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2006 SOUTHEASTERN NATURALIST 5(2):311–316
Breeding Biology of Mottled Ducks on Agricultural Lands
in Southwestern Louisiana
R. Scott Durham1,2,* and Alan D. Afton3
Abstract - Breeding biology of Anas fulvigula maculosa (Mottled Ducks) has been
described in coastal marsh and associated habitats, but little information is available
for agricultural habitats in Louisiana. We located nests to determine nest-initiation
dates and clutch sizes during the primary breeding season (February–May) in 1999
(n = 29) and 2000 (n = 37) on agricultural lands in southwestern Louisiana. In
1999, 60% of located nests were initiated between 22 March and 10 April, whereas in
2000, only 22% of nests were initiated during the same time period. Average clutch
size was 0.9 eggs smaller in 2000 than in 1999. Annual differences in reproductive
parameters corresponded with extremely dry conditions caused by low rainfall before
the laying period in 2000. Flooded rice fields appear to be important loafing and
feeding habitat of Mottled Ducks nesting in agricultural lands, especially during
drought periods when other wetland types are not available or where natural wetlands
have been eliminated.
Anas fulvigula maculosa Ridgway (Mottled Duck) is a resident west Gulf
coastal species strongly associated with coastal marsh environments and
adjoining agricultural land. Because of population concerns and habitat loss
across their range, Mottled Ducks are a priority species in the Gulf Coast
Joint Venture of the North American Waterfowl Management Plan
(Esslinger and Wilson 2001). Nesting studies of Mottled Ducks in Louisiana
have focused on coastal marsh habitats, or areas associated with river deltas
or islands (Allen 1981, Baker 1983, Holbrook 1997, Walters 2000). The
breeding biology of Mottled Ducks in agricultural areas of Texas is well
documented (Engeling 1950, Singleton 1953, Stutzenbaker 1988), but it has
not been studied in Louisiana.
Grand (1992) suggested that low autumn and winter rainfall before the
nesting season in Texas coastal marsh habitat would reduce wetland availability
and thereby limit food resources necessary to nesting Mottled Ducks.
We hypothesized that variation in precipitation would influence initiation
dates and clutch sizes of Mottled Ducks nesting on agricultural habitats in
southwest Louisiana. We recorded and compared these reproductive parameters
between two years of varying rainfall amounts.
1Sweet Lake Land and Oil Company, 358 Chalkley Road, Bell City, LA 70630.
2Current address - Louisiana Department of Wildlife and Fisheries, 2000 Quail
Drive, Baton Rouge, LA 70898-9000. 3USGS-Louisiana Cooperative Fish and Wildlife
Research Unit, Louisiana State University, Baton Rouge, LA 70803. *Corresponding
author - firstname.lastname@example.org.
312 Southeastern Naturalist Vol. 5, No. 2
We searched for Mottled Duck nests on 11,493 and 12,764 ha of agricultural
lands owned by Sweet Lake Land and Oil Company (SLLOC) in
southwest Louisiana in 1999 and 2000, respectively (Durham and Afton
2003). Sweet Lake Land and Oil Company agricultural lands were located in
Cameron and Calcasieu Parishes, southeast of Lake Charles, LA, and encompassed
a range of permanent, semi-native, and improved pastures, rice
field complexes, and other habitats. Soils on SLLOC lands are Mowata-
Vidrine-Crowley, and Morey-Leton-Mowata (Midkiff et al. 1995, Roy and
Midkiff 1988). Originally, this agricultural region was part of a 10,360-km2
triangular shaped prairie (Taylor 1956). Native grass species were
Andropogon gerardii Vitman (big bluestem), Tripsacum dactyloides L.
(eastern gama grass), Sorghastrum nutans (L.) Nash (Indian grass),
Schizachyrium scoparium (Michx.) Nash (little bluestem), and Panicum
virgatum L. (switch grass) (Smeins et al. 1992).
From observation stations (elevated locations) selected each year near
wetlands where Mottled Ducks were consistently observed, nests were located
by observing “drop flights” and subsequently searching areas where
females landed (Durham and Afton 2003). Upon nest discovery, we estimated
initiation date using an egg-laying rate of 1 egg per day (Singleton
1953), and estimated stage of incubation by candling (Klett et al. 1986,
Weller 1956). To minimize disturbance, we did not revisit nests until after
estimated hatch date. We used Statistix8 software (Analytical Software
2003) to compare the distribution of nest initiation dates between years with
a chi-square test for differences in probabilities as described by Conover
(1971). We compared mean clutch sizes of nests between years using a ttest.
The a priori level of significance for each test was P ≤ 0.05.
The distribution of nest initiations differed between years ( χ2 = 13.35,
df = 6, P = 0.04). In 1999, we determined initiation dates for 23 nests. The
first egg was laid on 22 March, and 7 nests were initiated within the first 10-
day period, 22 to 31 March (Table 1). The following 10-day period, 1 to 10
April, produced 7 more nests. Fewer weekly nest initiations occurred during
the remaining 10-day periods. In 2000, we determined initiation dates for 32
nests. The first egg was laid on 19 March, but most nest initiations did not
occur until the 10-day period of 11 to 20 April, when 9 nests were initiated
(Table 1). The two following 10-day periods each produced 7 nests.
Mean clutch size differed between years (t = 1.83, df = 37, P = 0.04). In
1999, clutch size for 11 incubated nests averaged 10.4 eggs (± 0.12 SE) with
a range of 8 to 12 eggs, whereas in 2000, clutch size for 28 incubated nests
averaged 9.5 eggs (± 0.05 SE) with a range of 4 to 11 eggs.
2006 R.S. Durham and A.D. Afton 313
Although dates of first eggs were similar between years, most nests were
initiated later in 2000 than in 1999. In 1999, 60% of located nests
were initiated between 22 March and 10 April, whereas in 2000, under
extremely dry conditions across the landscape (Table 2), only 22% of nests
were initiated during the same time period (Table 1). Combined autumn and
winter rainfall before the 2000 breeding season was considerably less (49.9
cm) than that preceding the 1999 breeding season (Table 2). Fewer wetlands
suitable for feeding and loafing were available in spring 2000, and we were
only able to locate 22 observation stations (1/580 ha), compared to 30
observation stations (1/383 ha) in 1999, a 27% decrease.
On our study area, Mottled Ducks did not lay eggs in 2000 until farmers
flooded rice fields in early spring. Prior to flooding, we observed few
suitable wetlands available for Mottled Ducks to loaf or feed. Lack of
suitable wetlands probably reduces the amount of foraging habitat available
Table 1. Number of Mottled Duck nests initiated and percentage of total nests initiated by 10-
day periods on or near Sweet Lake Land and Oil Company agricultural lands in southwest
Louisiana, 1999 and 2000.
Number of nests Percentage of total
10-day period 1999 2000 1999 2000
22–31 March 7 1 30 3
1–10 April 7 6 30 19
11–20 April 3 9 13 28
21–30 April 2 7 9 22
1–10 May 2 7 9 22
11–20 May 2 1 9 3
≥ 21 May 0 1A 0 3
AThis nest was initiated on 3 June 2000.
Table 2. Annual rainfall (cm) by month at Lake Charles, Louisiana, 1998–2000. From NOAA
climatalogical data (www.nws.noaa.gov).
Month 1998 1999 2000
January 25.43 13.79 3.99
February 13.03 3.35 1.88
March 9.53 9.47 5.74
April 6.20 0.10 13.94
May 0.10 10.31 21.46
June 12.83 24.92 13.23
July 4.90 9.91 11.84
August 9.40 traceA 3.12
September 31.95 5.00 7.95
October 13.74 3.25 4.32
November 7.42 2.51 30.10
December 9.19 11.40 5.16
Total 143.71 94.03 122.73
314 Southeastern Naturalist Vol. 5, No. 2
to breeding females. Aquatic macroinvertebrates (associated with wetland
availability) are an important food source to mallards (Krapu and Reinecke
1992) and the closely related Mottled Ducks (Moorman and Gray 1994)
during the breeding season. We believe further research is needed to examine
the relationship of wetland availability and invertebrate abundance to
Mottled Duck breeding biology.
Mean annual clutch sizes were within the previously reported range of 8
to 10.4 eggs for this species (Singleton 1953, Stutzenbaker 1988); however,
the upper range of clutch sizes (12) was slightly lower than the reported
maximum of 13 in more coastal habitats (Stieglitz and Wilson 1968, Walters
2000). It is possible that the annual difference in clutch size that we observed
also may have resulted from the extremely dry conditions and concomitant
later nest initiations in 2000 (Table 2), perhaps caused by reduced availability
of food resources. Individuals among waterfowl species that nest later
within a breeding season generally produce fewer young than those that nest
early (Rohwer 1992).
Our observations may indicate that seasonal and permanent wetland
habitats located in close proximity to quality nesting cover are important to
Mottled Ducks breeding in agricultural lands. Observed nesting activity
occurred near flooded rice fields and other wetlands adjacent to dense
nesting cover. Because in 2000, nests were initiated only after farmers
flooded fields for rice planting, flooded rice fields are likely important
loafing and feeding habitats for nesting Mottled Ducks in agricultural areas,
especially during drought periods when other wetland types are not available
or where natural wetlands have been eliminated.
Rice farming acreage in Louisiana is driven by local, continental, and
world markets. United States agricultural economics, farm programs,
and trade agreements with other nations that affect the amount of rice being
farmed in Louisiana also may affect Mottled Duck populations using ricebased
agricultural habitats in the Louisiana coastal region.
We appreciate the financial support of A.C. Leach and family, Sweet Lake
Land and Oil Company, Region 4 of the United States Fish and Wildlife Service,
Louisiana Department of Wildlife and Fisheries, and Louisiana Cooperative Fish
and Wildlife Research Unit and School of Renewable Natural Resources at Louisiana
State University. We are grateful to G.A. Harris, P.M. Yakupzack, T.
Delaine, and Cameron Prairie NWR for providing housing and technical support.
We thank M.J. Anteau for helpful comments on the manuscript and with field
work. We thank E. Johnson for her assistance with field work. We thank Dr. S.H.
Schweitzer and several anonymous reviewers for helpful comments resulting in
the publication of this manuscript.
2006 R.S. Durham and A.D. Afton 315
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