Natural Resource Ecology and Management Natural Resource Ecology and Management Publications 2006 Changing Seasons: Weatherbirds Stephen J. Dinsmore Iowa State University, [email protected] Andrew Farnsworth Cornell Laboratory of Ornithology Follow this and additional works at: http://lib.dr.iastate.edu/nrem_pubs Part of the Meteorology Commons, Natural Resources Management and Policy Commons, Ornithology Commons, and the Population Biology Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ nrem_pubs/44. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Article is brought to you for free and open access by the Natural Resource Ecology and Management at Iowa State University Digital Repository. It has been accepted for inclusion in Natural Resource Ecology and Management Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Changing Seasons: Weatherbirds Abstract The fall migration marks a transition between the breeding and non-breeding seasons. While some species, such as Mourning Dove, are still reproductively active well into autumn, most species that breed north of Mexico and the Caribbean have completed their primary breeding period, and those that migrate are making their way to wintering areas. The ojs ourn to nonbreeding sites includes some epic migrations, some of which are still being discovered--for example, the 11,000-km presumably non-stop flight of baueri Bar-tailed Godwits from coastal Alaska to New Zealand. Most species have much shorter flights, usually broken into segments, and other species reside in the same area year-round or make only facultative movements. Keywords Fall migration, breeding seasons, wintering, migratory paths, weather patterns Disciplines Meteorology | Natural Resources Management and Policy | Ornithology | Population Biology Comments This article is from North American Birds 60 (2006): 14. Posted with permission. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/nrem_pubs/44 TheChanging Seasons: Weatherbirds STEPHENJ. O SMORE ß DEPARTMENTOF NATURALRESOURCE ECOLOGY AND MANAGEMENT ß 339 SCIENCEII ß IOWASTATE UNIVERSITY MES IOWA50011 ß EMAIL:[email protected] I ANDREW FARNSWORTH ß DEPARTMENT OFECOLOGY ANDEVOLUTIONARY BIOLOGY ßCORNELL LABORATORY OFORNITHOLOGY ß 159 UCKERWOetROAD ß I .CA,NE ORK14' i EMAIL: [email protected] It wasanother autumn season filled with •emarkable records ofseabirds inunlikely places. Red- billedTropicbird went un•eported inthe Atlantic after July, despite a wandering bird north to NewBrunswich in summer, but many dozens were •eported off California by birders and re- searchersalike. This adult was photographed nicely off La Manzanilla, Jalisco, Mexico 24 Novem- ber2005. Photoõrapb byStephen J.Dinsmore. of us: birders. betweenthe breedingand non-breed- Here we exam- heingfallseasons. migration While markssome species, atransition such ine the fall 2005 asMourning Dove. are still reproductively ac- migration season livewell intoautumn, most species that breed inlight of some of • north of Mexico and the Caribbean have com- the major weather pleted their primarybreeding period, and patterns, particu- thosethat migrateare makingtheir way to larly the mid-sea- winteringareas. The sojournto nonbreeding sonfrontal activity Figure1. Geostationary Operational Environmental Satellite (GOES) image of North America at0000 UTC, in the East and the 4 October2005. A low-pressure system approaches thePacific coast of North Amaica, visible asa large sitesincludes some epic migrations, some of cloudmess inthe upper left. 5nch storm systems ae sometimes associated withthe appearance ofNearc- which are still beingdiscovered--for exam- record-breaking ticmigrants inwestern Alaska. Note also a largestorm system inthe upper rightof the image over north- ple, the 11,000-kmpresumably non-stop 2005 tropical cy- easternCanada. This type of image shows heat-based radiation from the infrared spectrum, with cooler flight of baueri Bar-tailedGodwits from clone season. In surfacesbrighter and warmer surfaces darker. Because theatmosphere cools with an increase inaltitude, coastal Alaska to New Zealand (Gill et al. reading the sea- cloudsappear asbright areas and land surfaces asdark areas. Itfollows, generally, thatlow clouds will be 2005). Most specieshave much shorter son• regionalre- grayerand higher clouds will he whiter. Tall thunderstorm clouds appear as bright white areas, and fog is difficultto distinguish from land areas. flights,usually broken into segments,and ports, one cannot other speciesreside in the samearea year- fail to noticehow manyof the sightingsdi- Coastregion of theUnited States and Mexico. roundor makeonly facuhative movements. gestedin themare linked to specificweather As in spring,migrating birds balance the pauerns.The more noteworthyreporls are Fallouts:October 2005 costsand risks of migrationwith thebenefits highlightedin SpecialAttention (S.A.) boxes. As manyhave commented, on thesepages of residingin warmerclimes during the non- While the newsfrom pelagicPacific Ocean and elsewhere,there are elementsof bird mi- breedingseason. Chief among those risks is waterswas electrifying, and is coveredexten- grationsuch as its seasonaland daily tim- bad weather.Driven by the forcesof evolu- sivelyin this issue'sarticles, the S.A. boxes ing--and to someextent its magnitudeand tion, inherentmemory, and cuesfrom their weremost often used in regionsin theeastern speciescompositions--that we understand surroundings,birds' decisions about migra- half of the continent, where storm fronts and fairlywell. Indeed,a marvelousaspect of mi- tion affect their survival, and, for most tropicalcyclones dominated the newshead- grationis that it is often somewhatpre- species,these decisions appear to function lines--for humans, birds, and our shared dictable,in the temperatezones at least.Yet, relativelywell, at leastat thespecies level. But habitats--literallyevery day of this season regardlessof the year,there is usuallya sur- whathappens when the forcesof naturein- andwell into December, even overshadowing prising event or two to illuminatethe unpre- terveneand movebirds off their migratory warningsof a coming"bird flu" pandemic. dictablequality of the phenomenawe call paths,that is, when severe weather events dis- The devastatingeffects of theweather events bird migration--amoment when seasonal placethem on a largescale? We knowlittle of thisseason will persistand reverberatefor timing, atmosphericconditions, and geo- about such events,and most of our knowl- decades,in memoryas well as thelandscape: graphicfeatures combine to producean unan- edgeis anecdotal--andgathered by the likes especially,but by no meanssolely, in theGulf ticipatedspectacle of migration:a fallout. Oc- 14 NORTH AMERICAN BIRDS CHANGINGSEASONSI, tober2005 produceda seriesof Boreal Chickadeesalong the such events. When viewed in shores of the Great Lakes was de- broad spatial-temporalterms, tected. Great numbers of both October'sfallouts were spectacu- kingletsand of Yellow-rnmped lar notjust on oneor two nights Warblerswere talliedat typical but overweeks, and not just at migrationhotspots such as Point isolated locations but across en- Pelee,Ontario: 14,000 kinglets tire regions.Though many mi- on 8 Octoberis a mind-boggling gration-relatedevents can be count.By the morning of 9 Octo- connected or related to one an- ber, the frontal boundaryhad other on some level, the events pushedeastward off the Eastern of October 2005 manifest con- Seaboard, where it stalled and nectionswith startlingclarity. occluded.During the week that Global weather systems followed,low pressureintensi- spawn,shift, merge,and dissi- Figure2.GOES image ofNorth America at0000 UTC, 9October 2005. Another storm system isapproaching the fied off southernNew England, pateconstantly and in complex Pacificcoast of North America. Extensive cloud cover associated withthe now-stalled low-pressure center off keepingskies cloudy and ceil- manners,making it difficultto NewEngland isapparent over the northeastem United States. The frontal boundary associated withthis low ings low, as well as producing decidewhere we shouldbegin pressureisnicely demarcated offthe Atlantic coast ofNorth America. Note, also, the area over the central Unit- scatteredrain and light northerly edStates that is f•ee of clouds, apattern characteristic ofan area of high pressure. the narrative about October winds across the northeastern 2005.A reasonablepoint to begincould be in mostcertainly connected to someof the so- UnitedStates (Figure 5). Simultaneously,a late Septemberand earlyOctober over the called"reversed migration" of typicallyconti- largeridge of high pressurein the central northern North PacificOcean, as the first of nental Nearctic/Neotropicalmigrants ob- southernUnited Statesprevented any sub- several large low-pressure systemsap- servedin Alaskalate in Septemberand early stantialatmospheric energy from changing proachedwestern North America (Figure 1). in October,including several notable warblers this pattern but alsocreated favorable mi- This generalmeteorological pattern is well and even Black-headed and Rose-breasted grationconditions across much of the Ohio knownto readersof thisjournal, and meteo- Grosbeaks (one of the former at Gainbell!). Valley.A seriesof major nocturnalmove- rologistspredict the movementsof such