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Importance of Sycamores to Riparian Birds in Southeastern Arizona

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Importance of Sycamores to Riparian Birds in Southeastern Arizona j. Field Ornithol., 55(1):97-103 IMPORTANCE OF SYCAMORES TO RIPARIAN BIRDS IN SOUTHEASTERN ARIZONA BY CARL E. BOCKAND JANE H. BOCK Southwesternriparian woodlands are major centersof aviandiversity and abundance(Carothers et al. 1974, Stevenset al. 1977, Wauer 1977, Stamp1978, Szaro 1981). Cottonwood(Populusfremontii) communities in lowlandriver valleyshave been well-studied,and the importanceof theselarge trees to riparian birds is striking (Carotherset al. 1974, Andersonand Ohmart 1977, Ohmart et al. 1977). Riparian woodlands at higher elevationsin the Southwestinclude a greater variety of de- ciduoustrees (Paseand Layser 1977), but their bird populationshave not been as thoroughlyexamined (Szaro 1980). Intermittent and perennial streamsassociated with oak (Quercus) woodlandsof southeasternArizona supportriparian communitiesdom- inated by Arizona sycamore(Platanus wrightii), Arizona ash (Fraxinus velutina),and Arizona blackwalnut (Juglans major; Lowe 1964). Because thesestreams are lined with nearly continuousstands of oak, it is not clear that large riparian trees would be as important to birds here as they are in lowlanddesert situations. Among the mid-elevationriparian trees, sycamoresare of potential value to birds becauseof their large size and substantialdead wood. They alsoappear to be one of the mostthreatened tree species.Sexual reproductionseems limited or lackingin sycamorepopulations through- out the region (Glinsky1977, pers.ohs.). Livestock grazing, drying of formerlyperennial streams, and/or flashflooding all appearto play a role in causingthis reproductivefailure. The Appleton-Whittell Re- searchRanch is a 3160 ha sanctuaryof the National AudubonSociety, at about 1500 m elevationin SantaCruz County,southeastern Arizona. The site hasbeen protectedfrom livestockand other disturbancesince 1968. Seedlingsand saplingsof ashand walnut were commonin 1982- 83 along intermittent rocky streamson the sanctuary,but there were only three sycamoresaplings and no seedlingson the entire property. STUDY AREAS AND METHODS As part of a studyof the ecologyof Platanuswrightii, we counted summerand winter birds along 2 drainageson the ResearchRanch-- Lyle Creek, with mature sycamoresand O'Donnell Creek, lackingsyc- amoresbut otherwisecomparable in terms of adjacentupland vegeta- tion, streambedconfiguration, and other riparianplants. Our objectives were to describethe avifaunasof theseriparian ecosystems,and to assess the importanceof sycamoresto the birds associatedwith them. Each site included 1.8 km of streambed,with an averagefloodplain width betweenadjacent oak standsof about 50 m. Numbersof mature riparian trees >30 cm diameter-breast-heightwere as follows: Lyle Creek--47 sycamores,2 cottonwoods,12 ash, 6 walnut; O'Donnell 97 98] c. E. Bockand J. H. Bock j. FieldOrnithol. Winter 1984 Creek--0 sycamores,2 cottonwoods,13 ash, 3 walnut. Each creek was lined with comparablestands of two oak species,Quercus emoryi and Q. arizonica. Scattered shrubs and small trees common to both sites included desert willow (Chilopsislinearis), seep willow (Baccharisglutinosa), and groundsel(Senecio douglasii). Major floodplaingrasses were sacaton(Spo- roboluswrightii), vine mesquite(Panicurn obtusurn), blue grama(Bouteloua gracilis),and sideoatsgrama (B. curtipendula).Both streamswere dry during the summercensus period, and both were flowing in winter. We walked the length of each studysite, countingall birds seenor heard in the floodplainsor in the fringe of oaksimmediately adjacent. We notedwhether or not birdsactually were in sycamoreswhen counted, and recorded activitiesfor all species.Counts were usedas measuresof relative rather than absoluteabundance (Dawson 1981). Possiblebias causedby missingsome birds in the sycamorefoliage would have min- imizedrather than exaggeratedour estimatesof the differencesin abun- danceof the arboreal speciesbetween the canyonswith and without sycamores.Counts were conductedin the morningsof clear and rela- tivelycalm days. Each count required about 2 h, and no sitewas counted more than onceper day. Summercounts (n = 7 per stream)were made between20June and 15July 1982; winter counts(8 per stream)occurred between 19 December 1982 and 6 January 1983. F-ratios were calcu- lated comparingsample variances, and t or approximatet-tests applied accordinglyto test for differencesbetween mean countsper site (Sokal and Rohlf 1981). RESULTS AND DISCUSSION Despitethe general similarityof our two study sites,several species which never occurredin sycamoresdiffered significantlybetween can- yons(Table 1). These includeda varietyof emberizinesparrows which were more abundantin the area without sycamores--BrownTowhee, Rufous-crowned,Botteri's, and Lincoln's sparrows.Absence of syca- moresmay have improvedhabitat for theseground or shrub nesting and foraging species,a relationshipoutside the scopeof the present studywhich deservesfurther attention. We consideredbird speciesto be positivelyaffected by sycamoresif their numberswere significantlygreater in the riparian_site with the trees, and if this differencewas lost or substantiallyreduced when in- dividualsactually counted in sycamoreswere eliminatedfrom the data (Table 1). By thesecriteria, 12 summerspecies were dependentupon sycamoresin riparian habitat: White-wingedDove, Mourning Dove, Western Wood Pewee, Ash-throatedFlycatcher, Cassin's and Western kingbirds,Bridled Titmouse, White-breasted Nuthatch, American Rob- in, Lucy's Warbler, Summer Tanager, Lark Sparrow, and Northern Oriole. Winter birds showinga similar dependenceupon sycamores included the Ladder-backedWoodpecker, Northern Flicker, Bridled Titmouse, White-breastedNuthatch, Ruby-crownedKinglet, Yellow- Vol.55, No. 1 RiparianBirds in Arizona [99 TABLE1. Birdscounted in 1.8 km stripsof riparian habitatwith and withoutsycamores. For specieswhich usedsycamore trees, the secondcolumn of numbers= individualsnot actually in sycamoreswhen they were counted. N = 7 counts/site in summer, 8 in winter. Birds per count Sycamorespresent Sycamores absent All birds Not in sycamores Species • (SO) • (SO) • (SO) A. Summer Montezuma Quail 0.86 (1.57) 0.29 (0.76) (Cyrtonyx montezumae) White-wingedDove 4.00 (2.45)** 2.71 (2.29)* 0.14 (0.38) (Zenaidaasiatica) Mourning Dove 3.29 (2.69)* 1.43 (1.40) 0.14 (0.38) (Z. macroura) Yellow-billed Cuckoo 0.29 (0.49) 0.29 (0.76) (Coccyzusamericanus) Roadrunner 0.14 (0.38) 0 (Geococcyxcalifornianus) Black-chinnedHummingbird 0.71 (0.76) 0.71 (0.76) (Archilocusalexandri) Acorn Woodpecker 3.71 (1.11) 0.86 (0.69)*** 4.57 (0.79) (Melanerpesformicivorus) Ladder-backedWoodpecker 0.89 (0.96) 1.43 (0.79) (Picoidesscalaris) Strickland'sWoodpecker 0.57 (0.79) 0 (P. stricklandi) Northern Flicker 1.71 (1.50) 1.43 (1.27) 0.86 (1.22) (Colaptesauratus) Western Wood Pewee 5.14 (1.22)*** 2.29 (1.89)* 0 (Contopussordidulus) Say'sPhoebe 0 0.14 (0.38) (Sayornissaya) Vermillion Flycatcher 0.43 (0.79) 0.29 (0.49) 0 (Pyrocephalusrubinus) Dusky-cappedFlycatcher 0.29 (0.49) 0.14 (0.38) 0.29 (0.49) (Myiarchustuberculifer) Ash-throatedFlycatcher 8.00 (3.37)* 5.71 (3.25) 4.57 (0.98) (M. cinerascens) Cassin'sKingbird 11.43 (2.44)*** 6.71 (3.04)* 3.43 (1.90) (Tyrannusvociferans) WesternKingbird 1.42 (1.27)* 1.14 (1.68) 0 (T. verticalis) Barn Swallow 0.29 (0.49) 0 (Hirundo rustica) Gray-breastedJay 5.43 (3.95) 4.14 (2.85)* 8.29 (2.63) (Aphelocomaultramarina) Bridled Titmouse 4.00 (2.08)* 2.00 (1.73) 2.00 (1.00) (Parus wollweberi) Bushtit 4.00 (5.26) 3.71 (5.28) 1.14 (1.68) (Psaltriparusminimus) White-breastedNuthatch 2.00 (1.15)* 1.14 (1.22) 0.85 (0.69) (Sitta carolinensis) 100] C.E. Bockand J. H. Bock j. FieldOrnithol. Winter 1984 TABLE 1. Continued. Birds per count Sycamorespresent Sycamores absent All birds Not in sycamores Species • (SD) • (SD) • (SD) Rock Wren 0.29 (0.49)* 1.86 (1.07) (Salpinctesobsoletus) Bewick's Wren 9.29 (1.80) 8.57 (1.90) 8.14 (2.12) (Thyromanesbewichii) Eastern Bluebird 1.00 (1.00) 0.71 (0.95) 1.29 (1.25) (Sialia sialis) American Robin 1.00 (1.00)* 0.71 (1.11) 0 (Turdusmigratorius) Mockingbird 2.00 (0.82)*** 1.57 (0.53)*** 0 (Mimuspolyglottos) Lucy's Warbler 2.71 (1.60)** 1.85 (1.07)** 0.14 (0.38) (Vermivoraluciae) Common Yellowthroat 0.29 (0.49) 0.14 (0.38) (Geothlypistrichas) SummerTanager 1.43 (1.13)* 0.85 (0.90) 0.29 (0.49) (Pirangarubra) Black-headed Grosbeak 0.43 (0.53) 0.29 (0.49) 0.57 (0.53) (Pheucticusmelanocephalus) Blue Grosbeak 2.00 (1.15) 1.71 (1.25) 3.86 (2.61) (Guiracacaerulea) Brown Towhee 1.03 (1.52)* 3.29 (2.29) (Pipilofuscus) Rufous-crownedSparrow 1.43 (1.51) 1.14 (1.07)** 2.86 (0.69) (Aimophilaruficeps) Botteri's Sparrow 0.43 (0.53)* 1.57 (1.13) (A. botterii) Lark Sparrow 1.57 (0.98)** 0.71 (0.76) 0.29 (0.49) (Chondestesgrammacus) Brown-headed Cowbird 4.57 (2.51) 2.43 (1.27) 3.29 (2.43) (Molothrusater) Northern Oriole 1.86 (1.35)* 0.28 (0.49) O.14 (0.38) (Icterusgalbula) Scott's Oriole 0.29 (0.76) 0 (I. parisorum) House Finch 2.29 (2.43) 0.14 (0.38)* 1.71 (1.38) (Carpodacusmexicanus) Total birds 92.74 (8.44)** 60.68 (5.73) 58.86 (4.22) B. Winter Montezuma Quail 2.38 (4.41) Killdeer 0.88 (0.64) (Charadrius vociferus) Mourning Dove 3.75 (3.37) 1.75 (1.75) Acorn Woodpecker 0 0.38 (0.52) Yellow-belliedSapsucker 1.00(1.41) 0.13 (0.35) (Sphyrapicusvarius) Ladder-backedWoodpecker 0.88 (0.64)* 0.13 (0.35) 0.25 (0.46) Northern Flicker 1.50 (1.50)* 1.25 (1.39) 0.13 (0.35) Vol. 55, No. 1 Riparian Birds in Arizona [101 TABLE 1. Continued. Birds per count Sycamorespresent Sycamores absent All birds Not in sycamores Species .• (SD) .• (SD) .q (SD) Black Phoebe 2.25 (0.89)*** 0.25 (0.46)
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