Aplomado Falcon Abundance and Distribution in the Northern Chihuahuan Desert of Mexico

THE JOURNAL OF RAPTOR RESEARCH A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC.

VOL. 38 JUNF,2004 NO. 2 j Raptorlies. 38(2):107-117 ¸ 2004 The Raptor ResearchFoundation, Inc.

APLOMADO FALCON ABUNDANCE AND DISTRIBUTION IN THE NORTHERN CHIHUAHUAN DESERT OF MEXICO

KENDAL E. YOUNG 1 AND BRUCE C. THOMPSON 2 NewMexico Cooperative Fish and WildliJbResearch Unit and Fisheryand Wildli? SciencesDepartment, Box 30003, MSC 4901, New MexicoState University, Las Cruces,NM 88003 U.S.A.

ALBERTO LAF(SN TERRAZAS Facultad de Zootecnia, UniversidadAut6noma de Chihuahua, Chihuahua, Mexico

ANGEL B. MONTOYA ThePeregrine Fund, Boise,11) 83709 U.S.A.

RAUL VALDEZ Fisheryand WildliJkSdences Department, Box 30003, MSC 4901, NewMexico State University, Las Cruces,NM 88003 U.S.A.

AnSTRACT.--Thenorthern Aplomado Falcon (Falcofemoralis septentrionalis) historically occupied coastal prairies, savannas,and desert grasslandsfrom southern Mexico north to southern and southwestern Texas,southern New Mexico, and southeasternArizona. Current residentAplomado Falconpopulations are primarily in Mexico, with isolatedpopulations in southernTexas and from northern Chihuahuato southern New Mexico. We conductedsurveys in semidesertgrasslands/savannas and associatedhabitats in northern Chihuahua to locate Aplomado Falconsand to better delineate their distribution and abundancein the northern Chihuahuan Desert during 1998-99. Data were collectedby surveyinglarge tracts,transects in nonrandomlyselected grasslands, and from a falcon monitoring study.Based on all surveyeffort, the minimum knownpopulation of adult Aplomado Falconsin the studyarea in northern Chihuahua was79 individuals.Aplomado Falconswere primarily associatedwith grasslandcommunities. Most falcon nests (88%) were found in grasslandcommunities with soaptreeyucca (Yuccaelata) or Torrey yucca (Y. torreyi).Aplomado Falconswere found fairly clusteredin the north-centralto north- eastern part of the study area. We found falcons nesting ca. 50 km west of the Texas border (ca. 120 km south of E1 Paso) in northern Chihuahua. BecauseAplomado Falconsare associatedwith grassland communities,continued degradationof Chihuahuan Desert semidesertgrasslands will continue to in- fluence their distribution.

KEYWORDS: AplomadoFalcon; Falco femoralis; ChihuahuanDesert;, Chihuahua, Mexico; distribution.

ABUNDANCIA Y DISTRIBUCION DEL HALCON PERDICERO EN EL DESIERTO NORTElqO DE CHIHUAHUA EN MEXICO RESUMEN.--E1Halc6n perdicero del norte (Falcofemoralis septentrionalis) hist6ricamente ha ocupado praderascosteras, sabanas, y pastizalesdes6rticos desde M6xico meridional al notre, hastael sur y sur occidente de Texas, el sur de Nuevo Mfxico y el sur oriente de Arizona. Las poblacionesresidentes actualesdel halc6n perdicero se encuentran principalmente en M6xico, con poblacionesaisladas en el

E-mail address:[email protected] Presentaddress: New Mexico Department of Game and Fish, P.O. Box 25112, SantaFe, NM 87504 U.S.A.

107 108 YOUNG ET AL. VOL. 38, NO. 2

sur de Texas y desde el Chihuahua del norte hasta el sur de Nuevo Maxico. Conducimos esmdiosen pastizales/sabanassemides6rticas y h/tbitatsasociados en el Chihuahua del norte para localizarHalcones perdicerosy para hacer un mejor bosquejode su distribuci6ny abundanciaen el DesiertoNortefio de Chihuahua durante 1998-99. Los datos fueron colectadosestudiando distanciaslargas por medio de transeptosen pastizalesseleccionados (no al azar) y a partir de un estudio de monitoreo de halcones. Con base en todo el esfuerzo de estudio, la poblaci6n mfnima conocida de halconesperdiceros adultos en el/trea de estudioen el norte de Chihuahuarue de 79 individuos.Los halconesperdiceros estuvieron asociadosprincipalmente con comunidadesde pastizales.La mayoria de los nidos de halc6n (88%) rueton encontradosen comunidadesde pastizalescon firbolesde yucca (Yuccadata) o yuccaTorrey (Y. torreyi).Los halcones perdiceros se encontraron ligeramente concentrados en la parte norcentral a nororiental de la zona de estudio. Encontramos halcones anidando aproximadamente 50 kmal occidente de la frontera de Texas (ca. 120 km al sur de E1 Paso) en el Chihuahua del norte. Debido a que los halconesperdiceros estrin asociados con comunidadesde pastizales,la continua degradaci6nde los pastizalessemides•rticos del Desierto de Chihuahua continuar•tinfiuenciando su distribuci6n. [Traducci6n de C•sar M•rquez]

The northern Aplomado Falcon (Falcofemoralis R. Meyer, C. Perez, and S. Williams III unpubl. septentrionalis)occupied coastalprairies, savannas, data). Early reports in the northern Chihuahuan and desert grasslandshistorically from southern Desert indicated Aplomado Falconswere found in Mexico north to southern and southwestern Texas, open plains with sparsewoody vegetation (e.g., southern New Mexico, and southeastern Arizona Bendire 1892, Visher 1910, Bailey 1928, Ligon (Oberholser 1974, American Ornithologists' 1961). Specimen records and documented sight- Umon 1998, Keddy-Hector2000). In Mexico, Aplo- ings indicated that falconswere common through- mado Falconshistorically occurred along the east out their range in the U.S. until ca. 1930 (Bent coastfrom Tamaulipasto Yucatfm,and along the 1938, Hector 1987). Arnold Bay•lelocated the last west coastin lowlandsfrom Sinaloa and Nayarit to known historical falcon nest in southern New Mex- Oaxaca (Lawrence 1874, Cade et al. 1991, Keddy- ico in 1952 (Ligon 1961). The lastknown historical Hector 2000; Fig. 1). The U.S. Fish and Wildlife falcon nest in southeasternArizona was pre-1940s Service (1990) and Howell and Webb (1995) sug- (Phillipset al. 1964, Monson and Phillips 1981). gestedthat Aplomado Falconsoccurred through- There were occasionalAplomado Falcon sight- out the northern Mexican Plateau. However, the ingsin the GhihuahuanDesert in the 1960s,1970s, lack of documented occurrences leaves the falcon's and 1980s; however, these sightingswere usually historical distribution in the Chihuahuan Desert discountedbecause the specieswas believed to be and elsewhere in interior northern Mexico un- extirpated from the Ghihuahuan Desert. Williams clear. Aplomado Falcon reports in Durango are and Hubbard (1991) considered the origin of an limited to one falcon sightedin 1950 at high ele- Aplomado Falcon photographedin southernNew vation in a pine forest westof Durango City (Web- Mexico in 1991 a mystery,citing falcons in the sa- ster and Orr 1952). There were no documented vannas of Veracruz as the closestknown popula- reports of Aplomado Falconsin Sonora pre-1966 tion. The resident population in northern Ghihua- (Van Rossem 1945, Russell and Mortson 1998). Al- hua was not discovered until 1992. den (1969) and Gallucci (1981) reported falcon Gutrent resident northern Aplomado Falcon sightingsin Sonora in 1966 and 1979; however, populationsare primarily in Mexico (Fig. 1). Ex- Russelland Mortson (1998) claimed these sightings tant populationsexist along the Gulf of Mexico to were unsubstantiated. In Chihuahua, historical the Yucatan Peninsula (Howell and Webb 1995, Aplomado Falcon reports were sparse. Bailey Keddy-Hector 2000). Also, an Aplomado Falcon (1928) mentions a falcon was taken in 1892 at the population existsin the northern GhihuahuanDe- playasof Palomas,Chihuahua, near the New Mex- sert from north-central Ghihuahua to southern ico border. Further, a nest was located in Chihua- New Mexico (Montoya et al. 1997, Truett 2002, hua, Mexico, southwestof Antelope Wells, New Williams 2002, Young et al. 2002, R. Meyer, C. Mexico by Arnold Baynein 1952 (Truett 2002). Perez, and S. Williams III unpubl. data). Sincethe There was better documentation of early falcon 1990s, there have been occasional sightings of reports in the United States'(U.S.) portion of the Aplomado Falconsin northern Ghihuahua,Mexi- Ch•huahuan Desert (Williams 1997, Truett 2002, co near the New Mexico border, and near Lagunas JUNE 2004 APLOMADOFALCON DISTRIBUTION 109

• Year-round ->•--•Occasional orAnnual Sightings(1990to Present)l t• .i...... -,.•,•...... • i...... l•-• tJr,

• NotRepoaed ... GRS 1980 ,S•heroM

• HistoricalExtentUnk. . I tff-w 105':w I0•!"w 95•?w 90Pw : :

Figure 1. Distribution of northern Aplomado Falconsin the United Statesand Mexico. Map redrawn from information provided by Lawrence (1874), Websterand Orr (1952), Phillips et al. (1964), Alden (1969), Oberholster (1974), Gallucci(1981), Monsonand Phillips(1981), Cade et al. (1991), Howell and Webb (1995), Montoyaet al. (1997), Williams (1997), Russelland Monson (1998), Peterson and Zimmer (1998), U.S. Fish and Wildlife Service (1990), Keddy-Hector(2000), Williams (2002), Truett (2002), Meyer (unpubl. data), E. Ifiigo-Elias(pers. comm.), and data collected during this study.

Babicora, Mexicanos, and Bustillos, and La Perla 1997, 2000, Peterson and Zimmer 1998, Truett (Benitez et al. 1999, Lafon Terrazasunpubl. data). 2002, R. Meyer, C. Perez, and S. Williams III un- Further, an Aplomado Falcon was sighted in Coa- publ. data). The first successfulnest recorded in huila in the late 1990s(E. lfiigo-Eliaspers. comm.). New Mexico since 1952 fledged three young in In the U.S., there are annual falcon sightingsin 2002 (Williams 2002, R. Meyer, C. Perez, and S. southern New Mexico and occasionalsightings in Williams III unpubl. data). Along the southern westernTexas (Fig. 1) (Williams 1993, 1994, 1996, Texas coast,a population of Aplomado Falconswas 110 YOUNGET AL. VOL. 38, NO. 2 initiated from reintroduction efforts (Cade et al. STUDY AREA AND METHODS 1991). In addition, Aplomado Falcons were re- Our study area (100 735 km'•) consistedof a 160-km leased in western Texas in 9002. belt south of the U.S./Mexico border in Chihuahua, Mexico (Fig. 2). Municipalitiesin the studyarea included The AplomadoFalcon was first considereda can- Ahumada, Aldama, Ascensitn,Buenaventura, Camargo, didate for endangered statusin 1973 (U.S. De- CasasGrandes, Chihuahua, Coyame,Delicias, Galeana, partment of the Interior 1973) and was listed as Guadalupe, Janos, Ju/trez, Julimes, Manuel Benavides, endangered in March 1986 (U.S. Fish and Wildlife Nuevo Casas Grandes, Ojinaga, Praxedis G. Guerrero, Service 1986). At the time of listing, critical habitat and Zaragoza. Land ownership included private and communal (ejido) land. Annual precipitationis 200-300 was not designatedbecause there were no known mm, the majority(->80%) of whichoccurs during July- nests in the U.S. for at least 95 yr (U.S. Fish and September (COTECOCA 1978). Topographyis charac- Wildlife Service 1986). The Aplomado Falconwas terized by disjunct north-southeast-orientedmountain added to the endangered list due to its loss as a ranges with maximum elevations of ca. 2200 m. Plains, lowlands,and basinsare prevalentthroughout the study breeding bird in the U.S. and continued threats region and are ca. 1200 m above sea level. within its range. Factors that attributed to the fal- Setnidesert-basin-grasslandcommunities consistpri- con's decline were primarily habitat degradation marily of alkali sacaton (Sporobolusairoides) and tobosa due to woody plant encroachment, and secondar- (Pleuraphismutica) (COTECOCA 1978, Brown 1994, ily, egg and specimen collecting, and continued Young et al. 2002). Lowlandspredominantly contain to- bosawith honeymesquite (Prosopis glandulosa) and soap- pesticide contamination (DDT) within the range tree yucca (Yucca elata). Plains are comprised of blue of the falcon (Kiff et al. 1980, U.S. Fish and Wild- grama (Boutelouagracilis), black grama ( B. eriopoda),fluff life Service 1986, Cade et al. 1991). grass (Dasyochloapulchella), burrograss ( Scleropogonbrevi- The Mexican government listed the northern folius), alkali sacaton,and sanddropseed (Sporobolus cryp- Aplomado Falcon as endangeredin Mexico in May tanaltus)(COTECOCA 1978, Young et al. 2002). Com- mon woodyplants in plaint consistof honeymesquite, 1994 (DOF-Semarnat1994, Ceballosand Marquez creosote bush (Larrea tridentata),acacia (Acacia spp.), Valdelamar 9000). However, because information soaptree yucca, mariola (Partheniumincanurn), and tar- about population-levelstatus of each specieswas bush (Flourensiacernua). Sloped areas support sideoats lacking, governmental agencies, scientific institu- grama (B. eurtipendula),fluff grass,burrograss, creosote tions, and societies collaborated to review infor- bush, lechuguilla (Agavelechuguilla), and sotol (Dasylirion wheeleri)(COTECOCA 1978, Brown 1994, Young et al. mation and produce a new threatened and endan- 2002). gered species list for Mexico. This list was Falcon Surveys. Aplomado Falcon distribution and published in March 9002, and the status of the abundance were described from surveysconducted in northern AplomadoFalcon was changed from "en- large sample tracts and in linear transectsin northern Chihuahua during 1998-99. We also included distribu- dangered" to "subject to special protection" tion and abundanceinformation from a separatestudy (DOF-Semarnat 9002). Subject to special protec- designedto monitor falcon habitat and productivityin tion statusis given to a speciesor populationwhich northern Chihuahua (Macias Duarte 2002). could become threatened from factorsthat nega- Frequencyof occurrence (percent of tractsin which a tively affect their viability;thus, there existsa need speciesoccurred) analyseswere restrictedto raptors and ravensobserved during tract surveys.We define a falcon to promote their recoveryand conservation(DOF- nestsite as a location where Aplomado Falcons nested, Semarnat 9002). either successfullyor unsuccessfully.We refer to a falcon Increasesin reliable falcon sightingsin the Chi- detectionsite as a location where a nest was not found, but huahuan Desert in the early 1990s prompted ad- either a single or pair of falconswere found one or more ditional interest in recoveryof the speciesin New times. Reproductive activitywas not alwaysdetermined for detection sites.We use the term siteto refer to a spa- Mexico (Williams 1997, R. Meyer,C. Perez,and S. tially and temporally independent fhlcon location (in- Williams III unpubl. data). We conductedraptor cludes both nest and detection sites). As such, falcons surveysin semidesertgrasslands/savannas and as- located during both years of the study in the same or sociated habitats in northern Chihuahua, Mexico proximate area were only counted once. Tractsurveys. Survey tracts in northern Chihuahua were to locateAplomado Falcons and to better delineate selectedin two ways:(1) a stratified random sample in- their distribution and abundance in the northern dicated on the amount of dominant vegetation derived Chihuahuan Desert.We surveyeda varietyof dom- from a 1:250000 printed vegetation map (INEGI 1982), inant vegetationcommunities to identify habitat as- and (2) a simple random sample of prospectiveareas sociations.We recorded presence of raptors and identified during an aerial flight of the studyarea. For samplesderived from the vegetationmap, ca. amounts ravens (Corvusspp.) to investigatethe association of dominant vegetationwere estimatedby tracing poly- of Aplomado Falconswith presence of primary gon boundarieswith a planimeter.A 9 X 9 km grid was nest builders (U.S. Fish and Wildlife Service 1990). placed on the vegetationmap, and 60 grids (representing JUNE2004 APLOMADOFALCON DISTRIBUTION 111

.:.

•uenaven•raO •"•'

q Chihuahuaß •,S •'

'•''- •' ApproximateArea

. •,• Chihu•hua• ,,, .:_.•OccupiedStudy Areaby

5"''..•-"'X. • "•'::"•,F'" aAplomado Falcons / t•020 40 80 120160 /-.. .. Figure 2. Dist•bntion of tractss•veycd for Aplomado Falcons(ripper right corner) •d approximateareas occn- pied by Aplomado Falconsin northern Chihnahna during 1998-99. surveytracts) were randomly selectedin proportion to all raptors and ravens detected using 8X binoculars and the percent of vegetationcalculated (Table 1). We also a 20X spotting scope. In areas with limited road access, flew the entire study area in December 1998 to locate observerswalked and establishedpoint stationsto ensure prospective survey areas that represented vegetation complete coverageof the tract. Between point stations communities known to be used by Aplomado Falcons. on roads, observers drove <6 km/hr and recorded all Prospectiveareas for sampling were recorded with a individual raptors observed.Likelihood of double count- Global PositioningSystem (GPS) receiverfor subsequent ing individual raptors was minim'tzed by observers re- falcon surveys.We randomly selected 30 of the 58 pro- cording raptor and raven flight direction and movements spectivegrassland areas observedfor tract placement. Af- during the survey. ter a surveyarea waslocated in the field, observersestab- Actual surveyedarea in tracts was estimated by buff- lishedthe largesttract sizepossible to conductAplomado ering surveypoint stations600-m (ca. maximum observ- Falcon surveys. able distance from most point stations) in ArcView 3.2 Each tract received a complete, systematicsurvey by (Environmental SystemsResearch Institute, Inc. 2000). placingpoint stationsat 0.3-1.0 km intervalsalong roads, As such, tract size and configuration depended on jux- depending on vegetation and topography. Observers tapositionand number of surveystations established. spent3-5 rain at each point stationwhere they recorded Transectsurveys. Transect surveyswere road surveys 112 YOUNG ET AL. VOL. 38, No. 2

(not area based) conducted in nonrandomly selected grasslandsand around unconfirmed Aplomado Falcon sightingsin northern Chihuahua. Survey methods were similar to tract surveysin that point stationswere established at 0.3-1.0 km intervals along roads.However, transect surveyswere not designed to survey a given area completely,but provide additional information about selected areas thought to be used by Aplomado Falcons. Monitoring study.The Aplomado Falcon monitoring study was initiated in 1996 in two areas in northern Chi- huahua: one approximately 160 km north of Chihuahua City and the other approximately 160 km northeast of ChihuahuaCity (Montoyaet al. 1997). Falconterritories within the monitoring study area were surveyed for oc- cupancy in 1998 and 1999. A territory was considered occupied when a pair of falconswere observedat or near a nesting structure, and there was no reason to believe the pair was from another territory (Macias Duarte 2002). Each occupied and previously-occupiedterritory was visited at least twice/mo. In some cases, territories noted as unoccupied may have contained undetected pairs or singlebirds. Nonnesting pairs were recorded,but not monitored. Falcon surveysfor the monitoring studywere conducted from vehicles on roads in areas considered to be potential habitat. Observersstopped ca. every 1.0 km and scannedthe terrain for falconsusing 10 x binocularsand a 15x spotting scope. Surveyswere initiated prior to in- cubation and continued until fledging or failure wascon- firmed. Dominant Vegetation Community. Dominant vegetation community was estimated at two different scales.For falcon siteslocated by the monitoring studyand transect surveys,dominant vegetation type was estimatedocularly for an area ca. 500-m around the site center. Conversely, for falcons located during tract surveys,dominant vegetation type was estimatedocularly during falcon surveys and summarized over the entire tract. Surveyorsclassified dominant vegetation community among three shrub- dominated and ibur grass-dominatedvegetation communities: creosote bush-tarbush,mesquite-acacia, creosote bush-tarbush/mesquite-acacia,grass/creosote bush- tarbush,grass/mesquite-acacia, grass/yucca, or grassland (Buffingtonand Herbel 1965,Johnson 1977, Rzedowski 1990, Dinerstein et al. 2001). These communitiesgraded from structurallysimple types to structurallydiverse types varying in density,canopy, and interspersion.This clas- sification was used as a post-stratificationdescription of the tracts and falcon sites.

RESULTS

Survey Effort Among Vegetation Communities. We surveyed68 tracts(2005 km •) in 1998and 1999 (Table 2, Fig. 2). Ten tractswere surveyedin both 1998 and 1999, yielding a total of 78 different surveys.Tracts surveyedin both years had either an Aplomado Falcon detection in 1998, or potential Aplomado Falcon habitat. We were unable to survey 22 tracts (11 tracts from the vegetation map sample and 11 prospectiveareas identified during JUNE 2004 APLOMADOFAI,CON DISTRIBUTION 113

the flight of the study area) due to restricted land accessor time constraints (Fig. 2). During May-October 1998, four field crews spent 308 hr surveying47 tracts. Tract area averaged 26.4 +- 1.1 km9, but ranged from 7.0-41.8 km2. In 1998, we surveyed1242 km2 in the tracts and a total of ca. 1300 km= including transectsurveys. During February-October 1999, five field crews surveyed 31 tracts representing 438 hr of survey time. Tract area averaged 38.1 + 2.9 km•, but ranged from 16.4-77.7 km•. In 1999, we surveyed 1182 km • in the tracts and a total of ca. 1467 km • including transect surveys.Larger tracts were not feasible to establishand surveybecause of vegetation heterogeneity,restricted land access,and time constraints. Tracts surveyed in 1998 were primarily shrub- dominatedcommunities (84%), comprisedof creosote bush-tarbush,mesquite-acacia, or creosote- tarbush/mesquite-acacia. Conversely, in 1999, tracts surveyedwere primarily in grasslandcommunities (75%), representedby grasslandswith or without complexes of mesquite-acacia,creosote bush-tarbush,or yucca (Table 2). Aplomado Falcon Abundance and Distribution. Aplomado Falconswere detected in 17 (25%) of the 68 tracts surveyed.Tract surveysyielded four nestsand 14 detectionsites, representing 11 falcon pairs and sevensingles, for a total of 29 birds. No additional falconswere found in tractssurveyed in both years.An additional three pairs (one nestand two detection sites) were located during transect surveys.The monitoring study located 13 falcon nests and nine detection sites representing 22 pairs. Based on combined surveyeffort, the minimum known population of adult Aplomado Fal- considentified in the studyarea during the survey period was79 individuals(43 independentsites; 18 nest and 25 detection sites). However, given that detection ratesfor Aplomado Falconswas low (e.g., >40 surveyhr per site was needed for each detection), additional falconsprobably would be located with additional surveys. Aplomado Falcons were associatedwith most vegetationtypes, but they were detected most often in grass-dominatedcommunities (Table 3). Specif- ically, 16 (88%) Aplomado Falcon nests and 10 (40%) detectionsites were found in grasslandcommunities with soaptree yucca or Torrey yucca (Y. torreyi).Of the 79 individuals found in northern Chihuahua, only three single birds were located in 114 YOUNG ET AL. VOL. 38, NO. 2

shrub-dominated communities. No falcon detections occurred in creosote bush/tarbush communities (Table 3). Aplomado Falcons were fairly concentrated in the north-centralto northeasternpart of the study area (Fig. 2). This distribution coincides closely with the distribution of extensive grasslandsin northern Chihuahua identified from our aerial flight. We found falconsnesting ca. 50 km westof the Texas border (ca. 120 km south of E1 Paso, TX) in northern Chihuahua. Also, single Aplomado Falcons were detected in the same area ca. 12-18 km south of the New Mexico border near Palomas, Chihuahua, in each surveyyr. Reproductivestatus for these detections was not determined. Aplomado Falconsrely on nests constructedby other raptors or corvids. Potential nest builders present in northern Chihuahua included ravens (primarily Corvus cryptoleucus),Swainson's Hawk ( Buteoswainsoni) , Red-tailed Hawk ( Buteojamaicen- sis), Harris's Hawk (Parabuteo unicinctus), and White-tailed Kite (Elanusleucurus). Except Harris's Hawk and White-tailed Kite, these nest builders were common in tracts where Aplomado Falcons were detected (>70% frequency;Table 4). Swain- son's Hawks, Red-tailed Hawks, and ravens were more commonly detected in tractswith Aplomado Falcons than in tracts without Aplomado Falcons (X2 = 34.56, df = 3, P < 0.001).

DISCUSSION AND CONSERVATION IMPI,ICATIONS Aplomado Falconsare fairly conspicuouswhen foraging or perching on tall substrates.However, locating new falcons required >40 survey hr per site (estimated from tract surveys),and determin- ing nesting status required additional time. As such, methods that require complete surveysof large areas are more likely to detect falcons. We detected falconsin 25% of tractssurveyed, locating 18 falcon sites which were not previously known. Given the short duration of surveys,we feel the tract surveymethod provided reasonableresults. Before the 1980s,information on Aplomado Fal- cons in the Chihuahuan Desert was limited to a few incidental and historical accounts. The state of knowledgehas developedfrom the perception that Aplomado Falconswere extirpated from the Chi- huahuan Desert, to documentinga population that exists from north-central Chihuahua to southern New Mexico. However, it seems that the falcon populationon the M•xicanPlateau is geographi- cally isolatedfrom coastalpopulations (Fig. 1). Ad- ditional researchis necessaryto better define pop- JUNE2004 APLOM•)O FALCONDISTRIBUTION 115

Table 4. Associationof raptor speciesobserved in 17 surveytracts with Aplomado Falcon detectionsand 51 tracts without Aplomado Falcon detectionsin northern Chihuahua, Mexico in 1998-99.

NUMBER OF TRACTS

WITH APLOMADO FALCONS a WITHOUT APLOMADO FALCONS

NUMBER PERCENT NUMBER PERCENT

Swainson's Hawk 17 100 33 65 Ravens 16 94 49 96 Red-tailed Hawk 12 71 25 49 White-tailed Kite 2 12 1 2 Harris's Hawk 1 6 1 2 Detection of AplomadoFalcons was highly associatedwith tractswhere hawksand ravenswere detected (X2 = 34.56, df = 3, P = <0.001); White-tailedKite and Harris'sHawk detectionswere combinedfor analyses.

ulation dynamicsand connectivitybetween falcon diversity conservation. In the Chihuahuan Desert populationsin Mexico. portion of the Aplomado Falcon's range, four pri- The U.S. Fish and Wildlife Service (1990) stated ority areas for biodiversity conservation in grass- that critical information regarding falcon distribu- land habitats were identified (Arizmendi and Mgr- tion, abundance, and habitat requirements in Mex- quez 1999). CONABIO also established areas that ico was needed to aid in recovery of the species. were consideredimportant for the conservationof Our study, as well as studies by Montoya et al. birds (AIGAS) in Mexico. However, within the (1997), Truett (2002), and R. Meyer,C. Perez,and range of the Aplomado Falcon in the Chihuahuan S. Williams III (unpubl. data), will aid resource Desert, there was only one area designated near managersin developingrecovery strategies for the Janos, Chihuahua. Although there are occasional falcon in the Chihuahuan Desert by providing falcon sightingsin this AIGAS, there were no AI- baseline information on the current distribution of CAS designated in areas of known year-round the falcon. Aplomado Falcon habitation. Given the falcon's The Chihuahuan Desert is the largest desert (ca. statusof "subject to specialprotection" in Mexico, 629 000 km 2) in North America (Beck and Gibbens updated information on Aplomado Falcon distri- 1999, Dinerstein et al. 2001) and is among the bution may assistin evaluating areas for future AI- most biologically diverse desert ecoregionsworld- GAS in Chihuahua, Mexico and promote falcon re- wide (Ricklefs and Schluter 1993). Most of the Chi- covery and conservation. huahuan Desert is located in the states of Chihua- The U.S. Fish and Wildlife Service (1986) impli- hua and Coahuila in Mexico, but portions extend cates habitat degradation due to brush encroach- into eastern Arizona, southern New Mexico, and ment as the main factor responsiblefor disappear- western Texas. This vast and unique arid region ance of Aplomado Falcons from the U.S. The supportsa wide variety of habitatsincluding grass- Chihuahuan Desert has undergone considerable lands, scrublands, shrub communities, and yucca transition in vegetation communities since the woodlands as well as mixed conifer forests and oak mid-1800s, primarily from perennial grasslandto woodlands at higher elevations (Gehlbach 1993). shrubland (Buffington and Herbel 1965, Allred About 14% of Mexico's land area is coveredby 1996, Beck and Gibbens 1999). Over the past cen- grasslandsof which 90% occur in arid and semi- tury, factors such as climatic changes,diversion of arid regions (Burquez et al. 1998). Although lim- surface water for agricultural purposes, livestock ited in area, grasslandsare vital to certain species grazing, erosion, introduction of exotic plant and and to the biodiversityof the Chihuahuan Desert animal species,and increased urban development (Beck and Gibbens 1999). have profoundly and negativelyimpacted the nat- The Mexican government created the National ural processesof the Chihuahuan Desert (Lloyd et Commissionfor the Knowledge and Use of Biodi- al. 1998, Beck and Gibbens 1999). Changesin bird versity (CONABIO) in 1992 that establisheda net- assemblages,including raptors, associatedwith al- work of regional areas that were important for bio- tered vegetation structure and climatic conditions 116 YOUNG ET AL. VOL. 38, NO. 2 have been detected and discussedby Raitt and BENT, A.C. 1938. Life histories of North American birds Pimm (1976, 1977) and Lloyd et al. (1998) for Chi- of prey, part two. U.S.Natl. Mus. Bull. 170:96-99. BROWN,D.E. (ED.). 1994. Biotic communities: southwest- huahuan Desert environments. Change in grass- ern United States and northwestern Mexico. Univ. lands will naturally affect speciesthat are grassland Utah Press,Salt Lake City, UT U.S.A. adapted. The current state of knowledge on Aplo- BUFFINGTON,L.C. AND C.H. HERgEL.1965. Vegetational mado Falconsindicates that this falcon is likely to changeson a semiarid desert grasslandrange from be detrimentally affected by alteration and lossof 1858-1963. Ecol.Monog•: 35:139-164. grasslandhabitat. Further, key raptor or raven spe- BURQUEZ,A., A. MARTINEZ-YRzAR,M. MILI.ER, K. ROJAS, M. rm LOSANGELES-QUINTANA, AND D. YETMAN.1998. cies relied upon by Aplomado Falconsto provide Mexican grasslandsand the changing aridlands of nest structures have substantial association with Mexico: an overviewand a casestudy in northwestern grasslanddominated communities(Desmond et al. Mexico. Pages 21-32 in B. Tellman, D.M. Finch, C. in press). Grasslandconservation is paramount in Edminster, and R. Hamre lEDs. I, The future of arid conservingAplomado Falconsand other grassland grasslands:identifying issues,seeking solutions. Pro- birds in the Chihuahuan Desert. ceedings RMRS-P3, USDA, Forest Service, Rocky Mountain Research Service, Fort Collins, CO U.S.A. ACKNOWLEDGMENTS CADE,TJ., J.P.JENNY, AND BJ. WALTON.1991. Efforts to Researchwas funded by the Bureau of Land Manage- restore the northern Aplomado Falcon (Falcofemoralis ment, White SandsMissile Range, Fort BlissMilitary Res- septentrionalis)by captive breeding and reintroduc- ervation, U.S. Fish and Wildlife Service, Sevilleta Nation- tion. Dodo,J. JerseyWildl. Preserv.Trust 27:71-81. al Wildlife Refuge, The Peregrine Fund, Border Wildlit• CEBAIJ,OS,G. AN•) L. MA•Q.UEZ VALr)EI•X4A•. (Er)s.) 2000. Consultants, T & E, Inc., La Tierra Consulting, World Las avesde Mexico en peligro de extinci6n. Instituto Wfidlife Fund, and Geo-Marine Inc. Additional financial de Ecologia, Mexico, D.F. Mexico. support wasprovided by the New Mexico Agricultural Ex- COTECOCA. 1978. Comisi6n t6cnico consultirapara la periment Station. We greatly appreciate the Secretaria de determinaci6n regional de los coeficientesde agos- Medio Ambiente RecursosNaturales y Pescafor provid- tadero, Chihuahua, Mexico. ing the necessarypermits to conductresearch in Mexico. DOF-SEMARNAT. 1994. Norma Oficial Mexicana NOM- We thank A. Alvarez, E. Carreon, E. Carrillo, C. Mendez, 059-ECOL-1994,que determina las especiesy subes- R Meyer,J. Montoya, C. Morales, F. Pinion, R. Rodriguez, peciesde flora y fauna silvestreterrestres y acufiticas C. Sanchez, and E. Zamarron for their assistance in col- en peligro de extinci6n, amenazadas,raras y las su- lecting data. S. Lanham, Environmental Flying Services, jetas a protecci6n especial, y que estableceespecifi- TucsonArizona, provided a productiveflight over north- cacionespara su protecci6n. Diario Oficial de la Fed., ern Chihuahua. We thank M. Howard, B. Locke, R. Mey- Primera Secci6n. Mexico, D.F. Mexico. er, C. Perez, and S. Williams for helpful critiquesof this . 2002. Norma Oficial Mexicana NOM-059-ECOL- manuscript.We thank the numerousprivate landowners 2001, protecci6n ambiental---especiesnativas de Max- in Chihuahua, Mexico with a special thanks to A. Borun- ico de flora y fauna silvestres--categoriasde riesgoy da and E. Baeza for providing land access. especificacionespara su inclusi6n, exclusi6n o cam- LITERATURE CITED bio--lista de especiesen riesgo. Diario Oficial de la Fed., Segunda Secci6n. Mexico, D.E Mexico. ALDEN,P. 1969. Finding the birds in Western Mexico; a DESMOND,MJ., K.E. 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