Northern Prairie Wildlife Research Center
Temporal Flexibility of Reproduction in
Temperate-breeding Dabbling Ducks
By
Gary L. Krapu*
Abstract. I compared nesting intervals during three consecutive
years in five species of temperate-nesting dabbling ducks (Mallard [Anas
platyrhynchos], Northern Pintail [Anas acuta], Northern Shoveler
[Anas clypeata], Blue-winged Teal [Anas discors], Gadwall [Anas
strepera]) and assessed whether differences existed in timing of refractoriness.
Most nesting by females of all five species ended by the summer solstice. Nesting
ended earliest for Northern Shovelers and Northern Pintails and latest for Gadwalls.
Some Mallards, Blue-winged Teal, and Gadwalls continued to nest into mid- and
late summer, whereas Northern Shovelers and Northern pintails did not. Mallards,
Blue-winged Teal, and Gadwalls accounted for 99% (81 of 82) of flightless broods
resulting from nests initiated during mid- or late summer in North Dakota and
98% (58 of 59) of flightless juveniles shot on or after 1 October by a random
sample of duck hunters from across the United States. Early cessation of breeding
by Northern Shovelers may have evolved in response to the species' limited flexibility
in diet. Photorefractory mechanisms that limit most breeding to spring presumably
evolved in response to severe constraints on reproductive success when nesting
continued through summer(e.g. mortality of late-hatched young and molting females
due to low temperatures). Interspecific differences in photosensitivity may
account for variation in timing of cessation of nesting in late spring, but
controlled experiments are needed to assess the possible role of non-photic
influences. My results suggest that the refractory mechanisms controlling length
of the breeding in temperate-nesting dabbling ducks are more varied and complex
than previously thought, with non-photic influences (e.g. water conditions,
food availability, food quality) having a larger role than indicated by earlier
research.
This resource is based on the following source (Northern Prairie Publication
1103):
Krapu, Gary L. 2000. Temporal flexibility of reproduction in
temperate-breeding dabbling ducks. Auk 117(3):640-650.
This resource should be cited as:
Krapu, Gary L. 2000. Temporal flexibility of reproduction in
temperate-breeding dabbling ducks. Auk 117(3):640-650.
Jamestown, ND: Northern Prairie Wildlife Research Center Online.
http://www.npwrc.usgs.gov/resource/birds/dabduck/index.htm
(Version 27DEC2000).
Table of Contents
Tables and Figures
- Table 1 -- Mean range of Julian dates
when 50, 75, 90, 95, and 99% of nests initiated by Northern Shovelers, Northern
Pintails, Blue-winged Teal, Mallards, and Gadwalls were completed during
1993 to 1995 in North Dakota and north-central South Dakota.
- Table 2 -- Mayfield nesting success (95%
confidence limits in parentheses) for Northern Shovelers, Northern Pintails,
Blue-winged Teal, Mallards, and Gadwalls during 1993 to 1995 in North Dakota
and north-central South Dakota.
- Table 3 -- Species composition (%) of
Mallard, Gadwall, Blue-winged Teal, Northern Shoveler, and Northern Pintail
broods that hatched from nests estimated to have been initiated during mid-
and late summer (after 10 July).
- Table 4 -- Species composition and geographic
distribution of flightless juvenile dabbling ducks shot on or after 1 October
by a random sample of hunters during 1993 to 1995 based on the annual duck
harvest survey conducted by the U.S. Fish and Wildlife Service.
- Figure 1 -- Cumulative proportion of nest
initiations completed by Julian date among Mallards, Blue-winged Teal, Gadwalls,
Northern Pintails, and Northern Shovelers during spring and early summer,
1993 to 1995, in the Prairie Pothole Region of North Dakota and north-central
South Dakota.
- Figure 2 -- Breeding intervals for Mallards,
Northern Pintails, Northern Shovelers, Blue-winged Teal, and Gadwalls by
day length during spring and summer of 1993 in eastern North Dakota.
* United States Geological Survey, Northern Prairie Wildlife Research Center,
Jamestown, North Dakota 58401, USA.
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Dabbling Ducks
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