---

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

• Introduction
• Study Areas and Methods
• Results
• Discussion
• Acknowledgments
• Literature Cited

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.

---

---

NPWRC Home�|�Site�Map�|�About Us�|�Staff�|�Search�|�Contact�|�Web�Help�|�Copyright