Author Institution: Department of Zoology, The University of Illinois, Champaign, Illinoi

Cox, George W.

The Ohio Journal of Science

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A COMPARISON OF WINTERING BIRD POPULATIONS INTHREE OPEN FIELD TYPES IN CENTRAL OHIOGEORGE W. COXDepartment of Zoology, The University of Illinois, Champaign, IllinoisINTRODUCTIONThe study of wintering bird populations is still a relatively unexplored field.Although a large number of censuses are available for some habitats, manyimportant habitats and geographical areas remain unknown. Few studies havebeen made of winter bird populations in open field areas. Forbes and Gross (1921)surveyed bird populations in open fields in Illinois by means of a strip censusmethod and summarized their results according to field type and the generalsection of the state. Since then, few extensive studies have been made. Inrecent years the Winter Bird-population Studies sponsored by the NationalAudubon Society have increased interest in this phase of ornithology.A number of factors has limited the usefulness of many of these more recentstudies in determining average populations for various field types. Many censuseshave covered more than one field type without separating the data for the varioustypes. Inadequate descriptions of single field types have also made comparisonsdifficult. Often no distinction has been made between edge species, the populationsof which are not directly related to the field size, and true open field species.In the present study the author has attempted to eliminate some of thesedifficulties and to determine average populations of certain field types. Thesedata represent, however, only a preliminary step in this direction.PROCEDUREThe following three types of fields were chosen for the study:1. Undisturbed corn stubble.—Corn fields of this type had been harvestedwith a mechanical corn picker, which left the entire stalks rooted in the originalrows, their upper parts bent over at a uniform height of one to one and one-halffeet and lying parallel to the rows. Waste corn was abundant. These fieldshad not been otherwise disturbed.2. Disked corn stubble.—Corn in this type had been harvested in a mannersimilar to that of the previous type; but following the harvesting, the field hadbeen harrowed or disked and winter grain planted. This resulted in the uprootingand cutting up of the corn stalks, thereby eliminating much of the cover whichhad been present. The general appearance was that of a nearly bare field withscattered debris of corn stalks and short basal stubs sticking up at wide intervals.Much of the waste corn was still available. The winter grain had grown to aheight of only 1 to 2 inches, in rows about eight inches apart.3. Soybean stubble.—In this type the soybeans had been cut, leaving stubble2 to 5 inches high, with occasional small mats of soybean stems. The generalappearance was that of an almost bare field. In two of the fields, #11 and #12(table 1), winter grain had been planted following the cutting of the soybeans.Although this had resulted in some disturbance of the ground, much of the stubblestill remained, and this, along with soybean debris, still dominated the appearanceof the fields.These fields were located in Oxford, Troy, Radnor, and Marlboro Townshipsin north-central Delaware County, Ohio. The approximate sizes of the fieldswere obtained by pacing the sides and calculating the area from these measurements.Areas obtained in this manner ranged from 12 to 30 acres. Fields of undisturbedcorn stubble were numbered from 1 to 5, and in size were respectively 25, 30, 20,THE OHIO JOURNAL OF SCIENCE 58(3): 189, May, 1958190 GEORGE w. cox Vol. 5817, and 13 acres. Those of disked corn stubble, numbered 6 through 10, wererespectively 29, 20, 12, 12, and 27 acres in size. Soybean stubble fields, numbered11 through 15, were 24, 28, 14, 24, and 25 acres in size, respectively.Bird populations of the fields were determined by a series of six census tripsthrough each field. These trips varied from 10 to 30 minutes in length, dependingupon the size of the field, its type, and the number of birds present. Censusingwas carried out during two periods, December 25 to 28, 1956, and January 29 toFebruary 2, 1957. Three trips were taken through each of the fields during eachof these periods.TABLE 1Winter populations (birds per 100 acres) of open field birds in 15 fields of three types inDelaware County, Ohio, during the winter of 1956-57Undisturbed Diskedcorn stubble corn stubble Soybean stubbleField No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15SpeciesSize in acres 25 30 20 17 13 29 20 12 12 27 24 28 14 24 25Cooper's Hawk 1(Accipiter cooperi)Red-tailed Hawk 1 1 + 1 1 +(Buteo jamaicensis)Marsh Hawk + + 1 1 2 + 1 + 1 1(Circus cyaneus)Sparrow Hawk 1(Falco sparvenus)Bob-white 7 26(Colinus virginianus)Ring-necked Pheasant 7(Phasianus colchicus)Mourning Dove 12 84 9 162 95 1 1(Zenaidura macroura)Short-eared Owl 1 + +(Asio flammeus)Horned Lark 24 1 39 3 81 180 296 1 243 58 26 4 15 4 2(Eremophila alpestris)Starling 2(Sturnus vulgaris)Eastern Meadowlark 1 1 48(Sturnella magna)Lapland Longspur 19 95 35 12 35(Calcarius lapponicus)Snow Bunting 4(Plectrophenax nivalis)Total 37 101 50 194 180 200 443 1 278 75 61 5 16 5 2Only permanent residents of open fields or species which utilized the fieldsapparently independently of the edge during daytime feeding were considered inthe census. Birds of prey flying over the area were assumed to be foraging andwere included. Other species merely flying over were excluded.In many cases it was necessary to estimate large flocks of birds, resulting in theintroduction of some error in the final population figures.The average population per 100 acres for each of the 15 fields was calculatedfrom the size of the field and the results of the six census trips (table 1). Theaverage population per 100 acres for each type was calculated from the data forNo. 3 WINTERING BIRD POPULATIONS 191the five fields of that type (table 2). Figures were rounded to the nearest wholenumber. Where the average population was less than 0.5 birds per 100 acres,or where the species was recorded at times other than census trips, a + was usedto indicate presence only (tables 1 and 2). A frequency index was calculated foreach species in each of the three types by dividing the number of occurances ofthe species on individual census trips in all five fields of the same type by thenumber of possible occurances (table 2).TABLE 2A comparison of the populations of open field birds (average numbers per 100 acres) in threetypes of open field areas in Delaware County, Ohio, during the winter oj 1956-57SpeciesCooper's Hawk(Accipiter cooperi)Red-tailed Hawk(Buteo jamaicensis)Marsh Hawk(Circus cyaneus)Sparrow Hawk(Falco sparverius)Bob-white(Colinus virginianus)Ring-necked Pheasant(Phasianus colchicus)Mourning Dove(Zenaidura macroura)Short-eared Owl(A sio flammeus)Horned Lark(Eremophila alpestris)Starling(Sturnus vulgaris)Eastern Meadowlark(Sturnella magna)Lapland Longspur(Calcarius lapponicus)Snow Bunting(Plectrophenax nivalis)TotalUndisturbedcornave.pop.++1+6270+24+103stubblefreq.index.03.10.13.03.07.03.53.07.43.07Diskedcorn stubbleave.pop.++1+156+10321200freq.index.03.03.07.00.73.03.17.40.07Soybeanave.pop.+++10717stubblefreq.index.03.07.00.30.03RESULTS AND DISCUSSIONThe total population was found to be highest in the disked corn stubble type,where 200 birds per 100 acres were found, and second highest in the undisturbedcorn stubble, where 103 birds per 100 acres were found. Only 17 birds per 100acres were found in the soybean stubble (table 2).The nature of the populations from which the samples were taken makesstatistical interpretation of these differences difficult, but the high apparentdifferences in many cases suggest that they are real.The difference between populations in the disked corn stubble and the soybeanstubble is emphasized by the fact that in three cases fields of the two types wereadjacent to each other. These three pairs of adjacent fields were #6 and #11,#7 and #13, and #10 and #15 (table 1). For these three disked corn stubble fields192 GEORGE W. COX Vol. 58the average population per 100 acres was 220 birds while for the three soybeanstubble fields the population was only 28 birds per 100 acres. Since these adjacentfields were readily accessible to the same groups of birds, this difference seems toindicate a definite preference for the disked corn stubble.Among the individual fields of the same type, there was a high degree ofvariation in total population and populations of individual species (table 1);e.g., in the disked corn stubble total populations per 100 acres varied from 1 to 443birds. The causes of these variations were not investigated. Some variation mayhave been due to minor differences between the fields themselves. In addition,since many of the species involved are wide ranging in their winter activities,differences may also have been due to characteristics of the surrounding areaswhich were not always apparent from examination of the fields themselves.Populations of Horned Larks and Mourning Doves showed marked differencesbetween the three field types. The former had populations, in birds per 100acres, of 156 in disked corn stubble, 24 in undisturbed corn stubble, and 10 insoybean stubble (table 2). The high population in disked corn stubble seemed tobe due to a combination of available waste corn and absence of much cover. Thebirds were observed feeding on the corn and, at times when light snow coveredthe ground, tracks of the birds formed radiating lines to corn ears from whichmuch of the corn had been removed. The Mourning Dove showed the highestpopulation in the undisturbed corn stubble, 70 birds per 100 acres (table 2). Thehigh population of this species seemed to be related to the presence of waste cornand the cover provided by the basal parts of the corn stalks.Two other typical open field birds, the Lapland Longspur and the Snow Bunting,the latter in small numbers in one field only, showed preferences similar to thoseof the Horned Lark. Bob-white and Ring-necked Pheasant, on the other hand,appeared only in fields of the undisturbed corn stubble (table 2).The population figure of 10 birds per 100 acres for Horned Larks in the soybeanstubble fields (table 2) may not represent true winter density. On trips duringthe period from January 29 to February 2, territorial males and pairs of thisspecies were encountered in these fields where none were found during the firstseries of census trips. Future winter studies involving this species should probablybe concluded at an earlier date, if the objective of such a study is to determine therelation of the bird to the winter food supply of the species.Population figures calculated for the first three trips through each field, takenbetween December 25 and 28, and the last three, taken between January 29 andFebruary 2, often gave considerably different results. This would seem to indicatethat the winter population of the species under consideration was not a stable one.Horned Larks and Mourning Doves showed lower densities and Lapland Longspurshigher densities during the second series of census trips than during the first series.SUMMARYBecause of the existing lack of information on wintering populations of openfield birds, the author attempted to obtain accurate data in this regard by censusingfive fields each of disked corn stubble, undisturbed corn stubble, and soybeanstubble, ranging in size from 12 to 30 acres, and located in Delaware County, Ohio.Open field species were censused on six occasions during the periods fromDecember 25 to 28, 1956, and January 29 to February 2, 1957.Total populations were found to be highest in the disked corn stubble, secondhighest in the undisturbed corn stubble, and lowest in the soybean stubble.Considerable variation in both total population and populations of individualspecies occurred within the fields of the same type.Horned Larks showed the highest populations in disked corn stubble, seeminglybecause of availability of waste corn and absence of cover. Lapland Longspursand Snow Buntings showed similar preferences.No. 3 WINTERING BIRD POPULATIONS 193Mourning Doves were most abundant in undisturbed corn stubble, possiblyrelated to the presence of waste corn and cover. Bob-white and Ring-neckedPheasant showed similar preferences.Censuses involving Horned Larks should be concluded at an early date sincethese birds become territorial by late January.Differences in population densities for individual species between the twocensus periods indicate that winter populations of some species are very unstable.ACKNOWLEDGMENTSThanks are extended to Dr. W. D. Stull of Ohio Wesleyan University andRichard Brewer of the University of Illinois who critically reviewed the manuscript.LITERATURE CITEDForbes, S. A. and A. O. Gross. 1923. On the numbers and local distribution of Illinois landbirds of the open country in winter, spring, and fall. 111. State Natl. Hist. Survey Bull.14: 397-453.

A Comparison of Wintering Bird Populations in Three Open Field Types in Central Ohio

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A Comparison of Wintering Bird Populations in Three Open Field Types in Central Ohio

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