas 1.16
AG1KM Agriculture All active and fallow agricultural fields 0.65
2012 J.J. Valente, S.L. King, and R.R. Wilson 431
Table 2. Comparison of logistic habitat models constructed to explain secretive marsh bird occupancy of rice fields in northeast Louisiana in 2007 and 2008.
Model variables are defined in Table 1.
Parameter estimate (SE) Odds ratio estimate Model selection Goodness of fit
Model Intercept HERB_DITCH DITCH100M HERB_DITCH DITCH100M AICC ΔAICC ωi χ2 df P
HERB_DITCH -1.95 (0.54) 1.62 (0.68) - 5.06 - 32.26 0.00 0.72 3.92 4 0.42
HERB_DITCH, DITCH100M -1.97 (0.55) 1.73 (0.84) -0.17 (0.74) 5.63 0.84 34.53 2.27 0.23 4.55 7 0.71
DITCH100M -1.77 (0.46) - 0.75 (0.41) - 2.10 38.45 6.19 0.03 3.68 4 0.45
Null (intercept-only) -1.61 (0.41) - - - - 39.95 7.68 0.02 - - -
432 Southeastern Naturalist Vol. 11, No. 3
Rail (≥40%), Common Moorhen (≥26%), and Least Bittern (≥7%) nests. Meanley
(1953) also frequently recorded King Rails nesting in and around rice fields
on the Grand Prairie. Given the fact that the MAV was historically dominated by
forested floodplains and is located several hundred kilometers from high-density
SMB breeding habitat on the coast, it is possible that the area has never been
important for supporting SMBs in the summer. However, data from other parts of
the MAV indicate that SMBs do breed in the region (Budd and Krementz 2011).
Additionally, we found that many of these birds are, indeed, locally abundant, as
we detected one or more species at greater than 35% of the more natural wetlands
surveyed in our study region during the same time period (Valente et al. 2011).
In fact, when appropriate breeding habitat was available (i.e., flooded patches of
robust emergent vegetation ≥ 0.04 ha), over 80% of these wetlands were occupied
by at least one individual. Thus, we suggest that the MAV rice fields we surveyed
support very low densities of breeding SMBs primarily because of the paucity of
available early season nesting habitat.
Rice fields in the MAV tend to be planted relatively late in the season, and
the rice does not reach an appropriate height to support breeding SMBs until late
June. In addition, the ditches surrounding our target rice fields did not exhibit
characteristics that would make them attractive to early season breeders. Meanley
(1953) noted that King Rails primarily utilized overgrown ditches around
rice fields in Arkansas during the months of March through May, building nests
in dense stands of Typha latifolia L. (Cattail), Juncus effusus L. (Soft Rush),
and Carex hyalinolepis Steudel (Shoreline Sedge). Similarly, Pierluissi (2006)
found a positive association between the proportion of rice fields lined by ditches
and the density of King Rail and Purple Gallinule nests in those fields. These
researchers have suggested that ditches provide supplemental resources, refuge
from agricultural disturbances, and more sufficient nesting structure early in the
growing season for breeding birds. The irrigation ditches near the rice fields we
surveyed tended to be well manicured (i.e., mowed or treated with herbicides)
and dominated by open water or less robust wetland vegetation such as Echinodora
spp. (burhead), Sagittaria spp. (arrowhead), Alternanthera philoxeroides
Grisebach (Alligator Weed), and Polygonum hydropiperoides Michaux (Smartweed),
that would likely provide poor quality cover or nesting structure for SMBs
in the absence of mature rice.
As the rice grew taller, availability of ditch habitat did become an important
factor in predicting SMB occupancy. In fact, the only habitat variables we measured
that seemed to have any influence on site occupancy were the proportion of
the local survey area dominated by flooded ditches (DITCH100M), and flooded
ditches supporting herbaceous emergent vegetation (HERB_DITCH). Our models
yielded inconclusive results about the effect of DITCH100M on occupancy, as
it had a positive influence in one model and a negative influence in another. The
fact that DITCH100M was included in the global model at all may be due to the
fact that it was moderately correlated with HERB_DITCH (r = 0.64). The only
model we tested that had substantial support included HERB_DITCH alone as an
explanatory variable with a positive effect on SMB occupancy. Indeed, 4 of the
2012 J.J. Valente, S.L. King, and R.R. Wilson 433
13 (31%) birds we detected within the agricultural matrix were located in ditches
rather than in the rice field itself. Flooded ditches may be particularly important
to SMBs occupying MAV rice fields in the late summer because they can provide
flooded refuges when the fields are drained in early August. We never detected
any SMBs in our target fields in the absence of mature rice or standing water,
and both of these factors were extremely temporally and spatially variable among
the fields and farms we surveyed. Thus, it may be that mature rice and available
refuges (i.e., flooded ditches) are the overwhelming factors influencing SMB site
selection in the MAV, and birds simply choose areas with these traits regardless
of other habitat features. However, it should be noted that the average landscape
around our survey points was comprised of 90% agriculture, so there was very
little variability in landscape-level habitat characteristics.
Most SMB species are suspected of rearing multiple broods in a single season,
especially in the southern US, which is closer to the wintering grounds for
migrants and has a long growing season (Bannor and Kiviat 2002, Meanley
1992). It is possible that MAV rice fields provide habitat for late season breeders
or birds rearing a second brood. This resource may be particularly important for
the King Rail, which has suffered large population declines throughout its range
over the past 40–50 years (Cooper 2008, Meanley 1992). Estimates based on our
data and incidental field observations suggest that King Rails were at least twice
as abundant in MAV rice fields throughout June and July than in more natural
systems during the same time period (Valente et al. 2011). However, the seemingly
late season arrival of SMBs, in conjunction with the fact that we never
observed any nests or breeding behavior during our surveys, makes us question
whether the birds we detected were actually breeding in our target rice fields.
Indeed, there may not be enough time for birds arriving in the late summer to
fledge a successful nest, as most of the rice fields we surveyed were drained in
preparation for harvest within 2 to 3 weeks after the majority of the birds were
first detected. Another possible explanation for the pattern observed is that SMBs
tend to select more natural wetlands in the area for breeding (Valente et al. 2011)
and only use mature rice fields late in the summer as they disperse when breeding
is complete. While post-breeding dispersal has not, to our knowledge, been
documented in any of the SMB species we detected, it is common among many
birds with diverse life-history characteristics (e.g., Pagen et al. 2000, Rosier et
al. 2006, Shealer and Kress 1994).
While we were not able to account for detection probability in our models, we
feel confident in our conclusion that MAV rice fields are not used by SMBs until
relatively late in the breeding season, as the earliest we ever incidentally detected
any of these birds was 3 June (King Rail). The latest we ever detected any SMBs
in rice areas was 17 July, yet we cannot account for the time between mid-July
and mid-August because we did not conduct any surveys during that time period.
More frequent sampling during July and August is necessary to determine exactly
how long these birds are present and whether that allows for enough time for
breeding. Additionally, probability of detection decreases for many SMB species
later in the summer (Conway 2009), so it is likely that we underestimated
434 Southeastern Naturalist Vol. 11, No. 3
true abundance and distribution. Future studies of SMB use of rice fields in this
region should consider incorporating a variety of sampling techniques including
callback surveys, transect surveys, and nest searching to accurately estimate
population parameters, and to help determine whether birds actually breed in
these rice fields. Lastly, we combined occupancy data for all SMB species in
this study in order to augment sample size. This approach is justified because this
group of species shares many common life-history traits and habitat requirements
(Eddleman et al. 1988). However, it is probable that each species exhibits unique
habitat preferences that we were not able to identify due to our low number of
detections. More frequent late summer sampling over a larger number of sites is
necessary to help understand idiosyncratic resource needs.
At present, MAV rice fields probably contribute very little toward maintaining
or augmenting population sizes for SMBs. Yet research has shown that agricultural
habitats like these can support breeding individuals when conditions are
appropriate for nesting (Helm et al. 1987, Hohman et al. 1994, Meanley 1953,
Pierluissi 2006, Pierluissi and King 2008). Budd (2007) suggested that land
managers in the Arkansas Delta could potentially improve SMB habitat by limiting
management in irrigation ditches and allowing establishment of emergent
vegetation, and our results support that conjecture. Increasing the abundance of
overgrown ditches around MAV rice fields may help attract more nesting individuals
by providing critical early breeding season habitat.
We kindly thank L. Philley, E. Davis, and Grand Cote National Wildlife Refuge for
allowing us to use their farms for our study. We also thank J.A. Nyman, P. Stouffer,
K. McCarter, and B. Strader for their intellectual contributions. Reviews provided by
S. Pierluissi, D. Krementz, P. Leberg, and two anonymous reviewers helped improve
this manuscript. Lastly, we thank C. Duplechain, D. Crawford, E. DeLeon, T. Gancos,
E. Hunter, J. Unger, J. Keiser, M. Osinskie, J. Russell, R. Villani, H. Gee, B. Pickens,
P. Newell, S. R. Kang, and J. Davis for their assistance. This project was funded by US
Fish and Wildlife Service State Wildlife Grant T-41-R, which was administered by the
Louisiana Department of Wildlife and Fisheries. The use of trade, product, or industry
firm names or products is for informative purposes only and does not constitute an endorsement
by the US Government or the US Geological Survey.
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Delta of Arkansas. M.Sc. Thesis. University of Arkansas, Fayetteville, AR. 126 pp.
Budd, M.J., and D.G. Krementz. 2011. Status and distribution of breeding secretive
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