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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 1. March 2012 
Black-bellied Whistling-Ducks (Dendrocygna 
autumnal is) typically raise one brood per breeding 
season, although they may renest if the first clutch 
is destroyed or their first brood is lost early in 
brood-rearing (Delnicki 1973). Currently, the 
Wood Duck (Aix sponsa) is the only North 
American duck species know n to commonly raise 
two broods in a single nesting season (Haramis 
1990). Double brooding has been documented less 
frequently in several other species of dabbling 
ducks including White-cheeked Pintail (Anas 
bahamensis) (Sorenson ct al. 1992). American 
Black Duck (A. rubripes ) (Benson and Foley 
1962). and Mallard (A. platyrhynchos) (Olsen ct 
al. 2003). The growing season in south Texas is 
>300 days (Tunnel 2002), and ample time may 
exist for Black-bellied Whistling-Ducks to pro¬ 
duce two broods provided adequate habitat 
conditions are available. Johnson and Barlow 
(1971) possibly observed a pair of Black-bellied 
Whistling-Ducks with a second brood in the same 
breeding season, but the pair was not marked and 
the observation could not be confirmed. Other 
researchers that studied the breeding ecology of 
Black-bellied Whistling-Ducks found no evidence 
of double brooding (Bolen 1967, Delnicki 1973). 
Delnicki (1973) speculated that a female Black- 
bellied Whistling-Duck may be physiologically 
incapable of double brooding. Our observation is 
the first confirmed documentation of a Black- 
bellied Whistling-Duck successfully producing two 
broods in a single breeding season. 
METHODS 
We studied the reproductive ecology of Black- 
bellied Whistling-Ducks on the Rob and Bessie 
Welder Wildlife Refuge near Sinton, Texas in 
1998 and 1999 (28° 07' N, 92 22' W). We 
monitored nesting activity in 151 nest boxes at the 
refuge. We captured all incubating pairs of Black- 
bellied Whistling-Ducks in their nest box during 
late incubation during the 1998 and 1999 breeding 
seasons. We marked captured birds with an U.S. 
Geological Survey aluminum band on the right 
tarsus and a uniquely coded, plastic band on the 
left tarsus in accordance with U.S. Geological 
Survey (Permit #10360) and Texas A&M Uni¬ 
versity—Kingsville Institutional Animal Care and 
Use Committee protocols (Approval #1-97-34). 
OBSERVATIONS 
We discovered a clutch of six eggs on 16 April 
799 in nest box A near a small windmill pond. 
Seven days later on 23 April 1999, the clutch was 
being incubated and we left it undisturbed Wc 
captured the female (WB49) on 18 May 1999 
while she incubated 21 eggs. W'e captured her 
male mate (YB03) while incubating the clutch on 
21 May 1999. We observed this pair of birds on 
24 May in the nest box with young and the next 
morning 18 ducklings exited the nest box and 
were observed with the marked pair. Thirty-eight 
days later on 1 July 1999 we observed the marked 
pair with 13 fully-feathered ducklings on Paloma 
Tank, -2.5 km from nest box A. We discovered a 
clutch of three eggs on 13 July 1999 in nest box B 
at Paloma Tank and on 20 July we flushed the 
same marked pair and 13 recently fledged Black- 
bellied Whistling-Ducks from the shoreline of 
Paloma Tank. The clutch in nest box B contained 
nine eggs on this visit (20 July). By 26 July, we 
discovered that female W'B49 was incubating a 
second clutch of 15 eggs in nest box B. The male 
(YB03) and previously fledged young were no! 
observed. We captured female WB49 on 10 
August 1999 and male YB03 the next day while 
incubating the second clutch in nest box B. Wc 
revisited nest box B on 21 August 1999 and found 
12 hatched and three unhatched eggs. Neither ot 
the two broods was observed again. 
DISCUSSION 
We documented that Black-bellied Whistling- 
Ducks are capable of double brooding. This is a 
single observation, but there are several aspects of 
Black-bellied Whistling-Duck ecology that could 
increase the propensity for double brooding. First, 
their potential breeding season is long relative to 
other species of waterfowl because they breed 
primarily in subtropical and tropical regions. Tire 
growing season in south Texas is >300 days 
(Tunnel 2002), and a breeding season of this length 
provides ample opportunity to lay, incubate, and 
raise two clutches when habitat conditions are 
favorable. Second, both males and females share n 
incubation and brood-rearing duties (James aiw 
Thompson 2001). Biparental care in these aspect 
of reproduction may allow females to maintain a 
positive nutrient/energy balance throughout ne> 
ing and brood rearing, reducing the time ber^ei. 1 
fledging their first ducklings and laying the seconu 
clutch. Black-bellied Whistling-Ducks may al* 1 
rely largely on exogenous versus endogenous 
nutrients for egg production, as these birds to 1 
readily feed on high-energy waste grains at sioe 
yards, grain mills, and sorghum fields during e 
