THE PRACTICED EYE by Kenn Kaufman and Rick Bowers Photographsby Rick Bowers Curve-billed Thrasher and Bendire's Thrasher for their deeply sickle-shapedbills: billed Thrashersare often among the California Thrasher (Toxostomaredi- most conspicuousbirds in their habi- vivum), Crissal Thrasher (Toxostoma tats. Their loud whit-wheet/ call is crissale), and Le Conte's Thrasher heardin a wide variety of deserttypes, T HOMEIN THEDRY COUNTRY OF (Toxostomalecontei). Ironically, the from saguaro-palo verde associations theWest and Southwest are half bird officially known as the Curve- in Arizona to Texas thom scrub, and a dozen speciesof big ground- billed Thrasher (Toxostoma cur- even in many residential neighbor- foragingsongbirds known as thrashers. virostre) shows less curvature to the hoods.An importantfactor seems to be Their loud and rich songsoften make bill than any of the precedingtrio. Its the presenceof cholla cactus,the pre- them conspicuousto the ear, but they bill is curvedjust a little too muchfor a ferrednest site of the species. areusually less apparent to the eye: not "normal" bird. The main challengein Although Bendire'sThrasher is of- only do they wear subtlesandy browns identifying the Curve-billed Thrasher ten found side by side with its Curve- (the colorsof desertsoil), but they also is separating it from an essentially billed cousin,their habitatpreferences tend to hide in whatever cover is avail- straight-billedbird, Bendire'sThrasher are not identical. Bendire's seems to able. (Toxostomabendirei). This "Practiced avoid mosthilly country,and is absent When scientistswere first naming Eye" looksat the distinctionsbetween from many desertfoothill areaswhere these birds, they threw us a curve. thesetwo subtlesongsters. Curve-billed is common. On the other Three of these birds are most notable Unlike most of their relatives, Curve- hand, Curve-billed is missing from Curve-billed Thrasher. Bendire's Thrasher. Volume 44, Number 3 359 some favored habitats of Bendire's, suchas grasslandwith scatteredyuc- cas, or hedgerowsin farmingcountry. Their rangesoverlap only in Arizona and New Mexico; beyondthis mutual range, Bendire'sextends locally west into California and north into Utah, while Curve-billed is found as far east as the Oklahomapanhandle and the On this Curve-billed central Texas coast. So habitat and Thrasher, photo- graphed in Febru- rangeoften help in identification. ary, the numerous Bendire's is a quieter bird than roundedspots on the Curve-billed Thrasher. It has no atten- underparts are less tion-getting double whistle; its main sharply defined and callnote is a soft chuck. Bendire's earns a bit larger than kudos for its song, however,a sweet those of Bendire' s Thrasher. This is an melodiouscaroling that runs on and individualof the race on, withoutthe start-and-stopjerki- palmeri,from central ness of Curve-billed's (and most other Arizona; birds far- thrashers')songs. Bendire's often sings ther east, such as from lower, more obscureperches, those in southern while Curve-billed tends to burst forth Texas, would tend to show more contrast with songfrom the highestperch avail- able. on the underparts, but the general pat- While they are singing,the open tern there would be bills of thrasherscan give misleading the same. impressionsof shape.But when they are silent, bill shapeis an important field character. Both specieshave fairly long, stoutbills, with somecur- vature to the upper mandible.But the lower edge of the lower mandible shouldbe inspectedcarefully. On typi- cal Bendire's,this lower edgeis virtu- ally straight.On typical Curve-billed, this lower edgeis stronglycurved, and the bill overalllooks longer and heav- ier. Were it not for individual variation, we could identify adults of thesetwo thrashersby bill shapealone; however, some birds look confusinglyinterme- diatein this regard. Bill coloris alsoworth a look. Typi- cally, Curve-billedThrasher has an all- black bill, right to the base.Bendire's often looks slightly paler-billed- dark gray insteadof black -- and the base of the lower mandible is paler still, light tan or flesh. This is often mentionedas a diagnosticmark, but unfortunately,on someCurve-billeds the base of the lower mandible is dis- tinctly pale. Also, both speciesdig in the soil for food, and their bills are of- ten encrusted with bits of dirt or dust, making actualbill color harderto see. Although eye color is sometimes mentioned as a field mark, we have A Curve-billedThrasher singing atop a cholla,the cactusin whichit usuallynests. Pres- had little success with it. It's true that enceor absenceof wing-barsis nol a fieM markfor thesethrashers: this bird is infamy the iris sometimes tends to be more or- wornplumage, and anypale tips on the coverts(which wouM haveformed wing-bars) ange in the adult Curve-billed, more havesimply been worn away. yellow in the adult Bendire's(and in 360 AmericanBirds, Fall 1990 Close-upof a Curve-billedThrasher. Photographed in May, this bird is in fairly worn plumage,but the large rounded spotson its underpartscan still be discerned.The bill looksgenerally heavy and black, but note that the baseof the lower mandiblelooks a little pale-- contradictingan often-quotedfield mark. youngbirds of both species),but many adultsshow an intermediateyellow-or- ange cast to the iris. Practiceon these eyeswill not do you muchgood. On adultsin reasonablyfresh plum- age (mid-autumn to at least early spring), breast pattern is the most reliable field mark. Curve-billed has a pattern of oval-shaped spots, while Bendire's has numerous smaller, darker, arrowhead-shapedmarks. As the plumagebecomes worn duringthe springand early summer,the spotson Curve-billedbecome blurry and faint, while those of Bendire's become less distinctand often smaller.By mid-to- late summer, both species can look completely unmarked on the under- parts. A particularlythorny problem arises in late spring and summerwhen juve- nile thrashers,not longout of the nest, may be encountered.They are easy to separatefrom adults, since juveniles will be in very fresh plumage while adults are rather worn at that season; but separating juveniles of the two speciesfrom each other can be much harder. At this stage, young Curve- billeds may have bills that are shorter and straighterthan thoseof adults.Ju- venilesof both specieshave fine dark marks on the upper breast, somewhat Bendire'sThrasher in winter (photographedin December).At thisangle, thepattern of the similar to the pattern shown by the upperbreast is partially obscured:but we can still seethat the spotsthere are smallerand darkerthan the lowerones, which retain something of the "arrowhead"sitape. adult Bendire's. In some cases, such Volume 44, Number 3 361 birds must be left unidentified. A behavioral quirk worth noting is Bendire'sfrequent habit of cockingits tail up as it runson the ground.Curve- billed seldom raises its tail above hori- zontal as it runs, except for brief momentsas it stopsand the tail swings up and then back down. Of course, this trait is not diagnosticby itself- but the same could be said for most of the field marks discussed here. These two thrashersprove the impor- tanceof checkingas many field char- acters as possible, to build a solid identification. ß •. •\ '• ,•. •. • •' Editor's note: This column is usually writ- ten by Kenn Kaufman and illustratedwith Onthis Bendire sThrasher invery fresh plumage (September), the•ne dark "arrowhead" photographs from VIREO (Visual Re- spotson the underpartsare obvious. sourcesfor Ornithology), the great bird- photocollection at theAcademy of Natural Sciencesof Philadelphia. For this issue, however, we have taken on a guest co- author and photographer, to take advan- tage of Rick Bowers' extensiveexperience At someangles, bill shapeis no help with these thrashers. at all. But on this November bird. we can still see that the spots on the upper breast are small, sharply defined,and dark. These two photos make another com- parison that should not, but sometimes does, create a problem: Bendire's Thrasher (left) rs. Sage Thrasher (right). These birds are both in fresh plumage; their chestpatterns are simi- lar. but the Sage Thrasher showsfat' more contrast. By mid-summer; when the plumage is worn, the contraston SageThrasher will be reduced--but by then. Bendire's will look practically plain-breasted. At any given season, Sage will be the more contrasty bird. and a glance at the calendarshouM be enoughto ride out confusion. 362 American Birds. Fall 1990 .