Within North America, there are KennKaufman many areaswhere the speciescan be identifiedby rangemost of the THEPRACTICED EYE time. Mountain Bluebird, a western IllustrattonsbyKenn Kaufman speciesthat nestsat highelevations andat highlatitudes, has strayed to the Atlantic Coast a number of times. Eastern Bluebirds from eastern North Americahave strayed as far westas southern Arizona, thus enter- ingthe range of thesedentary race S. s.fulva, the "Mexican" Eastern Blue- bird. Surprisingly,the Easternhas not yet beenfound in California.I Bluebirds suspectthat eventuallyCalifornians will find oneby carefullychecking With birdsas brightly HE BLUEBIRDSREPRESENT A throughflocks of MountainBlue- distinctivelyNorth American birdsin theeastern part of the state in colored as male trio.There are only three species in the winter. bluebirds,we mayfall world:Eastern Bluebird (Sialia sialis), With birdsas brightly colored as into the trap of not Western Bluebird ( Sialia mexicana), malebluebirds, we may fall into the and Mountain Bluebird (Sialia cur- trapof not reallynoticing anything really noticinganything rucoides).All threeare found in Cana- but the colors. However, with rela- but the colors.However, da, the United States,and Mexico, tivelyplain females or with problem with relativelyplain but that is practicallythe extentof males,we need to considermore sub- their range--althoughthe Eastern tie clues.There are minor points of females or with problem Bluebird, like a number of other shapeand behavior and non-obvious males,we need to "northern"birds, gets as far southas markingsthat are important for iden- tification in such cases. consider more subtle thepinelands of Nicaragua. clues.
Figure1. Adultmales of WesternBluebird (left), MountainBluebird (center), and EasternBluebird (•ght).
Volume46, Number 1 - 159 Figure2. Adultfemales of WesternBluebird (left), MountainBluebird (center), and EasternBluebird (fight). Noticethe colorsof the undertailcoverts, chest, and back.The differences in shapeshown by MountainBluebird are oftenmore evident than colorsor markings at a distance.
Femalebluebirds are lessflashy and tail (more in adults,less in first- fairlydose to theappearance of the than the males,but theywear soft winterfemales) but theslight differ- graythroat of theWestern. colorsthat are particularlypleasing encesin shadeof blueare not helpful On femaleWesterns, there is often with a dosestudy. In general,their forseparating the species. a distinct line of contrast between the patternsshadow those of the males-- Throat color is often mentioned as brownish-grayback and the blue- with blue replacedby blue-grayor a fieldmark for separatingEastern graynape. Dull femaleEasterns can gray,and deep rust replaced by pale and Western bluebirds,but it can be bebrownish above, but without any rustor warm brownish-gray. Females difficultto judgeon females,since back-to-napecontrast. But on a par- alwaysshow some blue in thewings the whitish chin of the Eastern can be ticulady dull individualof either
Figure3. Variationson EasternBluebird. Left: adult male of the race S.s. fulvafrom Mexico,a permanentresident locally in southeastern Arizona.It tendsto be paler and duller everall (for a givenage/sex class) than the EasternBluebirds found farther east in the United Statesand Canada. Rust• edgings on the feathersof the upperback may be a little moreprevalent on this race, butthey are alsoseen on othermale Easterns in freshplumage. Center and right:two variations on dullfemale Easterns. Some first-winter females look essentially dullgray and brownin the field. An individuallike the oneat the fight, with brownishback and mostly grayish-white threat, mighteven be mistakenfor a WesternBluebird, although its bellyand undertailcoverts are muchwhiter than in that species.
1•0-AmericanBirds, Spring 1992 Figure4. Seasonalvariation in femaleMountain Bluebirds. Fresh plumage (late fall) onright, worn plumage (mid-summer) on left. The paleedges on the wingfeathers are far moreobvious when the plumageis fresh. Worn birds may look darker above, but they also actually mayshow more blue on the upperpartsthen. The wash of orange-buffon the chestis variableat all seasons,but it is occasionallybright enoughto suggesta dullfemale Eastern Bluebird. species,one of thebest marks is the bird,but thedifference is not appar- colorof thelower belly and undertail ent on perchedbirds. (Contrary to coverts:gray in Western,extensively Birders can some publishedstatements, the white in Eastern. wingtipsof MountainBluebird do Mountain Bluebird females are avoidgetting not extend"to or beyondthe tip of oftendepicted as being all shadesof into trouble if they the tail"when the bird isat rest.)The gray.But at times,especially in fresh wingtip-to-tailratio looks about the plumage,they show a strongwash of will look at the same on perchedWestern and orange-buffon thechest and throat. Mountain bluebirds.Western may The brightestof suchindividuals whole bird rather evenseem relatively longer-winged have been confused with Eastern then, perhapsbecause its body is Bluebirdson occasion.Like Eastern, than relyingon shorterand more compact. thisspecies has bright white undertail one or two The longerwings of Mountain coverts. Bluebirdsbecome more apparent Mountain Bluebird has, on aver- "diagnostic"field whenthe birds are flying: in the air age,distinctly longer wings than marks. theylook longer-winged and slightly EasternBluebird. It averagesslightly longer-tailedthan the other two longer-wingedthan WesternBlue- species,and their wingbeats are slow-
Volume 46, Number 1 ß161 Figure5. Theamount of rusty-browncolor on the backof the maleWestern Bluebird is quitevariable. The birds shown do not represent the mostextreme examples, however; some male Westerns lack anytrace of rustycolor on the back.The extent of blueon the throat also varies,although it t•picallyends at the baseof the thruat,as onthe left-handbird here. Many show a patchof blueat the centerof the lowerbreast and upper belly. A fewindividuals have patches of rusty-brownon the face (likethe birdon the left).
erand more graceful. canavoid getting into trouble if they In addition to longer wings, will look at the whole bird rather than Referencesand acknowledgments MountainBluebird also has a longer relyingon oneor two "diagnostic" My illustrationsfor thiscolumn were basedon my fieldsketches done in field marks. bill and longerlegs than the other severalparts of North America,and twospecies. Its bodyshape and pos- There is one bluebirdproblem on specimensin the collectionof the ture alsolook different, with lessof a that may stymieeven a carefulob- Departmentof Ecologyand Evolu- "hunchback"look. With practice, its server:the possibilityof hybrids. tionaryBiology at the Universityof moreelegant stance is apparent even Eastern Bluebird and Mountain Arizonain Tucson.As always,I am atlong distances. Bluebird do interbreed in small num- gratefulto StephenM. Russelland ThomasR. HueIsfor allowing me ac- Male bluebirdsare generallyre- berswhere their nesting ranges over- cess to that collection. Some of the gardcdas easy to identify,and usually lap,primarily in thesouthern Prairie field marks discussedhere were first theyare. However, Western Bluebird Provincesof Canada. In thatregion, pointedout to me by JonL. Dunn. is quitevariable, and some of its ex- hybridsmight be identifiedin the Thanksalso to JanetWitzeman for tremescould be confusing.Some field, with caution; elsewhere,a bird importantinformation. males have no rufous color on the that appearsintermediate might be back,for example.Conversely, some oneof thesehybrids, but the only male Eastern Bluebirds do have ru- safe field identification would be fousedgings on the backfeathers in "unidentified." '• freshplumage. In eithercase, birders
162-AmericanBirds, Spring 1992