April 2001] ShortCommunications 513 Acknowledgements.--VicCarpenter, Bennie Cock- COULTER,M. C., W. D. MCCORT,AND A. L. BRYAN,JR. erel, Carol Eldridge, Lara Hopkins, William Hicks, 1987. Creation of artificial foraging habitat for Michael Reider and Tanya Youngbloodassisted with Wood Storks. Colonial Waterbirds 10:203-210. the various24 h observations.Dan Connellyand Paul DARNELL, R. M., AND R. R. MEIEROTTO.1965. Diurnal Koehler of the National Audubon Society'sSilver- periodicity in the black bullhead, Ictalurusmelas bluff Sanctuarymanaged and maintained the Kath- (Rafinesque). Transactions of the American wood foraging ponds. Keith Bildstein, Carol El- FisheriesSociety 94:1-9. dridge and two anonymousreviewers improved FASOLA,M., AND L. CANOVA.1993. Diel activity of earlier drafts of this manuscript.This projectwas resident and immigrant waterbirds at Lake Tur- funded by financial assistanceaward DE-FC09-96- kana, Kenya. Ibis 135:442-450. SR18546from the U.S. Department of Energy to the KAHL, M.P. 1964. Food ecology of the Wood Stork Universityof Georgia'sSavannah River EcologyLab- (Mycteriaamericana) in Florida.Ecological Mono- oratory,and the U.S. Fish and Wildlife Service--Jack- graphs 34:97-117. sonvilleField Office through a grant to the U.S. Fish KREBS,J. R. 1978. Optimal foraging: Decision rules and Wildlife Service--SavannahCoastal Refuges. for predators. Pages23-63 in BehavioralEcolo- gy, an Evolutionary Approach (J. R. Krebs, and LITERATURE CITED N. B. Davies, Eds.). Blackwell Scientific Publi- cations, London. BAUMAN,P. C., AND J. F. KITCHELL.1974. Diel pat- KUSHLAN,J. A. 1978. Feeding ecology of wading terns of distribution and feeding of bluegill (Le- birds. Pages249-297 in WadingBirds (A. Sprunt pomismacrochirus) in Lake Wingra, Wisconsin. IV, J. C. Ogden, and S. Winkler, Eds.). National Transactionsof the American FisheriesSociety Audubon SocietyResearch Report 7. New York. 103:255-260. KUSHLAN,J. A. 1979. Prey choiceby tactile-foraging BENT, A. C. 1926. Life histories of North America wading birds. Proceedingsof the Colonial Wa- marsh birds. Smithsonian Institution, U.S. Na- terbird Group 3:133-142. tional Museum Bulletin 135. KUSHLAN,J. A. 1981.Resource use strategiesof wad- BRYAN,A. L., JR., M. C. COULTER,AND J. c. PENNY- ing birds. Wilson Bulletin 93:145-163. CUICK. 1995. Foraging strategies and energetic MCNEIL, R., P. DRAPEAU, AND R. PIEROTTI.1993. Noc- costs of foraging flights by breeding Wood turnality in colonial waterbirds: Occurrence, Storks. Condor 97:133-140. special adaptations, and suspected benefits. COMER,J. A., M. C. COULTER,AND A. L. BRYAN,JR. Current Ornithology 10:187-245. 1987. Overwintering locations of Wood Storks SHENKER,J. M., AND J. M. DEAN. 1979. The utilization captured in east-centralGeorgia. Colonial Wa- of an intertidal salt marsh creek by larval and terbirds 10:162-165. juvenile fishes:Abundance, diversity and tem- COULTER,M. C., ANDA. L. BRYAN,JR. 1993. Foraging poral variation. Estuaries2:154-163. ecology of Wood Storks (Mycteriaamericana) in east-centralGeorgia. I. Characteristicsof forag- Received27 December1999, accepted 8 November2000. ing sites. Colonial Waterbirds 16:59-70. Associate Editor: K. Bildstein The Auk 118(2):513-519, 2001 Timing of BreedingRange Occupancy Among High-latitude PasserineMigrants ANNA-MARIE BENSON •'3 AND KEVIN WINKER 2 •AlaskaBird Observatory,P.O. Box 80505, FairbanksAlaska, 99708, USA; and 2Universityof AlaskaMuseum, 907 YukonDrive, Fairbanks Alaska, 99775, USA ABSTRACT.--The brief subarctic summer limits the tumn migration among 18 passerinespecies to ob- time availablefor birds to completetheir reproduc- tain indirect estimatesof the time they occupytheir tive activities,yet the temporalrequirements of high- breeding ranges in northwestern North America. latitude passerinemigrants are not well understood. From 1992 to 1998, the Alaska Bird Observatory Our analysesexamined the timing of springand au- (64ø50'N, 147ø50'W) banded 31,698 individuals dur- ing the most intensive standardizedmist-netting study ever conducted in subarctic North America. 3E-mail: ambensøn@alaskabird'ørg Among the migrants examined, the estimated num- 514 ShortCommunications [Auk, Vol. 118 ber of daysthat specieswere presentin interior Alas- TABLE1. Net-hours of operationand total days of ka ranged from 48 days for adult Alder Flycatchers netting in spring and autumn at Creamer'sField (Empidonaxalnorum) to 129 days for American Rob- Migration Station in Fairbanks, Alaska (1992- ins (Turdusmigratorius). Adults departedsignificant- 1998). ly later in autumnthan immaturesin 10 of 18 species Spring Fall we examined and significantlyearlier than imma- turesin only onespecies, Alder Flycatcher.Breeding Year Net-hours Days Net-hours Days range occupancyof Nearctic-Neotropicmigrants oc- 1992 6,903 42 5,822 46 cursin this regionwithin the range of averagefrost- 1993 10,552 43 13,472 50 free temperaturesin Fairbanks,Alaska, and is sig- 1994 11,252 41 13,935 52 nificantly shorterin duration than amongNearctic- 1995 12,731 45 13,944 57 Nearctic("short-distance") migrants at this latitude. 1996 12,411 44 14,985 57 1997 7,548 42 14,617 66 The high latitudesof North America support a di- 1998 6,800 39 11,853 54 verse avifauna,because during the summermonths Total 68,196 296 88,627 382 the region is characterizedby a nutrient-richenvi- ronment,an extendedphotoperiod, and a hospitable climate.But summerat high latitudesis brief. For ex- ample, the average frost-free period in Fairbanks, The studysite, at Creamer'sField Migration Station Alaskawas 105days from 1905to 1999(from 20 May (CFMS), encompasses-20 ha of the southwestern to 2 September;National Weather Service data). portion Creamer'sField Migratory WaterfowlRefuge Birds that migrate to Alaska are therefore under (731 ha). It is owned by the State of Alaska and op- greatertemporal pressure to completebreeding-sea- eratedby the Alaska Departmentof Fish and Game. sonactivities (such as territory and mate acquisition, The northern portion of CFMS is dominatedby ma- nestbuilding, egg laying, incubation,care of young, ture willow (Salixspp.) and paperbirch (Betula papyr- and molt) than birds at lower latitudes. Yet, the total ifera)bordering a seasonallyflooded wetland domi- amount of time passerinesspend completing the nated by sedges(Carex spp.) and one grassspecies breeding effort is not well known. Few studieshave (Calamagrostiscanadensis). The central sectionof the been conductedover the entire breeding seasonat study area is characterizedby late successionalwhite high latitudes, and thosestudies that have examined spruce(Picea glauca) and balsam poplar (Populusbal- breedingchronology at northernlocations (e.g. Rim- samifera).The southernportion of the study area has mer 1988) may not accuratelydocument departure tremblingaspen (Populus tremuloides), balsam poplar, from the breedinggrounds because of small samples and willow growingnear an agriculturalfield. Except and postbreedingdispersal. for the agriculturalfield, that mosaicof habitattypes Studiessampling migrant passageduring spring is representativeof thehabitats occurring in theboreal and autumn provide an indirect measure of time forestfloodplains of interior Alaska. spenton the breeding grounds.The accuracyof that A standardized mist-netting protocol was con- measureincreases with proximity to a population's ducted at CFMS from 1992-1998using an array of breeding area.We sampledmigrants near the north- 22-50 standard mist nets (30 mm mesh, 2.6 x 12 m). ern and westernlimits of their migrationsduring Nets were arrangedin a north-south direction,per- spring and autumn.Here we examinetiming of pas- pendicularto the TananaValley migrationcorridor, sage at the specieslevel in that region to obtain in- and operateddaily from 0600 to 1300 (Alaska) dur- direct estimatesof the time birds occupytheir breed- ing spring migration (25 April-15 June).During au- ing ranges in the northwestern extreme of North tumn migration (15 July-30 September),nets were America. Additionally, we answer the following openedat approximatelysunrise and closed7 h later. questions:(1) How compressedare breeding-season Samplingat the endsof both seasons(10-15 Juneand activitiesamong high-latitude migrants?(2) Do Ne- 25-30 September)was limited to every other day. arctic-Neotropicmigrants differ from Nearctic-Ne- Nets were closed during inclement weather. Fewer arctic ("short-distance")migrants in the timing of nets were operated in 1992, 1997, and 1998 than in breeding-rangeoccupancy? other years (Table1), and netswere not operatedbe- Studyarea and methods.--Thestudy area is located tween 17 July and 2 August 1992. in Fairbanks, Alaska (64ø5'N, 147ø5'W), near the con- Birds were banded with U.S. Fish and Wildlife Ser- fluence of the Chena and Tanana rivers (elevation 130 vice bands,and data were collectedto determineage m). The TananaValley is a well documentedmigra- (autumnonly, using degree of skull ossification),and tion corridor for many speciesof birds, including breeding condition (spring only, using incubation SandhillCranes (Grus canadensis; Kesse11984), many patchesin femalesand enlarged cloacalprotuber- speciesof raptors(Mcintyre and Ambrose1999), wa- ancesin males).During autumnmigration, estimates terfowl, shorebirds,and passerines(Cooper and Rit- of the percentageof juvenal plumagewere recorded chie 1995). for first-year individuals. April 2001] ShortCommunications 515 To ensureindependence of recordsin thoseanalyses, ing thoseseven years, 31,698 birds of 58 specieswere we used only