Spring migration of Great EgretsintoOntario: an eBird analysis -46 OB Vol...Spring migration of...

Spring migration of Great Egrets into Ontario:

an eBird analysisD.V. Chip Weseloh and Tyler Hoar

36 Ontario Birds April 2012

IntroductionIn spring, Great Egrets (Ardea alba,henceforth egrets) are known to arrivein Ontario in late March and early April(Speirs 1985, Curry 2006, Weir 2008,Black and Roy 2010). Both Bent (1926)

and McCrimmon et al. (2011) gavespring dates by which egrets reachedcertain northerly migration points, e.g.20 March in Ohio. So, although thereis good information on the timing ofthe egrets’ arrival in or near Ontario,

Literature CitedBlack, J.E. and K.J. Roy (Eds.). 2010. Niagara Birds: a compendium of articles andspecies accounts of the birds of the NiagaraRegion in Ontario. Brock University printingand digital services, Ontario, 703 pp.

Cadman, M.D., D.A. Sutherland, G.G.Beck, D. Lepage and A.R. Couturier (Eds.).2007. Atlas of the Breeding Birds of Ontario,2001-2005. Bird Studies Canada, Environ-ment Canada, Ontario Field Ornithologists,Ontario Ministry of Natural Resources, andOntario Nature, Toronto, xxii + 706 pp.

Curry, R (Ed.). 2006. Birds of Hamilton andsurrounding areas: including all or parts ofBrant, Halton, Haldimand, Niagara, Norfolk,Peel, Waterloo and Wellington. HamiltonNaturalists’ Club, Hamilton, xx + 647 pp.

McNicholl, M.K. and J.L. Cranmer-Byng(Eds.). 1994. Ornithology in Ontario. Special publication number 1, Ontario FieldOrnithologists. Hawk Owl publishing,Whitby, xix + 400 pp.

North American Bird Conservation Initia-tive, U.S. Committee. 2011. The State of theBirds 2011 Report on Public Lands and Wa-ters. U.S. Department of Interior: Washing-ton, DC. 48 pp.

Tozer, R. 2012 (in prep.). Birds of AlgonquinPark. The Friends of Algonquin Park, Whitney, Ontario.

Wood, C., B. Sullivan, M. Iliff, D. Fink andS. Kelling. 2011. eBird: Engaging Birders inScience and Conservation. PLoS Biol 9(12):e1001220. doi:10.1371/journal. pbio.1001220Available online at: http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001220

Mike Burrell, Natural Heritage InformationCentre, Ontario Ministry of Natural Resources, 300 Water St., Peterborough, Ontario K9J 8M5 E-mail: [email protected]

Volume 30 Number 1 37

there is little specific information avail-able on where they arrive from or theroutes that they use to enter Ontario.Considering that there are nestingcolonies of egrets in Ontario located inwestern Lake Erie, on the north shoreof Lake Ontario, on the west shore ofthe Bruce Peninsula and in southernGeorgian Bay, there are several possibleroutes of arrival. For example, egretscould arrive pre dominantly from NewYork via the Niagara Peninsula, fromMichigan and Ohio through EssexCounty and the Lake Erie islands, fromupstate New York around the east endof Lake Ontario or they could come ona broad front across all these areas andlakes Ontario and Erie. The main win-tering area of egrets in eastern NorthAmerica is along the southern Atlanticcoast from North Carolina throughFlorida and into the Caribbean islandsas well as along the Gulf of Mexico(Bystrack 1974, Root 1988).

Spring observations of egrets at vari-ous provincial locations have beenrecorded by Ontario birders for decades(see above) but these observations werenot available widely until well after thefact. In recent years, Ontbirds, the list-serv of the Ontario Field Ornithologists,has facilitated greatly the immediate andwidespread reporting of arriving mi-grants. Now, however, a new online tool,eBird, makes it possible to track species-specific migration (spring or autumn)in real-time and to portray that infor-mation visually on maps to a wide au-dience immediately. eBird is an inter net-

based method of recording bird obser-vations (Burrell 2012, Cadman 2012,eBird. com); it accepts current as wellas historical bird observation records inthe form of “checklists” for given areas.More importantly for one who maywant to analyze bird data, if species-spe-cific records are requested for sequentialtime periods (e.g. the first week of April,second week of April, and third weekof April), eBird will plot the distributionof sightings for those time periods onindividual maps.

Comparing the maps sequentiallyshows the progression of migratorymovements for the requested species.eBird can also provide data on flock sizeand the number of individuals perchecklist. These kinds of data contributeto interesting information on the mi-gration strategy for individual species.In this paper, we demonstrate how eBirdcan be used to track the spring migra-tion of Great Egrets from their winter-ing grounds (in February), throughspring migration (March and April) andinto June, when they are resident ontheir colonies and migration has ceased.The Great Egret is a very suitable speciesfor this exercise as it is large, very visible,often reported and easy to identify.

MethodseBird data were retrieved and analyzedthrough the Avian Knowledge Network(AKN,http://www.avianknowledge.net/content/contribute/the-bird-monitor -ing- data-exchange). For this paper, ourstudy area was the Great Lakes Basin


Figure 1. The Great Lakes study area including state/provincial boundaries, place names and locations of breeding colonies of Great Egrets (purple dots, those in Canada are numbered). 1. Gull Island, Presqu’ile Provincial Park, Brighton, 2. Toronto Harbour, 3. Nottawasaga Island,Collingwood, 4. Chantry Island, Southampton, 5. Walpole Island, Wallaceburg.

though larger areas were often used toshow a show a broader perspective. Werequested all eBird records of GreatEgrets for North America (AKN ac-cessed 26 February 2012). This pro-vided a dataset in excess of 400,000records and allowed for analysis of dailyegret records from the study area.

From the above records, we screenedfor reports of egrets for six time periodsfor the years 1900 – 2012. Taking lateMarch as the earliest average arrivaldates for egrets in southern Ontario(see above), we estimated that recordsfrom the first week of March onwards,would show the migration towards andinto Ontario. We chose the dates 1 –15 and 16 – 31 March and 1 – 10 and

11 – 20 April to reflect the initial andongoing stages of spring migration intoOntario. We used the shorter time pe-riods in April to allow for a finer pres-entation and analysis of the data andfor the greater volume of reports as mi-gration into the Great Lakes Basin pro-gressed. We also used data from 1 –15February to show the winter distribu-tion of egrets in eastern North Americaand data from 1 – 15 June to show thesum mer distribution of egrets in south-ern Ontario after migration was over.

The locations of checklists reportingegrets were plotted on maps. Politicaljurisdictions, geographical place namesand locations of breeding colonies ofegrets within the study area (Peck 2007,


CWS unpubl. data, F. Cuthbert unpub-ldata), to which at least some of thesebirds probably were headed, are shownin Figure 1. For clarity’s sake, these areonly shown on Figure 1 and not onFigures 2 – 7.

ResultsThe winter distribution (1 – 15 Febru-ary) of egrets in eastern North Americais shown in Figure 2. There are threesightings from Ohio (south of LakeErie) but the rest of the sightings comefrom the U.S. coast from New York toNew Orleans, the inland half of thesoutheastern U.S. and the CaribbeanIslands.

Figure 2. The distribution of eBird checklists report-ing Great Egrets from the area east of the MississippiRiver during the winter period 1 – 15 February.


Figure 3. The distribution of eBird checklists reporting Great Egrets fromthe Great Lakes Basin during 1 – 15 March.

Figure 4. The distribution of eBird checklists reporting Great Egrets from the area east of the Mississippi River during 16 – 31 March. Arrows indicate possible areas of concentrated migration (see text).

For the period 1 – 15 March (Figure 3), eBird data showed 10 locations whereegrets were reported: five from Ohio, two from Michigan and one each from Indi-ana, Illinois and Wisconsin. None were reported in Ontario and none were reportedfrom the Niagara Peninsula or along the eastern end of Lake Ontario. For thelatter half of March (16 – 31 March, Figure 4), there was a massive increase in thenumber of checklists which reported egrets in the Great Lakes Basin area (on eachchecklist the number of egrets reported is variable). Along the Great Lakes, therewere major areas of concentration in western Lake Erie and southern Lake Michigan.There is evidence of a line of observations (a migration corridor/ route?) from justnorth of Chesapeake Bay in Maryland northwest towards western Lake Erie. Thereis also evidence of an area of concentration in southern Illinois with possible linesof observation moving northeast towards both southern Lake Michigan and,

slightly more easterly, towards western Lake Erie. It also appears thatthere is a line of observations northward along the west coast of LakeMichigan. There are a few reports of egrets from the Niagara Penin-sula-Finger Lakes. This may be suggestive of a minor migration cor-ridor along this route as well. It is noteworthy to see that there are noreports from the eastern two-thirds of the south shore of Lake Erie orthe eastern end and north shore of Lake Ontario.

During the first ten days of April (Figure 5), the areas of intenseegret reporting and the lines of observation observed in late Marchare still evident. Areas of concentration include south/southwesternLake Michigan and western Lake Erie. Lines of egret reporting extendfrom southwestern Illinois at the Missouri border to southern LakeMichigan and then up the west shore of that lake to southern GreenBay and into south-central Wisconsin. A line of observation also ex-tends from southern Illinois to the northeast towards western LakeErie. This line seems to be joined by one extending northwestwardfrom the area of Delaware-Maryland and the Chesapeake Bay on theAtlantic coast. Once at the western end of Lake Erie, lines of obser-vation go NNW towards Saginaw Bay (Michigan) and to the eastand northeast into Ontario. The minor line of observation throughthe Finger Lakes-Niagara Peninsula still persists and may be originatingin Massachusetts.


For 11 –20 April (Figure 6), all ofthe apparent lines of observation de-scribed for 1 – 10 April (Figure 5) arestill present. The concentration of egretreports in S/SW Lake Michigan haveexpanded northwestward into SE Min-nesota. The two-pronged movement NEout of southern Illinois is still evident.The movement out of the ChesapeakeBay areas appears to be on more of abroad front than previously. There are

more egret reports in central southernOntario and along the north shore ofLake Ontario than previously, as well.

There are still noteworthy areas offew if any reports: the eastern shore ofLake Michigan and the upper peninsulaof Michigan and all of eastern Ontarioand the Adirondack mountains in north-ern New York. There are a small numberof reports up the east side of New YorkState, perhaps following the Hudson


River and Lake Champlain valleys. Tothe northwest of there, egrets appearagain in the St. Lawrence River and theOttawa River. It remains to be seen, how-ever, if that is a continuous migrationcorridor. Back on the Atlantic coast,egrets have moved into coastal Maineduring this period.

The data for 1 – 15 June (Figure 7)show the summer distribution of egretsightings in southern Ontario and the

Great Lakes. The major areas of reportingare the corridor from western Lake Erieto Saginaw Bay and the entire westernshore of Lake Michigan and inland incentral Wisconsin. Lesser areas of report-ing are the north shore of lake Ontario,the base of the Bruce Peninsula and sur-rounding area and the area from the Ni-agara River east to the Finger Lakes.

DiscussionThe eBird data for early spring migration(March – mid-April) of egrets into theGreat Lakes Basin show the largest areaof reporting comes from the western endof Lake Erie after arriving from the south-east and the southwest. From there, thereis a strong movement NNW towardsSaginaw Bay (Michigan) and, oncearound the west end of Lake Erie, egretsalso appear to go eastward along thenorth shore of Lake Erie, where therecould be a mixing with egrets who havecrossed Lake Erie via the archipelago ofthe western Lake Erie islands. The southend of Lake Michigan (though not ofconsequence for Ontario) is a secondarea of major arrivals. Egrets may havearrived there via a NW movement from(or before reaching) western Lake Eriebut also via a strong line of observationfrom southern Illinois. Such a movement

Figure 5. The distribution of eBird checklists reporting Great Egrets from the area east of theMississippi River during 1 – 10 April. Arrows indicate possible areas of concentrated migration.

Figure 6. The distribution of eBird checklists reporting Great Egrets from the area east of the MississippiRiver during 11 – 20 April. Arrows indicate possible areas of concentrated migration.


would suggest those birds originated from the Gulf of Mexico as opposed tothe birds at the west end of Lake Erie which probably arrived from the Atlanticcoast. There appears to be a small and not very concentrated movement ofegrets westward through the Niagara Peninsula and little or no movementaround the east end of Lake Ontario. Thus, most Great Egrets would appear tocome into Ontario via Essex County.

In using eBird data, it must be remembered that records come from wherebirders submit their checklists. When an area does not show any birds (egrets)present, the first question one must ask is “Does the lack of reports indicate nobirds or no birders in a given area?” For example, the few reports of egrets inspring from the Ontario portion of the Niagara Peninsula is probably reflective

Figure 7. The distribution of eBird checklists reporting Great Egretsfrom the Great Lakes Basin area during the summer, non-migratoryperiod 1 – 15 June.


of few egrets. There would seem to be many birdersin that area given the human population of the area(Buffalo, Fort Erie, Niagara Falls (NY and ON), St.Catharines, Grimsby, Hamilton, etc.). However, thelack of reports in other areas, i.e. on the east shoreof Georgian Bay or the relatively few reports fromsouthern the Georgian Bay area (given it is the loca-tion of Ontario’s largest breeding colony of egrets),probably reflects a small number of birders reportingin those areas.

Given this caveat, the small number of reportsof egrets using the east end of Lake Ontario, as aspring access route into the province, might be fairlyaccurate. There is a good representation of Ontariobirders at the east end of Lake Ontario and appar-ently few egrets in spring (Weir 2008). However, asecond caveat, noted by Cadman (2012) is that(until recently) birders in Ontario/Canada did notyet use eBird as widely as did birders in the U.S.


This has changed dramatically in the lastyear; eBird reports from Ontario birdersare now second only to those from bird-ers in California (see eBird.com).

Another interesting feature con-tributed by this eBird analysis pertainsto the use of roost sites by egrets inspring. Birders reporting egrets on theOntbirds listserv and other Ontario bird-ers have helped us locate upwards of 40autumn roosting sites of egrets in theLower Great Lakes Basin (DVCW un-publ. data). Very few of these roosts ap-pear to be occupied in the spring, thoughour coverage then is somewhat limited.However, one of the roosts that is activein spring is at Muddy Creek in easternEssex County (Weseloh and Worming-ton 2010). It stands to reason that therecould be large numbers of egrets in theEssex County area in the spring, as a re-sult of a major movement of birds east-ward along the north shore of Lake Eriefrom the Detroit River and northwardacross the Pelee Island archipelago. Theroost site at Muddy Creek might be oneof the first traditional and safe overnightresting areas egrets encounter as theycome from northern Ohio, followingthe migration routes proposed here.

Hopefully, this account gives ourreaders a first-hand view of the type ofinformation and analysis that is availableby contributing their checklists of birdobservations to eBird. We also encourageOntario birders to visit eBird and theAKN and investigate the data for theirfavourite species.

AcknowledgementsWe would like to thank Christian Friis, DaveMoore, Chris Risley, Glenn Coady, KarlKonze, Brigitte Collins and Sue Humphreyfor commenting on earlier versions of thismanuscript.

Literature CitedBent, A.C. 1926. Life histories of NorthAmerican marsh birds. Bulletin of the U.S.National Museum, No.135, Washington,D.C. 392 pp. (Dover reprint 1963).

Black, J. E. and K. J. Roy. [Eds.]. 2010. Niagara Birds: a compendium of articles andspecies accounts of the birds of the NiagaraRegion in Ontario. Brock University Printingand Digital Service, St. Catharines, Ontario.703 pp.

Burrell, M.V.A. 2012. eBird: a proposedprovincial standard for regional bird record-keeping. Ontario Birds 30: 30-35

Bystrack, D. [Ed.] 1974. Wintering areas ofbird species potentially hazardous to aircraft.National Audubon Society and the U.S. Fishand Wildlife Service. 156 pp.

Cadman, M. 2012. Your local birding canhelp conserve Canada’s Boreal Birds. OFO News 30:6-7

Curry, R. 2006. Birds of Hamilton and surrounding area. Hamilton NaturalistsClub. Hamilton, Ontario. 647 pp.

McCrimmon, D. A., Jr., J.C. Ogden andG.T. Bancroft. 2011. Great Egret. (Ardeaalba). In Birds of North America, No. 570(A. Poole and F. Gill, eds.). The Birds ofNorth America, Inc., Philadelphia, Pa.


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SV 42-8

Peck, G.K. 2007. Great Egret, pp 160-161in Cadman, M.D., D.A. Sutherland, G.G.Beck, D. Lepage, and A.R. Couturier, eds.Atlas of the Breeding Birds of Ontario, 2001-2005. Bird Studies Canada, Environ-ment Canada, Ontario Field Ornithologists,Ontario Ministry of natural resources, andOntario Nature, Toronto, xxii + 706 pp."

Root, T. 1988. Atlas of wintering NorthAmerican birds: an analysis of ChristmasBird Count data. University of ChicagoPress, Chicago. 312 pp.

Speirs, J.M. 1985. Birds of Ontario. NaturalHeritage/Natural History Inc., Toronto, Ontario. 986 pp.

Weir, R.D. 2008. Birds of the Kingston Region. 2nd Ed. Kingston Field naturalists.Kingston, Ontario. 611 pp.

D.V. Chip Weseloh, Environment Canada,Canadian Wildlife Service – Ontario Region,4905 Dufferin St., Toronto, Ontario. M3H 5T4. E-mail: [email protected]

Tyler Hoar, 746 Bessborough Drive, Oshawa, Ontario. L1G 4H2

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