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Potential Impacts of Climate Change on the SummerDistributions of Southern Ontario's Passerine Birds

Jeff Price

IntroductionWater vapor, carbon dioxide (C02),methane, and other trace gases in theEarth's atmosphere act much likethe glass in a greenhouse, helping toretain heat by trapping and absorb­ing infrared radiation. This "green­house effect" acts to keep the Earth'ssurface temperature significantlywarmer than it would otherwise be,allowing life, as we know it, to exist.However, since pre-industrial times,there have been significant increasesin the concentration of greenhousegases in the atmosphere. The currentlevels of the two primary greenhousegases are now greater than at anytime during at least the past 420,000years (likely much longer) and arewell outside of the bounds of naturalvariability (IPCC 2001).

Accompanying the increases ingreenhouse gases has been anincrease in temperature. The 1990swere the warmest decade and the1900s the warmest century of thelast 1000 years. Of the more than100 years for which instrumentalrecords are available, 1998 was thewarmest year on record, and 7 ofthe top 10 years all occurred in the1990s. The annual global mean tem­perature is now 0.6°C above thatrecorded at the beginning of thecentury. Limited data from other

ONTARIO BIRDS APRIL 2004

sources indicate that the globalmean temperature for the 20th cen­tury is at least as warm as any otherperiod since approximately 1400AD (IPCC 1996,2001). And, "thereis new and stronger evidence thatmost of the warming observed overthe last 50 years is attributable tohuman activities" (IPCC 2001).These activities include the burningof fossil fuels, increases in agricul­ture, and other land use changes(such as deforestation).

Increases in greenhouse gases(past and projected), coupled withthe length of time these gasesremain in the atmosphere, areexpected to cause a continuedincrease in global temperatures.Models estimate that the averageglobal temperature, relative to 1990values, will rise by 1.4°-5.8°C by theyear 2100 (IPCC 2001). Warmingdue to increases in greenhousegases is expected to be even greaterin some areas, especially NorthernHemisphere land areas. Modelsbased on various scenarios for pop­ulation growth, economic wellbeing, improvements in technology,and fossil fuel use project annualaverage temperature increases insouthern Ontario of 3°-6°C in win­ter and 4°-8°C in summer by 2100(Kling et al. 2003). This could leave

southern Ontario with a summer cli­mate similar to that currently expe­rienced in Maryland and northernVirginia in the United States.

How might these changesimpact the summer distributions ofsouthern Ontario's passerine birds?"Recent regional changes in climate,particularly increases in tempera­ture, have already affected hydro­logical systems and terrestrial andmarine ecosystems in many parts ofthe world" (IPCC 2001). For exam­ple, changes in growing season, earli­er spring green-up and earlier arrivaland breeding in some birds have allbeen documented (Root et al. 2003).If these changes have been observedwith only a small rise (0.6°C) in theglobal average temperature, whatmight happen if temperatures con­tinue to rise? In addition to risingtemperatures, many climate modelsalso project an overall increase inevaporation-leading to increases inprecipitation (mostly in storms) butalso to overall declines in soil mois­ture. Lake levels in each of theGreat Lakes are projected todecline, potentially by as much as0.23-0.47 m in Lake Superior and0.99-2.48 m in Lake Huron (Kling etal. 2003). Shifts in the timing of pre­cipitation and snowmelt anddeclines in duration of ice cover arealso all possible. Even after emis­sions are reduced, C02 concentra­tions, temperature and sea level willall continue to rise for a period rang­ing from decades/centuries (C02stabilization, temperature rise) tomillennia (sea-level rise). Thus, cli-

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mate change will likely have a con­tinuing impact on southernOntario's birds and their habitats forsome time to come.

Projected Habitat ChangesTemperature, precipitation and soilmoisture are important factors limit­ing the distribution of both plants andanimals. As the climate changes, sowill plant and animal distributions. Ingeneral, the geographic range ofNorth American plants and animalswill tend to shift poleward and/orupwards in elevation in response totemperature changes. Range shifts inplants will be dependent upon factorssuch as soil types, migratory pathways(e.g., no cities blocking the way), seeddispersal mechanisms and pollinatoravailability. Range shifts of wildlifepopulations will be dependent uponfactors such as the availability ofmigration corridors, suitable habitatsand the concurrent movement of for­age and prey. It is very unlikely thatplant and animal species will respondin the same manner to climatechange. The best available evidencefrom paleoclimatic studies, modelsand observations suggests that eachplant and animal species will moveindependently. Thus, communities aswe now know them will look differ­ent in the future. Indeed, there is evi­dence indicating that many ecosys­tems have already begun to change inresponse to 0 bserved climaticchanges (Root et al. 2003).

Models project possible majorchanges in the suitable climates ofmany vegetation communities

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occurring over the next 75-100years. In the neighbouring GreatLake states, for example, thesemodels estimate that climate suit­able for maple (Acer) - beech(Fagus) - birch (Betula) and elm(Ulmus) - ash (Fraxinus) - cotton­wood (Populus) forests will ulti­mately become more suitable foroak (Quercus) - hickory (Carya )forests (NAST 2000). It is notunreasonable to expect some ofthese changes to occur in southernOntario as well. Increasing temper­atures may also lead to declines inthe extent of boreal forest, at leastalong its southern boundary.

As many tree species are long­lived and migrate slowly, it couldpotentially take decades to cen­turies for species in some vegeta­tion communities to be replaced byothers (Davis and Zabinski 1992).However, as increased tempera­tures and drought stress plants, theybecome more susceptible to firesand insect outbreaks. These distur­bances could playa large role in theconversion of habitats from onetype to another. There could verywell be instances where existingplant communities are lost to dis­turbance but climatic conditionsand migration rates limit the speedat which they are replaced. Thus,invasive species, grasslands andshrublands may transitionallyreplace some of these areas.

Projected Changes in BirdDistributionsSummer bird ranges often are

ONTARIO BIRDS APRIL 2004

assumed to be tightly linked to spe­cific habitats. This generalization isonly partially true. While certainspecies are usually only found inspecific habitats, e.g., Kirtland'sWarbler (Dendroica kirtlandii)breeding in jack pines, others may bemore flexible in their habitat use.Species found in a particular habitattype throughout their breedingrange may not be found in apparent­ly equivalent habitat north or southof their current distribution. Birdsare also limited in their distributionsby their physiology and food avail­ability. The link between physiologyand the winter distributions of manyspecies is well established (Kendeigh1934; Root 1988a, 1988b). Researchincreasingly shows that physiologyplays a role in limiting summer dis­tributions as well (Dawson 1992; T.Martin, pers. comm.). Often, thechoice of a specific habitat may actu­ally be to provide a microclimatesuitable for a species' physiology.While habitat selection, food avail­ability, and competition may all playa role in influencing local distribu­tions of a given bird species, lookingat a species' overall distributionoften yields different results. Thispaper presents results from a studythat examined the associationbetween summer bird distributionsand climate and how these distribu­tions may change with a changingclimate.

MethodsLogistic regression was used todevelop models of the association

between bird distributions (fromBreeding Bird Survey data) and cli­mate. The climate variables used inthis study encompassed both tem­perature and precipitation-the cli­mate variables acting as surrogatesfor the many factors potentiallylimiting a species distribution (e.g.,physiology, habitat, food availabili­ty). One way of determining how"accurate" these models are is tocompare how well the predictedspecies distribution map based onclimate (Figure Ib) matches a mapof the actual distribution (Figurela) based on similar bird data(Price et al. 1995). This comparison(and various statistical tests) indi­cated that at least a portion of thesummer distributions of manyNorth American birds could bemodeled accurately based on cli­mate alone.

The next step was to examinehow bird distributions might changein response to climate change. Forthis study, climate projections fromthe Canadian Climate Centre(CCC) were used to determine whatthe average climate conditionsmight be once C02 has doubled,sometime in the next 75-100 years.For example, for a given point, thedifference in average summer tem­perature between the "current" and"future" (both model-derived) cli­mate might be +2°C. This value isthen added to the actual averagesummer temperature at that point toestimate what the climate at thatpoint might be with a doubling ofC02. These new climate data were

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then used to estimate the probabili­ty of a given BBS route having theproper climate for a species. A morecomplete explanation of methodsused to develop the models andmaps has been published elsewhere(Price 1995; Price, in press).

These results were then used tocreate maps of the projected possi­ble future climatic ranges foralmost all North American passer­ine birds (e.g., Figure lc). Whatthese maps actually show are areasprojected to have the proper cli­mate for a species, or climatic range,under conditions derived from theCCC model. While the results of themodels cannot be used to look atthe fine points of how a givenspecies' distribution might change,they can provide an impression of

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Figure la: Map depicting the distribution of House Wren as detected by theBreeding Bird Survey. This map is based on one found in Price et aI. (1995).

• 40%.60%.80%

Figure Ib: Map depicting a model of the distribution of House Wren based solelyupon the climate of 1985-1989. The scale represents the probability of the species'occurrence, with shaded areas depicting the distribution of the species (i.e., areaswith suitable climate).

ONTARIO BIRDS APRIL 2004

40%.60%.80%

r

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Figure Ie: Map depicting the possible distribution of House Wren under the doubledC02 climate conditions projected by the CCc. The scale represents the probability ofthe species' occurrence, with shaded areas depicting the distribution of the species (i.e.,areas with suitable climate for the species).

the possible direction and potentialmagnitude of the change in the suit­able climate for the species. Thesemaps of projected summer climaticranges of birds were then comparedwith the maps and informationfound in Atlas of the Breeding Birdsof Ontario (Cadman et al. 1987) todetermine how southern Ontario'savifauna might change under thisclimate change scenario.

ResultsSpecies whose future climatic sum­mer ranges might exclude southernOntario (i. e., possibly extirpated assummer residents) - Olive-sidedFlycatcher (Contopus cooperi),Yellow-bellied Flycatcher (Empi-

donax flaviventris), Alder Flycatcher(E. alnorum) , Blue-headed Vireo(Vireo solitarius), Philadelphia Vireo(V. philadelphicus) , Bank Swallow(Riparia riparia) , Cliff Swallow(Petrochelidon pyrrhonota) , BorealChickadee (Poecile hudsonica), Red­breasted Nuthatch (Sitta canadensis),Winter Wren (Troglodytes trog­lodytes), Blue-winged Warbler(Vermivora pinus), TennesseeWarbler (V peregrina), NashvilleWarbler (V ruficapilla) , MagnoliaWarbler (Dendroica magnolia),Cape May Warbler (D. tigrina) ,Yellow-rumped Warbler (D. corona­ta), Black-throated Green Warbler(D. virens) , Blackburnian Warbler(D. fusca) , Bay-breasted Warbler (D.

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castanea), Northern Waterthrush(Seiurus noveboracensis), Connecti­cut Warbler (Oporornis agilis) ,Mourning Warbler (0. philadelphia),Hooded Warbler (Wilsonia citrina) ,Wilson's Warbler (w. pusilla) ,Canada Warbler (w. canadensis),Clay-colored Sparrow (Spizella palli­da), Savannah Sparrow (Passerculussandwichensis), Lincoln's Sparrow(Melospiza lincolnii) , White-throat­ed Sparrow (Zonotrichia albicollis),Dark-eyed Junco (Junco hyemalis),Rusty Blackbird (Euphagus caroli­nus), Brewer's Blackbird (E.cyanocephalus) , Purple Finch(Carpodacus purpureus), PineSiskin (Carduelis pinus) andEvening Grosbeak (Coccothraustesvespertinus).

Species whose future climatic sum­mer ranges in southern Ontariomight contract - Willow Flycatcher(Empidonax traillii) , Least Fly­catcher (E. minimus), WarblingVireo (Vireo gilvus), Tree Swallow(Tachycineta bicolor), Black­capped Chickadee (Poecile atri­capillus), White-breasted Nuthatch(SUta carolinensis) , House Wren(Troglodytes aedon), Gray Catbird(Dumetella carolinensis) , Golden­winged Warbler (Vermivora chry­soptera) , Northern Parula (Parulaamericana), Yellow Warbler (Den­droica petechia), Chestnut-sidedWarbler (D. pensylvanica) , Black­throated Blue Warbler (D.caerulescens) , Black-and-whiteWarbler (Mniotilta varia), Ameri­can Redstart (Setophaga ruticilla) ,

ONTARIO BIRDS APRIL 2004

Ovenbird (Seiurus aurocapilla) ,Scarlet Tanager (Piranga olivacea) ,Vesper Sparrow (Pooecetesgramineus) , Song Sparrow (Melo­spiza melodia), Swamp Sparrow(M. georgiana), Rose-breastedGrosbeak (Pheucticus ludovicia­nus), Bobolink (Dolichonyxoryzivorus) and Baltimore Oriole(Icterus galbula).

Species whose future climaticsummer ranges in southern Ontar­io might expand - Acadian Fly­catcher (Empidonax virescens) ,Loggerhead Shrike (Laniusludovicianus), White-eyed Vireo(Vireo griseus), Yellow-throatedVireo (V. flavifrons), Horned Lark(Eremophila alpestris) , PurpleMartin (Progne subis), TuftedTitmouse (Baeolophus bicolor),Carolina Wren (Thryothorusludovicianus), Eastern Bluebird(Sialia sialis) , Northern Mocking­bird (Mimus polyglottos) , PineWarbler (Dendroica pinus), PrairieWarbler (D. discolor), CeruleanWarbler (D. cerulea), LouisianaWaterthrush (Seiurus motacilla) ,Kentucky Warbler (Oporornis for­mosus), Yellow-breasted Chat(Icteria virens), Eastern Towhee(Pipilo erythrophthalmus) , FieldSparrow (Spizella pusilla) , Grass­hopper Sparrow (Ammodramussavannarum), Northern Cardinal(Cardinalis cardinalis) , Dickcissel(Spiza americana), EasternMeadowlark (Sturnella magna)and Orchard Oriole (Icterusspurius).

Species whose future climatic sum­mer ranges might eventually includesouthern Ontario - Say's Phoebe(Sayornis saya) , Scissor-tailed Fly­catcher (Tyrannus forficatus), Bell'sVireo (Vireo bellii) , CarolinaChickadee (Poecile carolinensis) ,Bewick's Wren (Thryomanesbewickii), Blue Grosbeak (Guiracacaerulea) and Great-tailed Grackle(Quiscalus mexicanus).

DiscussionThese lists are not all-inclusive,since results obtained from modelsof some species were not adequateto assess how their climatic rangesmight change. Nor do the listsinclude those species whose climat­ic ranges in southern Ontario mayundergo little change. Finally, theselists are based on output from a sin­gle commonly used climate model.Using output from different climatemodels may yield somewhat differ­ent results. In addition, the geo­graphic scale of these models, likethose of the underlying climatechange model, is relatively coarse.As such, the models are unable totake into account localized topo­graphic changes and the possibleexistence of suitable microclimates(e.g., along rivers or on north-facingmountain slopes). Therefore, someof the species whose climatic rangesare projected as shifting out ofsouthern Ontario may be able topersist in refugia if suitable micro­climates are available.

It is helpful to consider howspecies' ranges may change to know

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what sorts of changes to look for inthe future. As the average tempera­ture (climate) increases, weatherwill still occur-some years beingcooler and others warmer than oth­erwise expected. So, colonizationwill most likely occur in fits andstarts before a species can truly beconsidered to be established as partof southern Ontario's breeding avi­fauna. In some cases, a species maystart appearing as a vagrant, off andon, for several years before breed­ing is attempted. In other cases, aspecies may start breeding in anarea, then become extirpated, andthen resume breeding-possibly ingreater numbers than before.

How quickly these distribution­al changes might occur is unknown;the rate of change will largely

VOLUME 22 NUMBER 1

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depend on whether limits to a givenspecies' distribution are more close­ly linked with physiology (i.e., cli­mate), vegetation, or some otherfactor. The rate of change will alsolikely be tied to the rate of changeof the climate itself. If the climatechanges relatively slowly, thenspecies may be able to adapt to thenew climate. However, manychanges could occur (and are occur­ring) relatively quickly. One pilotstudy found that the average lati­tude of occurrence of some speciesof Neotropical migrants has alreadyshifted significantly farther north inthe last 20 years, by an average dis­tance of almost 60 miles (100 km)(Price and Root 2001; Price, unpub­lished data). In another study, thearrival date of 20 species of migra­tory birds in Michigan was found tobe 21 days earlier in 1994 than in1965 (Price and Root 2000; Root,unpublished data). Many otherspecies have been found to be arriv­ing and breeding earlier, not only inNorth America but also in Europeand elsewhere (Root et al. 2003).

ConclusionProjected future rapid climatechange is of major concern, espe­cially when viewed in concert withother population stresses (e.g., habi­tat conversion, pollution, invasivespecies). Research and conservationattention needs to be focused notonly on each stressor by itself, butalso on the synergies of multiplestressors acting together. These syn­ergistic stresses are likely to prove

ONTARIO BIRDS APRIL 2004

to be the greatest challenge to birdconservation in the 21st century.Because anticipation of changeimproves the capacity to manage, itis important to understand as muchas possible about the responses ofbirds to a changing climate.

Society may ultimately need toadapt not only to range changes butalso to the loss of ecological servicesnormally provided by birds. Forexample, it may be necessary todevelop adaptations to losses of nat­ural pest control, pollination andseed dispersal. While replacingproviders of these services maysometimes be possible, the alterna­tives may be costly. Finding areplacement for other services, suchas contributions to nutrient cyclingand ecosystem stability/biodiversityare much harder to imagine. In manycases, any attempt at replacementmay represent a net loss (e.g., lossesof the values of wildlife associatedwith recreation, subsistence hunting,cultural and religious ceremonies).

In summary, a high probabilityexists that climate change couldlead to changes in bird distribu­tions. Some of these changes couldoccur (and may be occurring) rela­tively quickly. While these changesmay have some ecological and, pos­sibly, economic effects, the magni­tude of these effects is unknown.Ultimately, the greatest impact onwildlife and vegetation may notcome from climate change itself,but rather from the rate of change.Given enough time, many specieslikely would be able to adapt to cli-

matic shifts, as they have done inthe past. However, the current pro­jected rate of warming is thought tobe greater than has occurred at anytime in the last 10,000 years (IPCC1996). This rate of change couldultimately lead to many changes insouthern Ontario's avifauna.

Birders can help scientists lookfor and document changes in birdranges and populations. Besidesparticipating in regular events likethe Breeding Bird SurveyorChristmas Bird Count, informationis also needed on nesting, arrivaland departure. If you, or your club,

Literature CitedCadman, M.D., P.F.J. Eagles, and F.M.

Helleiner (compilers). 1987. Atlas of theBreeding Birds of Ontario. University ofWaterloo Press, Waterloo, Ontario.

Davis, M.B. and C. Zabinski. 1992. Changesin geographical range resulting from green­house warming: effects on biodiversity inforests. Pp. 297-308 in Global Warming andBiological Diversity (R.L. Peters and TE.Lovejoy, editors). Yale University Press,New Haven, Connecticut.

Dawson, W.R. 1992. Physiological responsesof animals to higher temperatures. Pp.158-170 in Global Warming and BiologicalDiversity (R.L. Peters and TE. Lovejoy,editors). Yale University Press, NewHaven, Connecticut.

[IPCC] Intergovernmental Panel on ClimateChange. 1996. Summary for Policymakers.Pp. 3-7 in Climate Change 1995: TheScience of Climate Change (1.THoughton, L.G. Meira Filho, B.A.Callander, N. Harris, A Kattenberg and K.Maskell, editors). Cambridge UniversityPress, Cambridge, England.

[IPCC] Intergovernmental Panel on ClimateChange. 2001. Climate Change. 2001:Synthesis Report (R.T Watson, editor).Cambridge University Press, Cambridge,England.

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have 10 or more years of data,please contact me at the addresslisted below.

AcknowledgmentsThis study was funded by coopera­tive agreements between the U.S.Environmental Protection Agency,the U.S. Geological Survey andAmerican Bird Conservancy. Theviews expressed herein are solelythose of the author and do not rep­resent the official opinion of theEnvironmental Protection Agencynor the U.S. Geological Survey.

Kendeigh, s.C. 1934. The role of environ­ment in the life of birds. EcologicalMonographs 4: 297-417.

Kling, G.W., K. Hayhoe, L.B. Johnson, J.J.Magnuson, S. Polasky, S.K. Robinson, B.J.Shuter, M.M. Wander, D.J. Wuebbles, D.R.Zak, R.L. Lindroth, S.C. Moser, and M.L.Wilson. 2003. Confronting Climate Changein the Great Lakes Region: Impacts on OurCommunities and Ecosystems. Union ofConcerned Scientists, Cambridge,Massachusetts, and Ecological Society ofAmerica, Washington, D.C.

[NAST] National Assessment SynthesisTeam. 2000. Climate Change Impacts onthe United States: The PotentialConsequences of Climate Variability andChange. Cambridge University Press,Cambridge, England.

Price, J.T. 1995. Potential Impacts of GlobalClimate Change on the SummerDistributions of Some North AmericanGrassland Birds. Ph.D. Dissertation, WayneState University, Detroit, Michigan.

Price, J.T. In press. Potential Impacts ofClimate Change on the SummerDistributions of Some North AmericanGrassland Birds. United States GeologicalService Technical Report.

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Price, J.T. and T.L. Root. 2000. Focus: effectsof climate change on bird distributions andmigration Patterns. Pp. 65-68 in PreparingFor a Changing Climate: The PotentialConsequences of Climate Variability andChange (PI Sousounis and 1M. Bisanz,editors). Atmospheric, Oceanic, and SpaceSciences Department, University ofMichigan, Ann Arbor, Michigan.

Price, J.T. and T.L. Root. 2001. Climatechange and Neotropical migrants.Transactions of the 66th North AmericanWildlife and Natural ResourcesConference: 371-379.

Price, J., S. Droege, and A. Price. 1995. TheSummer Atlas of North American Birds.Academic Press, San Diego, California.

Root, T.L. 1988a. Environmental factorsassociated with avian distributionalboundaries. Journal of Biogeography 15:489-505.

Root, T.L. 1988b. Energetic constraints onavian distributions and abundances.Ecology 69: 330-339.

Root, T.L., J.T. Price, K.R. Hall, S.H.Schneider, C. Rosenzweig and J.A.Pounds. 2003. Fingerprints of global warm­ing on animals and plants. Nature 421:57-60.

Jeff Price, Director of Climate Change Impact Studies, American BirdConservancy, 6525 Gunpark Drive, Suite 370, PMB146, Boulder, Colorado80301

OFO Annual ConventionOakville, Ontario

2 and 3 October 2004

Plan to attend the OFO Annual Convention in Oakville on2 and 3 October 2004. It will be a great weekend of fallbirding, interesting presentations and displays, and fun withfriends. On both Saturday and Sunday, experienced OFObirders will lead groups of convention participants to localhotspots for waterfowl, shorebir~s, and other fall migrants.

Saturday's events at the Pavilion On The Park in Oakvillewill include Ron Scovell's popular book sale, an eveningbanquet, and a special presentation by expert birder BruceMactavish on "Newfoundland Birds: Land, Sea andVagrants". Watch for further details and registration infor­mation with the June issue of OFO News.

ONTARIO BIRDS APRIL 2004