Thedecline of theAplomado Falcon in the United States

Dean P. Hector

In 19761 begana studyof the ecology National Museum of Natural History (Falcofemoralis)once nested reg- and behavior of the Aplomado Falcon (NMNH), Virginia PolytechnicalState LTHOUGHularly in THEpartsAPLOMADO of Arizona, FALCON New in easternMexico. A long-term objec- University (VPSU), Western Founda- Mexico, and Texas,population declines tive of the projectwas to provideinfor- tion of Vertebrate Zoology (WFVZ), in the early 20th centuryhave essentially mation which might help to improve University of Michigan Museum of eliminated the speciesfrom the United the statusof the Aplomado Falcon in Zoology (UMMZ), Oklahoma State States (Bailey 1928; Ligon 1961; Ob- the United States.Management of any UniversityWildlife Collections(OSU) erholser1974; Murphy 1978; and Hec- speciesrequires some understanding of Nineteen collections contained only tor 1980). Aplomado Falcons are ex- its basic ecological relationshipsand specimenscollected by F.B. Armstrong tremely rare, with a limited distribution how these relate to any population de- (seeDiscussion) and are not referredto in the United Stateson the gulf-coastal clines that have occurred. Results of the individually. plain of Texas and in the desert grass- initial ecologicalinvestigations dealing In addition, I attempted to locate all lands to the west, where many birders with feedingecology and habitat selec- late 19th and early 20th century refer- searchfor them annually.Only recently, tion have been completed(Hector 1981 ences to the Aplomado Falcon, and however,has the status of this species and 1985). This paper presentsa sce- contact individuals who had seen the been calledto the attention of manage- nario which describes and attempts to speciesin the United Statesor Latin ment-oriented agencies (Bond 1972; explain the decline of the Aplomado America. Although my sample of spec- Wildlife Habitat Management Staff Falcon in the United States. imen recordsand observationsis surely Group 1975; Murphy 1978; Evans incomplete, I have probably garnered 1982; Millsap 1983; LeFranc and Mill- collection dates and localities for over sap 1984). LeFranc and Millsap (1984) 90% of North American specimensof classifiedthe Aplomado Falcon one of METHODS the Aplomado Falcon. the most "sensitive" of North American In the remainder of this paper num- raptors. bers in parentheses(#1-#34) refer to Reasonsfor the decline of the Aplo- I solicited specimen recordsfrom 57 locationson Figure 1. mado Falcon are unknown. Ligon museums and private ornithological (1961:82) says that "consideringthe collectors in the United States and permanent sourceof their food and the Canada. A total of 43 responded and abundance of suitable nesting places, 29 contained specimens from the RESULTS the disappearance [of the Aplomado United States. Falcon] from most of its former range Specimens from the following col- remains somewhat of a mystery." He lections (in order of appearance)are Early History in New Mexico felt that shooting pressure may have mentioned in this paper: San Diego been a factor because Aplomado Fal- Natural History Museum (SDNHM), conswere very tame. Oberholser(1974: United States National Museum In March 1852, Heermann (1854; 257), however, saysthat "... none of (USNM), Cincinnati Museum of Nat- Brewer 1856) collectedthe first U.S. the usual causes of bird decimation ural History (CMNH), Museum of Aplomado Falcon (# 1) in southwestern seem to apply to the Aplomado Fal- Vertebrate Zoology (MVZ), American New Mexico. Stephensadded a third con" Museum of Natural History (AMNH), U.S. specimen (SDNHM) in August,

Volume41, Number3 381 1875,when he shotan adult female(#2) one bird 20 miles southeast of Sfiver Aromas(#9, Hidalgo County) Arnold near Silver C•ty, New Mexico (Grant City (#2; Luna County, Barley 1928), Bayne located the last documented County). Anthony (1892) reported a and in November Ligon (1961) and United Statesnest sitein May 1952 near pair of falcons(#3) near Hachita (Grant A.K. Fisher observeda pair of falcons Deming, New Mexico (#1; Luna County) in June 1886. On the Jornada near Engle (#7; Sierra County). In De- County; Ligon 1961). del Muerto (#4; Dona Ana County), cember 1918, Ligon observeda pair of Ligon discovered several nests with AplomadoFalcons 10 miles north of young in June 1908 and 1909 (Bailey Engle(#7; Bailey 1928). In May 1919, Early History in Arizona 1928). In July of the sameyear, Gold- Ligon shot an adult male (CMNH) 30 man collected an adult (USNM) at miles southeastof Silver City. Henshaw(1875) sawAplomado Fal- Hachita, and observeda bird in August In May 1924, Ligon took an adult cons severaltimes near Ft. Bowie, Ar- in the Playas Valley (#5; Hidalgo male(YPM) 15 milessoutheast of Cut- izona (#10) in 1873-1874. Fourteen County; Bailey 1928). ter (#7; SierraCounty). In June,Kellogg years later in April and May, Benson In June 1917, Ligon collected an collectedtwo adult males(CMNH) and located five nesting pairs (#11) at Ft adult female (USNM) 45 miles north an adult female (MVZ) on the Tadpole Huachuca, Arizona (CochiseCounty, of Alamogordo(#6; Otero County). He Ranch, 4 miles north of Separ (#8; Bendire 1887). In 1910, Lusk (Visher observeda pair of adults25 milesnorth Grant County).In September1928, Li- 1910), observed a bird near Tucson of Engle (#7; SocorroCounty, #25) in gon collectedanother falcon (CMNH) (# 12;Pima County),and Willard (1910) August (Bailey 1928); and collecteda southeastof Silver City. saw one in February along the San pair of adults (USNM) in September Toomey collectedthe last skin from Pedro River near Fairbanks (#11, near Nutt (# 1; Luna County). In Sep- New Mexico in October 1939. This was Cochise County). Monson spotted a tember of the next year, he observed an immature male (CMNH) taken near falcon in the Sulphur SpringsValley

i

NEW

ARIZONA ICo

•2 TEXAS

MEXICO

Figure1. AplomadoFalcon collection and observationlocalities in the US. NEW MEXICO localities.'#1-Hidalgo Co.; #2-SilverCity andFt Bayard,Grant Co.; #3-Hachita, Grant Co.,' #4-Jornada del Muerto, Dona Ana Co.;#5-Playa Valley, Hidalgo Co.; #6-Alamogordo, Otero Co, # 7-Engle,Sierra Co.,'#&Tadpole Ranch, Grant Co.,'#9-Animas, Hidalgo Co.,'#25-Socorro Co.,' #32-Lea Co. ARIZONA localities.'#10-Ft Bowie,Cochise Co.; #11-Ft. Huachuca,Cochise Co.; #12-Tucson, Pima Co.,'#13-Sulphur Springs Valley, Cochise Co.; #14-St. David, Cochtse Co.;# 33-ChiracahuaMtns. TEXAS localities:# 15-Pecos,Reeves Co.,' # 16-Brownsvilleand Pt. Isabel, CameronCo.; # 17-Alpine,Brewster Co, #18-JeffDavis Co.,'#19-Bellville, Austin Co.; #20-Midland Co.; #21-Brooks Co.; #22-Big Bend National Park, BrewsterCo.; #23-El PasoCo, #24-Riviera,Kleberg Co.; #26-PresidioCo.; #27~WelderWR, San PatricioCo.; #28-NorthPadre Island, Kenedy Co.,' #29-Roma, Starr Co, #30-Mission,Hidalgo Co.; #31-AransasNWR, AransasCo.; #34-Culberson Co.

382 American Birds, Fall 1987 LIFE

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YEAR OF COLLECTION Figure2. Temporaldistribution of US. specimensof theAplomado Falcons. Outlined histogram bars show numbers of eggsor skinscollected per decade.Dark bars shownumbers of specimenscollected per year habtts oak and pine savannas(Hector Turner 1964; Harris 1966; York and croachedby woody vegetation,mostly 1981, 1985; Howell 1982), open grass- Dick-Peddie 1969). As in other grass- mesquite; over one-half of the area was lands, coastaldeserts (Johnson 1963), lands, control of range fires, especially coveredby high densitiesof brush(50- riparian woodlandsin the midst of de- on the coastalplain of Texas,probably 100% coverage). sert grassland(Henshaw 1875), and further acceleratedthe spreadof mes- In Mexico, trees at falcon nest sites marshes(Hector, pets. obs.). quite (Humphrey 1958'). averaged46 metersapart and 9.5 meters S•nce the early 1900s much of the Accordingto Camp (in Brooks1933), in height (Hector 1981). Tree densities lower Rio Grande valley, gulf-coastal the area congestedby mesquite near averaged19/40 hectares(19/100 acres; plmn of Texas, and river floodplainsof Brownsvillehad increasedin coverage Hector 1981). Ground cover tended to New Mexico and Arizona have been and encroached about 5 miles on the be lessthan 25 centimetersdeep (Hector convertedfrom grasslandto farmland-- coastalprairie in 20 years. Buffington 1981). Pastures not maintained by pnncipally cotton, sorghum, citrus, and Herbel (1965) describedthe brush burning or clearing rapidly became beansand corn. Farming activitieshave encroachment on the Jornada del congestedwith thorny legumes(mostly also altered much of the Rio Grande Muerto between 1858-1963; evidently Acaciafarnesiana).Aplomado Falcons Valley, Texas coastal plain, and por- this area containedthe highestknown tended to abandon nesting territories tions of New Mexico and Arizona. In nestingdensities of Aplomado Falcons where grassyground cover had given addition, brush encroachment has con- outside of south Texas. The Jornada way to brush (Hector 1981). When I gestedmuch of the semi-opengrassland ExperimentalRange may coincidewith carried out a statisticalcomparison of onceinhabited by the species(Bogusch the areain whichJ.S. Ligon found birds habitat structure measurements for a 1952; Glendening 1952; Humphrey nestingin 1908-1909 (Bailey 1928). In sampleof easternMexican nestingter- 1958;Hastings and Turner 1964;Harris 1858, an estimated 83,625 acresof the ritories,I foundthat althoughoccupied 1966; York and Dick-Peddie 1969). 144,475 acre study site was free of sites tended to have greater overall Unregulated grazing by livestock woody vegetation (mesquite, creosote, ground cover density,ground cover at surely acceleratedthe spread of mes- or tarbush). By 1915, the grassland these sites was concentrated below 0.5 qmte by openingup ground coverveg- acreagehad decreasedto 35,459 acres, meter above the ground (Hector 1981) etationand by ingesting,scarifying and then to 32,833 acresby 1928. In 1963, Abandoned sites tended to be more dispersingwhole seeds(Hastings and the study site was completely en- congestedwith vegetationbetween 0 5

Volume 41, Number 3 387 and one meter above the ground (Hec- nated open to semi-opengrassland. Ef- ture Lehmann beheved that pesticide tor 1987). A number of studieshave de- fectsof brush encroachmenton hunting contamination may have causedtheir tected a relationship between raptor successand prey availability probably disappearance. Furthermore, cotton habitat selection and structure of accountin part for thesedeclines. This agriculturedominated most areas--the ground cover vegetation(Howell et al. is significant not only because the TexAscoast, and desert rivers of Arizona 1978; Bechard 1982; Hector 1987; and AplomadoFalcon shares similar habitat and New Mexico--near areas where reviewedby Janes1985). Janes(1984), preferenceswith thesespecies, but also Aplomado Falcons once occurred using simple geometric models, has because Aplomado Falcons depend An obvious effect of pesticideqn- shown how habitat structure should af- largelyon other raptors(as well as cor- ducedreproductive problems would be fect prey detectionability and optimal vids) for nestingplatforms. In eastern a reductionin the ability of a speciesto perch heightsof raptors. Presumably, Mexico, most nest platforms were the colonizeunoccupied patches of habitat. capture efficiency should also be af- abandonednests of the Brown Jay (Psi- Consequently,although brush cleanng fectedby vegetationstructure. lorhinusmorio), Black-shouldered Kite, activitiesare rapidly opening up south Although birds are the staplefood of or RoadsideHawk (Buteomagnirostris) Texas ranches,Aplomado Falconsmay the Aplomado Falcon (Hector 1985), (Hector 1981). I alsofound falconsin not reoccupy their former range until the speciesfeeds on a variety of prey old nestsof the Crested Caracara (Po- pesticideuse abatesin Latin America, •ncludingbats, rodents,lizards, and in- lyborusplancus). In the United States, or some effort is made to artificially re- sects(Brooks 1933;Ligon 1961; Mader falcons used nests of the Chihuahuan establishthe species. 1981;Hector 1985). Many prey animals Raven (Corvuscryptoleucus) (Bendire are captured on the ground following 1887), Swainson'sHawk (Buteoswain- ACKNOWLEDGMENTS h•gh-speedchases begun from vantage soni)(Strecker 1930), and probablyalso postsin trees (Hector 1981, 1985, and those of the Black-shouldered Kite, My work with the Aplomado Falcon 1986). Hunting falcons often force White-tailed Hawk and Caracara. has greatlybenefitted from equipment fleeingbirds to hide in limited patches Populationsof the Black-shouldered or financial support provided by the of thickerground cover or in the crowns Kite and White-tailed Hawk have re- following organizations: the Depart- of isolated trees. Aplomado Falcons, covered in coastal Texas. This seems ment of Zoology at Brigham Young however,are agileenough to cornerand related to intensive brush clearing and University, Chihuahuan Desert Re- capture suchgrounded prey. With prey the use of prescribedburns to revert search Institute, Hawk Mountran •n continuous forest, dense brush, or rangelandto some semblanceof its Sanctuary Association, the Nalaonal dense, deep grass, however, falcons former openness.Unlike thesetwo ro- Wildlife Federation's Environmental tended to quickly abandon pursuit. dent-oriented species, however, the Conservation Fellowship Program, Although grazing pressure could Aplomado Falcon hasfailed to recover Oklahoma Cooperative Wildlife Re- conceivably have improved hunting despite increased availability of open searchUnit, Frank M. Chapman Me- successfor Aplomado Falconsby mak- range. morial Fund, and the Western Foun- ing prey more vulnerable to detection dation of Vertebrate Zoology. In addi- and capture, lack of cover probably re- tion, the following individuals deserve ducedpopulations of many prey species The Effect of Pesticide Contamination special thanks for their help: W G by destroyingfood plants and protected Hunt, J.R. Murphy, L.F. Kiff, J. Lang- nesting situations (Brown 1900 and Aplomado Falconsoccupy a feeding ford, H. Flanders, J. Hubbard, K.A. 1904). This may account for the de- niche similar to that occupied by the Arnold, P. Duval, S.F. Fox, L. Ashford, chnessuffered by the MaskedBobwhite PeregrineFalcon, a specieswhose pes- D. Latham, F.L. Knopf, R. Pratt, V ( Colinus virginianusridgwayi) (Brown ticide-related declines have been well- Lehmann, R. Quigley, H. Snyder,and 1900 and 1904; Ellis et al. 1977; Tom- publicized(Ratcliffe 1970). Kiff et al. A.C. Keddy. hnson 1972), ScaledQuail (Callipepla (1981) discoveredthat post-DDT (post- squamata) (Phillips et al. 1964), 1947) eggsof Aplomado Falconsfrom Mearn's Quail ( Cyrtonyxmontezumae) easternMexico averaged25% thinner LITERATURE CITED (Brown 1900 and 1904; Phillips et al. than pre-DDT eggsof this species.This ANTHONY, A. W. 1982. Birds oœsouth- 1964; Oberholser 1974), and a number is a greaterdegree of thinning than that western New Mexico. Auk 9:357-369 of open country fringillids such as found in decliningpopulations of the BAILEY, F. M. 1928. Birds oœNewMexico McCown's Longspur (Calcarius Peregrine(Kiff et al. 1981). New Mexico Department oœGame and mccownii), and Botteri's Sparrow Becauseof their dietary preferences Fish, Sante Fe. (Aimophila botterii), Rufous-winged (Hector 1985), and evidence that the BAIRD, S. F., T. M. BREWER, and R species is heavily contaminated in RIDGWAY. 1905. A history of North Sparrow (Aimophila carpalis), and American Land Birds. Little Brown and Baird'sSparrow (Ammodramus bairdii) Mexico, it is reasonableto assumethat Co., Boston. (Phillips et al. 1964) in 1890-1910. Aplomado Falcons surviving in the BALCH, L. G. 1975. Aplomado Falcon Populations of the White-tailed United Statespast the 1940s may have (Arizona, Southeastern).Birding 7 27- Hawk, Black-shoulderedKite (Elanus been further decimated by pesticide 28. leucurus) (Eisenmann 1971; Pruett- contamination.According to Lehmann, BECHARD, M. J. 1982. Effectof vegetative Jones et al. 1980; Larson 1980), and 5-9 falconsinhabited one 12,000 acre cover on foraging site selection by Swainson's Hawk. Condor 84:153-159 Ferruginous Hawk (Buteo regalis) pastureon the northernpart of the King BENDIRE, C. E. 1887. Notes on a collection (Houston and Bechard 1984) have all Ranch until the early 1950s.These birds of birds' nestsand eggsfrom southern declined in portions of their ranges disappearedbefore brush encroachment Arizona territory. Proc. U.S. National where vegetationalchange has elimi- had an appreciable effect on this pas- Museum 11:551-558.

388 American B•rds,Fall 1987 / BOGUSCH, E R 1952 Brush invasion in HEERMANN, A L 1854 Additions to OBERHOLSER, H C 1974 The bird life the Rao Grande plain of Texas Texas J North American ornithology, with de- of Texas Edited by E B Kancald, Jr, Science,pp. 85-91. scriptionsof new speciesof the genera The University of Texas Press,Austin BOND, F. M. 1972. The Peregrine,Prairie, Actidurus,Podiceps, and Podylymbus. PHILLIPS, A., J. MARSHALL, and G and Aplomado Falconsin the Southwest. Proc. PhiladelphiaAcademy of Sciences MONSON. 1964. The birds of Arizona pp. 51-55 in Symposiumon Rare and 7:177-180. Univ. Arizona Press,Tucson. EndangeredWildlife of the Southwestern HENSHAW, H. 1875. Report upon geo- RATCLIFFE, D. 1970.Changes attributable United States.New Mexico Dept. Game graphicaland geologicalexplorations and to pesticidesin egg breakagefrequency and Fish, Santa Fe. surveyswest of the one hundredth me- and eggshellthickness in some British BREWER, T. M. 1856. North American ridian, Vol. 5--Zoology. U.S. Govt. birds.J. Applied Ecology7:67-107. Zoology, Part I--Raptores and Fissi- Printer, Washington, D.C. PRUETT-JONES, S. G., M. A. PRUETT- rostres. Smithsonian Contribution to HOUSTON, C. S. and M. J. BECHARD. JONES, and R. L. KNIGHT. 1980. The Knowledge.Metcalf and Co., Cambridge. 1984. Decline of the FerruginousHawk White-tailed Kite in North and Middle BROOKS, A. 1933. Some noteson the birds in Saskatchewan. Am. Birds 38:166-170. America. Am. Birds 34:682-688. of Brownsville,Texas. Auk 50:59-63. HOWELL, J., B. SMITH, J. B. HOLT JR., SMITH, A. P. 1910. Miscellaneous bird BROWN, H. 1900. The conditions govern- and D. R. OSBORNE. 1978. Habitat notes from the lower Rio Grande. Condor lng bird life in Arizona. Auk 17:31-34. structureand productivityin Red-tailed 12:93-103. __. 1904. Masked Bobwhite (Colinus Hawks. Bird-Banding49:162-170. STRECKER, J. K. 1930. Field notes on ndgwayi).Auk 21:209-213. HOWELL, T. R. 1972. Birds of the lowland westernTexas birds. Contr. Baylor Uni- BUFFINGTON, L. C. and C. H. HERBEL. pine savannaof northeasternNicaragua. versityMuseum. 22:1-14. 1965.Vegetation changes on a semidesert Condor 74:316-340. TOMLINSON, R. E. 1972. Summary of re- grasslandrange from 1858 to 1963. Eco- HUMPHREY, R. R. 1958. The desert search upon the Yumma Clapper Rail logical Monographs 35:139-164. grassland.The BotanicalReview 24:193- and the Masked BobwhiteQuail. pp. 64- EISENMANN, E. 1971. Range expansion 252. 73 in Symposiumon rareand endangered and population increasein North and JANES, S. W. 1985. Habitat selection in wildlife of the southwestern United Middle America of the White-tailed Kite raptorial birds. pp. 159-188 in Habitat States. New Mexico Dept. Game and (Elanus leucurus).Am. Birds 25:529- selectionin birds, M. Cody (ed.). Aca- Fish, Santa Fe. 536. demic Press,Inc., VAN TYNE, J. and G. M. SUTTON. 1937 ELLIS, D. L., S. J. DOBROTT, and J. G. JOHNSON, A. W. 1965. The birds of Chile The birds of Brewster County, Texas GOODWIN, JR. 1978. pp. 345-354 in and adjacent regions of Argentina, Bo- Museum of Zoology, Univ. Michigan, Endangered birds: Management tech- livia, and Peru. Platt Establecimientos Misc. Pub. No. 37. niquesfor preservingthreatened species. Graffcos, S.A., Buenos Aires. VISHER, S.S. 1910. Notes on the birds of S A. Temple (ed.). Univ. Wisconsin JOHNSTON, M. C. 1963. Past and present Pima County, Arizona. Auk 27:279-288 Press,Madison. grasslandsof southernTexas and north- WAUER, R. H. 1973. Birds of Big Bend EVANS, D. L. 1982. Statusreports on twelve easternMexico. Ecology44:456-466. National Park and vicinity. Univ. Texas raptors.U.S. Dep. Int., Fish and Wildlife KAUFMAN, K., J.P. HUBBARD, and J. Press,Austin. Serv. Spec.Sci. Report--Wildl. No. 238. WITZEMAN. 1980. SouthwestRegion, WEBSTER, F. S. 1972. SouthTexas Region, FISHER, A. K. 1893. The hawks and owls Raptors (Special Attention). Am. Birds Hawks. Am. Birds 26:780-783. of the United States in their relation to 34:918-920. __. 1973. South Texas Region, Hawks agriculture.USDA Bulletin No. 3. KIFF, L. F., D. B. PEAKALL, and D. P. Am. Birds 27:637-639. GLENDENING, G. E. 1952. Some quan- HECTOR. 1980. Eggshellthinning and WILDLIFE HABITAT MANAGEMENT titative data on the increaseof mesquite organochlorineresidues in the bat and STAFF GROUP. 1975. Endangeredand and cactuson a desertgrassland range in aplomadofalcons in Mexico. Proceedings unique fish and wildlife of the south- southernArizona. Ecology33:319-328. 17th International OrnithologicalCon- western national forests. USDA-Forest HARRIS, B. K. 1964. Recent bird records gress.pp. 949-952. Service,Wildlife Habitat Technical Bul- from southeastern New Mexico. Condor LARSON, D. 1980. Increase in the White- letin No. 2. 66:159-161. tailed Kite populationsof California and WILLARD, F. C. 1910. Seenon a day'•sout- HASTINGS, J. R. and R. M. TURNER. Texas--1944-1978. Am. Birds 34:689- ing in southernArizona. Condor 12:110 1964. The changingmile. University of 690. WILLIAMS, F. 1979. SouthernGreat Plains, Arizona Press, Tucson. LEFRANC, M. N. JR., and B. A. MILLSAP. Raptors. Am. Birds 33:191-193. HECTOR, D. P. 1980. Our rare falcon of 1984. A summary of state and federal WITZEMAN, J., J.P. HUBBARD, and K the desertgrassland. Birding 12:92-102. agency raptor management programs. KAUFMAN. 1979. Southwestern Re- 1981. The habitat, diet, and foraging Wildl. Soc. Bull. 12:274-282. gion, Raptors.Am. Birds 33:302-304. behaviorof the AplomadoFalcon, Falco LIGON, J. S. 1961. New Mexico birds and YORK, J. C. and W. A. DICK-PEDDIE femoralis(Temminck). OklahomaState where to find them. Univ. New Mexico 1969. Vegetation changesin southern University, Cooperative Wildlife Re- Press,Albuquerque. New Mexico during the past hundred searchUnit, Unpublished Master's The- MERRILL, J. C. 1878. Notes on the orni- years. Arid Lands in Perspective SlS. thology of southern Texas. Proc. U.S. W. G. McGinnies and B. J. Goldman, 1985. The diet of the Aplomado Fal- National Museum l:118-173. eds. Univ. Arizona Press,Tucson. con (Fa/cofemora/is)in easternMexico. MILLSAP, B. A. 1983. Status reports: The Condor 87:336-342. Aplomado Falcon. Eyass 6:4-5. 1986. Cooperativehunting and its re- MONSON, G. 1942. Notes on some birds lationshipto foragingsuccess and prey of southeastern Arizona. Condor 44:222- size in an avian predator.Ethology 73: 225. --Department of Biology, 247-257. MURPHY, J. R. 1978. Management con- Universityof California, 405 Hilgard 1987. Vegetativestructure, small bird siderations for some western hawks. abundance, and Aplomado Falcon hab- Trans. 43rd North American Wildlife Avenue,Los Angeles,Califorma itat quality in easternMexico. Proc. Nat. and Natural Resources Conference. 90024; SouthwestTexas State Wildlife Federation SouthwestRaptor Wildlife ManagementInst., Washington, University,San Marcos, Texas 78666- ManagementSymposium (in press). D.C. 4616 (presentaddress)

Volume 41, Number 3 389