Introduction
The biological community of a farm is a system manipulated for economic gain. Primary land-use is for crop production while wildlife uses are generally secondary. With the large amount of land devoted to crop production, the habitat available for wildlife is affected by different farming practices. The authors conducted a population census of birds during May, June, and July 1979, as part of a study to investigate the differences in wildlife between organic and conventional farms.
Many bird species were observed on the study area and considerable data were obtained on bird nesting and use of crops.
Study Area
The study area was located in Douglas County, Nebraska. It is close to Valley and near the Platte River, on land that was once a flood-plain. Three farms which totaled 567 ha (1400 acres) were used as the study area (Figure 1). The farm which used organic crop production totaled 308 ha (760 acres). This farm consisted of a brome (Bromus sp.), clover (Melilotus sp.) pasture, two oat (Avena sativa) fields, two corn (Zea mays) fields, three alfalfa (Medicago sativa) fields, two soybean (Glycine max) fields, one winter wheat (Triticum aestivum) field and one rye (Secale cereale) field. The one large corn field was separated by grass waterways which divided it into three smaller fields. Eighty cattle grazed on the 40.5 ha (100 acre) pasture during the study.
 Figure 1. Map of study area and crop production method. |
The two conventional farms totaled 259 ha (640 acres) and had two corn fields and one soybean field. Three farmyard areas and an area used for paunch manure composting were also on the study area. Adjacent farmlands followed conventional chemical methods and were utilized for crop production, primarily corn. Two wooded farmyards were also located adjacent to the study farms.
Methods
The breeding bird census on the study area followed recommendations of the International Bird Census Committee (Svenson et al. 1969). The location and activity of each bird observed was recorded on a scale map of the study area. A grid pattern was prepared for the entire study area and each grid sector was assigned an identification number. Markers numbered according to grid locations were placed at approximately 50 m intervals along field borders to aid in accurate plotting of birds observed. All censuses were conducted between 0600 and 1000. The study area was censused 3 times weekly during June and at least twice weekly during July. Census data for all species began 31 May. The last census was conducted 20 July.
A search for nests started once any sign of nesting was noted or nests were found by other workers. However, most nests were found during population censuses along roads and field borders. Each nest found was given a number and marked by tying a strip of plastic tape on vegetation new- the nest. The date, number of eggs and/or nestlings, location, and nest support were recorded for each nest located. Nests were checked every 1-3 days.
A nest was considered successful if one or more nestlings fledged; broken up if the nest was torn down, had broken eggs, or had eggs or young disappear. A deserted nest was one that had been started but never finished, completed but never had eggs, or abandoned with eggs or young (Case and Hewitt, 1963).
Data on farmyard birds were limited because the primary objective was to investigate field use and avoiding the farmyard areas minimized disturbance to tenants. Species were considered nesting if adult birds were observed carrying food or if a nest or fledglings were found.
To obtain the area in hectares (ha) or acres of roadsides, irrigation ditches, grass waterways, and fence lines used for nesting, the length and width of these areas were multiplied. This square meter value was then converted to obtain hectares. Only areas where actual nests were found were used. The ditch or fenceline was measured along its entire length, but limited to 800 m (1/2 mile) limits. Portions of other ditches were used if nesting was concentrated in one area. For any area at least 400 m (1/4 mile) was used unless the actual length of the area was less.
Vegetation analysis consisted of determining percentage composition from the basal cover of the vegetation. A ten-point sampling frame was used to determine basal cover. Frequency of occurrence for each species was calculated by use of a 0.1 m2 (.12 yd2) quadrat placed on the ground once per 200 m2 (239 yd2) and recording the presence of each species.
Results and Discussion
General Nesting Information
Nesting data were kept on 88 nests of seven species. We located 71 Red-winged Blackbird (Agelaius phoeniceus) nests, 8 Robin (Turdus migratorius) nests, 3 Barn Swallow (Hirunda rustica) nests, 2 nests each of the Western Meadowlark (Sturnella neglecta) and Grasshopper Sparrow (Ammodramus savannarum), and a nest each of the Blue Grosbeak (Guiraca caerulea) and Black-billed Cuckoo (Coccyzus erythropthalmus) (Table 1). Nests of 34 Pheasant (Phasianus colchicus), 3 Upland Sandpiper (Bartramia americana), and 1 Meadowlark were also found after they had been destroyed or broken up because of alfalfa cutting. Thirteen species were reported as nesting species in the farmyard areas.
Table 1. Passerine species nest habitat and fate. | ||||||||||
Species | Habitat | Number of Eggs | No. Nestlings | Status (defined in text) | ||||||
| Including Cowbird | Cowbird only |
| |||||||
Black-billed Cuckoo | irrigation ditch | 3 | - | - | broken up | |||||
Barn Swallow | culvert | 3 | - | 2 | successful | |||||
Barn Swallow | culvert | ? | ? | 3-4 | broken up | |||||
Barn Swallow | culvert | ? | ? | 4 | successful | |||||
American Robin | irrigation ditch | 2 | - | 2 | successful | |||||
American Robin | roadside | 4 | - | - | deserted | |||||
American Robin | roadside | 3 | - | 3 | successful | |||||
American Robin | roadside | 3 | - | 3 | successful | |||||
American Robin | fence row | 2 | - | - | broken up | |||||
American Robin | farmyard | 4 | - | 4 | successful | |||||
American Robin | farmyard | 3 | - | 3 | successful | |||||
American Robin | farmyard | ? | ? | 2 | successful | |||||
Western Meadowlark | roadside | 4 | 2 | - | deserted | |||||
Western Meadowlark | pasture | 1 | - | - | broken up | |||||
Red-winged Blackbird | oats | 3 | - | - | broken up | |||||
Red-winged Blackbird | grass waterway | 1 | 1 | - | deserted | |||||
Red-winged Blackbird | grass waterway | 5 | 2 | 4 | successful | |||||
Red-winged Blackbird | irrigation ditch | - | - | - | deserted | |||||
Red-winged Blackbird | irrigation ditch | 1 | 1 | - | deserted | |||||
Red-winged Blackbird | irrigation ditch | ? | ? | 2 | successful | |||||
Red-winged Blackbird | irrigation ditch | - | - | - | deserted | |||||
Red-winged Blackbird | irrigation ditch | 1 | 1 | - | deserted | |||||
Red-winged Blackbird | irrigation ditch | 4 | - | 4 | successful | |||||
Red-winged Blackbird | irrigation ditch | 4 | 1 | 3 | successful | |||||
Red-winged Blackbird | irrigation ditch | 6 | 2 | - | broken up | |||||
Red-winged Blackbird | irrigation ditch | ? | ? | 3 | broken up | |||||
Red-winged Blackbird | irrigation ditch | 4 | - | 4 | successful | |||||
Red-winged Blackbird | irrigation ditch | 5 | 2 | 2 | successful | |||||
Red-winged Blackbird | irrigation ditch | ? | ? | 4 | successful | |||||
Red-winged Blackbird | irrigation ditch | 6 | 2 | - | broken up | |||||
Red-winged Blackbird | irrigation ditch | 4 | - | - | deserted | |||||
Red-winged Blackbird | irrigation ditch | ? | ? | 2 | successful | |||||
Red-winged Blackbird | roadside | 4 | 1 | - | broken up | |||||
Red-winged Blackbird | roadside | 6 | 3 | 3 | successful | |||||
Red-winged Blackbird | roadside | - | - | - | deserted | |||||
Red-winged Blackbird | roadside | 6 | 2 | 4 | successful | |||||
Red-winged Blackbird | roadside | 4 | - | 3 | successful | |||||
Red-winged Blackbird | roadside | 1 | - | - | broken up | |||||
Red-winged Blackbird | roadside | 4 | - | 4 | successful | |||||
Red-winged Blackbird | roadside | 1 | - | - | broken up | |||||
Red-winged Blackbird | roadside | 5 | - | - | broken up | |||||
Red-winged Blackbird | roadside | - | - | - | deserted | |||||
Red-winged Blackbird | roadside | 4 | - | - | deserted | |||||
Red-winged Blackbird | roadside | 2 | 1 | - | deserted | |||||
Red-winged Blackbird | roadside | - | - | - | deserted | |||||
Red-winged Blackbird | roadside | - | - | - | deserted | |||||
Red-winged Blackbird | roadside | 5 | - | 5 | successful | |||||
Red-winged Blackbird | roadside | 4 | - | 2 | successful | |||||
Red-winged Blackbird | roadside | 1 | - | - | deserted | |||||
Red-winged Blackbird | roadside | 2 | 2 | - | deserted | |||||
Red-winged Blackbird | roadside | 3 | - | 2 | successful | |||||
Red-winged Blackbird | roadside | ? | ? | 2 | successful | |||||
Red-winged Blackbird | roadside | - | - | - | deserted | |||||
Red-winged Blackbird | roadside | 3 | - | - | deserted | |||||
Red-winged Blackbird | roadside | 3 | - | 2 | successful | |||||
Red-winged Blackbird | roadside | 1 | - | - | deserted | |||||
Red-winged Blackbird | roadside | 4 | - | 2 | successful | |||||
Red-winged Blackbird | roadside | 5 | 1 | - | broken up | |||||
Red-winged Blackbird | roadside | 5 | 1 | 4 | successful | |||||
Red-winged Blackbird | roadside | 3 | - | - | broken up | |||||
Red-winged Blackbird | roadside | 2 | 1 | - | broken up | |||||
Red-winged Blackbird | roadside | 1 | 1 | - | deserted | |||||
Red-winged Blackbird | roadside | 1 | - | - | deserted | |||||
Red-winged Blackbird | roadside | ? | ? | 3 | successful | |||||
Red-winged Blackbird | roadside | 4 | 1 | 4 | successful | |||||
Red-winged Blackbird | roadside | 1 | 1 | - | deserted | |||||
Red-winged Blackbird | roadside | 1 | 1 | - | deserted | |||||
Red-winged Blackbird | roadside | 7 | 3 | 5 | successful | |||||
Red-winged Blackbird | roadside | 3 | 2 | - | broken up | |||||
Red-winged Blackbird | roadside | 4 | 1 | 2 | successful | |||||
Red-winged Blackbird | roadside | 4 | - | 4 | successful | |||||
Red-winged Blackbird | roadside | 5 | 2 | 3 | successful | |||||
Red-winged Blackbird | roadside | 3 | - | - | broken up | |||||
Red-winged Blackbird | roadside | 5 | 1 | 3 | successful | |||||
Red-winged Blackbird | roadside | 4 | 2 | 3 | successful | |||||
Red-winged Blackbird | roadside | 4 | 2 | - | deserted | |||||
Red-winged Blackbird | roadside | 4 | 1 | 2 | successful | |||||
Red-winged Blackbird | roadside | 3 | - | 2 | successful | |||||
Red-winged Blackbird | roadside | 4 | - | - | broken up | |||||
Red-winged Blackbird | roadside | 3 | 1 | - | broken up | |||||
Red-winged Blackbird | roadside | 4 | - | 3 | successful | |||||
Red-winged Blackbird | fence row | 4 | 1 | 4 | successful | |||||
Red-winged Blackbird | fence row | ? | ? | 4 | successful | |||||
Red-winged Blackbird | fence row | 3 | - | - | deserted | |||||
Red-winged Blackbird | fence row | ? | ? | 1 | successful | |||||
Blue Grosbeak | roadside | 4 | - | 3 | successful | |||||
Grasshopper Sparrow | pasture | 4 | - | - | broken up | |||||
Grasshopper Sparrow | pasture | 3 | 1 | 1 | broken up | |||||
With the exception of farmyard nests, nests were located in alfalfa fields, the pasture, fence lines, grass waterways, irrigation ditches, and roadsides on or adjacent to the organic farm. No nests were found on the chemical farms. Those habitats producing successful nests included roadsides, irrigation ditches, grass waterways, and a fence line. There were 16 ha (40 acres) of these areas available for nesting but only 7 ha (17 acres) were utilized.
Species Nesting Account
Red-winged Blackbird
The highest nesting densities of Red-winged Blackbirds occurred in 3 areas. The first of these was a roadside ditch (1a, west end, and 1b, east end, Table 2). It was 14 m wide and extended for 1600 m (1 mile) east from the county road 112 on the north side of Nebraska highway 36. This ditch was bordered on the north by a corn field. Land across the highway to the south was organic wheat and alfalfa fields for 1200 m and was a conventional corn field for the remaining 400 m. This, as well as all roadsides, was mowed to some degree. It was not known if county road maintenance included spraying of chemical herbicides. Water was present in the ditch at the beginning of the study (May) but disappeared during June with the exception of the very west end which retained water throughout the study. The vegetation consisted largely of smooth brome (Bromus inermis), sedges (Carex sp.), and Kentucky bluegrass (Poa pratensis).
The second area was an irrigation ditch which ran north from the east end of ditch 1, on the west side of a county road, and which was bordered by corn and oat fields to the west (2, Table 2). A wooded farmyard and corn fields were located to the east. The ditch was 5 m wide, 800 m (.5 mile) long and contained water throughout the study. Vegetation was mainly sedges and dock (Rumex sp.).
The third area was a 5 m wide, 400 m (.25 mile) long ditch between a corn field and an oat field (3, Table 2). This ditch ran west from the north end of ditch 2. Herbicide drift from the corn field killed plants such as dock. However, spraying occurred after peak Red-wing nesting. Vegetation analysis showed a high frequency of marijuana (Cannabis sativa), dock, and wild violet (Viola sp.).
Table 2. Plant frequency1 in areas of highest blackbird nesting density. | ||||
Plant | Ditch | |||
1a | 1b | 2 | 3 | |
Rough Pigweed (Amaranthus retroflexus) | 6.7 | 6.7 | - | - |
Common ragweed (Ambrosia artemisiifolia) | 8.3 | 10.0 | 17.5 | 25 |
Meadow anemone (Anemone canadensis) | - | - | 17.5 | - |
Smooth brome (Bromus inermis) | 68.3 | 75.0 | 20.0 | 30 |
Marijuana (Cannabis sativa) | - | - | 2.5 | 45 |
Sedge (Carex sp.) | 28.3 | 36.6 | 57.5 | 15 |
Lamb's quarters (Chenopodium album) | - | - | 12.5 | - |
Field bindweed (Convovulus arvensis) | 8.3 | - | 17.5 | - |
Horseweed (Conyza canadensis) | - | - | 10.0 | - |
Tansy mustard (Descurainia pinnata) | - | - | 7.5 | - |
Barnyard grass (Echinochloa crusgalli) | - | - | 12.5 | - |
Canada wild rye (Elymus canadensis) | - | - | 7.5 | - |
Smooth horsetail (Equisetum laevigatum) | - | 25.0 | - | - |
Kochia (Kochia scoparia) | - | - | 5.0 | 25 |
Rice cutgrass (Leersia oryzoides) | 8.3 | - | - | 5 |
Virginia pepperweed (Lepidum virginicum) | - | - | 10.0 | 15 |
Black medick (Medicago lapulina) | 18.3 | 3.3 | - | - |
Catnip (Nepeta cataria) | - | - | 7.5 | - |
Yellow wood sorrel (Oxalis stricta) | 1.7 | - | 20.0 | - |
Pennsylvania pellitory (Parietaria pennsylvanica) | - | - | 10.0 | - |
Kentucky bluegrass (Poa pratensis) | 28.3 | 26.7 | 12.5 | - |
Smartweed (Polygonum sp.) | 11.7 | 15.0 | 22.5 | 30 |
Dock (Rumex sp.) | - | 6.7 | 52.5 | 40 |
Prairie cordgrass (Spartina pectinata) | 3.3 | 1.7 | 22.5 | 20 |
Penny cress (Thlaspi arvensis) | - | - | 10.0 | - |
Wild violet (Viola sp.) | 3.3 | 10.0 | 17.5 | 50 |
Miscellaneous species (less than 5% each) | 28.4 | 37.0 | 32.5 | 15 |
1) Frequency is expressed as a percentage of the area sample quadrats which contained the species. | ||||
Dock was plentiful throughout most ditch areas of the farm and was used for 64.8%, of the Red-wing nests (Table 3). Although Red-wings may nest in a variety of vegetation types, a few plants are preferred and this preference changes as the season progresses (Case and Hewitt 1963). We found that with several renesting attempts late in the season, plant species other than dock were used. By this time, dock had reached its peak, the plants were very tall and had few leaves present.
Nest height above the ground ranged from 0.2 m to 1.4 m with most between 0.4 to 1.0 m, (16 to 39 inches).
Although nesting success may be underestimated due to effects of nest visitation effects (Burt 1977), results of this study indicate a 46.0% success rate of Red-winged Blackbird nests. Thirty-one percent of the nests we found were deserted and 23% were broken up (Table 1). Dolbeer (1976) reported a success rate of 31% for an old field habitat in Ohio while Case and Hewitt (1963) found an average success rate of 20% in an upland habitat of 180 acres of forage crops, alfalfa, timothy, and weedy fields bordered by woodlots.
Table 3. Support of red-winged Blackbird nests. | ||
Support Used | No. Nests | Percent |
Dock (Rumex sp.) | 46 | 64.8 |
Milkweed (Asclepias sp.) | 5 | 7.0 |
Barbed wire fence | 4 | 5.6 |
Sedge (Carex sp.) | 3 | 4.2 |
Mulberry (Morus sp.) | 2 | 2.8 |
Catnip (Nepeta cataria) | 1 | 1.4 |
Willow (Salix interior) | 1 | 1.4 |
Prairie dropseed (Sporobolus cryptandrus) | 1 | 1.4 |
False indigo (Amorpha fruticosa) | 1 | 1.4 |
Common sunflower (Helianthus annus) | 1 | 1.4 |
Smartweed (Polygonum sp.) | 1 | 1.4 |
Sweet clover (Melilotus sp.) | 1 | 1.4 |
Prairie cordgrass (Spartina pectinata) | 1 | 1.4 |
Giant ragweed (Ambrosia trifida) | 1 | 1.4 |
Smooth brome (Bromus inermis) | 1 | 1.4 |
Total | 71 | 99.8 |
Nest height above the ground ranged from 0.2 m to 1.4 m with most between 0.4 to 1.0 m, (16 to 39 inches).
Although nesting success may be underestimated due to effects of nest visitation effects (Burt 1977), results of this study indicate a 46.0% success rate of Red-winged Blackbird nests. Thirty-one percent of the nests we found were deserted and 23% were broken up (Table 1). Dolbeer (1976) reported a success rate of 31% for an old field habitat in Ohio while Case and Hewitt (1963) found an average success rate of 20% in an upland habitat of 180 acres of forage crops, alfalfa, timothy, and weedy fields bordered by woodlots.
Brown-headed Cowbirds (Molothrus ater) parasitized 42% of all Red-wing nests. This compared with a 52% parasitism rate with 1 to 3 cowbird eggs found in each Red-winged Blackbird nest by Hergenrader (1962). Dappen (1967) found a 66% parasitism rate in colonial Red-winged Blackbird nests near Lincoln, NE. He found no more than two Cowbird eggs per nest.
Cowbirds usually remove a host egg before or after laying their egg-in the host nest (Hann 1937) so clutch size remains the same in most cases. Many nests that contained one Cowbird egg had been abandoned by the Blackbirds. These nests were not included in determination of clutch size, but Cowbird eggs in an attended nest were included. Nests that were destroyed before the clutch was completed were not used in clutch size calculation. Average clutch size was 4.14. Dolbeer (1976) found an average clutch size of 3.38 in upland habitat and Case and Hewitt (1963) reported average clutch sizes of 3.15 and 3.65 in upland habitat. Our figure is somewhat high, possibly due to the high incidence of cowbird eggs. In several nests, it appeared that Cowbirds did not always remove Blackbird eggs, which caused clutch size to appear larger.
In come cases, Cowbird eggs did not hatch although Red-wings did. But in most nests, Cowbird eggs hatched and these nestlings fledged along with the Red-winged Blackbird young. Identification of fledglings of the two species were not separated so the number of fledglings per nest includes both Brown-headed Cowbird and Red-winged Blackbird fledglings. We found an average of 1.29 fledglings per nest and 2.71 fledglings per successful nest. Dolbeer (1976) reported 1.0-1.4 fledglings per nest during May and 2.8-3.1 fledglings per successful nest throughout the entire nesting season. Case and Hewitt (1963) reported values of 0.45-1.09 fledglings per nest and 2.47-2.92 fledglings per successful nest. All these values were obtained in upland habitat.
Western Meadowlark
Meadowlarks attempted nesting on a roadside, an alfalfa field, and the pasture. A fledgling was also observed in an alfalfa held. Lanyon (1956) found the Western Meadowlark selects an environment resulting from the creation of a drier habitat attributed to farmland cultivation.
American Robin
Eight nests were found, 3 in a farmyard and the remainder were located in isolated trees and a bush on field borders. Trees used for nesting were green ash (Fraxinus pennsylvanica), mulberry (Morus sp.), and eastern red cedar (Juniperus virginiana). A bush, wahoo (Euonymus occidentalis), was also used.
Barn Swallow
The three nests found away from the farmyards were built on the walls of a cement culvert connecting roadside ditches.
Grasshopper Sparrow
Two nests were found in the pasture. Nests were located in clumps of brome grass with only the upper dome of the nest structure visible. One of the two nests contained one Cowbird egg. Observations of juvenile Grasshopper Sparrows indicated successful nesting. Cattle were thought to have contributed to nest break-up.
Territory size was .9 ha (2.33 acres). Smith (1963) reported an average size of 2.03 acres on cultivated grasslands, particularly fields with bunchgrasses and alfalfa or clover. The oats field adjacent to the pasture contained one-third the amount of territories in the pasture. No Grasshopper Sparrows were seen in an oats field 800 m (.5 mile) to the east. Smith (1963) reported Grasshopper Sparrows densities in small grains a fraction of those found in grasslands.
Black-billed Cuckoo
Johnsgard (1979a) listed the Black-billed Cuckoo as characteristic of wooded habitats while Kendeigh (1944) described it as a forest edge species that may nest in woods but also required grassy or shrubby fields, open forests, or other external habitats for their complete activity. The nest located was in an isolated ash tree growing in a 16 m wide irrigation ditch. Primary plants in the ditch were brome, sedges, marijuana, wild rye (Elymus canadansis), and foxtail (Setaria sp.). An alfalfa field was located to the south with a corn field across the ditch to the north.
Blue Grosbeak
Although this species is uncommon and quite local in the east (Johnsgard 1979a) we found a nest in an elm (Ulmus americana) sapling in a roadside ditch. A wooded farmyard was located across the road from the nest. Three young were successfully fledged.
Upland Sandpiper
Three destroyed nests were found in the alfalfa following mowing. These birds showed a preference for untitled areas since nesting was attempted in the alfalfa and most sightings were in the alfalfa and pasture. Higgins (1975) found that Upland Sandpipers in North Dakota croplands preferred nesting in standing stubble and growing small grain fields. In his study, 57% of the nests found were located in untilled habitats which comprised only 7% of the study area.
Farmyard Nesting Species
Thirteen species nested in a large variety of places on the farmyards. Rock Doves (Columba livia) used a semi-open cattle barn and Mourning Doves (Zenaida macroura) used a pine tree (Pinus sp.). A Common Flicker (Colaptes auratus) nested in a cavity of a catalpa (Catalpa speciosa) tree. The catalpa was also used for nesting by an Eastern Kingbird (Tyrannus tyrannus). A semi-open grain storage building was used by Barn Swallows, and young were successfully fledged. House Wrens (Troglodytes aedon) utilized nest boxes while Robins used trees scattered throughout the barnyard and a metal structure supporting fuel tanks. Common Grackles (Quiscalas quiscula) were early nesters that used cedar trees while House Sparrows (Passer domesticus) used shed eaves and a large variety of other sites. Starlings (Sturnus vulgaris) and a Red-headed Woodpecker (Melanerpes erythrocephalus) were observed nesting in tree cavities. Three Blue Jay (Cyanocitta cristata) nestlings were found dead in a nest built in a red cedar.
Other Species
Three species which exhibited nesting behavior were Dickcissels (Spiza americana), Common Yellowthroats (Geothlypis trichas), and Bobolink (Dolichonyx oryzivorus). The Common Yellowthroat showed a preference for moist grassy areas located in ditch areas. Dickcissels showed indications of nesting in an irrigation ditch and a nest with nestlings was found in a small pine tree adjacent to an alfalfa field. Bobolinks were observed copulating in the pasture. These birds were seen foraging and singing in the pasture and oats. Johnsgard (19796) includes ungrazed to lightly grazed mixed grass prairies, and small grain croplands as breeding habitat of the Bobolink.
Use of Fields
Corn. This was the only crop present on all three farms. Acreages of all corn fields were approximately 50% of the total crop area. The Horned Lark (Eromophilia alpestris) and Mourning Dove were the predominant species observed. Owens and Myres (1973) and Dambach and Good (1940) reported similar findings in which these species used cultivated fields. Killdeer (Charadrius vociferous), Robins, Brown-headed Cowbirds, Grackles, Upland Sandpipers, and occasionally Pheasants foraged in the corn fields. Upland Sandpipers used these areas prior to crop emergence and while corn was still fairly short. Pheasants and their broods used these fields later in the season as crop height increased plant cover.
Soybeans. Horned Larks and Mourning Doves were the most common species observed in the three separate soybean fields. More Horned Larks were seen on the one large (65 ha, 160 acres) conventional field. This may have occurred because of the larger field size and bare areas caused by chemical damage to crops.
Alfalfa. Use of the three alfalfa fields was very abundant and diverse. Birds which unsuccessfully nested here included Dickcissels, Meadowlarks, Upland Sandpipers and Ring-necked Pheasants. Barn Swallows foraged above the crop prior to cutting. After the alfalfa was cut and baled, Robins, Grackles, Starlings, Cowbirds, Sparrows and Killdeer foraged in the stubble.
Small grains. These crops included two oat fields, one winter wheat, and one rye field. These crops provide good habitat for many grassland species (Dambach and Good 1940). Birds which attempted to nest in the oats were Red-winged Blackbirds, Grasshopper Sparrows, Dickcissels, and Bobolinks. Blackbirds and Dickcissels used winter wheat fields for nesting.
In most observed cases, weeds, not the crop itself, were used as the site for actual nest building. Winter kill of grain seedlings could contribute to increased emergence of weeds which were used as nest sites. Pheasant broods were observed using the rye, oat, and winter wheat fields as well as the pasture. Warner (1979), Mohler (1959), Hanson and Progulske (1973), and Gates and Hale (1974) found that small grain fields were important for pheasant broods.
Pasture. The pasture was used for nesting by a large number of Grasshopper Sparrows. Meadowlarks, Robins and Pheasants nested in or around the pasture. Birds which foraged in this area included Upland Sandpipers, Brown-headed Cowbirds, and Barn Swallows. Vegetation analysis showed the primary species were smooth brome, Kentucky bluegrass, prostrate spurge (Euphorbia supine), dandelions (Taraxacum officinale) and alfalfa.
Notes on Other Bird Activity
Other bird behavior was observed during the study period but not included in the above narrative. This section is meant to supply some information on certain species and their behavior.
Farmyard species which were recorded singing during censuses included Black-capped Chickadees (Parus atricapillus), Cardinals (Richmondena cardinalis), Northern Orioles (Icterus galbula), and Chipping Sparrows (Spizella passerina).
Great Horned Owls (Bubo virginianus) were flushed during censuses from a roost located in tall maple trees growing in a field border separating the center of the section. Kestrels (Falco sparverius) hunted from a line of catalpa trees, telephone poles, and fence posts located on the area. These birds were a family group but it was not known if they moved into the area after nesting in another location or nested on the study area. A marsh Hawk (Circus cyaneus) was observed hunting over a small grain field on one occasion.
The area used to compost paunch manure was utilized by Killdeer, Grackles, and House Sparrows. The number of Killdeer observed averaged 5-6 but up to 20-25 were observed at one time. These larger numbers foraged in this area.
An important food source for birds were red mulberry (Morus rubra) and while mulberry (Morus alba) trees on the area. Robins, Blackbirds and Dickcissels were some of the birds which fed on the ripe berries.
Other birds observed during the study period included Blue-winged Teal (Anas discors) seen in an irrigation ditch, an American Goldfinch (Spinus tristis) pair, Brown Thrasher (Toxostoma rufum), and Chimney Swift (Chaetura pelagica).
Conclusion
Study results showed the importance of a diverse cropping system and edge area for survival. Crop diversity and the associated smaller field size create a greater amount of edge. This edge includes irrigation ditches, grass waterways, fence lines, and roadsides, which comprise a small amount of the total area but are important breeding habitat. These edge areas contain a rank growth of mixed plant species. The variety of vegetation present differs greatly from cultivated fields with limited plant cover which provides poor cover during the nesting season.
Farmyards also create important habitat for birds. These areas contain trees and other nesting sites for bird species which cannot survive in open cropland habitat.
Acknowledgements
We thank Cathie Wiederspan for vegetation analysis data and Ron Case who served as project advisor. Research was supported by National Science Foundation grant SPI-7905254.
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