- 2055 30 10 20 30 9 10 20 30 9 19 29 9 19 APR MAY JUN AUG SEP OCT 17 12 4 CENTRAL a a a 2 20 3 10 20 30 9 10 20 30 9 19 29 9 19 APR MAY JUN AUG SEP OCT 30 9 10 20 a 9 19 29 20 10 20 9 19 APR MAY JUN AUG SEP OCT r 2 3- 24.—Migration seasons of Swainson’s thrush in different areas of the state (see Fig. 1) y count of each 2 days. Star symbols represent counts made in other years or by he state; lines without dots represent the eastern side. .
Spring and fall graph lines (1967-1970) show the highother observers. Dot symbols represent counts made on the western s (34 in the spring to 1 in the fall) and southern IIli- There are no published banding data to show destina- '4 in the spring to 1 in the fall). The paucity of fall tions of Swainson’s thrushes that pass through Illinois. Our its in west-central Illinois is a phenomenon which we only record was a bird banded at Almirante, Panama about Nany species. 2,000 miles south-southeast of Illinois on October 13, 1965 25
andkilledatatelevisiontowernearMonticello,Illinoisthe nightofSeptember20-21,1966. FoodHabits Forbes (1903) examined six specimens of Swainson’s thrushestakenincentralandnorthernIllinoisinApriland May, and five taken in September in extreme southern Ilinois. He found the Swainson’s thrush to have the highest consumptionofinsects(98percentofthediet)ofanyofthe thrushes inthe spring. Hymenoptera (31 percent of all food, mainly ants) were a primary food, and the intake of Coleoptera (30 percent) was typically high for thrushes. Caterpillars(22percent)werealsoveryimportant. In the fall the diet was changed greatly, with wild fruit (grapes especially, plus cherries, elderberries, and blackberries) making up 60 percent of the food. Gault (unpublished notes, 1906-1918) frequently observed Swainson’sthrusheseatingelderberriesinthenorth,aswe have also in all parts of the state, but if they have a choice thebirdswilltakepokeberriesbeforeelderberries.Wehave also seen these thrushes feeding on the fruit of Virginia creeper (Parthenocissus quinquefolia). SpecimenData From the large September and October kills of Swainson’s thrushes at television towers in central Illinois, we measuredandcloselyexaminednearly300specimensand saved93asstudyskins.Mostofthebirdscanbeplacedinto three fairly distinct color types with no size differences. About 16 percent cannot be thus segregated. Each type is representedinallsexandagegroups. About 26 percent of all specimens are definitely gray backed(versusreddish)withgray(versusbuffy)faces,indistinct spectacles, and dark lead-gray flanks. We believe thesebirdsrepresentthewesternrace,incana. Another 24 percent of the specimens are gray backed butlessgraythanincana,withveryrichbufffacesanddark olive-grayflanks.Infaceandventralcolorationthesespecimensmatchbirdsfromtherangeofthenominaterace,but theyaremuchtoograybacked.Ifthegroupdoesrepresent a distinct population we cannot identify it. Dr. Earl Godfrey of the National Museum of Canada examined a few specimensofeachofthecolortypesandfeltthatthisgroup wasbestconsideredacolorvariantoftheeasternpopulation swainsont. Specimensinthethirdgroup(34percent)aredefinitely Tas_e 4.—Weights and measurements of Swainson’s thrushes kil ber, mainly since 1966.
1263 225 175 1166 \4 125 S 827 466 ~I on SWAINSON’S THRUSHES KILLED mR SEP. OC Fig.
25.—Numbers of Swainson’s thrushes killed at central. television towers during night migration. The numbers on the graf indicate the total numbers of specimens of all species picked up.
: : : : nite | swainsoni, with reddish backs, distinct spectacles, bufffaces,andpalegrayflanks. Bond(1963)alsobelievedtherewasastrongmig ofwesternbirds(whichheidentifiedasa/mae)throug nois.Forthepresent,preciseallocationofspecimens populationortheotherislessimportantthanthene furthercorroboration,particularlythroughbandins somewesternpopulationisanimportantconstituent Illinoisfauna.Thedefinitewestwardflightsofteler Swainson’sthrushesinthespring(Cochranetaller furtherindicationofthepresenceofwesternbirds. The sex ratio in the sample of specimens was even for adults (Table 4), but immature males ot beredimmaturefemalesabouttwotoone.Theage (three adult males to one immature male, andsi? femalestooneimmaturefemale)donotindicatehis ductivity. Annan (1962) said that immatures £ outnumberedadults,butgavenoprecisefigures:7 alsogivesweightsandmeasurementsofthespecimer led at television towers in central Illinois in September ant Bee Gross Weight (grams) Wing Length (mm) Tail Lengt! Number of ee —— | Age and Sex Specimens Range Mean Range Mean Range | Adult male 18) 27.8-42.0 Soe 95-105 100.1 66-77 | Immature male 41 28.4-43.0 33.5 93-102 97.7 63-73 Adult female 118 26.0-36.8 BOrO 91-99 95.3 63-74 Immature female iN DY f= DI) 31.6 90-99 93.4 60-68 26
RAY-CHEEKED THRUSH (Catharus minimus) (Fig.26and27) ring Migration The spring migration of the gray cheek is similar to t of Swainson’s thrush (Fig. 24 and 28). Both species erallybegintoappearinlateAprilandbecomecommon in early May. Records for northern Illinois on April 2 (Bartel & Reuss 1932, and Bartel 1935a) are abnormal. Even records prior to April 20 are exceptional. By May 30 nearlyallofthegray-cheekpopulationhaspassednorthof the state (Fig. 28). In the south, arrivals around April 20 are expected, and the population is virtually through the south by May 20. A specimen (Southern Illinois University g.
26.—Gray-cheeked thrush.
(Similar in color to the Swainson’s thrush, but without “‘spectacles”’ or buffy face.)
Fig.
27.—General distribution of the graycheeked thrush.
collections)takenJune10insouthernIllinoismustbeconsidered accidental.
Springnumbersofgray-cheekedthrushesshowafairly uniform distribution through the state (Fig. 28), but phenomenalaggregationshavebeenrecordedinnortheastern Illinois especially (Eifrig 1913, and Lewis 1923). Eifrig saw hundreds of gray cheeks in late May and felt that Du PageCountywasonamajor“highway”forthespecies. Gray-cheeked thrushes sing as they pass through Illinois,buttheirsongismuchmoresubduedthanthesongof Swainson’sthrushes,andingeneralgraycheeksappearto be less vociferous. Nelson (1876-1877) noticed that graycheeked thrushes are more likely to sing at times of misty weather. We translate the call notes most often given as “peeeur” and “peee-oort,’” but occasionally gray cheeks also call ‘‘whit,’? a note much more characteristic of the Swainson’sthrush.Wecannotdifferentiate,withcertainty, 28 the migration calls of gray cheeks and veeries. Th piercingcallsareutteredbothatnight,duringactiv ration,andduringtheday,whenthebirdsaregroun TherearenopublishedbandrecoveriesofIllinoi sients,buttelemeteredgraycheekshavetendedtofly lyeastofnorthfromChampaign(Cochranetal.196 FallMigration In nearly 50 years of observations, Benjamin ( earliestfallrecordforthegraycheekinnortheaste noiswasAugust11,anabnormalarrivaldate.Usui firstgraycheeksdonotreachnorthernIllinoisunt August20,andmostofthepopulationhaspassed Illinois by the end of September, though a few! found almost every year until mid-October (Fig. extremesouthernIllinoisthespeciesisconsistently' moninfall.Wehavenorecordsofmorethanones
CENTRAL OCT SOUTH | SPAN OF DATES 10 20 30 10 20 30 J 20 30 9 19 29 9 19 APR MAY JUN AUG SEP OCT -8.—Migration seasons of gray-cheeked thrush in different areas of the state (see Fig. 1).
Spring and fall graph lines (1967-1970) show the laily count of each 2 days. Star symbols represent counts made in other years, or by other observers. Dot symbols represent llinois; lines without dots represent the east. Dashed graph line (north) 1875 and 1927 mainly in Du Page County, and shows the long-term peaks 2 counts made in westrepresents the cumulative counts of birds made by Benjamin T.
Gault and range of migration dates.
day,butgraycheekshavebeenrecordedfromSeptember6 to October 15 in the south (George 1968, and U.S. National Museum specimen).
Wehavefoundthefallpopulationtobegenerallythin, exceptineast-centralIllinois,whereweregularlyseegraycheekedthrushesinnumbers(Fig.28).Ourdataonspringfall ratios of this species, as in the case of the Swainson’s thrush,contrastwiththoseofAnnan(1962).BurtisWilson (Hodges1954)alsonotedthateray-cheekpopulationswere muchsmallerinthefallthaninthespring.Inthenorth,we saw12graycheeksinthespringforevery1seeninthefall. In east-central Illinois the ratio was 2 to 1, in west-central Illinois it was a remarkable 125 to 1, and in the south it wasevenmorelopsided—morethan400inthespringto1 inthefall.
Gray-cheekedthrushes,likeSwainson’sthrushes,are commonfallvictimsoftelevisiontowers.About11percent of all birds killed at central Illinois towers have been gray cheeks. The largest kills occurred between September 16 and 25, which is also the period of our highest fall counts (Fig.
28).
FoodHabits Forbes(1903)examined10gray-cheekspecimenstaken in May. The locality was not given. In its spring insect consumption(93percentofthediet),thegray-cheekedthrush wassecondonlytotheSwainson’sthrush,butthemostdistinctivefeatureofthegraycheek’sdietwasthatantsconstitutedalmosthalfthefood.Nootherthrushapproachedthat intake. Caterpillars (15 percent) were typically prominent in the diet as were crane flies and their larvae (9 percent), butgraycheekstookfewerColeoptera(18percent),especially Carabidae, than other thrushes. Grasshoppers (3 percent),Myriapoda(2percent),andmolluscs(5percent) madeuptherestofthefood.Theintakeofmolluscs,notablySuccineaandHelix,washighforathrush. There have been no studies of the food in fall. Gault (unpublishednotes,1917)sawgraycheekseatingelderberriesinOctober,andwehaveoftenseenthemeatingpokeberriesinSeptemberandOctober.
SpecimenData From the kills of gray-cheeked thrushes at television towers we preserved 265 as study skins. As described by Wallace(1939),twocolorphasesareapparent.Ours shows complete gradation from brownish to grayisl tremes.
In size the gray cheeks vary according to sex anc (Table5).Oneadultmaleandoneadultfemalefellw! thesizerangeofthesmallersoutheasternform,bicl (Wallace 1939), but statistically both were near the i ble extreme limits of normal distribution for our sai Thereisalsothepossibilitythatbothspecimenswel tuallyimmatureswhichhadlostallmarksofimmat) Becauseoftheseconsiderations,weassignedallofthy nois specimens we have examined to the northern, minima.Thusalthoughtheallegedoccurrenceofbie in Illinois (see Ford 1956) is doubtful, the final ar dependsuponothertypesofinvestigationssuchasba operations,telemetryobservations,andbiochemica dies.
The age ratios in our specimens, less than one immatures,(Table5)donotindicatehighproductivit thesamplemaynotberepresentativeofthespecies. VEERY (Catharus fuscescens) (Fig.29and30) SpringMigration The veery’s spring migration coincides very | with the migration of the gray-cheek and Swail thrushes (Fig. 24, 28, and 31). The first veeries 1 appeararoundApril20insouthernIllinoisandApri thenorth.ArrivalsearlierthanApril18areunusual cially in central and northern Illinois, and reco} March and early April (Sanborn 1935, Abbott et al. Sparks 1905, and Walter & Walter 1904) are accide erroneous. | Mostoftheveerypopulationhaspassedsouthe nois by May 20, and the north by May 30 (Fig. 31, thinpopulationremainsincertainareasofnorthe nois to nest. The spring veery populations appea fairlyuniformlydistributedinthestate. The migration calls of the veery are very mu thoseofthegray-cheekedthrush.Ourphonetics calls are ‘‘peee-oort”” or ‘““wheee-ur’” with emphasis first syllable. The calls are uttered both nightal Taste 5.—Weights and measurements of gray-cheeked thrush specimens killed at television towers in central Illinois in Sep and October, mainly since 1966.
Tail Leng Gross Weight (grams) Wing Length (mm) Number of nee Age and Sex Specimens Range Mean Range Mean Range | Adult male 97 BD) 2-28 33.8 96-108 102.8 66-78 Immature male 38 29.5=3929 34.3 95-105 100.6 63-75 Adult female 86 Dat 5) 31.4 94-105 98.1 61-12 Immature female 44 28.3-40.3 32.8 92-102 96.2 56-71 30
spotted of the Illinois Catharus thrushes. (With reddish back).
Fig.
30.—General distribution of the veery.
a noe se ao > gon? RS te oF + AF vn % > if ws p ee ow | a (9° miles Transientveeriesalsosing,butthesongisnotheardasoftenasthesongsofSwainson’sorgray-cheekedthrushes. Distribution The general distribution of the veery is shown in Fig. 30. The nesting distribution in Illinois (Fig. 32) is still poorlyknown,andonlyafewstudentshaveactuallyfound nests (Cooke 1888, Pratt 1890, Ford 1956, and Thompson 1958). The two central Illinois records (Fig. 32), one an allegeddroppedegg(Barnes1890),andtheotherasinging male in Peoria in late June (Silloway 1922), are questionableasactualbreedingrecords.Observersshouldlookfor thespeciesinthesummerthroughoutnorthernandcentral Illinois.
Two types of habitat have been recorded in Illinois. In areas of Winnebago county, Lee Johnson (personal communication)hasfoundnestingveeriesinmaturebottom- 32 land forest. The species has also been recorded in residential habitat (Pratt 1890, and Farwell 1919). field (1951) reported the best nesting habitat in I andOhiotobesandyhillocksinterspersedwithbo; nesting veeries should be looked for in the Illinois areas also.
FallMigration AlfredReuss(personalcommunication)hasnot thebreedingpopulationofveeriesinnortheastern becomesveryinconspicuousinAugust,followingthe alpatternofothernestingspecies.Thedefiniteinc! veeriesinlateAugustisindicativeofmigrationas| ciesalsoappearsthenincentralandsouthernIllinc 31). An August 13 record for extreme southern (Gower1933)isprobablyerroneous.TheveeryS grationislessprolongedthanthemigrationperiod