Influence of Agriculture on Waterbird, Wader, and Shorebird Use Along the Lower Colorado River 1
Robert D. Ohmart2 , Be rtin W. Anderson3 , and
Wil liam C. Hunter 4
Abs t ract.--Wat er bird, wader, and shorebird use of the Colorado River was restricted to habitats i n or i mmediately ad j acent to t he river prior to agricultural development. ~e studied agricultural habitats systematicall y for t hree years and identified those agricultura l se t ting s t hat were most import ant for individual spe cie s and groups of wa t erbirds , waders , and shorebirds .
I NTRODUCTION waders are associated with open wa t er and marsh habitats which, l i ke agricult ural areas, hav e The importance of ri par i an habit ats to wild increased substa ntially since t he beginning of t he and t heir rapid disa ppearance in t he wes tern 20th cent ury (Ohmart et al. 1977). Many of these has received much attent ion ov e r the pa st species make use of both aquatic and agricultural Conversion of riparian habitats t o areas for roosting and f or aging, res pectively. al l and accounts fo r a major portion of Geese, cranes, and sever al heron species are loss of riparian habitats . Yet, a gricultural examples. In addition, shoreline and sandbars are tats have r eceived l i t t le attent ion with very local in distributi on; whereas, agricultural to wi ldlife value s, with the exception of areas have proven to be among the most productive es on i nter f acing agriculture-riparian situa habitats for finding and stud ying many trans ient (Ca r others e t al . 1974 , Co nine et al. 1978) and resident shor ebird species on t he lower mo r e compr ehensive study of the influence of Colorado River (Anderson and Ohmart 1984) . ure on wi ldlife in the lowe r Color ado val ley ( Anderson and Ohmart 19 82). Fr om the We descri be agr i cultural featur e s most assoc study, we report here on the f a ctors that iated with occur r ence of waterbi rds, waders, and nee waterbird, wader, and shorebird use of shorebirds . ~e r eport habi tat use by pre sence/ icultural area s of the lower Color ado River a bsence cr i t er ia becaus e of t he er r atic oc cur ley. rences of some agricultural f eatures , the f locking tendencies of s ome species vs. t he sol itar y natur e man y terrest rial riparian bird of others, and t he overal l low densiti e s of many suffered f r om heav y habitat loss in species treated here. Finall y, we exam ine the conv ersion of land to agricult ural production minimum range of agricultural features nec es sary the l owe r Colorado River valley (approximately t o maximize use of an area by wa t e rbirds, wader s, 000 ha si nce 1890) , seve ral groups of species a nd shorebirds in t he lowe r Color ado River valley. ag ricultura l habita ts have increased. rds, waders, and shorebirds are among the lpe ci es t ha t have benefitted from or a t l east make DBe of agricultural features. llist waterbirds and METHODS
1 The general s t ud y area i ncl udes agr i cultural Pa pe r present ed a t t he Ri parian Ecos ys tems land in southwe s t e rn Arizona and southeastern Their Management: Reconciling Conflicting Californi a . Fi ve localities we r e s t ud ied; these COnfe r ence . [University of Arizona, Tucson, included t he Wellton- Mo hawk and I mperia l-Coachella 16-1 8 , 1985 ]. valleys, the Mohave and Colorado River Indian Rober t D. Ohmart is an Associate Director of Reserva tions, and Cibola National Wildl i fe Ref uge :he Center for Environmental Studies at A.rizona (Anderson and Ohmart 1982) . The l a tte r three tat) Uni versity, Tempe , Ariz. s ites are directl y ad j a cent to t he l Ower Colorado Bertin W. And e rson is a Research Associate of River. :he Center for Environmental Studies at Arizona ta t ~ Universit y, Tempe, Ariz. Birds we re censused along 23 4. 8-km transects Ia William C. Hunter is a Graduate Re search three times pe r mo nth . Agricultural land along Bistant in the Center for Env i ronmental St udi e s each transect wa s subdivided i nto 0.2- or O.4-km It Ari zona Sta t e University, Tempe, Ar i z . s ections; each secti on usuall y repr esented a dis
117 Table 1.--Numbe r of times each fi t inct unit containing only one field t ype . Sam (4 eld ty pling included the area wi t hin 0 . 2 km l ateral to ha or more) on agricultural c pe occurr wa terbirds and waders ( full h ensuses f ed each side of the transect , and t he t otal numbe r of h t ree or hectares censused was calculated . In additi on, we s orebirds (migration periods onl years) alld times cr op/fea t ure censused' P y) . 1/ .. mea sured the extent of inhabi ted areas, margins, ' r op. '" pr canals , and feedlots. tion. °por_
Major crop types included cotton , alf alfa, grass, wheat , and milo . In ad diti on , f ields gr ow Waders and Wa ter birds ing lettuce , squash, t omatoes, onions , a nd melons ----Shorebirds were grouped under the cat egory of truck crops because they are structurally similar , and -:------. cultivation and harvesting techniques are simil ar. Crop/ Prop. feature Irrigated N of t otal Prop. When a field was be i ng changed from one crop type N of tOt al to another, it often was cleared; such f ields were ref e r red to a s plowed. Each field t ype wa s cate Plowed Yes 73 0 .017 gorized as to whether or not i t was irrigated and 54 --0.032 No 46 8 whether t he crop was > or <25 cm tall. 0 .109 308 Alfalfa 0. 185 Yes Waterbirds and waders were censused monthly >25 cm 55 0 .013 34 No 0.02 0 from March 19 78 through Octo ber 1980. The number >25 cm 432 0 ~101 162 cm Yes 49 0.097 of times each crop /feature type was censused and <25 0.011 21 <2 5 cm No 39 3 O.Ol l the numb er of t imes each species was present in 0 .092 95 Cot ton 0.057 t he field type was t abulated . A significant num >2 5 cm Ye s 75 be r of occurrences i n a given situation was deter 0 .018 57 0.034 cm No 388 mined by finding t he proportion of that feature >25 0 .091 220 0.132 Ye s 23 among the total crop/feature occurrences. This <25 cm 0 .005 12 0.007 No 177 proportion was t he number of times a species would <25 cm 0 .041 99 0.059 Milo be expected to have been recorded in t hat situa Ye s 11 tion if its occurrence was purely random. A sig >25 cm 0.003 No 48 nificant as sociation between the species and the >25 cm 0 . 011 Ye s 0 crop/feature was defined a s t hose cases where the <25 cm 0 .000 number of occurrences within a pa rticular situa <25 cm No 16 0.004 ,\. tion was significantly larger than expected at Whea t PiO .05 . The number expected was the proportion of >25 cm Yes 22 0 . 005 25 0. 015 >2 5 cm No 163 0 . 038 121 0.072 '.~ the crop/feature occurrences in the total pool of 15 i crops and features multipl ed by the total number <25 cm Ye s 0.004 18 0.01 0 148 of occurrences of the speci e s . This approach <25 cm No 0.035 51 O.Oll ide ntified important crops and feature s fo r each Truck crop s pecies, and general t rends amo ng spe cies groups >2 5 cm Ye s 6 0.001 3 0.002 were defined to maximize agricultural use by >25 cm No 51 0.012 29 0.017 0 .002 2 bi r ds • <25 cm Ye s 9 0.001 <2 5 cm No 82 0 . 019 23 0.015 Sho rebird occurrences were t a bula ted for Grass 0 . 002 7 0.0 04 Ma rch-May (vernal migration) and July-Octo ber >25 cm Yes 10 0 . 025 70 0.041 ( autumn al migration) during 197 8, 1979 , and 1980. >25 cm No 107 1 0.003 14 0.008 These months were periods of peak occurrence f or <25 cm Ye s 14 <25 cm No 132 0.031 62 0.037 mos t s pe c ies~ Shorebi rd associations wi th crop/ 0.039 182 0.1 09 feature type s were identified f o r each species as Canal 165 0.116 de termined for waterbirds and waders. Addi t ional Margins 496 0.021 a nal ys is was used to determine overall use of Inhabited 88 crop/fea tures by shorebirds. We determined if the number of fields with shorebirds was significantly l arger or smaller t han would be expected by cha nce Perce ntage of irrigated field types for the entire (PiO .05) for each crop/feature type. Lastly , we census period was 8.4% , and during the period of determined if there was a greater use of either s horebird censusing the percentage was 14.6% . i rrigated or noni r riga ted f ields acr oss all crop Mi lo, marg ins, and inhabited areas were not used types f rom a rand om distribution (PiO.05 ) for ea ch by any shorebirds so were not included in anal ysis shorebird s pecies. for this species group .
RESULTS Wading Birds The Great Egret (Ca smerodius albus) , Great Crop/Feature Types Blue Heron (Ardea he rodias), Gree~ked Heron The mo st often encountered crop/feature types (Butorides str iatus) , and Snowy Egret (~ thula ) were ass oci a t ed with canals far more than i nclude, in order of highest-to-lowe st frequency Oi with a ny other agricultural fea ture (table 2). 1 of occurrence , margins, nonirrigated plowed, non t he se spec ies, the Green-backed Heron was the irrigated alfalfa >25 em , non1rrigated alfalfa o~ ,; heron to be largely restricted to canals with t 1 <25 cm , and nonirri gated cot ton >25 cm ( t able 1). 2.--Fields i n wh ich use by wading birds was signif icant ly ( P<0.05) grea ter than expected wi th a random distr i bution . IR = i r r igated ; NI = no t irrigated ; ) = height greater than 25 cm; < = height l ess t ha n 25 cm; + i nd i c ates pr e s ence in crop/feature but not significantl y associated with i t . Not all fiel d types are r epresented, only those are shown t hat had at l eas t one species s i gnif ica ntly associated with i t.
Percent of total occurrences
Alfalfa Plowed Milo Grass To t al % Total sign. oc currences Canals 109 55 + 15 + + 70 64 56 + 17 + + 73 37 81 81 Egret 26 19 8 + 4 + + 4 35 Eg ret cus ibi s) 109 + + 4 6 + 6 + 4 6 15 41 \ ~:.:.:--....,. Ibis \~;><-_ chi hi) 15 + 33 7 20 + 7 67 74 + 20 + 24 + 19 8 4 + 75 f or 81% of its t otal occurrence important to puddle ducks and ge e s e , given the t ural area s . Snowy and Cattle egret num ber of occurrence s compared with other species i ons were closest to a random distri bu within this group. ac ros s available agricultural features among Shorebirds Cattle Egr et, Wh ite-fa ced Ibis, and Sa nd Fifteen of 17 species of shore birds were Crane were not signific an tly associated with significa ntly associated wi th irrigated plowed (table 2). The Ca t tle Egre t was signifi f ields (tabl e 4) . In addit i on, four species each plowed, alfalfa, and gras s were significantly associated wi t h nonirrigat ed matter wh e t her the fields plowed, i rrigated and nonir rigated grass <25 cm; In contrast, t he wint e ring t hree species with i rrigated wheat )25 cm; two Cr ane occurred almost exclusively in non specie s each wi th nonirrigated alfalfa <25 cm, alfalfa , plowed, a nd milo f i elds; where i rrigated and nonir rigated grass )25 cm, and the other extreme, t he migratory Whi te canals. Significant associations with f i eld types s occurred only in i rrigated alfalfa, we r e r estricted to plowed fiel ds for nine s pecies I and grass fields. with all but t wo of these only wi t h irr i gated plowed fie lds ( t he exceptions were Bl a ck-bellied Wat erbirds Plover and Mountain Plover). Common Snipe and Spotted Sandpi per were associated mos t signifi bes , cormorants , coots, and diving ducks cantly with cana l s over all other crop/fe atures. rds and mergansers) were overwhelmingly with canals (table 3). Gee se were Eight specie s occurred significantly more exclus ively with plowed, alfa lfa, milo, oft en in irriga ted than in nonirrigated fields and grass fie lds , wi th all but the Snow (table 4). Four s pe cies occur r ed signi f i cantl y Occurring l argel y in nonirrigated fields. mo re often i n nonirrigated than in i rri gated ducks we re associated both with canals and fields. Ove r a l l, ther e were 26 signifi cant ted crop s wi t h t wo s pecies (Ame rican Wigeon associati ons between shore birds and irr i gated tn Pintai l) occuring only in irrigated f i elds and 12 with nonirrigated fields, wi th e i ght species signif icantly associated wi t h at least one each i rriga ted and nonir r igated crop/feature type. 1i1ne teen of the 25 species t reated under t his have 100% of their occur rences associated All shor e bi r d oc cur rences t05ether ind i cated y wi th one or more agricultur al crop/ that they were f ound more of t en t han expected by types. Ho wever, t hree species (Snow chance alone i n irrigated and nonirrigated plowed, 6 0~l1 a rd , a nd Northern Pintail) have less irrigated grass )25 cm and <25 cm, irri gated wheat of their occurrences associated signifi )25 cm, and canals (table 5) . Shorebirds occurred h ~t h some agricultural crop/f eatur e and less often t han expect ed by chance alone i n non ~ve a mor e r and om distribut ion in agricul irriga ted alfal fa )25 cm, i rriga ted and nonirri abitat s. Ag ricultural situations were mos t gated cotton )25 cm, and non i r rigated cotton 1 19 -- Tabh 3 .--Agricultural c rops and f eatures with ~hich grebes, cormo rants, coots, ducks . a nd geese 'Were associat ed ~ith a frequency g reater t han expec ted with a random dist r ibution . Abbre viat ions, symbols, and notes as i n t a hIe 2. Percent of tot al occurrenc es Plowed Alfa lfa Milo Wh e at Grass To t al % To tal sign. Spe c ies occurrences Cana ls l R Nl >IR >Nl Pied-billed Grebe (Podilym bu s podiceps) 100 100 Eared Grebe (Pod1ceps nl gri collis) 100 100 Double- c res ted Cormo rant (Pha lac roc orax aurl t us) 100 100 Amer i can Coo t ( Fu lica ame ricana ) 100 100 Common Me rgans e r Cr (Mergus mer ganser ) 12 100 100 fe Red-breasted Me rga nse r (M. serratod 3 100 100 Bufflehead (Bucephala albeola ) 2 100 100 Commo n Gol deneye (!. c langula ) 15 80 80 Total Me rgi ni 32 91 91 P: Grea t er Scaup eAy thya marUa) I 100 100 Lesser Sc aup ( ~. ~) 4 100 100 Redhead (A . americana) 4 25 50 25 100 Ring-necked Duck (~.' c011aris) 3 100 100 To t al pochards 12 7S 17 100 Wood Duck ( Aix sponsa) I 100 100 Cinnamon Teal ( Anas cyanoptera ) 63 S6 16 5 86 Blue -winged Teal (A . discors) 5 60 20 80 Green-winged Teal (A.~) I S 47 40 100 Nor the r n Shoveler (:! . clypeata) .3 33 67 100 Malla rd (.! . pla t yrhynchos) 12 25 33 + + + 58 Ame rican Wige on (A . amer icana) 6 83 17 100 Nor t he r n Pinta il TA .~ 27 48 + + + S9 Total pud d le du cks - - 131 38 31 78 Canada Goos e (Brant a canadens is) 30 30 23 27 90 Bran t (8. bern1cla ) I 100 100 G re B te r-Wh~t ed Goo se ( Anser al b1 frons) 100 100 Ros~se (Chen ross11 ) 100 100 Snow Go ose C.£. . cae rules c e ns ) 9 II + + II + + + 22 Total ge e se 43 24 22 36 4 88 , ~ Ta ble 4 . - - Agr 1cult ural crops and fea t ures with wh ich shorebirds were associated with a f requency g reate r tha n expected with a random distribution on transects . Ab breviations I s ymbols I a nd notes as 1n t able 2 . Percent of total occurre nces All c ropl Plowed Al fal fa Grass Whe a t Pe rcen t feature s accounted TotCll f or by Spe c ies occurrences 1R N1 (N1 )IR ) N1 Black-bellied Plover (Pluv1al1s s quataro la) 19 42 37 + + 79 + + Killdeer (Chsradrius vociferus) 287 II + to + + + + + 25 + 68 Mounta in Plove-r -- (C . montanus) 16 25 63 88 + 69 Black -~tUt (Himantopus mexicanus ) 28 2S + + II 11 54 + + American Avocet (Recurviros t ra americana) 67 + 67 78 + Greate r Yellowleg-.-- (Tringa melanoleuca) 36 30 10 53 + + Lesse r Yellowlegs (!. flav1pes ) 50 + + 50 + + Wil l et ( Ca tOEtroEhorus semiealmatus) 18 39 + + + + + 39 + + Spotted Sandpiper (Aetltis macularia ) 29 + 83 100 Whimhel --- (.Numen 1us phaeopus ) 45 36 + + 22 75 75 + Long-billed Curlew ( N. amer icanus ) 53 II 27 13 + + 19 + 78 + 68 Western Sandpiper (Calidris mau!"i) 10 40 + + 40 70 + Least Sandpi~ (C . minu t illa ) 61 30 + + + + IS + 48 64 + Long-b~it che r (Limn od r omus scol opaceus) 27 41 + + + + 41 63 + Common Sni pe (GalUnago 8al11n8go) 17 + + 12 59 71 82 + Wi! son Pha l a rope ( PhalaroEu s t!" icolor) 38 + + 38 88 + Ring-bil led Gu-n-- (~ delawsrensis) 37 30 46 + + + + + 76 + 65 1 2 0 __overall s ho rebi rd use of agriculture by t ion of the environment by humans . Clearing of 5~bers of s pecies and all shorebi rds com land for agricul tural purposes creates new habi tat • d Irr . - i rrigated; Pres . = present ; f or species t hat previously may not have occurred e bin •a ssoc. = s ignifica ntly a ssociated; Obs . i n t he area while , a t the same t ime, destroying S ig~:erved· Exp . = expe c t ed ; NS = not sign i f habi tat that may cause t he origi nal fauna to dis . o ~ , a ppear unle ss these latte r specie s are a ble to take advantage of t he new s i tuation. All of the s pecies treated here have i ncreased i n t heir occurrence in Number of Fields with the valley since the 1800' s due l a rgely to t he species shorebirds a ctivities of man, including agricultural prac tices, s torage of wa t e r i n large reservoir s ( pri marily for irriga tion), and creation of stable Sign . Binomial marshlands. I rr. Pres. assoc. Obs . Exp. P Grinnell (1914) described t he lower Colorado River's aqua tic and semiaquatic avifauna as depaup e r ate; he recorded few s pe cies and low numbers of Yes 17 15 32 12 .5 +<0.001 herons, waterfowl, and shorebirds north of the No 13 4 130 72 .3 +<0.001 Gila-Colorado river conf luence. Presently, all of these species occur in rather stable numbe rs re Yes 5 0 8 7.8 NS sponding to the food resources provided by agricul No 7 0 18 37.9 -<0 .001 tural a reas, roosting and foraging sites of open Yes 8 0 9 5.1 NS water areas, and/or a comtinati on of these . The No 8 2 23 22.3 NS vast majority of species treated here are transient and winter visitors and do not depend on agricul Yes 5 0 7 13 .3 -<0.05 tural areas for nesting. Exce pti ons are Killdeer No 4 0 9 51.6 -<0.001 and a few Cinnamon Teal. Ye s 4 0 3 2.7 NS No 2 0 6 23 .1 - <0.001 Cranes and geese are almost totally dependent on agricultural areas for forag ing . On t he three Yes 9 2 3 1.2 NS lower Colorado River national wi ldlif e refuges, No 9 2 12 16 . 8 NS recent increases i n abundance for both cranes and Yes 11 4 10 2 .4 +<0.001 geese a re a t tributed to managing aquatic or semi No 8 4 21 16.8 +<0.025 aquatic roosting sites with adjac ent agricul t ural f oraging sites ( mo stly alf alfa and milo f ields). Yes 1 0 2 0 NS Shore bird , wa terbird, and wading species associated No 1 0 6 7.4 NS with irrigated fields mus t t r a ck this resource as Yes 1 0 1 0 NS f looded f ields a re infrequent a nd ephemeral. No 3 0 4 5.9 NS Flooding of fields attracts not only spec ies t r eated here, but also swallows, water pipits, and Yes 6 3 12 5.9 +<0 . 01 blackbirds, which flock to f eed on inve r-t ebr ates No 7 0 12 28 . 2 - <0.001 d ispla ced by irrigation water. Wa terbird and some Ye s 4 0 2 3.9 NS wading s pe cies (especially Green- backed He r ons) No 2 0 7 12.1 NS find more stable foraging sites in the extensive canal systems, e speci ally along large r dirt-banked 7 2 59 42 .6 +<0.01 c anals that usually have a constant flow of wa t e r. Spotted Sandpipers and some wa terbirds use the more sterile cement-l ined canals to a greater extent. The most abundant f i eld type s were no t the places where shor ebirds occurred Several species trea ted here have undoubtedly equently. Although cotton f ields were undergone range extensions directly associated with largely by shorebi r ds , these f i e lds the expansion of agricultural practices. Most dra "'--" "'C.l ~ enhanced shorebird habit a t because t hey matic has been t he expansion of the Cattle Egret, ~ri odically plowed and attracted significant origi nally i n troduced fr om the Old World into t he of shorebirds . Overall, shorebird New World Tropics . This s pe cies became establ i s hed , ~curr.n,'~ i n agricult ur al area s wa s related to in the southeastern United States in the 1950's and icultural pra ctices (plowi ng, has s pread north and wes t into a reas of extensive and wi th t he presence of canals. agri cultural and horticultural production. Cattle , 12 of the 17 species pref erred either Egrets we re f irst found on t he lower Colorado River ted or noni rriga t ed fields and did not ran i n 1970 and are on the verge of establishing sever occur in both situations. In order to maxi al breeding colonies . Mo unt ain Plovers and Wh im diversity of shorebirds, a mosaic of irri breIs were considered casual in Arizona before the and nonirrigated fields are desirable. 1940's (Monson and Phillips 1981), but both species a r e now regula r, and hundreds of i nd ividuals occa sional l y occur in agricultural sit uations . DISCUSS ION Most , if not all, s horebirds have benefitted As Or ians (1975 ) has stated, t here is a need to from vari ous agricultural features on t he lower organisms t hat have be en exposed to pertur Colorado River, although this r egion is not a major resulting from the unprecedented modifica migration route for t his group . However, shorebird 121 use of agricul ture in regions where shor elines and Cali fornia and western Ar izona . US ' estuaries have been extensively developed , such as of Reclamat ion , 316 p . Lowe r COlo;a~ Buteau in Florida and California, i s in need of i mmediate Boulder City , Nev . 0 RegioQ att ention , given t he de sperate situa t ion out l i ned Anderson, B. W., and R. D. Ohmart. 1984 ' by Myers (1983) f or this group. Our paper outlines Vegetation management study for the • important agricultural features for shorebird use enha ncement of wildlife along t he 1 OWe t t ha t may be compared with data collected in othe r Colorado River. Comprehensive final reg i ons. U.S. Bureau of Re clamation, 529 p. Lrepott to Colorado Reg ion, Boulder City , Nev . OWet Of all the ha bitat changes experienced in the Carother s, S. W., R. R. J ohnson , and S. W 10wer' Colorado River valley , as we ll a s many other Aitchison . 1974. Population structu' , . f h re and major southwestern r iparian systems, the conversion socia1 organ~ z at~on 0 sout western r1 of vas t areas to agricultural production is cer birds. American Zoologist 14:97 -108 patian t ainly the most drama t ic. The abundant foods pro Conine , K. H., B. W. Anderson, R. D. O hm~ t vided by agri cultural habitats benefit a wide J. F. Drake. 1978. Responses of rip: 1and variet y of bir ds that can opportunistically use species to agr icultural habit a t conver:ian them . Si nce ne sting s ites a r e not a concern for p . 248-262. In Strategies fo r protectio~ns . ma ny of these s pe cies on the lowe r Colorado River , management of floodplain wetl ands and oth e~nd t hey may a ttain relative ly hi gh densities. If sur riparian ecosystems. Pr oceedi ngs of the v ival has been high i n these over wintering or s ym pos ium. [Callawa y Ga rdens, Ga • , De cetn,Ler mi grator y indi viduals, then the population biology 11 - 13~ 197 8] US DA Forest Service General of these s pecies may be changing, with effects per Tech~~cal Rep?rt WO-12, 41 0 p. USDA Forest haps ev i dent on their northerly breeding grounds. Serv ~ce, Wash~ng t o n , D.C. Grinnell, J. 1914 . An account of t he mammal Although a numce r of specie s are benefitting from • • 5 and the development of agriculture, t he futur e of many b~ rds , of the lower Colorado R~ ver Valley with ripa rian species in agricultural areas is not opti es pec ~al r eference to t he dist ributional mistic unles s a mosaic of native riparian habitats problems presented. Unive rsit y of California and devel oped lands is managed for conserving both Publ i cations in Zoology 12:51-294 . the original and new avifaunas. Monson, G. , and A. R. Phillips. 1981. Annotat ed checklis t of birds of Ar i zona, Second edition. University of Arizona Press , Tu cson, Ar iz . ACKNOWLEDGME NTS 240 p. Myers, J. P. 1983. Conservation of migratory ,~" . The developmen t of this work and t he agr i cultural s horebi rds: s taging area s, geographic study a s a whole was aided by George F . Dr ake and bott lenecks, and r egional moveme nts. Americ an Kathleen Conine. ¥~r k Kaspryzk and Camil le Romano Birds 37: 23- 25. organized and accom plished much of the original Ohmart, R. D., W. O. De ason, and C. Burke. 1977 . data analys is . We thank the many dedicated biolo A r iparian case his tory: the Co l or ado River. gist s ~n o assisted in data collection and analysis . p . 35- 47. In Impor t ance, preservation and Edi t or ial a s sistance was provided by J ane R. Durham management Of r i parian habitat: a symposium. and Cindy D. Zi sner . Cindy D. Zisner also t yped Pr oceedings of the symposium. [Tucson, Ariz" t he manuscript. Th is s tudy was supported by U.S. July 9 , 1977J USDA Forest Service General Bureau of Re clamation Contract No. 8-07-30-X0027. Te chnical Report RM-43, 21 7 p. Rocky Moun ta io Forest and Range Expe r iment Stat ion, Fort Collins, Colo. LITERATURE CITED Orians, G. H. 1975. Diversity, stability and ma t urity in natur al e cosystems. p. 139-151. Ander son , B. W., and R. D. Ohmart. 1982. The In W. H. van Dobber and R. H. Lowe, eds., infl uence of the inters persion of agriculture Unifying Concepts i n Ecology. W. Junk, The and natural habi t a t s on wildli fe in southe rn Hague, Holland.