Studies in Avian Biology No. 27:52-60, 2004.

WATERBIRD COMMUNITIES AND ASSOCIATED WETLANDS OF THE RIVER DELTA,

0SVEL HINOJOSA-HUERTA, STEPHEN DESTEFANO, Y AMILETT CARRILLO-GUERRERO, WILLIAM W. SHAW, AND CARLOS VALDES-CASILLAS

Abstract. Despite extensive losses of wetlands caused by water diversions upstream, the Delta in northwestern Mexico remains an important wetland system in the . The purpose of our study was to describe waterbird communities across a variety of wetland habitat types and zones that exist in the Delta. We measured species richness and abundance of waterbirds from September 1999 to August 2000. We observed a total of 11,918 individuals of 71 species at sites within seven wetland areas. The waterbird communitie differed with respect to guild composition and species abundances among the wetland zones. Wetlands along the eastern portion of the Delta (Cienega and Indio). which are upported by agricultural drains and managed under conservation initiatives, exhibited the highest species richness in our ummer and winter censuses, and highest abundance in summer. Shorebirds were the dominant guild in the summer period, while waterfowl were dominant during winter. Breeding marshbirds were also abundant, with the Yuma Clapper Rail (Rallus longirostris yumanensis) being most notable. Wetlands along the western Delta (Hardy and Cucapa) were al. o supported by agricultural drains, but were not managed specifically for wildlife. The Double-crested Cormorant (Phalacrocora:x auritus) and American Coot (Fulica americana) were dominant during winter, while long-legged wader (Ardeidae) were dominant in ummer. The com­ po ition of waterbird communities along the mainstem of the Colorado River was similar to that of wetlands along the western portion of the Delta. The shallow and ephemeral Laguna Salada, along the western boundary of the Delta, exhibited the highest waterbird abundance among our winter censuses when it was flooded in 2000. The results of our study suggest that even minimal levels of instream flows would lead to habitat improvements for waterbirds in the Delta floodplain. A bi-national wetland management program for the Delta should consider the impacts of flood control measures and diversions for agricultural and urban uses to the health of wetland habitats on both sides of the international border. Key Words: avian communities; Baja ; ; migratory birds; ; water management; waterbirds; wetlands. COMUNIDADES DE AVES ACUATICAS Y HUMEDALES ASOCIADOS DEL DELTA DEL RIO COLORADO, MEXICO.

Resumen. A pesar de las amplias perdidas de hurnedales causadas por ta desviaci6n de cauces aguas arriba, el Delta del Rfo Colorado en el noroeste de Mexico continua siendo un importante si ·tema de humedale · en el Desierto Sonorense. El prop6sito de nuestro estudio fue describir comunidades de aves acuatica a traves de una variedad de tipos de habitat y zonas de humedales que existen en el Delta. Medimos la riqueza

52 OLORADO RIV R DELTA WATERBIRDS-Hinojosa-Huerta et al. 53

Pa/obros cla1·es: a es acuaticas; aves migratorias; ; comunidades d aves; Delta del Rfo Colorado; humedales; manejo de aguas; onora.

Many waterbirds ha e uffered population de­ the Delta wetlands has been de ignated a· a nat­ clines ar und the w rld sine the beginning f ural area under the category of Bio. phere Re­ the twentieth century (Rosenberg et al. 1991, . er e, which is recognized by the United Na­ DeGraaf and Rappole 1995). Cau es for the. e tions as part of a global network of natural re­ declin s are thought to include the degradation serve. (SEMARN P 1995). and loss of wetland , which pr ide breeding, While ome worker have f cu ed on the ea­ wintering, and migratory stopover habitat (Na­ sonal tatu and abundance of bird. at particular tional Re. earch Council 1995). On a regional wetland in the Delta (Mellink et al. 1996, 1997; scale, wetland lo s ha been significant along the Ruiz-Campos and Rodriguez-Meraz 1997) we Pacific Flyway, where up to 50~ of coastal wet­ sought to characterize and compare a variety of lands in the western U.S. (Helmer 1992) and wetland habitat types aero the Colorado River ome 35% of wetland in western Mexico (Hails Delta and de cribe the waterbird communities 1996) have been de. troyecl, while losse in the that use them. Here we pre ent information n interior of California have been estimated at specie richne and relative abundance of wa­ 95 % (Zedler 1988). Brown ( 19 5) and Ohmart terbird acros various wetland zone of the Del­ et al. ( 1988) indicate that wetland lo s along the ta, identify area with high wildlife habitat al­ Lower Colorado River in and California ue, and make recommendations for re toration. has also been . ub tantial. The Colorado River Delta had long been rec­ STUDY AR AND M THODS ognized as one of the rich ·t regions for wildlife We surveyed wetlands in the Colorado River Delta in the southwe tern United States and north­ in Baja California and onora. M xico. from eptem­ western Mexico (Grinnell 1928, ykes 1937, Le­ b r 1999 through August 2000. We categoriLed these opold 1966, Glenn et al. 200 l ). D spite suh ·tan­ ~et lands into se en wnes (modified from Valdes-Ca­ tial reductions in w tland area (approximately sillas et al. 1998) according to their en ironmental 76% has be n lo t), and the modification of veg­ characteristics (Fig. I: Table I). The /Ones included riparian areas maintained by flooding events, shallow etation commu111t1e. b non-native, inva ive !age om. and mudf1ats influenced by tidal action of th plant sp cies (Glenn et al. 1996, Zamora-Arroyo ulf of alifornia. marshes with emergent vegetation et al. 200 I), the Delta is thought to b a critical fed b agricultural run-off and natural springs. and area for a ariety of resident and migratory wa­ channeli/ec.l rivers, streams. and agricultural drains. terbirds within th Pacific lyway (Anderson et Vegetation was composec.l of emergent plants (mostly al. 2003). cattail. Trpha domengemi\ ). monotypic stands of in­ The modification and degradation of water­ troducec.l tamarisl-. (Tamari.\ rwno\is.\inw). nati e alt­ bird habitat. is often related to intensive man­ gra..,-, (DiHich/i\ palmerii). and -.tands of cottc nwood agement practices that divert water supplies (Popu/11\ fi·e111011t11) and willo~ (Salix gooddingii). A c.le. cription of each /One is in ·Ju e.I c.l 111 Glenn t al. away from their source for U'\c by more di<>tant (2001 ). urban and agricultural centers (Lemly et al. We grouped -;pecies into seven waterbird guilds 2000). Perhaps nowhere is this more apparent basec.l on characteristics of foraging behavior: divers: than in the arid basin of Colorad River Delta long-legged waders; gulls, terns. and ..,kimmers; peli­ region (Lemly 1994, Morrison et al. 1996). cans anc.l cormorants; mar..,hbird-.; shorebirds; and wa­ How ver, in recent years agricultural runoff, terfowl (Table 2; Weller 1988, 1995; Croonquist and sporadic flood flows, and their interaction with Brooks 1991 ). the tidal regime of the upper We censu..,ed birds uo;;ing a circular station/point count procedure (Ralph et al. 1996). urvey stations s em to have re. tored and maintained portions were circular plots located 500 600 m apart, and of th Delta wetland (Glenn et al. 1996). The grouped into mini-routes (five to 14 stations per mini­ importanc of the Colorad River Delta to wild­ route; Bystrak 1980), dep nding on th si1e of the life has been recognized by a variety of conser­ 1one. We used Arc View 3. I NT (ESRI 1998) and an vation initiative. at multiple geographic Tales. existing spatial database for the olorado River Delta The Delta has been identified a. a con er ation (Valdes- asillas et al. 1998) to determine the location priority within the Sonoran De. ert Ecoregion of mini-routes. Routes were selected non-randomly to (Briggs and Comeliu 1998 ), an Important Area maximi7e coverage of the different ?Ones in the Delta for Bird Conservation in Mexico (Roman-Ro­ and the differem wetland environments at each Lone. The number of mini-routes varied for each wetland driguez et al. 2000), and a wetland of interna­ ;;one. We est:iblished four routes each at the Hardy and tional (Ramsar Convention Bureau 2003) and Cienega wetland , and two routes each at the Indio and hemispheric importance (Western Hemisphere olorado River wetlands. Because access was limited. Shorebird Reserve Network 2002). A portion of we could establish only a single route ach at the Cu- 54 STUDIES IN A VIAN BIOLOGY NO. 27

California,~~ ------exicali, Baja California, Mexico

Colorado

San Luis Rio Colorado, Sonora, Mexico

CIENEGA

5 0

FIGURE 1. Zon s (uppercase) and wetland areas (lowerca e) of the Colorado River Delta included in our study. The location of mini-route are shown by solid circle . The Delta floodplain (diagonal shading) is sur­ rounded by a y tern of levee<; (da hed line). Major streams are depicted by <>olid line . capa, El Zanj6n, and alada wetland zones. The last at Salada (in winter; Fig. 2). Species richne wetland contained water only during the winter p riod. and abundance w re greater during ur winter To elucidate general patterns of waterbird occur­ censuse for all zon s except Cienega, where rence, we surveyed each wetland zone once during the they were greater in ummer (Fig. 2). Suitable winter period (mid Nov mber through late February) waterbird habitat at Salada wa ab ent during and once during the summer period (late May to early our ummer censu . Augu t; Table 3). We recorded all waterbird pecies that were detected within a 200-m radius for a five WATERBIRD COMMU !TY COMPOSITIO AND min duration at each tation. We u ed playback re­ WETLA D ZONES cording at each station to aid in the detection of se­ The guild composition and overall abundance cretive marshbird , following the protocol used for rail of waterbird communitie differed among our urveys in the Colorado River Delta (Hinojo a-Huerta et al. 2001 a). wetland zone and between cen us period (Fig. 3). Below we provide general de. cription of RESULTS wetland habitat , dominant guilds, and pecies that were mo t abundant among guild for each We observed 11,918 individuals of 71 pecie zone. of waterbirds during our tudy. Among zone , pecie richness wa highe t at Indio (in winter) Cienega and at Cienega (in ummer). Waterbird abun­ The waterfowl guild was dominant during our dance wa greatest at Cienega (in summer) and winter cen u at Cienega (Fig. 3). Here, the most COLORADO RIV R DELTA WATERBIRDS-Hinojosa-Huerta et al. 55

TABLE I. WETLAND Zo E OF THE COLOR Do R1vER DELTA l L OED 1 o R ST DY

Zone Included wetland'> Water '>ources Habitat type5 Cienega Cienega de Santa Clara Agricultural run-off and Typha-dominated marshes and and El Doctor natural pring mudflats Cu ca pa Cucapa Complex in Hardy/ Agricultural runoff and Alkali flat dominated by halo­ Colorado floodplain flood flow phyte /Tamarix, transected by natural channel ; river bank dominated by Tamarix Hardy Hardy and El Mayor river Agricultural runoff Open water canal and Typha­ Phragmites-Tamarix marshes Indio Laguna de! Indio and ea t- Agricultural runoff Typha-Tamarix mar hes and hal­ em drains low lake El Zanj6n Intertidal flat Tidal inundation, agricul­ Mudflats, broad tidal channel , tural runoff, and flood and saltgra bank flow Colorado Ri er Riparian corridor Flood flow and agricul­ Populus- alix-Tanzarix corridor, tural runoff river channel, and backwater lake and pond. Salada Laguna Salada Flood flow and tidal in­ Exten ive shallow lagoon and tru i n mudflats

abundant pecie were the Greater White-front­ were ob erved on the hallow lagoons at the ed Goose, Canada Goose, and Snow Goo e, ea tern ide of the Cienega de Santa Clara on which u d the inner Iago n , alt grass flat , 21 May 2000. and adjacent agricultural fields. Northern Shov­ eler, Northern Pintail, and innamon Teal were Cucapa numerou along the inner lag on of the Cie­ The ucapa wetland zone wa dominated by nega. The pelican and corm rant guild, of which . pecie that benefit from open water habitat or American White Pelican wer mo t numerou , by tho not trongly dependent upon native was aL fairly abundant during this period in vegetation. Double- re ted ormorant were the de p r (> 0.8 m) op n water area of the Cie­ most abundant here in m and ring river chan­ nega ( ig. 3). nel and ft odplain lag on during our winter During th -ummer censu. a div r guild of cen u (Fig. 3). Although n t abundant, ten pe­ shorebird wa · dominant (Fig. 3). The mo t ci · f waterfowl wer pr . nt (Fig. 3), includ­ common <.;pecie. of migratory shorebirds includ­ ing Blue-winged Teal, American Widgeon, and ed 'W t rn Sandpipers, dowitcher., and Red­ Mallard. Marshbird w r" al abundant, with n eked Phalaropes, which foraged along the out­ American oot being m . t numerous. er ·hallow ( ·:.... 0.5 m) lagoons and mud ft at . The During the summer census, pecies compris­ most abundant breeding sh r bird were th ing the long-legg d wader guild were most Black-necked tilt and Killdeer. As our umm r abundant (Fig. 3), with nowy Egrets, Great c nsu es in th ienega were conducted in late Blue Herons, Black-crowned Night-Herons, May, well after the pring migration peak for Great gret , and Green Her n being most nu­ most h rebird , this guild i likely even more m rous. Mar hbird wer rare; only two Yuma dominant earlier in thi period provided that Japp r Rail pair were found ne ting in tama­ habitat condition are uitable. ri k and common reed (Plzragmites pp.). The mar hbird guild wa well represented here in the ummer cen us a we recorded a total Hardy of eight pecie . The dominant p cie were The diver , particularly grebe , and long-leg­ Yuma Clapper and Virginia rail ', American ged wader , con i ting primarily of Snowy Coot , and Lea t Bittern . Black Rail and Egret , Black-crowned Night-Herons, and Great American Bittern were al o det cted, but in Egret , were the mo t abundant guild during lower number . our winter censu of the Hardy River (Fig. 3). The long-legged wader , of which White­ Here the river channel running adjacent to the faced Ibi e. , Snowy Egret , and Great Egret floodplain i deep, teep- ided, and sparsely veg­ were mo t abundant, u ed mainly the outer shal­ etated. The gull , tern , and 'kirnmers guild of low lagoons. Eight White Ibi , a previou ly un­ which California Gull , and Ca pian and For - recorded species for the delta region in Mexico ter' tern predominated, wa al o abundant (Ru ell and Monson 1998, Patten et al. 2001 ), here. 56 STUD! IN A VIAN BIOLOGY NO. 27

T BLE 2. COMPO ITION OF WATERBIRD G ILD l CLGDED rN 0 R T DY

Guild Common name Diver Gavia pacifica Pacific Loon Podiceps auritus Horn d Grebe Podiceps 11igricollis ared Grebe Podilymbus podiceps Pied-billed Grebe Aechmoplzorus occidentalis Western Grebe Aechmophorus c/arkii Clark'. Grebe Pelican. /cormorants Pelecanus erythrorhynchos merican White Pelican Pelecanus occidentalis Brown Pelican Phalacrocorcu: auritus Double-ere ted Cormorant Long-legged waders Ardea herodias Great Blue Heron Ardea alba Great Egret Egretta rhula nowy Egret Bubulcus ihis Cattle Egret Butorides virescens Green Heron Nycticorax nycticorax Black-crowned Night-Heron Egretta tricolor Tricolored Heron Eudo imus a/bus White Ibis Plegadis chihi White-faced Ibi Waterfowl Branta canadensis anada Goo e Anser alhifrons Greater White-fronted Goo. e Chen caeru/escens now Goose Anas platyrh_vnchos Mallard Anas strepera Gad wall Anas acuta Northern Pintail Anas americana merican Wigeon Anas c/ypeata Northern hoveler Anas cyanoptera Cinnamon Teal Anas discors Blue-winged Teal Anas crecca Green-winged Teal Ayrhya 1•alisineria anvasback Aythya a111erica11a Rcdh ad A vthya qffinis Lesser caup Buceplwla cla11g11/o ommon Goldeneye Buceplwla alheola BufAehead Oxyura ja111aice11.\is Ruddy Duck Marshbirds Botaun1s lentiginosus merican Bittern Ixnhrychus exilis Least Bittern allinula ch/oropu.\ ommon Moorhen Fulica americana merican Coot Rallus longirostri.\ lapper Rail Rallus limico/a Virginia Rail Por-ana ca rot ina ora Laterallus jamaicensis Black Rail horebirds Clwradri11s alexandrinus nowy Pio er Charadrius 1•oc(ferus Killdeer Recurvirostra americana merican A vocet Himantopus mexicanus Black-necked Stilt Tringa melanoleuca Greater Yellowlegs Tringa fia1·ipes Les er Yellowleg Catoptrophorus se111ipalmatus Willet Actitis macularia p tted Sandpiper Nw11e11i11s phaeopus Whimbrel Numenius americanus Long-billed Curlew Limosa fedoa Marbled Godwit Calidris mauri West rn Sandpiper Calidris minutilla Lea. t Sandpiper Limnodromus sco/opaceus Long-billed Dowitcher Limnodromus griseu hort-billed Dowitcher Phalaropus lobatus Red-necked Phalarope COLORADO RIV R DELTA WATERBIRDS-Hinojo a-Huerta et al. 57

TABL 2. ED

Guild pecies Common name Gulls, tern s. and skimmer. Larus philadelphia Bonaparte's Gull Larus delawarensis Ring-billed Gull Larus californicus California Gull Larus argentatus Herring Gull Larus heermanni Heerman '. Gull terna caspia Ca pian Tern terna maxima Royal Tern Stema forsteri Forster's Tern Sterna nilotica Gull-billed Tern Chlidonias niger Black Tern Rynchops niger Black Skimmer

In summer, the long-legged wader guild wa El Zanj6n again mo t common (Fig. 3), especially in the Specie richness wa. relatively low in our , ur­ northern tretches where the river forms sand­ veys of the intertidal zone of El Zanj6n. Here bars, and patch s of tamarisk and cattail line the Jarid were the dominant guild overall, but the river' edge. The most abundant specie includ­ speci . compo ition differed between cen. use ed nowy grets, Black-crowned Night-Heron , (Fig. 3). In our winter censu ·, the dominant pe­ and Great Egrets. Mar hbirds were al o abun­ cies w re Ring-billed Gull', California Gull , dant with American Coot a the mo t common and Heermann 's Gull ; in ummer, the dominant peci . Yuma Clapper Rail , L a t Bittern , and ·pecies wa the Ring-billed Gull. Repre enta­ Am rican Bittern were al o present to a les er tives of th horebird guild, e. pecially Bia k­ degree. Rail were found in a few areas along n eked Stilt and Am rican Avocets, were fairly the north rn ·tretches of the 1 May r and Har­ abundant in winter. Brown P licans were abun­ dy riv rs ( ig. 1) that support d cattail . dant, and long-legged wader were fairly abun­ Indio dant during our ummer cen. us (Fig. 3).

Wat rf wl wa the mo t abundant guild dur­ o/orado River ing winter at the Indio zone ( ig. 3). The most abundant sp cie were North ·rn Shovel r, Can­ Th m rican o t as th dominant pec.:ie vasback, and Ruddy Duck. The shorebird and during our winter c nsus along the Col rado marshbird guilds were also common, with the Ri r ( ig. 3), e pecially within variou ba k­ Long-billed Dowitcher and American Coot be­ wat r Iago n, . Double-crested ormorant wer ing th most abundant species or their re pective abundant along the main channel of the river. groups. Double-crested orrnorants were abo Long-I gg d wad r., primarily Snowy gr t~ fairly numerous. The . h rebird guild dominat d and Great Blue Herons, were also common in th summer census ( ig. 3) with Whimbrel, backwater lagoon and in riparian habitats along Blac.:k-n eked Stilt, and Killd r being the most th bank of the river. abundant pecies. Long-I gged waders were al o The long-legged waders dominated thi · zone common, particularly the nowy Egret, Black­ during our ummer census ( ig. 3); the most crowned Night-Heron, and r at Blue Her n. abundant pecies were attle grets and nowy Breeding mar hbirds were abundant and includ­ grets, which roo ted in the den e willow tand. ed . ix pair of Yuma lapp r Rails. of backwater lagoons, while White-faced Ibise

TABL 3. S RVEY DATE AT EA H WETL ND Zo E 1 THE- OL RADO RIVER DELTA

Zone Summer Wimer Cienega May 21-22, 2000 January I 0, 2000 Cu ca pa May 28, 2000 November 13, 1999 Hardy May 26-27, 2000 January 8-9, 2000 Indio June 6, 2000 November 12, 1999 El Zanj6n May 25, 2000 February 26, 2000 Colorado River ugust 8, 2000 November 11, 1999 Salada May 29 and August 9, 2000 ebruary 27. 2000 58 STUDIES IN A VIAN BIOLOGY NO. 27

50 Winter A) Species richness 45 8% 40 DWinter Cienega 2% ~35 • Summer 52% ·c:; ~30 (/) 025 Q) -E20 ::i 6% z 15 Cucapa 16% 80'!' 57% 10 8% 5 0 C1J C1J >. Q c 0 C1J OJ ~ 0 "O "O a. ~ "O ~ ~11~

6000 l B) Abundance 5000 Indio (/) (ij DWinter -6 4000 • Summer ·:; ~ 3000 0 42% 12000 ~ ZanJ6n 86% ~ 1000 1

0 To.. , cm r C1J C1J 0 c 0 C1J OJ a. '6 0 "O "O Q) C1J ·c: ~ C1J c CJ E C1J (ij

Salada FIGURE 3. Proportions by guild for each c n-;us p - The Laguna Salada, an ephemeral hallow riod at wetland wnes of the olorado River Delta. Jake, contained water only during our winter cen us. Here the shorebird guild, composed pri­ marily of nearly 5000 American Avocet , dom­ factor in haping waterbird communitie (Wel­ inated the flooded alt flat (Fig. 3). Ring-billed ler 1988, 1995; King ford et al. 1999, Lemly et Gull , feeding along the hore, were al o nu­ al. 2000). Our preliminary data show that wet­ merou . A few Le er Scaup, Eared Grebe , and land zone in th Colorado River Delta provide cormorant were found in the deeper water of a variety of wetland habitat types upporting wa­ the inflow canal to the Laguna Salada. terbird communitie of varying composition. Difference in community compo ition among DISCUSSION zones are likely a . ociated with variation in a On a global cale, water and wetland man­ number of physical characteristics including to­ agem nt practic s have b en found to be key pography, water depth and alinity, vegetation OLORADO RIV R DELTA WAT RBlRDS- Hinojosa-Huerw et al. 59 composition and ~tructure, and flood control and olumes, will further enhance wildlife habitat agricultural practices in these areas. quality and quantity. The general pattern of a greater abundance The Laguna Salada probably b st represents and diversity of waterbirds in the eastern wet­ the impacts of long-term reduced flows to the lands of th Delta, in contrast to th western Delta, a-. it more commonly remains a dry salt areas, is likely due to the more consistent supply flat than a lake. Neverth less, the Laguna Salada of wat r in the ea t and perhaps also to the in­ has been inundated on several occasions ov r clu ion or the eastern wetlands in the core zone the last 20 yrs (Luecke et al. 1999). This was of the Upper Gulf of California and Colorado the case during our study when average winter River Delta Biosphere Reserve. As such, these flows or 230 m3/s in the main stem of Colorado wetlands are managed under cons rvation objec­ River w re recorded at the international bound­ tives and environmental review protocoL to pre- ary (IBW 2000), which flooded the Laguna Sa­ erve habitat for migratory birds and ndangered lada salt flats, attracting thousands of shorebirds. marsh birds, and limit human activitie to re­ The low and alty plains, traversed by mean­ search, education, and artisanal hunting, fishing, dering canal., of the Hardy, El Indio, and Cu­ and agriculture (SEMARNAP 1995). capa /Ones pre ent additional opportunities for Many of the wetlands in the Delta have been th restoration of marsh areas with the use of tre ed by the lack of adequat flows for most drainage water, although their design and oper­ of th last 50 yrs (Valdes-Casillas et al. 1998). ation will need to consider the potential for the Except in years of high precipitation in the Col­ accumulation of selenium and other contami­ orado River watershed, most or the Delta re­ nants that may adversely affect wildlife. Com­ main dry ( ohen et al. 200 I). Th invasion of munity-based restoration project , currently un­ tamarisk throughout th D !ta was a result of derway at each of the-.e /Ones, expect to restore manipulat d water regimes that subjected the re­ appro imat ly 1500 ha or habitat for waterbirds gion to long periods of reduced freshwater flows (0. Hinojosa-Huerta, unpubl. manuscript). or flows of higher salinity (GI nn et al. 1998, Nevertheless, the future of continuing conser­ Vandersand et al. 200 l ). In spite or this, those vation and restoration efforts in the region is in ­ habitats that remain in the olorado Ri er Delta secure. Most of the Delta wetlands exi ·t today largely as a result or flood control and agricul­ continue to supp rt large numbers or waterbirds. tural practice ·. Plans recently proposed to per­ ln recent surveys, over 160,000 shorebirds have manently r duce flows to the i ' nega (Glenn et been found wintering in the Delta (Morri. on et al. 1996, .. Bureau of Reclamation 1996) will al. 1992), along with tens of thousands of wa- likel reduce important habitat for breeding terfowl (Payn t al. 1992), making it one of th Yuma lapper Rails (Hinojosa-Huerta t al. critical sites for migratory waterbinls in north­ 2001 a) and alifornia Black Rails (Hinojo. a­ we. tern M xico (Massey and Palacios 1994) and Hucrta et al. 2001 b), as well as for myriad mi ­ al ng the entire Pacific Flywa (Anderson et al. gratory -;horebirJs and waterfov.. I. Although th The delta also provides important breed­ 2003 ). re. toration or the Delta to conditions that exist ·d ing habitat r )I" at least 12 spccieo.;, or aterbirus before the construction of dams 1s neither likely at Isla Montague (Peresbarbosa-Roja-. and Mel­ no1 practicable. the expan-.ion of wetland habitat link 2001) and north or the headwaters of the and a-.sociatcd use hy waterbirds after recent pe­ Hardy River at Campo eotermico rro Prieto riodic flooding highlight-. opportunitie"> for the (Molina and Garrett 200 I). Furthermore, docu­ restoration of wetlands in the olorado Ri er mented seasonal and inter-annual movements of Delta. An awareness or the importanc of con­ some species between wetlands in the delta and serving and enhancing wetland hahitat for the the alton ea demon. trate a close connectivity maintenance of wildlife populations in the re­ between these areas (Molina this 110/ume). gion is developing among th local rural com­ Rec nt periodic flooding has increased the ex­ munities. However, the success of these habitat tent of wetland habitat along the Hardy and Col­ restoration projects will ultimately depend on orado riv L by restoring more than I 0,000 ha obtaining adequate supplie-. of water over the of marshes and riparian thicket'> in these drain­ long term. age . More continuou flows of brackish water A bi-national wetland management and res­ from agricultural drainage o er the last 20 yrs toration program for the olorado River Delta ha helped create the Cicn ga de Santa Clara should consider the impacts of water manage­ wetland , an extensive system of marshes and m nl and flood control on wildlife (Luecke et al. flooded alt flat that now total over 6000 ha 1999, Nagler et al. 2000). ven . mall volumes (Glenn et al. 1992, 2001 ). These example sug­ of p riodically released flows of freshwater ge t that the permanent allocation of dedicated ( < 2.5 ppl) that allow for the maintenance of pe­ flow to the e and other areas, at even minimal rennial shallow lakes and ponds with some 60 STUDIES IN A VIAN BIOLOGY NO. 27 emergent vegetation, and the re toration and toration would aL identify u tainable ap­ maintenance of native riparian vegetation in the proache for nhancing the arti anal ec nomies floodplain (Glenn et al. 2001 ), would lead to of local communities while maintaining and en­ habitat improvement for waterbird a well a hancing eco y tern function and the biological for riparian ne ting landbird in the region. Di­ richness of the Colorado River Delta. recting the more con tant flow of agricultural drainage water (3 to 8 ppt) to areas with e tab­ CKNOWL OGM NTS li hed emergent vegetation could al o u tain Thi project was funded by the North American wildlife habitat. Succe ful wildlife habitat re - Wetland Con ervation Council, through the Grant toration will al o require that drain maintenance Agreement No. 14-4 -9 210-99-G349. Our pecial and flood control operation be de igned to gratitude to 0 . Gonzale.l, M. Gonzalez, J. Butr6n, J. J. avoid damaging riparian and emergent vegeta­ Butr6n, M. Butron, J. Mo queda, 0. J. Mosqueda, and J. Garcia for their help during fieldwork. J. Campoy, tion and the clo ing of econdary streams. M . J. Maitfnez, and M. Roman provided helpful in­ Wetland restoration in the Delta hould re-cre­ formation and support with logi tics. We thank K. Mo­ ate a variety of habitat type including shallow lina, M. Patten, K. Garrett, and W. 0. Shuford for their p ols, exten ive mar h area , mud flats, and invaluable comments on earlier draft of this manu­ backwater lagoons. A ucce ful program of re - ·cript.