Our Liviitf' Rcsdiini'.s — The Gira! Plains 



JOJ 



Fig. 1. Areas of the Prairie Pothole region and time peri- 

 ods for which estimates of duck nest success were made. 

 See Fig. 2 for abbreviations. 



Mallard nest success was relatively steady 

 from 1966-74 to 1980-84. but increased from 

 1980-84 to 1985-89. In 1985-89, mallard nest 

 success was still less than 15% in two of four 

 regions where data were available. Predation 

 was the major cause of nest failure, accounting 

 for 85% of mallard nest failures in North 

 Dakota. 



Blue-winged Teal 



Data for 9.819 blue-winged teal nests 

 revealed that nest success of blue-winged teal 

 ranged from 12% to 29% (Fig. 2). Thekvel of 

 nest success needed to maintain stable numbers 

 of blue-winged teal is believed to be 20% (Klett 

 et al. 1988). Nest success of blue-winged teal 

 was generally below this level, except in South 

 Dakota. 



Nest success increased slightly from 1980- 

 84 to 1985-89, but was still generally less than 

 20%. Predation. the principal cause of blue- 

 winged teal nest failures, accounted for 92% of 

 the failed nests in North Dakota. 



Gadwall 



Data on 3,782 gadwall nests showed that 

 their average nest success ranged from 1 1 % in 

 western Minnesota ( 1980-84) to 26% in central 

 South Dakota (1966-74; Fig. 2). Nest success 

 was generally below 20%, the minimum level 

 believed necessary to sustain populations (Klett 

 etal. 1988). 



Gadwall nest success increa.sed from 1980- 

 84 to 1985-89 and reached or exceeded 20% 

 during 1985-89 in North and South Dakota. 

 Predation was the primary cause of nest failure, 

 accounting for 90% of failed gadwall nests in 

 North Dakota. 



Northern Shoveler 



Nest success in 1,212 shoveler nests ranged 

 from 5% in western Minnesota (1980-84) to 

 35% in central South Dakota ( 1966-74; Fig. 2). 



Nest success was generally below 20%, the 

 minimum level believed necessary to sustain 

 populations (Klett et al. 1988). In western 

 Minnesota and eastern North Dakota, nest suc- 

 cess was less than 10%, but it was greater than 

 20% in central North and South Dakota. 



Shoveler nest success increased from 1980- 

 84 to 1985-89, but was still much less than 20% 

 in western Minnesota and eastern North 

 Dakota. Predation was the primary cause of nest 

 failure in all regions, and in North Dakota 

 caused 88%' of shoveler nest failures. 



Northern Pintail 



Data for 1,633 pintail nests revealed that 

 their success ranged from 5% to 20%^ (Fig. 2). 

 Fifteen percent is the minimum level of nest 

 success believed necessary to sustain pintail 

 numbers (Klett et al. 1988), Only 2 of 14 nest 

 success estimates reached or exceeded 15%; 

 these were for central South Dakota (1966-74) 

 and central North Dakota (1985-89). 



Within each region, pintail nest success was 

 generally lowest in 1966-74 and highest in 

 1985-89. Even in 1985-89. however, nest suc- 

 cess was much less than 15% in all regions 

 where data were available, except central North 

 Dakota. Predation was the major cause of nest 

 failure; for example, in North Dakota it 

 accounted for 81% of pintail nest failures. In 

 addition, because pintails nest more frequently 

 in cropland than other species (Klett et al. 

 1988). fanning operations were also an impor- 

 tant cause of nest failure, accounting for 16% of 

 pintail nest failures. 



Trends 



Our results suggest that nest success of the 

 five species of ducks considered here was and 

 probably still is too low to maintain stable num- 

 bers of breeding ducks in most areas of the 

 Prairie Pothole region. For example, even 

 though nest success increased from 1980-84 to 

 1985-89, it was still below the level needed to 

 sustain populations for most species in most 

 regions. Except for pintails, whose nest success 

 generally increased, we observed no consistent 

 increases or decreases in nest success across 

 periods. In central South Dakota in the 1966-74 

 period nest success was much higher than in 

 other regions, exceeding the level needed to 

 sustain populations. This region likely con- 

 tributed a "surplus" of ducks in 1966-74 that 

 helped make up for the "shortage"" of ducks pro- 

 duced in other regions. Unfortunately, no data 

 for central South Dakota have been available 

 since then. 



Predation was the piimary reason for the low 

 nest success we observed. Predator species such 



Central North Dakota (NDC) 

 Eastern North Dakota (NDE) 

 Central South Dakota (SDC) 

 (limited data available) 

 Eastern South Dakota (SDE) 

 Minnesota (MN) 



Mallard 



N = 4.093 



Blue-winged teal 



N = 9.819 



Gadwall 



N = 3,782 



N shoveler 



1.212 



35- 

 30- 

 25- 

 20- 

 15- 

 10- 

 5- 

 0- 



N- pintail 



66-74 75-79 80-84 85-89 

 Year 



Fig. 2. Nest success (%) by peri- 

 od for five areas in the Prairie 

 Pothole region for fi\'e duck 

 species. Dashed line = level of 

 nest success believed necessary for 

 a stable population. 



