THE JOURNAL OF RAPTOR RESEARCH A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC. VOL. 30 DECEMBEg 1996 NO. 4 j. RaptorRes. 30(4):175-182 ¸ 1996 The Raptor ResearchFoundation, Inc. SURVIVAL, MOVEMENTS AND HABITAT USE OF APLOMADO FALCONS RELEASED IN SOUTHERN TEXAS CHRISTOPHERJ. PEREZ 1 New MexicoCooperative Fish and WildlifeResearch Unit, New MexicoState University, Las Cruces,NM 88003 U.S.A. PHILLIPJ. ZWANK U.S. NationalBiological Service, New MexicoCooperative Fish and WildlifeResearch Unit, New MexicoState University, Las Cruces,NM 88003 U.S.A. DAVID W. SMITH Departmentof ExperimentalStatistics, New MexicoState University, Las Cruces,NM 88003 U.S.A. A•sTv,ACT.--Aplomado falcons (Falcofemoralis)formerly bred in Texas, New Mexico, and Arizona. Nest- ing in the U.S. waslast documentedin 1952. In 1986, aplomadofalcons were listed as endangeredand efforts to reestablishthem in their former range were begun by releasingcaptive-reared individuals in southern Texas. From 1993-94, 38 hatch-yearfalcons were released on Laguna AtascosaNational Wild- life Refuge.Two to 3 wk after release,28 falconswere recapturedfor attachmentof tail-mountedradio- transmitters.We report on survival,movements, and habitat use of these birds. In 1993 and 1994, four and five mortalities occurred within 2 and 4 wk of release, respectively.From 2-6 mo post-release,11 male and three female radio-taggedaplomado falcons used a home range of about 739 km• (range = 36-281 km2). Most movementsdid not extend beyond10 km from the refuge boundary,but a moni- tored male dispersed136 km north when 70 d old. Averagelinear distanceof daily movementswas 34 _+5 (SD) km. After falconshad been released75 d, they consistentlyused specific areas to forageand roost. Woody plant density averaged 2.6 plants/ha on forage areas and 3.6 plants/ha at roost sites. Ground surfacearea was60% vegetatedin foragingareas and 46% vegetatedat roost sites. KEYWORDS: Aplomadofalctm; Falco femoralis;habitat use;, mortality; movementr, radio telemetry. Sobrevivencia,movimientos y uso de hibitat de Falcofemoralisliberados en el sur de Texas R•SUMEN.--Falcofemoralisse reproduce en Texas, New Mexico y Arizona. La nidificaci6n en los Estados Unidos fue documentadapor filtima vez en 1952. En 1986, F. femoralisfue categorizadocomo "en peligro"; los esfuerzospor reestablecerloen susiireas de reproducci6n comenzaron por liberaci6n de individuos, criados cautivamente, en el sur de Texas. Desde 1993-94, 38 halcones de un afio fueron liberadosen Laguna AtascosaNational Wildlife Refuge. Dos a tres semanasdespues de la liberaci6n, 28 halconesfueron recapturadospara montarlesun radio-transmisor.Nosotros reportamos sobrevivencia, movimientosy uso de hibitat de estasaves. En 1993, cuatro muertes conocidasocurrieron a dossemanas de la liberaci6n. En 1994, 5 muertes conocidasocurrieron durante las cuatro primeras semanasluego de su liberaci6n. De dos a seismeses post-liberaci6n, 11 machosy tres hembrasradio-marcadas usaron un imbito de hogar de alrededorde 73.9 km• (rango 36-281 km•). La mayoriade los movimientosno se extendla mils alii de 10 km del borde del refugio, excepto un macho que se dispers6 136 km al norte, luego de 70 d. E1promedio de distanciaslineares de movimiento diario fue de 34 (SD = 5) km. Present address: U.S. Fish & Wildlife Service, 320 N. Main, Room 225, McAllen, TX 78501 U.S.A. 175 176 PE•z ET •a•. VOL. 30, No. 4 Luegode 75 diasde liberadoslos halcones,ellos en forma consistenteusaron fireas especificas para forrajear y descansar.La densidadpromedio de plantas lefiosasfue de 2.6 plantas/ha en fireasde forrajeo y de 3.6 plantas/ha en sitiosde descanso.La cobertura vegetal fue de un 60% en fireasde forrajeo y de un 46% en sitiosde descanso. [Traducci6n de Ivan Lazo] The distribution of the aplomado falcon (Falco the majorityof the refuge is (2 m above'sea level. The femoralis) in the U.S. formerly extended from landscapeconsists of an irregular pattern of meandering oxbow lakes, brushy clay ridges, coastalsalt/tidal flats, southern Arizona and New Mexico to westcentral and impoundments(USFWS unpubl. rep.). and southern Texas (Sprunt 1955, AOU 1983). Natural vegetationon the refuge is a complex mixture Specimen records and documented sightings in- of temperate, semiarid, tropical, and seashorespecies dicate they were fairly common throughout their whose distribution is primarily determined by elevauon. Six general vegetativetypes occur on the refuge: marshy range until about 1940 but rarely seen thereafter wetland (8296 ha), coastalprairie (5666 ha), thorn scrub (Hector 1987). Nesting in the U.S. was last docu- (3237 ha), savannah(202 ha), grassland(445 ha), and mented in 1952 near Deming, New Mexico (Ligon cropland (421 ha) (USFWS unpubl. rep.). 1961). Reasonsfor the decline of the aplomado Monitored aplomado falcons were captive-bredand falcon are unknown, but habitat alteration by en- raised at the Peregrine Fund, Inc., Boise,Idaho. When about 4 wk of age, young falcons were transported to croachment of woody brush species in former LANWR. Releaseboxes were openedand fledglingswere grasslands,and later widespread use of hydrocar- releasedwhen about 37 d old. Food wasprovided at the bon pesticidessuch as DDT, appear to have been release site until releasedfalcons no longer returned to major contributorsof the decline (Hector 1987). feed. Two to 3 wk following release,21 of 26 falconsreleased Severe pesticide contamination in eastern Mexico in 1993, and seven of 12 releasedin 1994 were recap- and evidence of population declines in northern tured for attachment of tail-mounted radiotransmitters. Mexico (Kiff et al. 1980) led to the speciesbeing Transmittersweighing 4 g with a battery life of 4-6 mo listed as endangered in 1986 (Shull 1986). were attached to males and some females, while radios Failure of aplomado falcons to recolonize their weighing 5 g and lasting 11 mo were used only on female falcons. Reception distanceswere -•1.6 km on ground former range prompted the U.S. Fish and Wildlife and 6-10 km from aircraft. Telemetric monitoring was Service (USFWS) to implement the reintroduction primarily accomplished from the ground, but aerial phase of the Aplomado Falcon Recovery Plan in searcheswere conducted when ground efforts failed to southern Texas (U.S. Fish and Wildlife Service locate falcons for at least 3 d. Locations were derived from a minimum of two bear- 1990). This region was chosen as most suitablefor ings using the strongestsignal method as described by releases,because it appears to have been the area Springer (1979). Locationsestimated from radio bear- where aplomado falcons last occurred in high ings and sightingswere used to constructminimum con- breeding densitiesin the U.S.(Hector 1987, 1990) vex polygons(Jennrich and Turner 1969). Rangesize was and because it is near remnant populations in estimatedusing the Microcomputer Program for Analys•s of Animal Locations (Stiiwe and Blohowiak 1985). Mexico. We used the point-centeredquarter method (Cottam From 1986-89, Peregrine Fund, Inc. personnel and Curtis 1956) to describewoody vegetation structure released 22 aplomado falcons on or in the vicinity and density, and a modified version of the step-point of Laguna Atascosa National Wildlife Refuge method (Evansand Love 1957) to estimateground cover and botanical composition on foraging areas and roost- (LANWR; Cade et al. 1991). Outcomes of these ing sitesused by releasedfalcons. Areas were categorized releases are unknown because birds were not mon- as foraging areas if we observedrecurrent foraging by itored beyond 2 mo post-release.Herein, we report -•1 falcons for )2 wk. Roost sites were defined as areas the survival,movements, and habitat use of aplo- where -•1 falcons roosted -•3 times. mado falcons released in 1993 and 1994. Woody vegetation was sampled at sevenforage areas and two roost sites.Five forage areas and the two roost STUDY AREA AND METHODS sites were on LANWR; the remaining two forage areas were within 2 km of the western and southern bound- LANWR is an 18 268 ha Gulf of Mexico coastalrefuge aries of the refuge. Woody vegetationtransects were cen- located about 32 km north of Brownsville, Texas. The tered on frequently used perch or roost sites.From this refuge was establishedin 1946, primarily for the protec- center point, three linear transectswere establishedthat tion of wintering waterfowl.Management priorities now radiated outward 300 m. Initial transects were selected include protection of endangered species.The refuge randomly and each succeedingtransect was placed 120ø slopestoward the Laguna Madre about 27 cm/km. Ele- on either side of the initial transect. Sampling points vationsof 6-10 m occur on natural clay/sand ridges,but were at the site center, 100 m, and 200 m. Four 90 ø sam- DECEMBER 1996 AP•.OMADO FALCONS RE•.EASED IN TEXAS 177 Table 1. Sex, date released,number of locations,range sizeand number of daysmonitored for radio-taggedaplo- mado falcons released on Laguna AtascosaNational Wildlife Refuge during 1933 and 1994.a NUMBER OF l•q GE DAYS DATE LOCA- SIZE MONI- SEX RELEASED TIONS (km a)b TORED ß ß ß ß ß M I Aug 93 18 49.6 83 oo F 13 Jun 93 23 215.5 149 Gulf M 13 Jun 93 31 59.3 173 of ß M 7Jul 93 13 79.6 132 ß Mexico M 7Jul 93 11 67.1 103 ß ß M 14Jul 93 19 164.8 86 ß ß F 2Jul 93 10 35.7 112 ß ß M 11 Jul 93 24 78.1 89 0 10Km ß ß M 11 Jul 93 12 64.8 66 I I ß M 1 Aug 93 11 86.5 42 M 25 Jul 93 18 46.2 100 M 25 Jul 93 11 55.8 286 F 19 Jul 94 34 277.2 59 M 15 Jun 94 28 281.2 61 Brownsville Individuals monitored for a >2 mon and >10 telemetric and/ Mexico or v•sual locations. Rangesderived from minimum convex polygons. Figure 1. Locationsof 28 aplomado falconsrecorded 6 pling quadrantswere establishedat each samplingpoint mo following releasesin 1993 and 1994 at Laguna Atas- with the transect line and a line perpendicular to the cosa National Wildlife Refuge, Texas.