NONGAME WILDLIFE COMMUNITIES IN GRAZED AND UNGRAZED MONTANE RIPARIAN SITES

7 Pages·1991·3.7 MB·English

by  Terri Tucker Schulz

GreatBasinNaturalist51(3), 1991,pp.2S6-292
NONGAMEWILDLIFECOMMUNITIES IN GRAZED
AND UNGR.\ZED MONTANERIPARIAN SITES
TerriTuckerSchulz''and\\'a\neC. Leininger'
Keywords:birds, smallnunninals, Wilsons warbler, uvstcrnjinnpinfimouse, cattlegrazing. RockyMountains.
Colorado,riparianwildlife.
The riparian zone is an important habitat riparianzoneinnorthcentralColorado. Most
type for wildhfe, pro\'iding numerous forag- researchontheeifectsoflivestockgrazingon
ingandbreedingsites (Thomas etal. 1979b). riparian bird communities has been con-
Greater numbers and di\ersit\' of nongame ducted in the arid southwestern United
wildhfe have been found in riparian areas States, andlittleisknownabouttheeffectsof
whencomparedwithuplandhabitatsforbirds lixestock grazing on birds or small mammals
inColorado(Knopf1985)andsmallmammals inmoremesicenvironments.
in Oregon (Cross 1985). Fift\' percent ofthe
nesting bird species in the Southwest (John- StudyAre.\.\xdMethods
sonetal. 1977) and82% ofthose in northern
Colorado(Knopf1985)occurinriparianhabi- This stud\ was conducted within the ri-
tats. Thehighdensityandspeciesdiversityof parian zone bordering Sheep Creek, 75 km
wildlifeinriparianareashavebeenattributed northwest of Fort Collins, Colorado, in the
tothemanystructurallayersofriparian\ege- Roosexelt National Forest, at appro.ximately
tationandtoitsecotonalnature(Thomasetal. 2500m ele\'ation. SheepCreek\ariesfrom 3
1979a). to4min\\idth, withariparianzone25-75m
Livestock grazing can alter vegetative wide.
structureandcompositionofriparianhabitat. According to USDA Forest Service rec-
R>'der(1980)statedthatgrazing, especiallyb> ords, the Sheep Creek Grazing Allotment
livestock and big game, frequentK changes receivede.\tremel\-hea\'ycattlegrazingpres-
plant species composition and growth form, sure until the 1950s. B\' the late 1946s, the
density ofstands, vigor and seed production entire riparian areawas practicalh- denuded,
of plants, and insect production. Bull and with little herbaceous plant coverand only a
Skovlin (1982) attributed to livestock grazing few remnant willow {Salix spp.) stumps re-
the paucity of deciduous woody vegetation maining. The Forest Service and Colorado
thatwas requiredb\-somebird speciesalong Di\isionofWildlifebuilttwoe.xclosuresinthe
Oregonstreams. Annualli\estockgrazingde- fall of 1956 to protect the riparian area from
pressedthenumbersofallsmallmammalspe- lixestock o\ergrazing in an effort to improve
cies observed at Malheur National Wildlife the fisheries habitat. A third exclosure was
RefugeinOregon(Corneh'etal. 1983). Small constructed in the spring of1959. The three
mammal species richness and diversity was exclosuresprotectatotalof40haoftheripar-
higher in 11-year-old e.xclosures in Ne\ada ianzoneand2.5kmofstream. Fencesconsist-
thaninadjacentriparianareasgrazedIn cattle ing of three-strand barbed wire were de-
(MedinandClary1989). signed to restrict onl\ li\estockaccess to the
This study was designed to determine riparian zone. Exclosures and grazed areas
the effects of season-long cattle grazing on were interspersed along a 5-km section of
nongame wildlife communities in a montane SheepCreek(Fig. I).
'RangeScienceDepartment,ColoradoStateUniversity,FortCollins,Colorado80523.
"Presentaddress:RockyMountainForestandRangeExperimentStation.ForestService,Fortt:ollji
286
1991 NOTKS 287
H^
288 GreatBasinNaturalist [Volume51
Table1. Totalbirdobservationson14striptransectsingrazedandnngrazedmontaneripariansitesMay-June1986.
rdspecie; Scientiiicname Excl<
AmericanRobin Turdusmi^rcitontis
Broad-tailedHummingbird Selasphorusplatyccrcus
Brown-headedCowbird Molothrusatcr
Cassin'sFinch Carpodacu.scas.sinii
ChippingSparrow Spizellapasseriiia
Clark'sNutcracker Nucifragacolumhiana
Dark-eyedJunco Juncohyemalis
EmpidonaxFlycatcher Empidonaxspp.
HouseWren Troglodytesaedon
Killdeer Charadriuslocifenis
Lincoln'sSparrow Melospizalincotnii
MacGillivray'sWarbler Oporonistolmiei
MountainChickadee Parusgambeli
MountainBluebird Sialiocurrucoides
NorthernFlicker Colaptesauratus
PineSiskin Cardiielispinus
Ruby-crownedKinglet Reguluscalendula
TreeSwallow Tachycinetabicolor
WarblingVireo Vireogilvus
WesternTanager Pirangaludoviciana
White-crownedSparrow Zonotrichialeucophrys
Wilson'sWarbler Wilsoniapusilla
Yellow-belliedSapsucker Sphyrapicusvarius
Yellow-rumpedWarbler Dendroicacoronata
Numberofindividuals
6 m, following Johnson (1982). The starting have no species in common (Samson and
point of each transect line was randomly Knopf 1982), Morisita's index ofcommunity
locatedbetween 10and20mfrom thefence- overlap was also calculated. Morisita's index
line. Two Museum Special snap-traps were can be interpreted as the probability ofran-
baitedwithpeanutbutterandsetateachsta- domlydrawingtwoindividualsfromtwopop-
tion. Traps were checked and reset every ulations (i.e., grazed areas and exclosures)
morningand evening at dusk. Transect lines thatbothbelongtothesamespecies, relative
were runforfourdays and nights in lateJuly to the probability of randomly drawing two
through August 1986 for a total of 1920 trap individualsofthesamespeciesfromeitherof
nights. Pitfalltrapswerealsosetforcapturing thepopulationsalone(Horn 1966).
shrews. Since trends in shrew abundance
from pitfall traps were consistent with the Results
snap-trap data, only snap-trap data is re-
ported. All collected specimens were frozen Twenty-one bird specieswereobservedin
andlateridentifiedbyU.S. FishandWildlife thegrazedtransects,whereas14specieswere
Service museum personnel in Fort Collins. seen in the exclosures (Table 1). Elevenbird
Shrews were identified following the key of specieswerefoundin bothareas. Totalnum-
JungeandHoffmann(1981). bers ofbird sightings were the same in both
Paired t tests were used to compare total the grazed areas and the exclosures, with 92
numbersofindividualsofeachbirdandsmall observations. The American Robin {Tiirdus
mammal species by transect between grazed mi^ratoruis), with35sightings, wasthemost
areas and exclosures. Homogeneity of vari- abundant species in the grazed areas, while
ances was tested using Bartlett's test (Sokal the Mountain Chickadee {Parus gamhcli),
and Rohlf1981). Simpson's indexofdiversity with 17sightings, wasthe mostcommonspe-
(Simpson 1949) was calculated for exclosures ciesintheexclosmcs(Table 1).
and grazedareas usingbird surveyand small Wilson's Warbler {Wihonia piisilla) was
mammalsnap-trapdata. Siiicetwocommuni- significantly more abundant (F ^ .02) in
ties can have the same index ofdiversity but the exclosure transects. Lincoln's Sparrow
1991 Notes 289
Tmu.i;2. TotalsmallmaiurnalscapturedwitliMuscutnSpc, ip-traps(luinil) 192())in,ura/ed
duuiiia/A'dmontaneripariansitesJiiK-August 19<S(i.
Mammalspecie; Seientil'ie Cra/ed Kxel(
Deeri I'croiiiiisciisiiKiniculdlus
Golde mantled
Least( ipnnmk
Longtailvole
Maskedshrew
Montaneshrew
Mountain\()le
Northernpoeketgopher
Westernjumpingmouse
Total
290 GreatBasinNaturalist [Volume51
areasdominatedbyplaneleafwillowinsouth- Simpsonsdiversityindexindicated similar
eastern Wyoming contain a unique, but de- levels ofdiversity in the nongame communi-
pauperate, assemblageofbirdspecies (Finch tiesingrazedareasandexclosures. Thismea-
1988). Ourstudysupportstheabovefindings. sure of within-habitat diversity reflects the
Wilson's Warbler and Lincoln's Sparrow numberandabundanceofspeciespopulations
appear to have been replaced by ubiquitous within a habitat type (Samson and Knopf
species such as American Robin in grazed 1982). Morisita's index ofoverlap was quite
areasalongSheepCreek. low, suggesting that, although the nongame
SmallMammals communities in grazed areas and exclosures
haveasimilarlevelofdiversity, theyarequite
Patton (1977) stated that small rodents are different in species composition. This value
probably the least understood and docu- indicates a high between-habitat diversity
mented group ofanimals using the riparian across the entire riparian zone. Livestock
habitat. Johnson (1982) felt that grazing in- grazing appears to change habitat structure
creases the density of those small mammal (Schulz and Leininger 1990), resulting in a
speciesthatrequirelowlevelsofcover, while shiftinspeciescompositionofbirdsandsmall
subsequently reducing the density of those mammalsinthemontaneriparianzone,while
requiring higher levels ofcover. Our study maintaining the level of diversity. Riparian
agrees with earlier studies showing that the areas that contain imique species such as
deer mouse is more abundant under grazed Wilson's Warbler are important contributors
conditions(Black 1968,Johnson 1982). toregionaldiversityoftheforest.
In this study, the westernjumping mouse
was more abundant in the exclosures than ManagementConsiderations
in the grazed areas. According to Clark's Riparian zones can be managed for non-
(1971) study in western Wyoming, the west- game species richness by maintaining high
ern jumping mouse prefers moderately wet structural diversity ofvegetation. While the
aspen and shrub-sedge savanna habitats number of nongame species is important,
within 100 m ofwater. This type habitat is managersshouldalsousevaluejudgmentson
morecharacteristicinsidetheexclosuresthan the worth ofindividual species (Balda 1975).
in grazed areas along Sheep Creek (Schulz Thus, management should not maximize the
and Leininger 1990). OurdatasupportCran- numbers of two common species such as
ford's (1983) suggestion that the quality and AmericanRobinandBrown-headedCowbird
typeofvegetationismoreimportantindeter- at the expense ofone sensitive species such
miningsuitablehabitatforthewesternjump- asWilson'sWarbler. SpeciessuchasWilson's
ingmousethantheavailabilityofwater. Warbler, Lincoln's Sparrow, and western
While samplingonly one yearis aconcern jumping mouse that are sensitive to grazing
in this study, small mammal snap-trapping a pressureshouldbemonitoredasindicatorsof
second year would have sampled a replace- habitat change. Johnson (1982) pointed out
ment, notastable, community. Thisreplace- the need to coordinate range and wildlife
ment community may or may not have had habitat management to ensure the existence
the same species composition as the stable ofsensitivewildlifespeciesthatarenegatively
community. impactedbylivestockgrazing.
DiversityPatterns Thisstudysuggeststhatpreviousheavycat-
The three levels ofdiversity, within habi- mtlaelgrcaozmimnguncihtayngceodmptohseibtiirodnatnhdrosumgahllrmedaumc--
tat,betweenhabitat,andregional,areparam- tion of shrub and herbaceous cover. More
eters used to describe wildlife communities. research should be done to determine the
Within-habitatdiversityreferstothenumber effects ofdifferent season-long intensities of
ofspecieswithinanareaofuniformvegetation grazingaswellas different seasonsofgrazing
structure(Noss1983)suchastheSheepCreek onnongamewildlifecommunities.
exclosures. Between-habitatdiversityreflects
thedifferencesseenbetweenhabitatssuchas
Ac:kn()vvledgments
theentireriparianzone(grazedandungrazed
areascombined). Regional diversity refers to This research was funded by the Colo-
thediversityacrossthelandscape(Noss1983). rado State Agricultural Experiment Station,
1991 NOTRS 291
through Project No. 650, and the USDA IloK.N,II.S 1966.MeasnrcnuMitof"ovcMlai^'incompara-
Kangeland Research CIrants Program. Coop- tiveecological studies. .XTMcrican Naturalist 100:
419-424.
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thank Drs. Eric Anderson, Deborah Finch, and management of riparian habitat. USDA
aCnuorntxPi'nloatuhser,reRv.ieRwyedresr,foMr.Jr.evTireliwcian,ganeadrltiweor JohnsonoF,norSsemsJatl1Sl9e8rm2va.imcImemapGlaescnteosrfaolffodTroeesmcthensgitrciaaczlilniRgveepasoltlrootctkRmgeMrn-at4zs3in.ign
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