John T. Lokemoen and Julia A. Beiser

USD1 - NBS

Northern Prairie Science Center

Jamestown, ND 58401-7317

Sustainable cropping systems applied throughout the northern Great Plains could have important impacts on wildlife, including declining populations of songbirds and waterfowl. Wildlife populations may benefit because growers using sustainable farming practices have reduced mechanical disturbance or eliminated synthetic chemicals on their cropland. To determine the value of sustainable farming practices to wildlife, we compared numbers and nesting success of birds on minimum-tillage and organic farms to those on nearby conventional farms.

STUDY AREA AND METHODS

The study was conducted in the glaciated region of southeastern North Dakota. The terrain is gently to moderately rolling, and the land use is mainly cropland, with about 10-30% grassland and 5-10% wetlands. Cropland is used primarily for wheat, barley, sunflower, corn, and fallow.

We visited about 50 named 'zero-tillage" farmers in southeast North Dakota to locate study sites. During the interviews we learned that cultivation was used in nearly all of the zero-tillage farming systems, which were better defined as minimum-tillage. For the study, we defined minimum-tillage farmers as those who used reduced cultivation and normally seeded crops into plant residue. Herbicides, rather than tillage, were generally used to control weeds. organic farming is much more rigidly defined as each field was certified as free of synthetic chemicals by an authorized board. Weeds are controlled mainly through cultivation and crop rotation. Also, sweet clover is grown on organic fallow fields to add nitrogen to the soil. Conventional farmers all used standard agricultural practices, including cultivation and synthetic chemical herbicides and insecticides.

We obtained names of minimum-tillage growers from the Manitoba-North Dakota zero-Tillage Farmers Association and names of organic growers from the Northern Plains Sustainable Agriculture Society. Names of other growers were obtained at county offices of the U.S. Department of Agriculture (USDA) . We discussed the study with potential farm cooperators, selected those farms that met our criteria, and conducted research where we were granted access.

To estimate migrating and breeding bird use on fields, we surveyed birds on each field once or twice each spring, summer, fall, and winter season from April 1991 to July 1993. Spring surveys extended from March 2 to April 20, summer surveys from April 21 to July 2, fall surveys from August 29 to November 15, and winter surveys from December 2 to February 4. Data were collected for 3 years in summer and for 2 years in the other seasons. Birds were surveyed by individuals walking line-transects. All birds observed within 50 meters (164 feet) of the transect line were counted as part of the survey.

Each field was searched for bird nests twice during the nesting season using a 3/16-inch chain flushing device pulled between two all-terrain vehicles. The location of each nest was plotted on a map, and a marker flag was set 4 m north of the nest. Nests were checked every 7 days, and nest success was calculated using the Mayfield method. Estimates of nest success were compared among farm types and crops.

Bird surveys and nest searches were conducted on fields rather than farms, as most North Dakota farms consist of spatially separated agricultural fields. Each year we attempted to work on 10 minimum-tillage farms, 10 organic farms, and 10 conventional farms. On each farm, we sought to obtain 80 acres of wheat, sunflower, and fallow distributed in one or more fields.

The type, height, and density of plant cover were measured on each field. Records on the amount of fertilizer use, herbicide and insecticide use, number of cultivations, and crop harvest were obtained for each field from the cooperating farmer. We also estimated mean soil erosion rates using standard USDA Soil Conservation Service formulas for water and wind erosion.

We statistically compared the number of species, bird densities by season, and nest densities among years, crops, and farm types. The comparisons of the number of species were made for the average field size of 64 acres. We also tested for differences in soil erosion, wheat and sunflower yields, among years, crops, and farm types. Statistical notations are not expressed in this paper. However, contrasts reported in the text all were significantly different (P < 0.05) except for two instances where differences were marginal (P < 0.06).

RESULTS AND DISCUSSION

Species Use by Season

Seventeen species of birds were counted on the fields in the two spring surveys (Table 1). Horned larks were the most frequently observed species in spring and throughout the year. The frequency of other species varied considerably among seasons. In spring, migrating lapland longspurs and chestnut-collared longspurs were the second and third most frequently encountered species, but they were the most numerous because they usually occurred in large flocks. No other species exceeded l0% of the seasonal sightings in frequency or total number.Table 1. Percent frequency and total number of the more numerous birds recorded in cropland during spring, summer, fall, and winter in southeast North Dakota, 1991-1993.

INSERT TABLE 1

Seventy bird species were counted on the fields during the three summer surveys. As with other seasons, horned larks were most often observed, followed by vesper sparrows. However, fewer vesper sparrows were observed than red-winged blackbirds, brown-headed cowbirds, yellow-headed blackbirds, and lapland longspurs, all species that usually occurred as large flocks. For the summer season, we compared the number of species for the average size field among years, farm types, and crops. Tests indicated no differences in the number of species among farm types, but the average fallow field had more bird species (7.3/field) than the average wheat (4.8/field) or sunflower (4.6/field) field.

Forty bird species were observed during the two fall surveys. Mourning doves were again second to horned larks in frequency, but we found fewer individuals of both species than for all blackbirds combined. Blackbirds composed 63% of all birds counted in fall. Eighty-three percent of the blackbirds and 52% of all birds observed in fall surveys were recorded in conventional sunflower fields.

Only 11 bird species were observed during the two winter seasons surveyed. Second to horned larks in frequency were snow buntings and gray partridge, two late fall migrants or winter residents. Resident game birds, including ring-necked pheasant and sharp-tailed grouse were also fairly numerous in crop fields in winter.

BIRD DENSITY

In spring, minimum-tillage fallow fields had higher densities (116.1 birds/100 acres) than organic fallow fields (8.9 birds/100 acres). Also, we found higher densities in conventional sunflower fields (94.1 birds/100 acres) than in minimum-tillage sunflower (5.5 birds/100 acres) . For conventional crops in spring, we observed higher bird densities in sunflower fields (94.1 birds/100 acres) compared with wheat fields (11.2 birds/100 acres) . For minimum-tillage crops, tests indicated higher bird densities in fallow fields (116.1 birds/100 acres) than in either sunflower (5.5 birds/100 acres) or wheat fields (14.7 birds/100 acres). Bird densities are probably high in sunflower fields in spring because longspurs and red-winged blackbirds are feeding in this seed-rich environment. Bird densities may have been high in fallow fields in spring in response to a combination of food and cover.

In summer, tests showed no differences in bird densities in 1991, but did indicate differences in 1992 and 1993. In 1992 and 1993, fallow fields had higher bird densities than sunflower fields and wheat fields (Table 2). Also, we found no differences in bird densities between sunflower and wheat fields in either year. In each year, conventional fields generally had the lowest bird densities, but we detected no differences because of high variation among fields.

Table 2. Density of birds per 100 acres observed on cropland in summer in southeast North Dakota, 1991-1993.

In fall and winter, tests indicated no differences in bird densities among farm types or crops. The predominant birds in fall were blackbirds, which we counted mainly in conventional sunflower fields. However, most birds were observed in a few, large flocks so it was difficult to make reliable comparisons among farm types.

Bird densities may have been highest in fallow fields in summer because more cover was present in early summer. Although fallow fields usually had little plant growth by mid to late summer, most weed removal treatments were not initiated until June. Minimum-tillage fallow fields generally contained crop residue from the previous year, but green growth was likely reduced by herbicides. Organic fallow fields usually contained plant residue from the previous year plus sweet clover grown to increase soil nitrogen levels. Conventional fallow fields often retained plant residue over winter and into early summer when weed control was initiated.

In comparison with cropland, bird densities in Conservation Reserve Program (CRP) fields in North Dakota seeded to perennial grass were about 140 birds/l00 acres (R. Koford, National Biological Service (NBS) , Jamestown, pers. commun.) . Thus, the summer bird densities in CRP were about 50% higher than the densities we observed in cropland.

NESTING SPECIES AND NEST DENSITIES

We located 374 nests during the study (Table 3). Horned lark and vesper sparrow were the most numerous nesting species, accounting for 54~ of all nests found. Killdeer and lark bunting were the next two most abundant nesting species.Table 3. Species composition of the most common nesting birds in cropland in southeast North Dakota, 1991-1993.

Shorebirds and waterfowl may have been more important nesting species if the study had not been conducted during extreme drought conditions.

Overall, conventional fields had fewer nesting species (0.9/field) than organic fields (1.6/field) and minimum-tillage fields (1.9/field) . We were not able to detect differences in the number of nesting species between minimum-tillage and organic fields.

Based on the average field size, marginal differences were noted in the number of nesting species among the three crop types. Fallow (1.9 species/field) had more nesting species than sunflower (1.2 species/field) and wheat (1.3 species/field) Tests indicated no differences in the number of species observed in wheat and sunflower fields.Table 4. Nest densities of birds per 100 acres in cropland in southeast North Dakota, 1991-1993.

Among crop types, fallow fields had higher nest densities than sunflower and wheat fields (Table 4). We found no differences in nest densities between sunflower and wheat fields. Among farm types, minimum-tillage fields and organic fields had more nests than conventional fields. We found no differences in nest densities between minimum-tillage and organic fields.

More bird species and a higher density of birds were probably attracted to nest in minimum-tillage, fallow and organic fields because of increased plant diversity and vegetative cover. However, nest densities observed in minimum-tillage, fallow, and organic fields were much lower than the densities reported in grassland. In CRP fields in North Dakota, (R. Koford, NBS, Jamestown, pers. commun.) the nest density was about 32 nests/100 acres or nine times larger than the density we found in cropland. CRP fields also had a greater variety of nesting species than cropland.

NEST SUCCESS

Considering all causes of nest loss for the 3 years, we found no differences in the survival of songbird or shorebird nests among farm types or crops. Overall nest success for songbirds was 14%. Nest losses were attributed to predation (62%) , farm operations (22%) , abandonment (9%), and other causes (7%) In CRP fields in North Dakota, nest success for songbirds was about 20% (R. Koford, NBS, Jamestown, pers. commun.) . In our study, nest success was 18% for shorebirds and 0% for waterfowl. Nest losses for shorebirds and waterfowl were attributed to predation (48%) farm operations (42%) , abandonment (8%) , and other causes (2%).

We also related nest success to all causes of nest loss (mainly farm operations and weather) except predation. In this analysis, songbird nest survival rates were still not different among farm types. However, survival of songbird nests among crop types was different. Nest success in wheat was higher than nest success in sunflower. Nest success for shorebirds was not different among crops but was higher in minimum-tillage fields than in organic fields.

Nest predation was high in cropland, but predation was also high in CRP grassland in the same geographic region (R. Koford, NBS, Jamestown, pers. commun.). Loss of songbird nests to causes other than predation was probably less severe in wheat fields because there was little disturbance from farm operations after the crop was seeded. Loss of shorebird nests to causes other than predation was less severe in minimum-tillage fields where frequency of cultivation was reduced.

RELATIONSHIP BETWEEN PLANT COVER AND NESTING

We generally found no connection between our measurement of plant cover on fields and bird or nest density. Bird populations often respond to vegetative characteristics, but we were unable to find differences due to our sampling scheme or to the variation in cover among fields, years, or seasons.

We did, however, find positive associations between litter cover and bird and nest densities. Plant litter may be important to birds using cropland because it provides protection from predators and weather to feeding, nesting, and resting birds Also, increased amounts of litter may help enlarge the food base in the form of insects and seeds.

PESTICIDE, TILLAGE, SOIL EROSION, HARVEST EFFECTS

We did not make specific assessments of possible herbicide and insecticide toxicity to bird health; however, we did make general observations and comparisons. We did not observe any direct losses of adult or young birds to any chemical application. Also, we found no connection between the total amount of herbicide and insecticide used on a field and bird densities or nest success.

Our estimates of water-caused soil erosion suggests that it was less on minimum-tillage fields than on conventional or organic fields (Table 5). We found no difference in water erosion between conventional and organic farm types. Among crops, we observed less water erosion in wheat fields than in sunflower or fallow fields, but we recorded no difference in the rate of water erosion between sunflower and fallow fields. The rate of wind erosion among years, farm types, or crops was not different in our study.Table 5. Comparisons of wind- and water-caused soil erosion in tons per acre per year on minimum-tillage, organic, and conventional cropland in southeast North Dakota, 1991-l993.

Average yields of wheat for organic farmers (1,760 pounds/acre) were lower than those of conventional (2,146 pounds/acre) and minimum-tillage (2,201 pounds/acre) farmers. We found no difference in the average wheat yields between minimum-tillage and conventional growers.

Estimated sunflower yields were lower (723 pounds/acre) for organic growers than for conventional (1,374 pounds/acre) and minimum-tillage growers (1,660 pounds/acre) . We found a marginal difference in the yield of sunflower between conventional and minimum-tillage fields.

Use of synthetic chemicals (herbicides and insecticides) was zero on organic fields, intermediate on conventional fields, and highest on minimum-tillage fields.

SUMMARY

During the 3-year study, 28,590 birds were counted on 153 agricultural fields. Between 11 and 70 different species were identified during the four seasons. In general, bird populations benefited from minimum-tillage and organic farming systems in comparison with conventional farming. There were generally more species and higher densities of birds and nests on minimumtillage and organic fields than on conventional fields. Of the three crop types, fallow fields consistently had more species of birds, higher bird densities, and higher nest densities.

Unfortunately, nest success was low for all crops and farm types. Predation was the most important factor causing low nest success, but farm operations were another major disturbance factor. Higher nest success in wheat and minimum-tillage fields was likely related to reduced disturbance from farm operations. In comparison with other crop types, fallow fields had higher densities of nesting birds, but nest success was not different.

Minimum-tillage and organic growers appeared to be successful in their respective aims of reducing soil erosion and eliminating synthetic chemicals from farm operations. crop yields of minimum-tillage growers were similar to conventional crop yields. Yields of wheat and sunflower by organic growers were lower than minimum-tillage and conventional yields. However, the loss in yields was partly offset because organic growers received a premium price for grains free of synthetic chemicals.

Sustainable farming methods may benefit birds because of increased vegetative cover and reduced disturbance from farming operations. Increased vegetative cover provides protection to hiding and nesting birds and may increase food availability. Decreased cultivation helps maintain food and cover on fields for longer periods of time and reduces the number of nests destroyed by farm operations.

Decreases in mechanical disturbances on farmland will increase plant cover, improve cropland sustainability, and benefit wildlife populations. Judicious use of synthetic chemical pesticides would also seem appropriate because of the toxic properties of some chemicals. In southeast North Dakota, use of sustainable cropping systems has evolved slowly because of the difficulty in developing methods to control exotic weeds. New weed control methods are needed that are both effective and economically appealing. However, change is evident: Some conventional farmers have joined minimum-tillage and organic growers in utilizing new sustainable farming techniques.