DOMESTIC CATS AS PREDATORS AND FACTORS IN WINTER SHORTAGES OF RAPTOR PREY

Transcription

1 DOMESTIC CATS AS PREDATORS AND FACTORS IN WINTER SHORTAGES OF RAPTOR PREY WILLIAM G. GEORGE The domestic cat (FeZis catus) was itroduced ito the Uited States over 150 years ago. Imported i small umbers for the primary purpose of cotrollig rodets i our easter seaboard cities, cats remaied scarce for may years. Now a estimated 31 millio cats exist across the coutry (America Humae Associatio, 1972), ad rural cats probably rival i umbers all other large predators combied east of the Great Plais, west of the Sierra Nevada, ad i various other localities. I terms of impact o the avifaua, cats may pose little direct threat, for they are reported to kill relatively few birds i most situatios (Table 1). Yet as predators o rodets, cats ievitably compete for prey with may of our decliig raptors, ad therei may lie a serious problem. Cats are formidable competitors, able to kill rodets at a great ad rapid rate. For example, the removal i eight moths of over 4200 mice from a 35-acre study plot was ascribed pricipally to six cats by Pearso (1964). I am ot suggestig a cause-ad-effect relatioship exists betwee the historical icrease of cats ad the historical decrease of raptors; however, cats, which are as efficiet i their way as gus ad DDT, accompay ad add aother dimesio to ma s ecroachmet ito wildlife areas. The effects of cat abudace i ad about wildlife areas should be moitored as a matter of prudece, especially i view of the declie (see Arbib, 1972) of such formerly commo raptors as the Red-shouldered Hawk (Buteo Zieatus), Redtailed Hawk (B. jamaicesis), Marsh Hawk (Circus cyaeus), ad America Kestrel (P&o sparverius), each of which feeds o rodets to a marked degree (May, 1935; MacAtee, 1935). Most eviromets i rural America have suffered drastic ad repeated alteratios; may may be uable today to geerate prey i sufficiet desities to sustai both raptors ad sigificat umbers of cats. I decided to probe this possibility whe a female cat ad two of her offsprig killed a impressive umber of mammals at my home i souther Illiois. I have studied cotiuously the predatio by these cats over the past six years. Durig this time, shortages i the mammalia prey of hawks have appeared cosistetly i the cats hutig grouds each witer. The preset report describes ad discusses the aual ad seasoal predatio by these cats from 1 Jauary 1968 through 31 December Their predatio o o-mammalia vertebrates (various birds, reptiles, ad frogs) is tabulated to roud out the accout. 384

2 CATS AS PREDATORS ON RAPTOR PREY TABLE 1 FREQUENCY OF OCCURRENCE OF VERTEBRATE PREY IN THE DIET OF RURAL CATSI Percet or relative proportio of prey i each group Area Shrews-moles Rodets Rabbits Birds Reptiles Amphibias Marylad 8 Pesylvaiaz 9 Wiscosia 2 Michiga3 0.9 Otario Few Missouri 4 Oklahoma Few Texas - Califoria* May May May Few Few Few Few Cor iled from Bradt, 1949; Eberhard, 1954; Errigto, 1936; Hubbs, 1951; Korschge, 1957; Lf ew 11 y ad U&r, 1952: McMurry ad Swrry, 1941; Parmalee, 1953; ad Toer, Based o aalysis of s&ach~cotets. 3Based o observed predatio. MATERIALS AND METHODS The Study Site.-The hutig grouds of the cats cetered aroud our home i fallow farmlad ear the village of Cobde, Uio Couty, souther Illiois. The area is oe of uplads, kow as the Shawee Hills or Illiois Ozarks, which ru east to west betwee the floodplais of the Mississippi ad Ohio Rivers. This rollig coutry was oce domiated by forest but ow hosts orchards, cultivated crops, old field successio, pastures, secod-growth deciduous woods, ad impoudmets that at may poits itercept the atural watersheds. Characteristically, the area is dotted with small farms, of which my home plot (i lls, R, lw, Sectio 19, Uio Couty) is typical. The house stads atop a koll, 0.3 mi from the earest surfaced road ad dwellig of a eighbor. A acre of law ad a aged grove of coifers (Tsuga, Pius, Juiperus) ad deciduous hardwoods (Quer- cw, Fraxius, Acer, Juglas, Carya, Liquidambar, Liriodedro) surroud the house; a bar is close-by. Apple ad ectarie (Pyres) orchards (about 50 acres), old fields (25 acres), woods (15 acres), ad several impoudmets compose the adjacet habitats. Groud cover i the fields ad orchards agree i geeral compositio but differ i height, as a result of differetial mowig. I , aual ad sometimes biaual mowig occurred o about 75 percet of the total field ad orchard acreage. The woods o the plot skirt the fields; oe forest-like stretch exteds up a ravie to withi a few feet of the bar. The Mammalia Faua.-The three cats had merely to step out of the bar or off the law to eter habitats cotaiig 18 species of possible mammalia prey (Table 2), icludig three microties, seve other rodets, three shrews, ad the cottotail. Ohservatios, a program of ca-trappig for shrews (George, MS), ad specimes caught by the cats idicated the summer abudace of these species approximated that reported by Hoffmeister ad Mohr (1957) ad Laye (1958)) show i Table 2.

3 THE WILSON BULLETIN December 1974 vol. 86. No. 4 TABLE 2 OCCURRENCE AND SUMMER ABUNDANCE OF SMALL TERRESTRIAL MAMMALS (EXCLUDING CARNIVORES) AND THEIR STATUS AS PREY OF WINTERING HAWKS NEAR COBDEN, UNION COUNTY, SOUTHERN ILLINOIS Witer status as prey for? Species Summer Redabu- tailed Marsh America dam& Hawk Hawk Kestrel Opossum (Didelphis marsupialis) C Easter mole (Scdopus aquaticus) vc b b Log-osed shrew (Sorex logirostris) 4 U Short-tailed shrew (Blaria brevicauda) vc b b Least shrew (Cryptotis parva) C Woodchuck (Marmota mo~x)~ C Easter chipmuk (Tamias striatus) C Easter gray squirrel (Sciurus caroliesis) U a or b b Easter fox squirrel (Sciurus iger) U a or b Souther flyig squirrel (Glaucomys volas) U White-footed mouse (Peromyscus leucopus)3 VC b b Souther bog lemmig (Syaptomys cooperi) U b b Prairie vole (Microtus ochrogaster) vc a a Pie vole (Micro&us pietorum) C a a or b Muskrat (Odatra zibethicus) U b or House mouse (Mus musculus) C b a or b Meadow jumpig mouse (Zapus hudsoius), U Easter cottotail (Sylvilagus jloridaus) VC a h b a b or b b a a or b a 1 vc = very commo, c = commo, u = ucommo. 2 a = major, b = mior, = egligible. 3 Strogly crepuscular-octural. 4 Rare i most of souther Illiois. (i Take frequetly by owls but seemigly ot ofte by hawks. 6 Witer hiberator. No-felie Predators.-The study plot was raged over by the followig ative predators, which, to a greater or lesser extet, competed with the cats for prey the year roud (except as oted) : various sakes (witer hiberators), Red-tailed Hawk, Marsh Hawk (witer visitat), America KestreI, Screech Owl (&us asio), Great Hored Owl (Bubo virgiiaus), Barred Owl (Strix maria), Log-eared Owl (Asia otus; witer visitat), Loggerhead Shrike (Laius Zudoviciaus), raccoo (Procyo lotor), gray fox (Urocyo ciereoargeteus), red fox (Vulpes fulva), domestic dog (Cais familiaris), ad perhaps striped skuk (Mephitis mephitis). The log-tailed weasel (Mwtela jreuta) ad mik (IM. viso) have bee recorded i earby areas but ot o the study site, ad evidece is lackig to show that short-tailed shrews, which elsewhere may kill voles, prey o microties i souther Illiois.

4 William G. George CATS AS PREDATORS ON RAPTOR PREY 387 Huma predatio existed i the form of sportsme, who aually harvested gray ad fox squirrels (1 August to 15 November) ad cottotails (11 November to 15 Jauary) withi all but the ier core (six acres) of the study plot. A mior amout of trappig was doe by me to study the compositio of the small mammal faua, but either rodet cotrol or a chemical eradicatio program was i effect o the study site. The Cats ad Their Habits.-The mother cat, desigated Cat 1, was a bridle brought to the study site i She weighed about eight Ibs ad was sexually altered i I 1966 she gave birth to Cat 2 (black female) ad Cat 3 (gray male). Both are sexually altered, with Cat 2 weighig 12 lbs ad Cat 3 weighig 16 lbs. Prior to the birth of her kittes, Cat 1 caught chiefly house mice, depositig them i the kitche of my home. She brought rodets ad youg cottotails to her youg, which cosumed them with relish. Cats 2 ad 3 bega to hut prey, ad their mother s prey i- creased, i This expasio i predatio multiplied our observatios ad cofirmed our impressio that detailed iformatio o predatio by each member of the group could be obtaied. For oe thig, the combied home rage of the cats oly e- compassed selected spots withi about 17 acres of fields ad three acres of woods, with parts of about five adjacet acres of field habitat beig used i the late fall ad witer moths. Secodly, the cats ever ate or deposited prey where caught but istead carried it ito a delivery area, cosistig of the house ad law. The exclusive use of this delivery area was verified i 18 to 70 mammal captures per cat, as witessed betwee early 1967 ad late The cats had all assumed defiitive patters of hutig ad dietary habits before the study bega. Cat 1 sought prey o oly about five acres, which she shared with the other two; they i tur shared the balace. Cat 1 ate o prey, hutig fewer hours per day tha Cats 2 ad 3, each of which cosumed about percet of the microtie rodets ad cottotails that they had captured. They ate varyig lower percetages of their other mammalia prey. Cat 3 was the most successful mouser. This may have bee due to its ability to leap out as much as 6 to 8 feet over 3.foot-high grass, eablig it to reach microtie rodets cocealed i ruways beeath dese cover. These attacks appeared guided maily if ot etirely by auditory ad olfactory cues. Prior to 1968 ad throughout the study a daily allotmet per cat of g of raw beef, chicke parts, ad commercial pet foods was available i the kitche. A etry i the kitche door eabled the cats to come ad go freely betwee their hutig grouds ad the house. All the cats slept i the house ad cosumed varyig amouts of the food provided for them. Recordig Observed Deliveries of Prey.-Almost all of the outdoor portio of the de- livery area ad about six acres of the cats hutig grouds were visible from iside the house; vatage poits outside yielded a still wider view of the hutig grouds. Exploitig these advatages, the delivery of prey was moitored from a half hour to 24 hours per day o 1,387 days, durig a total of about 8,500 daylight ad 7,300 crepuscular- octural hours. Additioally, 17 periods of three to 14 days, ivolvig every seaso i early all the study years, were devoted to cotiuous moitorig of prey deliveries. Prey items were usually weighed idoors o a fie balace scale, although a small sprig scale, carried outside, was sometimes used. Most sexig was doe by exteral features; the coutig of fetuses was doe by opeig obviously pregat females before allowig the cats to eat them. The oly prey the cats were ot allowed to eat were small series of voles appropriated ad froze for future sexig ad/or idetificatio.

5 THE WILSON BULLETIN December 1974 vol. 86, No. 4 The delivery area, which was rarely left uatteded for loger tha 48 cosecutive hours, was examied ad cleared of prey remais at daw ad dusk whe circumstaces permitted. This facilitated attributio to diural or o-diural predatio of some whole ad may remat specimes stemmig from uobserved deliveries. Specimes ot accoutable with respect to time of delivery were distributed each moth betwee diural, crepuscular, ad octural colums, i proportio to the total specimes stem- mig from observed deliveries of the species. Uobserved deliveries of the day-shuig white-footed ad jumpig mice were allocated half to crepuscular ad half to octural predatio, i accordace with the cats observed patter of catchig these species. The cats sometimes left the etrails i cosumig microties (bog lemmigs, prairie ad pie voles) ad these remais were difficult to idetify as to species. Etrails stemmig from uobserved deliveries were allocated to species i ratio to the represetatio of each microtie i the total mothly captures recorded through observed deliveries. Besides specimes completely devoured durig the absece of observers, gaps i my records ad possible misleadig iformatio may have resulted from: (a) small prey beig swallowed very swiftly ad ot detected by observers; (b) the scavegig of prey remais by opossums, dogs ad other aimals, especially at ight; ad (c) failure to fid small prey or remats cocealed uder leaves ad grass i the delivery area. RESULTS Species ad Average Aual Totals of Captured Prey.-Mammals take by the three cats i the four years of study are listed i Table 3, alog with the umber of fetuses killed, the average weight of the prey specimes, ad TABLE 3 AVERAGE ANNUAL PREDATION (COMBINED) ON VERTEBRATES BY THREE CATS IN UNION COUNTY, SOUTHERN ILLINOIS, Number captured1 Combied weight Percet Of prey2 of prey2 of catch Log-osed shrew 6.0 Easter chipmuk 19.5 White-footed mouse 53.0 Souther bog lemmig 26.5 Prairie vole Pie vole 72.5 House mouse 19.5 Meadow jumpig mouse 2.5 Easter cottotail 46.5 Other vertebrates 35.0 Totals These figures are double the umber of observed captured specimes; see text for explaatio. 2Figures are to earest gram.

6 William G. George CATS AS PREDATORS ON RAPTOR PREY related data. The figures for total prey are double the logged prey, divided by four. This assumes the study registered 50 percet of the cats captures-a percetage roughly correspodig to : 1, the average amout of total time the the delivery area was uder observatio for recordig prey; ad 2, the umber of prey items logged i the same year whe the delivery area was uder cotiuous day-ad-ight scrutiy, compared to the umber logged (durig equivalet seasoal ad hourly periods) whe cotiuously scrutiized for lesser amouts of time. Figures are ot available o the rate at which scavegers expuged evidece of uobserved deliveries. If the rate was greater tha I believe, the totals for captured prey give i Table 3 are low. Diural predatio yielded 49.8 percet of the prey items, crepuscular predatio 20.1, ad octural predatio 30.1 percet. Youg cottotails costituted the leadig prey by volume (40 percet). Prairie voles were the prey most frequetly captured, composig more tha 41 percet of all captured vertebrates ad 45 percet of the captured mammals. A total of 33.8 percet of the captured prairie voles, plus 18.1 percet of the pie voles, cotaied fetuses (Table 4)) resultig i the average aual removal of over 251 microtie fetuses. Potetial mammalia prey ot kow to have bee caught icluded all age groups of opossum, mole, short-tailed ad least shrews, muskrat, woodchuck, gray, fox ad flyig squirrels, ad ative carivores. I additio, o adults of chipmuks or cottotails were take, or fetus-bearig bog lemmigs, house mice, ad jumpig mice. TABLE 4 SEX RATIOS AND FETUSES IN PREY OF THREE CATS IN UNION ILLINOIS, COUNTY, SOUTHERN Percetage of dissected specimes Prey Male Female Gravidl Average umber of fetuses Log-osed shrew (N = 10) Easter chipmuk (N = 36) White-footed mouse (N z 34) Souther bog lemmig (N = 23) Prairie vole (N = 152) Pie vole (N = 33) House mouse (N = 13) Meadow jumpig mouse (N = 12) Figures sigify percetage of species sample, ot percetage of females.

7 THE WILSON BULLETIN December 1974 Vol. 86, No. 4 TABLE 5 SEASONAL PERCENTAGE OF PREY CAPTURED IN BROAD DAYLIGHT BY THREE CATS IN UNION COUNTY, SOUTHERN ILLINOIS, IN PlX?y Dec.-Feb. Mar.-May Jue-Aug. Sept.-Nov. Log-osed shrew Easter chipmuk Souther bog lemmig Prairie vole Pie vole House mouse Cottotail Other vertebrates Total Comparative Seasoal Success of Diural Predatio.-Table 5 shows seasoal differeces i the frequecy with which the cats obtaied prey durig the o-twilight diural hours, which is whe most hutig by most hawks occurs. Almost 80 percet of these captures resulted from sprig ad summer predatio, compared to oly 7.4 percet for witer predatio. Other Seasoal Patters of Predatio.-I witer the cats sought prey chiefly durig the six middle hours of the day, hutig loger o clear bright days tha o overcast days, ad hutig little at ight ad o days with both very low temperatures (below 15 F) ad dark skies. I sprig they huted without seemig to cocetrate o a particular period, although hutig less i mid-day ad more ofte i twilight tha before, goig abroad ifrequetly i the middle of the ight. I summer ad fall they avoided mid-day to hut maily i the twilight periods ad at ight. Freezig weather icoveieced them, yet they caught prey durig ad after sow storms ad ice glazes; furthermore they rarely missed a opportuity to hut prey durig light rais ad immediately after heavy rais. Records from 24-hour periods of surveillace of the delivery area afford the oe cosistet meas of gaugig the average umber of combied hours per day the cats devoted to hutig prey. The per day figures were as follows: approximately 14-l-18 hours i sprig; hours i summer; lo-15 hours i fall; ad 8-12 hours i witer (Cat 1 huted little i this seaso). There were oly thirtee 24-hour periods (each i April, May, ad Jue) durig which ay cat was kow to have caught as may as three or more specimes. The greatest umber of prey items kow to have bee caught i a 24-hour period by the combied cats was six, ad oly three such istaces

8 CATS AS PREDATORS ON RAPTOR PREY 391 occurred. The average umber of o-capture days per year was 174, of which over 43 percet occurred i the three witer moths. DISCUSSION The reader who has digested my fidigs ca imagie that a hawk visitig my study site i the witers of was more apt to see a cat tha a rodet. I thik this a prudet speculatio, ad oe that I wish to examie i the cotext of the local cocetratio of Red-tails, Marsh Hawks, ad kestrels i late fall ad witer. Although tedig to iclude fewer participats each year (Graber ad Golde, 1960; Graber ad Graber, 1963)) this buildup occurs aually i souther Illiois. Potetially satisfactory hutig coditios precede the buildup as prey is probably ample ad relatively active (ad vulerable) i the mild climate. Aual sowfall averages oly about 11 i, as agaist 22 to 29 i i the cetral ad orther portios of the state (Rodesiler ad Qutub, 1973). Abset is the deep ad prologed sow cover that to the orth ofte protects microtie rodets, the prey of greatest importace to these witerig raptors throughout the middlewester prairie ad Great Lakes regios. For example, Craighead ad Craighead (1956 j f oud meadow voles (Microtus pesylvaicus) composed 84 to 98 percet of the witer diet of Red-tailed ad Marsh Hawks i Michiga, ad over 50 percet of that of kestrels. My observatios, while limited ad scattered over eight years, suggest that i souther Illiois the primary prey are prairie ad pie voles, which predomiated i the stomach cotets of the oly witerig, locally killed Red-tailed Hawks (3 specimes), Marsh Hawks (2)) ad America Kestrels (2) that I have bee able to examie. Birds of these species, uder observatio from a distace, ofte obtai what appear to be voles withi the geeral area cotaiig the hutig grouds of my cats. However, I believe that withi the cats home rage oly few microties occurred durig the witers of my study. The cats themselves could fid little prey of ay species from December through February. We logged o specimes o 302 of 361 total witer days. I cosider this strikig evidece of scarcity of prey, particularly of microties, which cats detect ad seize with special facility. I have watched cats hutig Microtus, Pearso (1960) commeted. The cosistet success of their vigils beside ruways makes Microtus-hutig seem absurdly easy. Other authors bear this out; for example, Bradt (1949) owed a farm cat that killed approximately 1,200 meadow voles of 1,628 mammals caught i 18 moths. A cat belogig to Toer (1956) usually brought i two or three voles each day. Especially my Cat 3, but also Cat 2, almost surely would have caught more microties i witer if they had bee able. They

9 392 THE WILSON BULLETIN December 1974 Vol. 86, No. 4 both relished microties as food ad showed o icliatio to omit them from their witer diet. O the cotrary, they ate every vole they are kow to have captured i witer. As a demostratio of their commitmet to witer predatio, they icreased their home rage by about 25 percet. Furthermore, all three cats had the advatage of combig familiar terrai o which they had moitored the microtie populatios cotiuously throughout their hutig years; probably each was well-acquaited with the seasoal activity of these prey, at least by the witer of As show i Table 5, the hutig success of my cats rose each sprig (peakig i May ad Jue), declied steeply i fall, ad became almost uggatory i the witer moths. This cycle almost certaily reflected seasoal differeces i desity of the prey, especially of microties. The problem is to kow to what extet the cats, by their predatio i sprig ad summer, cotrolled microtie reproductive cycles the year roud, helpig cause the depressed witer desities. Aually, from March through November, the cats removed from each acre of their combied home rage (25 acres) a average of over 27 mammals-ad-fetuses, of which 22.2 per acre were microties. At the same time, o fewer tha 10 species of warm-blooded ative predators, alog with other kids of evirometal resistece (i.e., litters drowed i dowpours, specimes killed i mowig operatios), presumably reduced the microtie populatios still further. With the arrival of late autum, o-residet hawks may well have bee faced by what amouted, by the, to a ear-completed harvest of microties. Witer Availability of No-microtie Mammals o the Cats Hutig Grouds.-A high proportio of the cats witer hutig was diural-thus closely parallelig the diural patter of hawks. It seems possible that hawks seekig mammalia prey i the same place ad time as the cats would have ejoyed better hutig had the raptors take prey that the cats either shued (moles ad shrews), could ot catch (squirrels, adult cottotails), or feared to attack (adult ative carivores). Eve if this occurred, it is difficult to discover a ample food supply i this list. The squirrels ad cottotails cosisted of few ad wary idividuals that had eluded oe or more seasos of harvestig by sportsme ad ative predators, ad that, i the case of the cottotails bor o the study site, had escaped the cats, which ate much of the aual crops of youg. Few if ay vulerable youg carivores existed o the study site, ad ormally the woodchucks ad chipmuks were i hiberatio. The remaiig potetial prey icluded maily moles, shrews, the few white-footed mice active o dark days ad i twilight periods, ad house mice; the last teded to overwiter i ad aroud buildigs, where they were more available to the cats tha to hawks. As moles sped little time foragig above groud at ay time, especially i witer (Hoffmeister

10 William G. GLVXge CATS AS PREDATORS ON RAPTOR PREY 393 ad Mohr, 1957), the supply of sizeable prey for hawks would appear to have bee cotracted seriously i the absece or uavailability rodets. of microtie I doubt that shrews, weighig oly 2.7 g to 11.6 g o the study site, could have represeted more tha a augmetatio i the diet of Red- tails, although perhaps importat to Marsh Hawks ad kestrels i the ab- sece of other prey. The Prairie Vole As Primary Prey of Hawks ad Cats.-Prairie voles, I be- lieve, would thus typically be the basic mammalia food for witerig buteos, harriers ad kestrels throughout most of souther Illiois. This species fre- quets grassy habitats of may types (Hoffmeister ad Mohr, op. cit.), hauts surface ruways i daylight (except perhaps i the coldest weather), ad has a tedecy to develop strog populatios due to a high reproductive rate (Krebs et al, 1969). ad more limited i distributio, Bog lemmigs ad pie voles are more specialized as well as sporadic i occurrece ad usually ucommo (Hoffmeister ad Mohr, op. cit.). Accordigly, the im- pact of aual cat predatio o the availability pose the pricipal threat to the success of witerig of prairie voles could well hawks i my area of study. Fetus-bearig specimes (Table 4) costituted over oe-third of the prairie voles take by my cats, ad this figure excludes fertilized females i which pregacy was udetected by the methods that I employed. After ivestigatig the itesity ad bioeergetics of carivore (maily cat) predatio o the Califoria vole (Microtus califoricus), Pearso (1964, 1966, 1971) argued that populatio cycles of microtie rodets may be cotrolled by carivores. The data support the theory that carivore predatio durig a crash ad especially durig the early stages of the sub- sequet populatio low determies to a large extet the amplitude ad timig of the microtie cycle of abudace. I other words, if a powerful force of carivores remais active i the habitats of a depleted ad vulerable species of preferred prey, the carivores may check ad overpower the breedig of the prey. Cats that are fed by ma, as were mie, will ievitably remai a sigificat force o their hutig grouds the year roud, i co- trast to ative predators, which ted to icrease ad decrease i a area accordig to the availability of prey. If prey aimals grow scarce or dif- ficult to catch, cats with a guarateed food supply are merely icoveieced, whereas ative predators either must leave for greeer pastures (i.e., hawks) or face upromisig prospects ad eve starvatio (Thompso, 1935; Pearso, 1966; Pitelka, 1961). Krebs et al. (1969) of the prairie vole i souther Idiaa. to be 3540 coducted a two-year study of the cyclic demography They determied maximum desity specimes (ot icludig fetuses ad est litters) per acre, uder more-or-less atural coditios i a favorable habitat, but usually desity was

11 394 THE WILSON BULLETIN December 1!X 4 Vol. 86, No. 4 much lower, ragig from about two to 15 idividuals (of trappable size) per acre. The Idiaa study also foud the prairie vole to be relatively trappable ad thus easily trapped out. Give such vulerability, sprig ad summer reproductio of prairie voles might be curtailed ad its amplitude reduced by cats, as by trappig. This would reduce local populatio levels severely eough that reproductio i the o-witer moths would ot provide a witer abudace of specimes. Work ow i progress at my study site is ivestigatig these ad related problems, which are fraught with the complexities of evirometal relatioships that regulate the desity of species i a give habitat at a give time (see Hollig, 1959, 1965). Meawhile, I thik it is worth emphasizig that the distributio ad umber of cats i rural habitats are regulated less by the carryig capacity of the lad ad evirometal resistece tha by the customs ad eeds of the huma populatio. No oe kows how may cats are hutig prey i ay part of the America coutry side. I recetly received iformatio from 45 of 49 queried wildlife protective agecies o the cotietal distributio ad desity of cats i the U. S.; most expressed a desire to be helpful but oe furished data established by a cat cesus. PROJECTIONS O the assumptio that oe-third of the estimated 31 millio U. S. cats occurs i rural areas, our coutryside cotais 10,333,333 cats. Assumig each such cat catches prey at the same average aual rate ad exploits the same average umber of acres per aimal as the average of my cats, the cats are removig about 5.5 billio rodets ad fetuses ad about 2.5 billio other vertebrates per year from a total of about 26,000 mi.2 These are coservative projectios, for they do ot take ito accout youg rodets that starve to death as a result of predatio o lactatig mothers, or the magitude of predatio by cats that catch most of their ow food ad more completely live off the lad. I terms of whole prey, the food requiremet of oe cat is about 180 g per day, or 65,700 g per year (Howard, 1957; Bouliere, 1962). My cats together did ot satisfy this level durig ay year, or did they i ay exteded period eve i the sprig ad summer moths. Yet may farm cats meet most of their aual food requiremets by predatio, with food subsidies beig give them chiefly durig periods whe their loss of weight ad beggig behavior poit to prey shortages (persoal observatio). SUMMARY A cotiuous study of predatio by three rural cats was coducted i Uio Couty, souther Illiois, from 1 Jauary 1968 through 31 December The results estab-

12 CATS AS PREDATORS ON RAPTOR PREY lished a basis for examiig the possibility that cat predatio may result i depleted witer populatios of microtie rodets ad other prey of Red-tailed Hawks, Marsh Hawks, ad America Kestrels. Although oe of the three cats ever ate prey ad each cat was assured a ample supply of daily food at home, all captured prey. Their combied predatio removed a aual average of vertebrates ad mammalia fetuses from a combied home rage of 22 acres of field habitat ad three acres of woods. By volume, the pricipal prey were o-adult cottotails, by frequecy of captures, prairie voles. Rodets of seve species costituted 81.9 percet of the total combied diural-crepuscular- octural catch, ad over 95 percet of the crepuscular-octural catch. The cats obtaied 92.6 percet of their average aual diural captures betwee 1 March ad 30 November. Their hutig stmcess i witer was very poor, probably as a result of prey shortages that their ow prior predatio may have helped create. It is suggested that whe captures of preferred prey by skillful, experieced cats o their atal hutig grouds sharply declie, the home rage of the cats cotais few such prey for rodet-seekig hawks. ACKNOWLEDGMENTS My wife, Maria, fed the cats ad assisted i every imagiable way to record their activities. I wish particularly to thak her, as well as express my gratitude to Shelly Bleiweis ad Howard Stais, who dissected some of the specimes of prey, ad Clark Casler, Tad Cooper, David Crotty, Maria Fabbri, James Fuller, ad A Thomas, who helped log the captures of prey. LITERATURE CITED AMERICAN HUMANE ASSOCIATION Aimal cotrol survey. Amer. Humae Assoc., Dever. ARBIB, R The blue list of Amer. Birds, 26: BOULIERE, F. B The atural history of mammals. A Kopf, New York. BRADT, G. W Farm cat as a predator. Michiga Coservatio, 18: CRAIGHEAD, J. J. AND F. C. CRAIGIIEAD, JR Hawks, owls ad wildlife. Stackpole, Harrisburg, Pa. EBERHARD, T Food habits of Pesylvaia house cats. J. Wildlife Mgmt., 18: ERRINGTON, P. L, Notes o food habits of souther Wiscosi house cats. J. Mammal., GRABER, R. AND J. S. GOLDEN Hawks ad owls: populatio treds from Illiois Christmas couts. Ill. Nat. Hist. Survey, Biol. Notes, No. 41. GRABER, R. R. AND J. W. GRARER A comparative study of bird populatios i Illiois, ad Ill. Nat. Hist. Survey, Bull., 28: HOFFMEISTER, D. F. AND W. M. MOHR Fieldbook of Illiois mammals. Ill. Nat. Hist. Survey Div., Maual 4. HOLLING, C. S The compoets of predatio as revealed by a study of small mammal predatio of the Europea pie sawfly. Caadia Et., 91: HOLLING, C. S The fuctioal respose of predators to prey desity ad its role i mimicry ad populatio regulatio. Et. Sot. of Caada, Mem. No. 45. HOWARD, W. E Amout of food eate by small carivores. J. Mammal., 38:

13 396 THE WILSON BULLETIN December 1974 vol. 86. No. 4 HUBBS, E. L Food habits of feral house cats i the Sacrameto Valley. Calif. Fish ad Game, 37 : KORSCHGEN, L. L Food habits of coyotes, foxes, house cats ad bobcats. Mis- souri Comer. Comm., Bull. No. 15. KREBS, C. J., B. L. KELLER, AND R. H. TAMARIN Microtus populatio biology: demographic chages i fluctuatig populatios of M. ochroguster ad M. pesyl- vaicus i souther Idiaa. Ecol., 50: LAYNE, J. N Notes o mammals of souther Illiois. Amer. Midl. Nat., GO: LLEWELLYN, L. M. AND F. M. UIILER The foods of fur aimals of the Paxtuxet Research Refuge, Marylad. Amer. Midl. Nat., 48: MACATEE, W. L Food habits of commo hawks. U. S. Dept. Agric., Circ MAY, J. B The hawks of North America. Nat. Assoc. Audubo Sot., New York. MCMURRY, F. B. AND C. C. SPERRY Food of feral house cats i Oklahoma, a program report. J. Mammal., 22:18s190. PARMALEE, P. W Food habits of the feral house cat i east-cetral Texas. J. Wildlife Mgmt., 19: PEARSON, 0. P. Carivore-mouse predatio: a example of its itesity ad bioeergetics. J. Mammal., 45: PEARSON, 0. P The prey of carivores durig oe cycle of mouse abudace. J. Aim. Ecol., 35: PEARSON, 0. P Additioal measuremets of the impact of carivores o Cali- foria voles (Microtus califoricus). J. Mammal., 52: PITELKA, F. A Ecology of lemmigs ad other microties i orther Alaska. Arctic Ist. of North America, Report RODESILER, J. AND M. QUTUB Precipitatio i Illiois. Tras. Ill. Acad. Sci., 66: THOMPSON, D. Q Ecology of the lemmigs. Arctic Ist. of North America, Fial report. TONER, G. C House cat predatio o small mammals. J. Mammal., 37:119. DEPARTMENT OF ZOOLOGY, SOUTHERN ILLINOIS UNIVERSITY, CARBONDALE, ILLI- NOIS ACCEPTED 18 MARCH 1974.