The VViiion Journal of Ornithology 123(2):332-338, 2011

INTERACTIONS OF RAPTORS AND LESSER PRAIRIE-CHICKENS ATLEKS IN THE TEXAS SOUTHERN HIGH PLAINS

ADAM C. BEHNEY,'^ CLINT W.HEATHER A. WHITLAW,' "̂ AND DUANE R. LUCIA' '

ABSTRACT.—We examined behavioral interactions of raptors, Chihuahuan Ravens (Corvus cr\pioleucus), and LesserPrairie-chickens {Tympamwlms pallidicinchis) at leks in the Texas Southern High Plains. Northern Harriers (OVCM.S-c\aneus) and Swainson's Hawks (Buteo swainsoni) were the most common raptors observed at leks. Only 15 of 61 (25%)raptor encounters at leks (0.09/hr) resulted in a capture attempt tO.O2/hr). Mean ( ± SD) time for Lesser Prairie-Chickens toreturn to lekking behavior following a raptor encounter was 4.2 ± 5.5 min suggesting the disturbance had little inliuencc onlekking behaviors. Lesser Prairie-Chickens engaged in different escape behaviors depending on raptor species and.generally, did not respond to ravens suggesting they are able to assess different prédation risks. The raptors in our study areaposed little prédation risk to lekking prairie-chickens. Behavioral disturbance at leks appears minimal due to the lack ol'successful prédation events, low raptor encounter rates, and short time to return to lekking behavior. Received 22 Aiii^tisl2010. Accepted 3 January 2011.

Lesser Praitie-Chicken {Tympanuchus pallidi-cinctus) populations have declined throughoutmuch of their historic range (Crawford and Bolen1976, Hagen et al. 2004). Taylor and Guthery(1980) cstitnated that >90% decrease had oc-curred in their occupied range since the 1800s.Currently, small populations exist in parts ofColorado, Kansas, New Mexico, Oklahoma, andTexas (Hagen and Giesen 2005). The populationdecline has resulted in Lesser Prairie-Chickensbeing designated as a candidate species by theU.S. Fish and Wildlife Service for protectionunder the Endangered Species Act of 1973 (USDI2008).

Lekking species may be more susceptible toprédation as they are congregated, focused ontuating, and exposed (Hartzler 1974). Lehmann(1941:39) stated that "Prairie chickens on thecourtship grounds seemed more intent on matingthan on self-preservation; consequently, lossesfrom prédation were probably heaviest at mating

' Texas Cooperative Fish and Wildlife Research Unit.Department of Natural Resources Management, Texas TechUniversity. Lubbock. TX 79409. USA.

"U.S. Geological Survey. Texas Cooperative Fish andWildlife Research Unit. Department of Natural ResourcesManagement. Texas Tech University, Lubbock, TX 79409,USA.

'Texas Parks and Wildlife Department. Luhbock. TX79415, USA.

^Current address: Cooperative Wildlife Research Labo-ratory. Southern Illinois University, Carbondale. IL 62901,USA.

' Current address: U.S. Fish and Wildlife Service, TexasTech University. Lubbock, TX 79409. USA.

"Corresponding author; e-mail: clint.boalfe'ttu.edu

time." Wolfe et al. (2007) reported male mortalitywas highest during peak lekking activity andsuggested the cause may be male conspicuousnessand/or predators focusing on lekking activity,although they did not report how many tnaleswere actually killed on leks. Schroedcr andBaydack (2001) speculated that habitat degrada-tion at prairie grouse leks may have exacerbatedprédation risks. Few studies, however, haveinvestigated prédation on North American prairiegrouse leks (e.g.. Berger et al. 1963, Hartzler1974, Boyko et al. 2004) and no study hasspecifically identified prédation on leks as a majorsource of mortality.

Direct prédation and disturbance of breedingactivities may limit reproduction of birds (Cress-well 2008). Baydack and Hein (1987) reportedfemale Sharp-tailed Grouse (T. phasiaiictlus)avoided disturbed leks (e.g., presence of humans,dogs, vehicles, snow fences, propane exploders,scarecrows, and tadio noises). Alternatively,congregation of birds at leks may teduce préda-tion risk due to increased probability of detectinga predator before it becomes a serious threat. Theprédation risk for each individual decreases as thenumber of individuals in a group increases, aslong as prédation events do not increa.se as well(Boyko et al. 2004). Flushing as a group mayconfuse a predator and make it harder to select anindividual (Lack 1968, Wittenberger 1978). Leksare generally in the same location year after year,possibly because they have proven to be .safe inthe pa.st (Lack 1968).

Raptors have been identified as predators ofLesser Prairie-Chickens (Campbell 1950, Haukos

332

Behney et al. • RAPTOR AND LESSER PRAIRIE-CHICKFN INTERACTIONS 333

1988, Haukos and Broda 1989, Hagen and Giesen2005, Hagen et al, 2007, Wolfe et al, 2007),Specific to our study area. Northern Harriers{Circus cyaneus) have been observed predatingLes.ser Prairie-Chickens in eastem New Mexico(Campbell 1950) and the Texas Southern HighPlains (Haukos and Broda 1989). Our objectiveswere to exatiiine; (1) encounter rates and inci-dences of raptor prédation at Lesser Prairie-Chicken leks, and (2) behavioral responses ofprairie-chickens to different raptor species andChihuahuan Ravens {Cor\'us cryptoleucus) at leksin the Texas Southern High Plains,

MFTHODS

Study Area.—Our study occurred on privatelands in Cochran and Yoakum counties in theTexas Southern High Plains ecoregion (LlanoEstacado). The topography is tlat to gentlyutidulating with small vegetated dunes. Thedominant vegetation in most areas was shinneryoak (Qiiercus havardii) intermixed with sandsagebrush (Artemisia filifolia) and grasses. Themajor land use in this area was agriculture with ahigh proportion of the area under intensivecultivation and cattle production. Oil developmentoccurred throughout the study area with YoakumCounty producing 23,730,647 barrels of oil in

2007 (Railroad Commission of Texas 2010).Field Methods.—We used a combination of

direct observation and video-recording to monitorraptor-Lesser Prairie-Chicken encounters at leksduring spring 2007 and 2008, We used four leksknown by landowners and Texas Parks andWildlife Department staff in 2007, and includedthree new leks located by roadside surveys in2008 (Behney 2009), We excluded two of the2007 leks due to logistical constraints in 2008,Direct observations were conducted from small,camouHaged, pop-up style blinds placed amongvegetation at the edge of the lek, or from a vehicleparked within 15 m of the lek. We arrived at leksbefore prairie-chickens were present; typically> 1.5 hrs before sunrise and remained stationaryfor the duration of the obsetvation period. Weused binoculars and spotting scopes to monitorprairie-chickens and identify predators. We didnot depart the lek until 20 min after the la.stprairie-chicken departed each morning.

We placed two video-recording systems at eachlek being video-monitored. One system wasplaced sufficiently far from the lek to ensure theentire area was recorded (far) and the second

system was placed close to or zoomed in (close) torecord behaviors of grouse and predators. Thiscamera arrangement was not possible on one lekand we used two camera systems placed the samedistance frotn the lek but at different angles.

Each video-recording .system consisted of asecurity style camera connected to a video camerarecorder (VCR) or digital video camera recorder(DVDR), Camera systems were powered by a 12-volt deep-cycle marine battery connected to apower inverter, and enclosed in weatherproofhousing, A power strip was connected to theinverter, into which the VCR and the securitycatnera were connected. The VCR or DVDRrecorded real-time video to facilitate identificationof fiying raptors and behavior of prairie-chickens.

Recording occurred 2-4 days/week at each lek.We recorded lek activities frotn 0,5 hrs beforesunri.se to 2-A hrs post-sunrise and from 2 hrsbefore sunset to 0,5 hrs after sunset. All tape andbattery changes were at mid-day ( 1100-1400 hrs)when prairie-chickens were not present to mini-mize risk of disturbance. We used an editing VCRto review the collected video footage of activitiesat leks. We initially viewed the far camerarecordings to identify behaviors (predator, flush-ing, disturbance) and then viewed the close uptape for a more in-depth view. We reviewed bothtapes completely in the case where two cameraswere placed the sarne distance from the lek.

We noted the time, date, lek, species, age (ifpossible), raptor approach type, and prairie-chicken response type if a raptor or raven wasobserved. The raptor or raven had to be within35 m of the lek (visually estimated) to be includedin the analysis. At this distance the raptor or ravenand Lesser Prairie-Chickens should have beenable to see each other. We classified raptors to thelowest taxonomic level possible when we couldnot identify the raptor species. We pooledPeregrine Falcon {Falco peregrinus). PrairieFalcon {F. mexicantis). Merlin {F. columbarius),and unknown falcons {Falco spp,) in a "falcon""group and Red-tailed Hawk {Buteo jamaicensis).Ferruginous Hawk {B. regalis), and unknownbuteos {Buteo spp,) in a "buteo" group. Wepooled Cooper's Hawks {Accipiter cooperii) andSharp-shinned Hawks {A. striatu.s) into an "ac-cipiter" group.

Statistical Analysis.—Raptor approach typeswere classified as prédation attempt, course,perch, or fly-by, "Prédation attempts" wereobvious dives at or chases of Les,ser Prairie-

334 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 2. June 2011

Chickens. "Coursing" was a low, slow glide overthe landscape in search of prey, typical ofNorthern Harriers. "Pereh" was noted any timea raptor landed in view of the camera, and a "fiy-by" was when the raptor paid no apparentattention to prairie-chickens as it flew over.Responses of prairie-chickens to raptors andravens were categorized as no response, squat,partial fiush, or flush. We considered a raptor/raven-prairie-chicken encounter as eliciting "noresponse" if we could not observe any alterationin behavior of the grouse when the encounteroccurred. "Squat" consisted of seeking cover orflattening against the ground. "Partial flush"consisted of at least one but not all prairie-chickens flushing from the lek, and "flush"occurred when every grouse on the lek fiushed.

We noted the time when lekking behaviorceased to when at least two Lesser Prairie-Chickens returned to lekking behavior. Raptorencounter rates were calculated by dividing thenumber of raptors observed at leks by the hours oflek observation or recording during which prairie-chickens were present. We used an exact rate ratiote.st assuming Poisson counts in Program R tocompare raptor encounter rates (R DevelopmentCore Team 2008, Eay 2009).

We used a G-test for goodness of fit to comparefrequency of occurrence of different raptorspecies observed at leks to the overall raptorcommunity in the area following Sokal and Rohlf(1995). We used frequency of occurrence at leksby Swainson's Hawks, Northem Harriers, falconspecies, and buteo species (not including Swain-son's Hawks) as observed values. Expected valueswere computed from data collected duringstandardized raptor surveys in the area (Behney2009). Only surveys conducted during Eebruary,March, and April were included and were pooledover years. The total number of each raptorspecies or species group observed during surveyswas divided by the total number of all raptorsrecorded during surveys. We then multiplied thisproportion by the total number of raptors observedat leks to sum to the same total as raptors seen atleks, while maintaining the same proportion ofeach species/species group.

We used Chi-square tests of independence(Conover 1999) to assess independence amongapproach, species, and response. We also used aChi-square test to assess differences in behavioralresponse of Lesser Prairie-Chickens to raptorencounters compared to raven encounters. We

used a Kruskall-Wallis test (Conover 1999) tocompare prairie-chickens return times associatedwith different raptor species because the data werenot normally distributed. We categorized thelekking season into five 2-week intervals to assesstemporal variations in encounter rates and speciesdynamics: 1 = 9 to 22 March, 2 = 23 March to 5April, 3 = 6 to 19 April, 4 = 20 April to 3 May,and 5 = 4 to 17 May.

RESULTS

Raptor Encounter Rates.—We conducted 155 hrsof direct observation at seven leks while LesserPrairie-Chickens were present between 24 Februaryand 21 May 2007 and 2008. We observed 21 raptorsand 37 ravens on or near leks while prairie-chickenswere present. We recorded 495 hrs of real-timevideo footage on seven leks while prairie-chickenswere present from 3 April through 9 June 2007 and8 March through 22 May 2008. We observed 40raptors and 104 ravens on or near leks while prairie-chickens were present during the video recordings.There was no difference in encounter rates betweenviewing platform (direct observations = 0.14raptors/hr, video = 0.08 raptors/hr; P = 0.08) andthe data were pooled (overall = 0.09 raptors/hr).Study leks averaged 12.3 males (range = 6-19).We did not observe any successful prédation eventson the video or through direct observations.

Northern Harriers (n = 30) were the mostcommonly observed raptor at leks followed bySwainson's Hawks (n = 11), other buteos (n = 9),falcons (n = 5), and accipiters (/i = 2). We wereunable to identify five raptors to the genus level.We observed one additional Peregrine Falconencounter at a lek during direct ob.servations butfailed to note the time Lesser Prairie-Chickensdeparted the lek and were unable to assess theduration of lek attendance by prairie-chickens thatmoming. This encounter was included in behav-ioral analyses but not in encounter rate calcula-tions. Encounter rates peaked during the second 2-week interval and steadily decreased to theirlowe.st rates during the la.st interval (Fig. I).Proportions of individual raptor species or speciesgroups at leks diverged from that expected basedon the observed raptor community (Xr = 45.4, P< 0.001). More Northem Harriers (contribution tooverall G-statistic = 28.92), fewer Swainson'sHawks (-12.08), and more falcons (8.20) wereobserved at leks than expected based on the raptorcommunity present in the area.

Behney et al • RAPTOR AND LESSER PRAIRIE-CHICKEN INTERACTIONS 335

Jo,

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LU

Northern HarrierSwainson's HawkOther or unknown ButeoFemale LEPC

" • • • . . ,

• • - , _

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Two-week intervalFIG. 1. Species and species group-specific raptor encounter rates (birds/hr) and female Lesser Prairie-Chieken

visitation rate (females/day) for 2-week intervals throughout the lekking season in the Texas Southern High Plains, 2007-2(X)8. Two-week interval start dates were: I = 9 March. 2 = 23 March. 3 = 6 April, 4 = 20 April, and 5 = 4 May.

Raptor Approach Types.—Coursing was themost commonly observed approach type (44% ofencounters) used by raptors, followed by perching(24%), fiy by (16%), and prédation attempt(16%). We detected 15 prédation attempts onLesser Prairie-Chiekens, primarily by NorthernHarriers {n = 7), Swainson's Hawks (n = 3), andfalcons (n = 2). Accipiters, other buteos, andunknown raptors accounted for one prédationattempt each. Northern Harriers were the mostcommon raptor ob.served coursing whereas buteohawks were more commonly seen perching.Approach type was related to raptor species {Xf,'= 17.25, P = 0.008). Northern Harriers perched

less than expected, Swainson's Hawks attemptedto prey upon prairie-chickens more than expected,and other buteos perched more than expected.

Lesser Prairie-Chicken Response Types.—Some or all Lesser Prairie-Chickens fiushed in62% of all raptor encounters. However, prairie-chicken response was as.sociated with raptor type(Northern Harrier, buteo, or falcon; Xf,' = 14.5, P= 0.02). Harriers and buteos were more likely toelicit fiushing responses (75 and 73% of allrespon.ses, respectively). In contrast, three of fivefalcon encounters elicited squat responses fromprairie-chickens (Fig. 2). This is likely a lowestimate because fiushes often occurred only after

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FIG. 2. Les.ser Prairie-Chicken response to Northern Harriers (n = 30), buteos (including Swainson's Hawks, n = 20),and falcons (n = 5) encountered at leks in the Texas Southern High Plains, 2007-2008.

336 THE WILSON JOURNAL OF ORNITHOLOGY • Vol 123. No. 2, June 2011

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FIG. .•?. Lekking behavior return time for at least two Lesser Prairie-Chickens following an accipiter. other or unknownbuteo, falcon. Northern Harrier. Swainson's Hawk, and unknown raptor encounters at leks in the Texas Southern HighPlains. 2007-2008. Boxes represent interquartile range about the median. Whiskers represent the most extreme datum pointthat is no more than the range x the interquartile range from the box. A.sterisks represent outliers in the data.

falcons repeatedly dove at prairie-chickens. Theinitial response in all falcon encounters was forprairie-chickens to .squat and stay on the ground;however, after repeated swoops by the falcon, afew eventually flushed in two encounters andwere recorded as partial flushes.

Lesser Prairie-Chickens are apparently able todifferentiate risk posed by different avian preda-tors and respond accordingly. Raptors elicitedsome type of response in 85% of encounterswhereas only 9% of raven encounters elicited aresponse (X,' = 138, P < 0.001). Mean (± SD)time for at least two prairie-chickens to bedisplaying at leks following a raptor encounterwas 4.22 ± 5.5 min. Return times were differentfollowing encounters involving different raptorspecies (Kru.skal-Wallis Rank Sum Test, X5- =11.895, P = 0.036; Fig. 3).

DISCUSSION

Sage- and prairie grouse spend a substantialamount of time on leks (typically 3-4 hrs/day,Hagen and Giesen 2005) during the spring. Theircongregation and exposure could lead to increasedprédation risk (Lehtrtann 1941, Hartzler 1974,Schroeder and Baydack 2001). Our data suggestraptor prédation on Lesser Prairie-Chickens atleks is uncommon. We did not observe anysuccessful prédation events at leks despite 650 hrsof data from when Lesser Prairie-Chickens wereon leks.

Our results are similar to those from otherstudies of lekking species as successful prédation

events on leks were rare or absent (Berger et al.1963, Moran 1966, Haukos and Broda 1989).Encounters classified as prédation attempts in ourstudy were rare (0.02 attempts/hr). This suggestsuse of a lek mating system tnay limit prédationevents and may be an efficient anti-predatorstrategy (Boyko et al. 2004).

Northern Harrier encounters peaked during the2-week interval of 23 March to 5 April, afterwhich they began migrating from the study area(Fig. 1; Behney 2009). Buteonine hawk encoun-ters were low throughout the lekking season butpeaked during the interval starting 6 April, whichcorresponded to migrants moving through the areawhile some wintering hawks were still present(Behney 2009, Preston and Beane 2009). Swain-son's Hawk encounters were low throughout theseason but peaked during the interval starting 20April. This corresponded to arrival of Swainson'sHawks migrating from the southern hemisphere(England et al. 1997, Behney 2009) and estab-lishment of breeding territories in the study area.The period of peak female attendance at lekscorresponded to dramatic decreases in raptorencounters at leks (Fig. I). Haukos (1988)reported a similar observation that peak femaleLesser Prairie-Chicken attendance at leks oc-curred just after most raptors had migratedthrough the area.

Lesser Prairie-Chicken responses to prédationattempts appear to correspond to the huntingstrategies of different raptor species. NorthernHarriers and buteo hawks (including Swainson's

Behney et at. • RAPTOR AND LESSER PRAIRIE-CHICKEN INTERACTIONS 337

Hawks) typically capture prey on the ground andwould likely have difficulty overtaking andcatching a prairie-chicken in the air (Macwhirterand Bildstein 1996, England et al. 1997). Theseraptor species elicited more flushing responsesfrom prairie-chickens. Falcons evolved to over-take and capture prey in the air (Webster 1944,White 1962), and elicited more of a .squattingresponse and an observable hesitancy to flush byprairie-chickens. This suggests Lesser Prairie-Chickens are able to assess the threat posed bydifferent raptors species and have evolved theappropriate behavioral re.sponse.

We are confident we detected all raptorprédation attempts on Lesser Prairie-Chickens atleks during monitoring and video-recording peri-ods. However, it is possible that we missed someraptor fly-bys or coursing that occurred behind orover the blind or camera. We believe any observereffect on raptor presence or behavior was minimaldue to the small size of the blind, our arrival wellbefore sunrise, and that we remained stationarythroughout the ob.servation period. Encounterrates were higher for direct observation thanvideo-recording, suggesting observer presencewas not inhibiting raptor presence.

Raptors were not a source of mortality ormarked disturbance of Lesser Prairie-Chickenswhile on leks in our study. This suggests mortalityof lekking Lesser Prairie-Chickens from raptorprédation is not a factor contributing to populationdeclines.

ACKNOWLEDGMENTS

We thank Texas Parks and Wildlife Department forluiullng this research. The USGS Texas Cooperative Fishand Wildlife Research Unit, and the Department of NaturalResources Management at Texas Tech University alsocontributed necessary resources. This research was con-ducted in accordance with Texas Tech University animaluse protocol T06043-09. We Ihank D. A. Haukos and M. J.Butler Tor suggestions and contributions throughout thisresearch. A. D. Apa, M. D. Giovanni, C. A. Hagen, T. A.Messmer, C. E. Braun, and an anonymous reviewerprovided helpful comments on earlier versions of ourmanu.script.

LITERATURE CITED

BAYDACK, R. K. AND D. A. HEIN. 1987. Tolerance of

Sharp-tailed Grouse to lek disturbance. WildlifeSociety Bulletin 1.5:535-539.

BKHNKY, A. C. 2009. Prédation and reproductive behaviorof Lesser Prairie-Chickens at leks in the TexasSouthern High Plains. Thesis. Texas Tech University,Lubbock. USA.

BERGER, D. D., F. HAMERSTROM, AND F. N. HAMERSTROM

JR. 1963. The effect of raptors on Prairie Chickens onbooming grounds. Journal of Wildlite Management27:778-791.

BOYKO, A. R., R. M. GtB.soN, AND J. R. LUCAS. 2004. Howprédation risk affects the temporal dynamics of avianleks: Greater Sage-Grouse versus Golden Eagles.American Naturalist 163:1.54-165.

CAMPBKt.t., H. 1950. Note on the behavior of Marsh Hawkstoward Lesser Prairie Chickens. Journal of WildlifeManagement 14:477^78.

CONOVER, W. J. 1999. Practical nonparametric statistics,John Wiley and Sons, New York, USA.

CRAWFORD, J. A. AND E. G. BOLEN. 1976. Effects of landuse on Lesser Prairie Chickens in Texas. Journal ofWildlife Management 40:96-104.

CRESSWEt.t,. W. 2008. Non-lethal effects of prédation inbirds. Ibis 15O:.1-I7.

ENGLAND, A. S., M. J. BKCHARD. AND C. S. HOU.STON.

1997. Swainson's Hawk (Buteo swainsoni). The birdsof North America. Number 265.

FAY. M. 2009. Package rateratio.test: exact rate ratio test. Rpackage Version 1.0-1. http://CRAN.R-project.org/package=rateratio.test

HAGEN, C. A. AND K. M. GIESEN. 2005. Lesser Prairie-Chicken (Tympanuchus pallidicinctus). The birds ofNorth America. Number 364.

HAGHN, C. A., B. E. JAMISON, K. M. GtbsbN, AND T. Z.

RiLEY. 2004. Guidelines for managing Lesser Prairie-Chicken populations and their habitats. WildlifeSociety Bulletin 32:69-82.

HAGEN, C. A., J. C. PITMAN, B. K. SANDKRCXK K. R. J. ROBEL,

AND R. D. Appt.EGATE. 2007. Age-spccific survival andprobable cau.ses of mortality in female l^s.ser Prairie-Chickens. Journal of Wildlife Management 71:518-525.

HARTZLER, J. E. 1974. Prédation and the daily timing ofSage Grouse leks. Auk 91:532-536.

HAUKOS, D. A. 1988. Reproductive ecology of LesserPrairie Chickens in We.st Texas. Thesis. Texas TechUniversity, Lubbock, USA.

HAUKOS, D. A. AND G. S. BRODA. 1989. Northern Harrier(Circus cyaneus) prédation of Lesser Prairie Chicken(Tympanuchus pallidicinctus). Journal of RaptorResearch 23:182-183.

LACK, D. 1968. Ecological adaptations for breeding inbirds. Chapman and Hall. London. United Kingdom.

LEHMANN, V. W. 1941. Auwater's Prairie Chicken, its lifehistory and management. USDI. Fish and WildlifeService. North American Fauna 57.

MACWHtRTKR, R. B. AND K. L. Btt.txsTEiN. 1996. NorthernHarrier (Circus cyaneus). The birds of North America.Number 210.

MORAN, R. J. 1966. Prédation on a Greater Prairie Chickenby a Goshawk. Auk 83:137.

PRESTON, C. R. AND R. D. BEANE. 2009. Red-tailed Hawk(Buteo jamaicensis). The birds of North America.Number 52.

R DEVELOPMENT CORE TEAM. 2(X)8. R: A language and

environment for statistical computing. R Foundationfor Statistical Computing, Vienna. Austria, http://www.R-project.org.

338 THE WILSON JOURNAL O F ORNITHOLOGY • Vol 123. No. 2, June 2011

RAILROAD COMMISSION OF TEXAS. 2010. Oil and gas

production data. http://webapps.rrc.state.tx.us/PDQ/change Vie wReport Action.do?viewType = MonthlyTotals

SCHROEDER, M. A. AND R. K. BAYDACK. 2001. Prédationand the management of prairie grouse. WildlifeSociety Bulletin 29:24-32.

SOKAL, R, R. AND F. J. ROHLF. 1995. Biometry: theprinciples and practice of statistics in biologicalresearch. Third Edition. W. H. Freeman and Co.,New York, USA.

TAYLOR, M. A. AND F. S. GUTHERY. 1980. Status, ecology,and management of the Lesser Prairie Chicken, USDA,Forest Service, General Technical Report RM-77.Rocky Mountain Station, Fort Collins, Colorado, USA.

U.S. DEPARTMENT OF INTERIOR (USDI) . 2008. Endangered

and threatened wildlife and plants; review of nativespecies that are candidates for listing as endangered orthreatened. Federal Register 73:7,S 176-75244.

WEBSTER JR., H, 1944. A survey of the Prairie Falcon inColorado. Auk 61:609-616.

WHITE, C. M. 1962. Prairie Falcon displays accipitrine andcircinine hunting methods. Condor 64:440—441.

WiTTENBERGER, J. F. 1978. The evolution of matingsystems in grouse. Condor 80:126-137.

WOLFE, D, H., M, A. PATTEN, E, SHOCHAT, C. L. PRUETT,

AND S. K. SHERROD. 2007. Causes and patterns ofmonality in Lesser Prairie-Chickens Tympamtchuspallidicinctus and implications for management.Wildlife Biology 13:95-104.

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