J. Field Ornithol., 67(2):307-320 LONG-DISTANCE MOVEMENTS BY AMERICAN AVOCETS AND BLACK-NECKED STILTS JULIEA. ROBINSON1 AND LEWISW. ORING Ecology,Evolution & ConservationBiology Program /186 and Departmentof Environmentaland ResourceSciences Universityof Nevada, Reno 1000 ValleyRd. Reno, NV 89512 USA Abstract.wColor-banded American Avocets(Recurvirostra americana) and Black-neckedStilts (Himantopusmexicanus) were resighted>50 km from their banding locationsin the Great Basin.Records from 90 migrationand winterresightings of birdsbanded in the Honey Lake Valley (northeasternCalifornia) and 3 birds banded at Great Salt Lake (Utah) provided unique data on long-distancemovements by individualsof thesespecies. Avocets and stilts left Honey Lake breeding areasand went to stopoverareas at Mono Lake and in the Tulare Basin as early asJuly. Some individualsspent 48 daysor more in the Tulare Basin.Both avocetsand stiltswere observedin siblinggroups during migration.Although one pair of bandedstilts was observed during migration,differences in sexratio at a migrationstopover sitesuggested that male and femalestilts might havedifferent wintering ranges or migration behavior.Avocets from Honey Lake were found wintering along the California coastfrom Arcata southwardand along the westcoast of Sinaloa,Mexico. First-yearavocets were more often seen in coastal areas of California (relative to inland areas) than were adults. Stilts were found wintering in central California. Avocetsand stiltsbanded in Utah were seen in the Tulare Basin (one stilt) and at wintering groundsin Mexico (one avocetand one stilt), indicatingthe potential for populationmixing. We proposethat avocetsmigrate in short hops,retain partial family group associationsduring migration,and may have age-specific differencesin migratorybehavior or winteringrange. We proposethat stiltsretain partial family group associationsduring migration, maintain pair bonds beyond the breeding at- tempt, and have sexualdifferences in migratory behavior or wintering range. These results have important ramificationsfor understandingimpacts of drainwaterevaporation ponds in the Tulare Basin on nonbreeding avocetsand stilts. MOVIMIENTOS DE LARGA DISTANCIA EN RECURVIROSTRA AMERICANA Y EN HIMANTOPUS MEXICANUS Sinopsis.--Individuosde Recurvirostraamericana y de Himantopusmexicanus anillados con colores fueron redetectados visuaimente sobre 50 km de los sitios donde se anillaron en la Gran Cuenca. Registrosde 90 casosde redetecci6n visual de avesmarcadas con bandas de coloresen el Valle del Lago Honey (California nororiental) y tres avesanilladas en Gran Lago Salado (Utah) son datos 6nicos para estudiar movimientosa larga distanciade estas especiesdurante la migraci6ny el invierno.Las aves dejaron las 5teas reproductivas del Lago Honey y fueron a •eas de descansoen el Lago Mono yen la Cuencade Tulare t•n temprano como en julio. Algunasaves estuvieron 48 diaso mssen la Cuencadel Tulare. Arebasespecies se observaronen gruposde hermanosdurante la migraci6n.Aunque durante la migraci6n se observ6un par de Himantopusmexicanus con anillasde colores,las diferenciasen raz6n de sexo detectadasen un lugar de parada migratoria sugierenque existendiferencias en •reas de invernaci6no en comportamientomigratorio entre los sexosde esta especie.In- dividuosde Recurvirostraamericana del Iago Honey se hallaron invernandoa lo largo de la costade California desdeArcata hacia el sur y a lo largo de la costaoeste de Sinaloa,Mexico. Las avesde un afio de Recurvirostraamericana se vieton m•s comfmmenteque los adultos en las costas de California (en relaci6n a zonas mss internas). Se hailaron individuos de Recurvirostra americana invernando en el centro de California. Individuos de Recurvirostra Currentaddress: Department of Biology,University of Houston,Houston, Texas 77204 USA. 307 308] j. A. Robinsonand L. W. O•ing J. Field Ornithol. Spring 1996 americanay de Himantopus mexicanusanillados en Utah se observaron en la Cuenca del Tulare (un ave) yen terrenos de invernar en Mexico (una de cada especie),indicando el potencialpara la mezclainterpoblacional. Proponemos que Recurvirostraamericana migra en pequefiossaltos, retienen asociacionesparciales de gruposfamiliares durante la migra- ci6n, y pueden tener diferenciasentre edadesespecificas con respectoal comportamiento migratorio o en su distribuci6ninvernal. ProponemosademJs que Himantopusmexicanus retienen parcialmenteasociaciones de gruposfamiliares durante la migraci6n,mantienen unionesde parejasm•s alia del esfuerzoen aparearse,y tienen diferenciassexuales en com- portamientomigratorio o en la distribuci6ninvernal. Estos resultados tienen ramificaciones importantespara entenderel impactode las charcasde evaporaci6nde aguasde escorrentia en la Cuencadel Tulare en avesno anidantesde ambasespecies. Wetlandsin the westernUnited Stateshave declined dramaticallysince 1780 (Dahl 1990). For example,inland wetlandsin the CaliforniaCentral Valleyhave declined 91%; wetlandsin Colorado,Idaho, and Nevadahave declined more than 50%; and wetlandsof Utah, Oregon, and Arizona havedeclined by 35% (Dahl 1990). AmericanAvocets (Recurvirostra amer- icana) and Black-neckedStilts (Himantopus mexicanus)are two of the most conspicuousbreeding birds in wetlandsof the Great Basin. Because avocetsand stilts rely on these inland habitatsfor breeding, migration, and wintering, their populationshave declined in responseto this habitat loss(Page and Gill 1994). Dramaticannual changesin wetlandavailability make information on large-scalemovements of shorebirdscritical to con- servingremaining wetlands (Alberico 1993, Skagenand Knopf 1993, Rob- inson and Warnock 1996). In addition to wetland losses,many remaining wetlandsin the western United Stateshave been contaminatedas a result of irrigation (U.S. Fish and Wildlife Service 1992). The discoveryof selenium-inducedteratoge- nesisin avocet and stilt embryosin central California (Hoffman et al. 1988; Ohlendorf et al. 1986a, 1989), has made an understandingof re- curvirostridlife historieseven more important. The impactsof complete reproductive failure at KestersonReservoir (Ohlendorf et al. 1990, Wil- liams et al. 1989), and adverseeffects at other California breeding sites (Grasslands,Ohlendorf et al. 1987;Tulare Basin,Skorupa and Ohlendorf 1991) can be better interpreted if the roles of contaminated wetlands in the species'annual cyclesare known. In particular,it is important to know the role that these wetlandsplay in the migration and wintering of re- curvirostridsbreeding at noncontaminated sitesin western North Amer- ica. Although recurvirostridbreeding and wintering behaviorhas been well- studied (e.g., Boettcher et al. 1994, Evansand Harris 1994, Gibson 1971, Hamilton 1975), and individualswere markedin severalpublished studies (Gibson1971, James 1995, Sordahl1984), relativelylittle informationex- istson long-distancemovements of knownindividuals. As part of breeding population studies,we have conductedlarge-scale banding of avocetsand stiltsat noncontaminatedsites in the Great Basin.The magnitude of this effort, coupledwith the assistanceof numerouscolleagues and volunteers, has provided considerableinformation on long-distancemovements of individual American Avocetsand Black-neckedStilts. Here, we present Vol.67, •o. 2 Avocetand StiltMovements [309 1500- 1371 American .•,, 1992 Avocets 1 1993 1 1994 '• 1000- 632 500 296 295 Females Males Chicks Chicks Honey Lake Valley Great Salt Lake 622 4001 355 200øø1 100 73 81 o Females Males Chicks Chicks Honey Lake Valley Great Salt Lake hou• 1. Numbers of American Avocetsand Black-neckedSdlts banded at Honey Lake Valley, California, and Great Salt Lake, Utah, 1992-1994. resightingsof migratory or wintering individualsand evaluatemigration routes and wintering areasfor each species. STUDY AREAS AND METHODS Totals of 591 adult avocets,2003 juvenile avocets,154 adult stilts,and 977 juvenile stiltswere banded at two sites:the Honey Lake Valley,Cali- fornia and Great Salt Lake, Utah (Fig. 1). Birdswere bandedwith unique combinationsof UV-resistantcolored bands (A. C. Hughes, Ltd., Middle- 310] J. A. Robinsonand L. W. Oring j. FieldOrnithol. Spring 1996 sex,U.K.). Avocetswere sexedby bill curvature(Palmer 1967), and stilts were sexedby plumage (Palmer 1967:151,Prater et al. 1977). Similar proportions of adult femalesand maleswere banded (386:391 for avocets, 73:84 for stilts). In California, most banding was conducted in the Honey Lake Valley from 1992-1994 at three managedwetlands: the Jay Dow, Sr. Wetlands (40ø10'N,120ø13'W), a researchfacility of the Universityof Nevada,Reno, and the two units of the Honey Lake StateWildlife Area, the Dakin Unit (40ø18'N,120ø23'W), and the Fleming Unit (40ø19'N,120ø17'W). Limited banding wasalso conducted at other sitesin the valleyincluding the Wild Goose Hunting Club. (40ø07'N, 120ø13'W), Amedee Hot Springs (40ø18'N,120ø12'W), and alongthe shoreof Honey Lake itself (40ø09'N, 120ø15'W). Juvenile avocetsand stiltswere marked with Utah-specificcolor band combinationsat Great Salt Lake in 1992 and 1993. Banding in Utah was conductedprimarily at Layton Marsh (41ø02'N, 112ø00'W), Ogden Bay Wildlife ManagementArea (41ø12'N, 112ø15'W),Harold Crane Wildlife ManagementArea (41ø20'N,112ø10'W), Bear RiverNational Wildlife Ref- uge (41ø25'N, 112ø15'W),and northeasternFarmington Bay (40ø53'N, 112ø03'W). After trying many different trapping protocols in 1992, the following protocol was adopted in 1993 to minimize disturbanceof breeding birds. Adultswere trapped on the nest after 14