1994-1997 Water Bird Surveys of Lake Powell, a Large Oligotrophic Reservoir on the Colorado River, Utah and Arizona

1994-1997 WATER BIRD SURVEYS OF LAKE POWELL, A LARGE OLIGOTROPHIC RESERVOIR ON THE COLORADO RIVER, UTAH AND ARIZONA

JOHN R. SPENCE, National Park Service, ResourceManagement Division, Glen CanyonNational Recreation Area, P.O. Box 1507, Page,Arizona 86040-1507 BENNY R. BOBOWSKI, NationalPark Service,Grant KohrsNational Historic Area, P.O. Box 790, Deer Lodge, Montana 59722-0790

ABSTRACT:We conductedmonthly boat surveys of aquaticbirds on Lake Powell from Septemberto April eachyear from 1994 to 1997. The surveyswere standard- izedin sevendesignated areas on the reservoir.Each survey took three daysand was done by two experiencedbirders and a boat pilot. In all, we recorded72,549 detectionsof 57 specieson 19 monthlysurveys. The most commonlydetected specieswas the AmericanCoot, followedby the WesternGrebe; these two species accountedfor 81% of all detections.Species rarely recorded in southernUtah and northernArizona but foundon the surveysincluded the Little Blue Heron, Barrow's Goldeneye,Greater Scaup, Herring Gull, Long-tailedDuck, Red-necked Grebe, Surf Scoter,and Pacificand Yellow-billedLoons. Species rarely recorded in winter for southern Utah and northern Arizona but detected on the surveysincluded the American White Pelican, Hooded Merganser,and Red-breastedMerganser. Lake Powellappears to be usedprimarily as a migratorystopover for aquaticspecies. Reservoirlevels fluctuate greatly from year to year,preventing the growthof aquatic vegetation.Fish populationsin the lake also fluctuate,and only in someyears are sufficientto supportwinter populations of fish-eatingspecies.

The widespreadconstruction of dams for power generationand flood controlthroughout the world in the 20th centuryhas createdopen-water habitatsthat in manyregions had been lacking. These newly created habitats have been colonizedby a varietyof aquaticbird species(e.g., Rahmani 1989, Pandey1993, Tremblay1993, Su and Liu 1995, Rizzoand Patrizia 1999, Utschick1998, 2000). Surprisinglylittle is known, however,about how reservoirshave affectedthe populationsizes, migration patterns, or breedingdistributions of aquaticspecies. To date, most studiesin North America have focusedon waterfowluse of particularfood resourcesand associatedhabitats in reservoirs(e.g., McKnightand Hepp 1995, Benedict and Hepp 2000). In particular,despite the constructionof numerousdams in the western U.S., littlework has been done on waterbirdcolonization and useof reservoirsin the more arid regionsof the southwesternU.S., over mostof which largebodies of open water were absentfrom the end of the PleistoceneEpoch until the 20th century(Rosenberg et al. 1991, McCaw et al. 1996). The constructionof Glen CanyonDam andthe subsequentfilling of Lake Powellin the southwesternU.S. createda largedeep-water reservoir on the centralColorado Plateau (Figure 1). The dam was completedin 1963 and the lake began filling in 1964, reachingfull pool in 1980. The reservoir covers67,900 hectares(679 km2) when at full-poolelevation of 1128 meters.Lake habitatshave been in existencefor 38 years.Since the dam wascompleted, a varietyof aquaticbird species previously rare or unknown from the Colorado River region have been recorded on the reservoir.

WesternBirds 34:133-148, 2003 133 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL

Trachyte

BullfrogBay Good Hope Bay

Warm Creek Bay

WahweapBay

UTAH

ARIZONA AntelopeIsland 7• 20 10 0 20 40 Miles r , Figure1. Sevensampling areas surveyed consistently throughout the surveyperiod, 1994-1997. Fromsouth to north,the locationsare Antelope Island, Wahweap Bay, WarmCreek Bay, Hall's Creek Bay, Bullfrog Bay, Good Hope Bay, and Trachyte.

Through2001, 82 speciesof aquaticbirds (see definition below) have been recordedon Lake Powell(LaRue et al. 2001), somein largenumbers. The ColoradoRiver was originallya dynamicsediment-laden river with peak flowsduring spring flooding and minimumflows during the winter (Carothersand Brown 1991). Springfloods scoured out the riverchannel, preventingthe establishmentof aquaticvegetation. Primary productivity was low becauseof poor light penetrationin the muddywaters. Early accountsindicate that few aquaticspecies occurred along the Colorado Riverprior to the constructionof the manydams now regulatingits flow (Behleand Higgins1958, Carothersand Brown1991, Rosenberget al. 1991). Grinnell(1914) conductedwildlife surveys along the lower Colorado River downstreamof Needlesin 1910 andnoted only a fewAmerican Coots and dabblingducks. The situationtoday is very different.The constructionof large damson the ColoradoRiver createdhabitat for waterfowland other aquaticspecies both aboveand belowthe dams.Hoover Dam was the first to be completedin 1936, creatingLake Mead.Other damswere soonbuilt

134 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL downstream(Parker, Imperial, and Davis). The generaleffects of thesedams have been to increaseboth winteringand breedinghabitat for aquatic avifaunagreatly (Rosenberg et al. 1991, Stevenset al. 1997). The clearcold watersbelow the damscreate conditions conducive to the growthof aquatic vegetation,supporting large wintering populations of waterfowl.The deep reservoirsabove the damsprovide wintering habitat for a varietyof aquatic birds,especially diving species such as grebes. Priorto 1994, onlytwo surveyshad been completed on Lake Powell,and no systematiclong-term winter surveys had been initiated. In January1988 a lakewidesurvey was conducted,documenting 3715 individualsof 21 species(National Park Service data). In November1992 a lakewidesurvey for the WesternGrebe (no distinction was made between the two speciesof Aechmophorus)yielded 3619 individuals(National Park Servicedata). In February1994 a surveyin WarmCreek Bay revealed three species of loons, the Common, Pacific, and Yellow-billed.The Yellow-billedLoon was the second recorded in Utah. In May 1994 the ResourceManagement Division of Glen Canyon NationalRecreation Area acquireda 32-foot MunsonHammerhead with a cruisingradius of 10-12 hours.This boat offeredample speed, a stable platformfor spottingscopes, and an enclosedcabin for wintersurvey work. Becauseof the lackof baselinedata on wintering aquatic bird populations on Lake Powell,we initiateda systematicsurvey program in October1994, continuingit throughApril 1997. This report documentsthe resultsof the threeyears of surveys.The primarygoal of the programwas to inventory selectedareas on LakePowell on a monthlybasis to determinethe numbers and kindsof migrantand overwinteringaquatic birds.

SURVEY METHODS

We choseto use boat surveysfor the projectprimarily because rare speciesare morelikely to be detectedand identified from boat surveys than fromaerial surveys (cf. Stancill and Leslie 1990). Preliminaryobservations by boatand fixed-wingplane located areas of LakePowell with significant concentrationsof birds.On the basisof theseobservations, earlier reports, andthe logisticsof operatingon a lake295 km long,we designatedseven areasfor monthly surveys: Trachyte Canyon, Good Hope Bay, Bullfrog Bay, Hall'sCreek Bay, Warm Creek Bay, WahweapBay, and AntelopeIsland (Figure1). AntelopeIsland is in Arizona,while the othersix survey areas are in Utah. No main channelreaches or narrowside canyons were includedin the designatedsurvey routes because few birdswere seenin theseareas. Oncea monthbetween September and April, we conducteda three-day survey,starting at GoodHope Bayand Trachyte Creek on day 1, movingto Bullfrogand Hall'sCreek bays on day 2, and endingat Warm Creekand Wahweapbays and AntelopeIsland on day 3. Fixedroutes were followed alongthe shorelinesof theseseven survey areas. Most birdsseen were individuallyider•tified and counted.Large rafts of WesternGrebes and AmericanCoots were occasionallyencountered, however, and in some casesnumbers had to be estimated.In thesecases, two observersindepen-

135 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL dently estimatednumbers, with an averagetaken where estimateswere close(within 10%). If the estimateswere different by morethan 10%, then new countswere madeuntil the estimatesconverged. We attemptedto avoid double-countingindividuals as a result of their movements.The counts reportedin this paper are thusconservative. One assumptionwas that birds countedon differentdays did not movebetween survey areas over night. In generalwe made no attemptto distinguishbetween Clark's and Western Grebesin largerafts. We made occasionalchecks, however, to determine the percentageof Clark'sand to documentits presenceon Lake Powell.In these checksthe numberof Clark's Grebe was always<1% of the flock number. Data recordedfor each bird or flock observedincluded location, time of day,species, habitat, behavior, and, where possible, sex and age. Incidental observationsof birdswere recordedwhile we were movingbetween designatedsurvey areas but were not includedin totalnumbers. Aquatic birds are definedas all membersof the following:all familiesfrom Gaviidaethrough Anatidae and all familiesfrom Rallidaethrough Laridae (AOU 1998 se- quence). We determinedthe principalmeans of foragingon Lake Powellfor each species,assigning it to one of four foragingguilds: aerialists (gulls, terns), dabblers(dabbling ducks), divers (diving ducks, coots, grebes, loons, cormorants, etc.), and waders (shorebirds,herons, etc.). Monthly surveyswere conductedby two experiencedbird observers. Because of stormyweather, boat problems,and governmentshutdowns, surveys were not conductedin November1995 and Octoberand December1997. Partial surveyswere conductedin Marchand April 1996, withonly southern lake areas (Wahweap andWarm Creekbays, Antelope Island) surveyed. Seasons were defined as fall (September-November), winter (December-February), and spring (March-April).

RESULTS AND DISCUSSION

BetweenOctober 1994 and April 1997, 117 surveysover 19 months detected57 speciesof aquaticbirds in the sevensurvey areas. This figure represents81% of the 70 aquaticspecies known from the reservoirby 1997. The two mostcommon wintering species on Lake Powellwere the AmericanCoot andWestern Grebe. These two speciesaccounted for 81% of all recordedindividuals (48% and 33% respectively).Other specieswith at least 1% of the total number recorded were the Gadwall (2.4%), Green- wingedTeal (1.7%), Ring-billedGull (1.5%), CommonGoldeneye (1.3%), and Redhead (1.1%). Several speciesrarely reported in Arizona and southernUtah were recordedduring the surveys.These include the LittleBlue Heron, Barrow's Goldeneye,Greater Scaup, Herring Gull, Long-tailedDuck, Pacific Loon, Red-necked Grebe, Surf Scoter, Wood Duck, and Yellow-billedLoon. Unusualwinter (December-February)records were obtainedfor several additionalspecies, including the AmericanWhite Pelican,Hooded Mergan- ser, and Red-breastedMerganser.

136 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL

Surveysprior to 1960 hadrecorded 24 speciesof aquaticbirds along the ColoradoRiver and its main tributariesfrom the Glen CanyonDam site to Hite (Table 1; Woodward 1958, Behle and Higgins 1959, Behle 1960). Between 1960 and 1963 an additional12 specieswere recordedin the area,primarily near the damsite (National Park Service files). Since 1964 an additional44 specieshave been recorded,the mostrecent being the first record of the Yellow-lootedGull for Utah and Arizona. The bird, an adult, was discoveredon 21 April 1999 in Wahweap Bay in Utah and then relocatedlater the sameday near Antelope Island in Arizona(Rosenberg and Benesh 1999). Becausefar more people, includingbirders and governmentbiologists, havebeen visiting the regionsince the completionof GlenCanyon Dam, the large increasein numberof speciesin the last 30 yearsmay be more a reflectionof number of observersrather than actual "discovery"of the reservoirby aquaticspecies. Earlier surveys and visitors were few, andmost were duringthe springand summermonths when the ColoradoRiver was mosteasily run. It isthus likely that some of the speciesrecorded since 1964 may haveoccurred in the regionearlier but went unrecorded. The two most common habitats in which birds were recorded were drownedtamarisk (Tamarix ramosissima)in shallowwater near shoreand largeshallow bays of openwater. Very few birdswere seenalong the rocky shorelinesthat constitute>90% of Lake Powell'smargin. The American Coot, other divingspecies, and the majorityof the dabblingducks were associatedwith drownedtamarisk. Growth of algae and in some cases aquaticvascular plants, with their associatedinvertebrates along with small fish, presumablyprovide the primaryfood for thesespecies. In the larger shallowbays such as Warm Creek or Hall's Creek bays(Figure 2) were the largeconcentrations of WesternGrebes. These birds were oftenseen diving for food, most likely schoolsof small fish such as the threadfinshad (Dorosomapetenense). Lake Powellprovides relatively poor habitatfor dabblingducks. Because of fluctuationsin reservoirlevels of 10 to 15 meters per year, extensive aquaticvegetation cannot develop. Rather, a thin layer of algae,primarily Chara, attachedto bouldersand drowned tamarisk stems, provides the only foodfor dabblers.Recently, however, the exoticaquatic vascular plant Najas marina has appearedin the reservoirand is spreadingrapidly along beaches.The abilityof this speciesto providefood for dabblersin the fluctuatingreservoir remains unknown. In general,most dabblers peak in fall and springmigration, and only a few hundredtypically winter on Lake Powell. The abundanceof fish-eatingdiving species such as grebes,cormorants, loons, and mergansersvaried greatly from year to year. Countsof the WesternGrebe, the most commonfish-eating diving species on the reservoir, were high when numbersof small fish in Lake Powellwere high (unpublishedNational Park Servicedata). Counts of the WesternGrebe on Lake Powell,however, rarely exceeded 5000 individuals,well belownum- bers known from naturallakes. In years when fish numberswere low, relativelyfew diving species lingered past December. It is perhapssignificant

137 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL

Table 1 Water BirdsDetected 1994-1997 on Lake Powell,Glen Canyon National RecreationArea, Utah and Arizona

Pre-dam Numberof Percentageof Species presencea detections surveysdetected

PacificLoon Gavia pacifica 7 26 Common Loon Gavia iramet 109 95 Yellow-billedLoon Gavia adamsii 5 26 Pied-billedGrebe Podilymbus podiceps X 377 100 HornedGrebe Podiceps auritus 92 58) Red-neckedGrebe Podiceps grisegena X 3 16 EaredGrebe Podiceps nigricollis X 636 100 WesternGrebe Aechmophorus occidentalis 23,712 100 Clark'sGrebe Aechmophorus clarkii 17 42 American White Pelican Pelecanuserythrorhynchos X 9 21 Double-crestedCormorant Phalacrocorax auritus X 547 89 Great Blue Heron Ardea herodias X 138 95 GreatEgret Ardea alba X 2 11 SnowyEgret Egretta thula X 2 11 LittleBlue Heron Egretta thula 1 5 CattleEgret Bubulcus ibis 2 5 Black-crownedNight-Heron Nycticoraxnycticorax X 2 5 White-facedIbis Plegadis chihi X 107 11 Canada Goose Branta canadensis X 166 79 Snow Goose Chen caerulescens 1 5 WoodDuck Aix sponsa 1 5 GadwallAnas strepera X 1764 100 AmericanWigeon Anas americana X 183 63 MallardAnas platyrhynchos X 534 95 Blue-wingedTeal Anas discors X 58 11 CinammonTeal Anas cyanoptera X 67 32 NorthernShoveler Anas clypeata X 323 79 Northern Pintail Anus acura X 588 79 Green-wingedTeal Anas carolinensis X 1270 84 RedheadAythya americana X 822 89 Ring-neckedDuck Aythya collaris 719 63 GreaterScaup Aythya marila 6 11 LesserScaup Aythya affinis X 654 84 SurfScoter Rlelanitta perspicillata 2 11 Long-tailedDuck Clangula byemalls 4 21 BuffieheadBucephala albeola X 515 84 CommonGoldeneye Bucephala clangula X 970 74 Barrow'sGoldeneye Bucephala islandica 10 11 HoodedMerganser Lophodytes cucullatus 31 32 CommonMerganser Mergus merganser X 733 95 Red-breastedMerganser R/ergus serratot 168 68 RuddyDuck Oxyura jamaicensis X 303 74 American Coot Fulica americana X 34,985 100 KilldeerCharadrius vociferus X 4 11 (continued)

138 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL

Table 1 (Continued)

Pre-dam Numberof Percentageof Species presenceø detections surveysdetected

American Avocet Recurvirostra americana X 13 11 GreaterYellowlegs Tringa melanoleuca 5 11 LesserYellowlegs Tringa flavipes 3 11 Long-billedCurlew Numenius americanus 6 5 WilletCatoptrophorus semipalmatus 22 11 MarbledGodwit Limosa fedoa 218 16 Franklin'sGull Larus pipixcan X 80 16 Bonaparte'sGull Larus philadelphia 2 5 Mew Gull Larus canus 1 5 Ring-billedGull Larus delawarensis X 1124 100 CaliforniaGull Larus ca liforn icus X 418 58 HerringGull Larus argentatus 4 21 Forster'sTern Sterna forsteri 4 5 aSpeciesrecorded in area priorto buildingof Glen CanyonDam.

that the mostcommon wintering species on Lake Powellwas the American Coot, a generalistthat has a broadarray of foragingbehaviors. Becauseof the timing of the surveys,some speciesgroups were not detectedin thisstudy. Regionally, the bulkof fall shorebirdmigration takes placein Augustand September,and we conductedrelatively few surveysin September.The onlysurvey month that yieldedgood numbers of shorebirds wasApril, when flocksof MarbledGodwits were oftenfound. Because of the shorelineof LakePowell is solong (about 2000 milesat full-poolelevation) it is likelythat manyshorebirds were missedsimply because of the amountof availablehabitat. Other groupsnot wellrepresented in the surveydata include phalaropes,terns, jaegers,and Sabine'sGull. Wilson'sand Red-necked Phalaropestend to migratethrough the regionin a shortinterval of a weekor so in late March(National Park Service files), and noneof the surveysin that monthapparently coincided with this window. In fall,these species tend to be morediffuse in theirmigration, and also typically move through in the largest numbersin late August.Most tern speciesmigrate through the Lake Powell area in May or Augustand were alsomissed because of the surveytimes. Jaegersare extremelyrare in the regionfor unknownreasons, with only a singledocumented sighting of an adultParasitic Jaeger over Wahweap Bay on 21 September2000 (LaRueet al. 2001). Finally,Sabine's Gull moves throughthe Lake Powellregion in very smallnumbers (four records of 10 individuals)during a short period betweenabout 18 and 25 September (LaRueet al. 2001) and was missedon the 1994-1997 surveys. The resultspresented in this paper are similar to survey resultsat reservoirsin the lower ColoradoRiver Valley such as Lake Havasuand Mohave Lake (Rosenberget al. 1991). The relativeabundance of the speciesin the two areasis similar,but many more birdswinter in the lower

139 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL

Figure2. DrownedFremont Cottonwood (Populus fremontii) in upperHall's Creek Bay. 29 November1994. Thisarea consistentlysupports high numbers and diversity of aquatic birds. includingmost of the wintering populationof Double-crested Cormorants on Lake Powell.

Photo by J. D. Grahame/Nationa! Park Service

valleythan on Lake Powell.This differenceis probablydue to a combination of milderwinters. a greateramount of food and other resourcesin the older reservoirs,and adjacentwildlife refuges and non-dammedsegments of the Colorado River. One major differencebetween the two regionsis that Clark'sGrebe is very rare on Lake Powellbut commonin the lowervalley (Rosenberget al. 1991). It is fairlycommon on Lake Meadas well (Spence pers.obs.). Reasons for thisdifference are unknownbut may be relatedto different migrationpatterns of the two specieswithin the Intermountain West flyway.

ANNOTATED SPECIES LIST

The followinglist details our resultsfor the 57 speciesseen in one or more of the sevendesignated survey areas during the 19 monthsof surveys.Table 1 summarizesthe countsfor each species. PacificLoon (Gaviapacifica). A rare migrantand possiblewinter resident.Seven records.of one in October1994. two in October1995, one in January1996, two in November1996. and one in April 1997. The specieshas been seen in all surveyareas exceptAntelope Island and Good Hope Bay. There is a slightpossibility for someof the earlyrecords to havebeen of the ArcticLoon, unrecordedinland in the westernUnited States,although the lastthree individualswere carefullyidentified as the PacificLoon

140 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL

Common Loon (Gavia iramet). A rare but regularmigrant and winter resident,with recordsfrom every surveymonth except September 1995. Peak numbersare recordedbetween December and February. The largestsingle count was five birds on Warm Creek Bay on 15 February1996. Common Loonsare generallysolitary on Lake Powell. Yellow-billedLoon (Gavia adamsii). A Yellow-billedLoon was first seen on 10 February1994 on Warm Creek Bay prior to our launchingthe lake surveys.The bird associated with both Common and Pacific Loons. The second record was on 21 December1994, againon Warm CreekBay. The birdthen movedto WahweapBay, where it was seentwice opposite the Coves,on 15 Februaryand 15 March 1995. Very likelythis same bird returned the nextyear, with sightingson Warm CreekBay on 15 Februaryand 15 March 1996. Pied-billedGrebe (Podilymbus podiceps). An uncommon but regularly seen species,with recordsfrom all surveymonths. Numbers tend to peak in late fall and winter(November-January). A majority of the recordsare from 1994-95, whenthe specieswas particularlycommon on Lake Powell.The largestcount was of 39 on WahweapBay in 20 January1995. HornedGrebe (Podiceps auritus). Prior to 1996-97 a rarefall and spring migrant, withonly two winter records, of singlebirds on GoodHope Bayon 18 January1995 and on BullfrogBay on 14 February1996. For unknownreasons the specieswas relativelycommon on Lake Powell during 1996-97, with 84 detectionsthat year comparedwith sevenin 1994-95 and one in 1995-96. During the five months surveyed,counts included 16 in November,10 in January, 11 in February,29 in March, and 18 in April. The singlelargest count was of 12 birdsaround Antelope Island on 21 March 1997. Red-neckedGrebe (Podiceps grisegena). A rare winter and springmigrant, with threerecords of singlebirds, 20 January1996 and 17 January1997 on Warm Creek Bay and 21 March 1997 near AntelopeIsland. These are the first recordsfor Glen Canyon National RecrationArea and Lake Powell. EaredGrebe (Podiceps nigricollis). A commonfall and uncommon spring migrant, oftenlingering in smallnumbers through the winter.The largestgroup seen during surveyswas 168 on WahweapBay on 23 January1997. WesternGrebe (Aechmophorusoccidentalis). Common to abundant;the second most commonspecies on Lake Powellduring the surveyperiod. Western Grebes generallyoccur in raftsranging from a dozenup to 1700 at the mouthof Trachyte Creek on 20 November1996. Traditionally,large numbershave been seen at this location,Good Hope Bay,and Bullfrog Bay. There is a stronggradient of increasing numbersfrom the dam toward Hite at the far northernend of the lake (NationalPark Service unpublisheddata). Peak numberstend to occur in fall or early winter (October-December),coinciding with southbound migration. A smallerpeak occurs in Marchand April as well. Largenumbers were counted in falland winter of 1995-96 and 1996-97, coincidingwith relativelyhigh populationsof the threadfinshad. Clark's Grebe (Aechmophorusclarkii). A rare migrantin spring(April) and fall (September-November).The occasionalinspection of raftsof WesternGrebes indi- catedthat <1% of theseflocks are Clark's.There is onlyone winterrecord, of one on GoodHope Bay on 18 January1995. Generallythis species occurs as single birds or more oftenpairs at the upperends of bays,associated with drownedtamarisk. AmericanWhite Pelican(Pelecanus erythroryhnchos). Pelicans generally migrate throughthe area in Augustand were missedon the surveys.However, two birds lingeredat WahweapBay from 20 Octoberthrough 21 December1994. A singlebird wasobserved on BullfrogBay from 29 November1994 to 19 January1995.

141 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL

Double-crestedCormorant (Phalacrocorax auritus). A commonfall migrantand winter residenton somebays, especially Hall's Creek Bay. Numberspeak in fall and winter,and generallymost birds are goneby Marchor April. The largestflock was of 41 on upperHall's Creek Bay on 19 October1994. Great Blue Heron (Ardea herodias).A rare year-roundresident, with migrants augmentingresidents during the winter.The largestgroups were of sevenbirds each at BullfrogBay on 14 March 1995 and WahweapBay on 14 March 1996. Great Egret(Ardea alba). A very rare springmigrant, with two records.Single adultswere seenalong the shoresof WahweapBay on 20 April 1995 and 12 April 1996. SnowyEgret (Egretta thula). A rare springmigrant to the shoresof Lake Powell, with onlytwo recordsof singlebirds, at BullfrogBay on 14 March 1995 andWarm Creek Bay on 18 April 1997. LittleBlue Heron (Egrettacaerulea). Extremely rare migrant,with a singlerecord of an immatureat upperWahweap Bay on 21 September1995. CattleEgret (Bubulcus ibis). Rare spring migrant. Two birdswere seen along the shoresof WahweapBay on 18 April 1997. Black-crownedNight Heron (I•ycticorax nycticorax).Rare migrant.Two birds were seenon 12 April 1996 in tamariskat the headof Warm CreekBay. White-facedIbis (Plegadischihi). Small flocksoccur regularlyin April during northboundmigration. These flocksoften linger into May and early June in the Wahweaparea. The largestflock was of 46 birdson 17 April 1997 at BullfrogBay. CanadaGoose (Branta canadensis).An uncommonfall and springmigrant on LakePowell, generally not lingeringin winter.The largestflock of 46 birdswas seen on Warm CreekBay on 21 March1997. Thisspecies overwinters commonly at the Pagesewage-treatment plant and the adjacentgolf course. SnowGoose (Chen caerulescens). Very rare winter visitor. A singlebird was seen with a flockof AmericanCoots off AntelopeIsland on 6 December1995. Wood Duck(Aix sponsa).A veryrare wintervisitor, with a singlerecord of a male that remainedat BullfrogMarina from November1994 to February1995 (Figure3). Gadwall(Anas strepera). A commonspecies, seen in all surveymonths. Numbers peakin winterand early spring (especially March) during migration. The largestflock wasof 103 birdson Hall'sCreek Bay on 19 January1996. AmericanWigeon (Anas americana). An uncommonspecies, generally seen only in fall(October) and spring (March) migration. Large flocks of thisspecies overwinter regularlyon golf coursesat Page, so apparentlythe lake doesnot provideproper foraginghabitat for wigeons. The largestflock was of 42 birdson WarmCreek Bay on 15 March 1995. Mallard (Anas platyrhynchos).An uncommonresident and commonwintering species,encountered in smallflocks in most surveyareas, with peak numbersin Decemberand January. Mallards were scarce in the winterof 1995-96. The largest flockwas of 56 birdson Hall's CreekBay on 29 November1994. Blue-wingedTeal (Anasdiscors). An uncommonmigrant in the Lake Powellarea, withonly a fewsightings of smallflocks in Septemberand October 1995. The largest flockwas of 30 on WahweapBay on 20 October1995. Becauseof difficultiesin distinguishingbirds in eclipseplumage, some teal seenduring the studywere left unidentifiedand couldhave been either this speciesor the CinnamonTeal.

142 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL

Figure3. Male Wood Duckat BullfrogMarina, 20 December1994 This bird stayed most of the winter 1994-1995 and becameextremely tame. Photo by J. I•. Spence/National Park Service

Cinnamon Teal (Anas cyanoptera). A rare spring (March-April) and early fall (September)migrant. with few birdsdetected prior to 1997. In 1997 smallflocks were seen in scatteredlocations. with the largestbeing 10 on Warm Creek Bay on 21 March 1997 and 14 on WahweapBay on 18 April 1997. Northern Shoveler(Anas clypeata). An uncommonmigrant and winter resident. scarcein 1995-96. Relativelylarge numbers were seenin springof 1997, with 91 in March and 189 in April. The largestflock was of 90 birdsat the mouthof Trachyte Creek on 16 April 1997. Northern Pintail (Anas acura). An uncommonfall and springmigrant and winter resident,scarce in 1995-96. Relativelylarge numbers were seenin latewinter 1997, with 255 birdson Wahweap Bay and 185 on Warm Creek Bay on 21 February1997. Green-wingedTeal (Anas crecca).An uncommonfall and early springmigrant, with peak numbersin October,February, and March. A few birdslinger through the winter.The largestflocks were seenon 21 March 1997, with 165 aroundAntelope Islandand 152 on Wahweap Bay. Redhead(Aythya americana). Common migrant and winter resident Birds start appearing in October and peak in December-January.A few linger into April. Redheadnumbers peaked on 21 December1994 and 20 January1995, whenflocks of 191 and 175, respectively,were seenon WahweapBay. Numbersof Redheads were very low in 1995-96, while more were seen in 1996-97, includinga flockof 164 on Warm Creek Bay on 23 January1997 Ring-neckedDuck (AChya collaris).Common migrantand winter resident,with numberspeaking in Decemberand January.Like other waterfowl.this species was

143 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL scarceon Lake Powellin the winter of 1995-96. The largestflock seen was of 141 on 17 January 1997 on Warm Creek Bay. Greater Scaup(Aythya rnarila). Very rare migrant;two records.A singlebird was seenflying over Bullfrog Bay on 20 January1995, and a flockof fivewas seen flying over Wahweap Bay on 14 March 1996. The Greater Scaup is a rare but regular overwinteringspecies on the ColoradoRiver below Glen Canyon Dam, with most recordsbetween December and February(LaRue et al. 2001). Lesser Scaup (Aythya affinis). A relativelycommon fall migrant and winter resident,with smallflocks most often seen on Wahweap Bay and aroundAntelope Island.Lesser Scaup start appearingin Octoberand most are gone by March. The largestflock was of 89 individualson WahweapBay on 21 March 1997. This is one of the more common overwinteringspecies on the Colorado River below Glen CanyonDam (LaRueet al. 2001). Surf Scoter (Melanitta perspicillata). Rare migrant: two records. A female- plumagedbird was seen on WahweapBay on 20 October 1994 (Figure4). while anotherfemale-plumaged bird was seen on Hall'sCreek Bay on 19 April 1995. This specieshas also been recordedseveral times from the ColoradoRiver belowGlen Canyon Dam (LaRueet al. 2001). Long-tailedDuck (Clangula hyernalis).Rare winterresident and migrant:three or four records.A male wasseen on Hall's Creek Bay on 19 January1996, then again on 14 February1996. A birdof unknownsex on Hall's Creek Bay on 13 March 1996 may havebeen the sameindividual. A birdof unknownsex was seen on Warm Creek Bay on 22 November 1996.

Figure4. FemaleSurf Scoter on WahweapBay, 20 October1994. The birdappeared to be exhaustedand flew onlywhen we approachedvery closein the surveyboat. Photo by J. D. Graharne/National Park Service

144 1994-1997 WATER BIRD SURVEYS OF LAKE POWELL

Buffiehead(Bucephala albeola). A common winter residentfirst appearing in October,with peak numbersbetween December and February.The speciesis mostly gone by March. Buffieheadsfrequent the upper ends of shallowbays, especially Bullfrogand Hall's Creek bays. The largestcounts were of 54 on 20 December1995 and 52 on 19 January1996, bothon BullfrogBay. CommonGoldeneye (Bucephala clangula). A commonwinter resident, with small flocksoccurring in most surveyareas, appearing in November,but most common betweenDecember and February.A few individualslinger into March. The largest singlecount was of 136 on Hall's Creek Bay on 14 February1996. Numberswere muchlower in 1996-1997 than in the previoustwo years.The CommonGoldeneye is one of the mostcommon overwintering species on the ColoradoRiver below Glen CanyonDam (LaRueet al. 2001). Barrow'sGoldeneye (Bucephala islandica). Rare winterresident; two sightings.A flockof eightwas on Hall's Creek Bay on 19 February1996, and two birdswere on WahweapBay on 21 December1995. On the ColoradoRiver below Glen Canyon Dam, however,small flocks overwinter regularly (LaRue et al. 2001). Hooded Merganser(Lophodytes cucullatus). Uncommon to rare migrant. Very small numbersmove through the region in late fall and early winter (November- January),with a singlespring record of a male on Hall's Creek Bay on 14 March 1995. The largestflock was of 13 birdson Warm Creek Bay on 29 November1994. CommonMerganser (Mergus merganser). Common migrant and winterresident, with recordsfrom most surveymonths. Numbers peak in Decemberand January. This specieswas much more commonin 1995-96 than in the other years of the study.The largestflock was of 48 birdson Warm CreekBay on 15 January1996. The speciesis a commonresident breeder on the ColoradoRiver below Glen Canyon Dam (LaRueet al. 2001) and occasionallybreeds on Lake Powell. Red-breastedMerganser (Mergus serratot). Regularmigrant in small numbers, with highestcounts in earlywinter and spring.In the winter of 1996-97 severalbirds overwintered,e.g., 18 in Januaryand 12 in February.The largestcount was of 26 on Hall's Creek Bay on 13 March 1996. Ruddy Duck (Oxyura jamaicensis).Uncommon fall and springmigrant, most common in October.A few birdslingered over the winter of 1996-97. The largest count was of 80 birdsoff Antelope Islandon 27 October 1995. AmericanCoot (Fulicaamericana). Abundant species over the three yearsof the study,particularly between November and January.American Coots accounted for over 48% of all birdsightings. They were abundantin 1994-95 and commonagain in 1996-97. In 1995-96, however,numbers were very low exceptin Decemberof 1995. The singlelargest count was of 3906 on Warm Creek Bay on 23 January 1997. Cootsforage in a varietyof ways,but on LakePowell they generally dive in very shallowwater, foraging on algaegrowing on rocksor drownedvegetation, associated crustaceans,and possiblysmall fish. Coots are stronglyconcentrated around the marginsof shallowbays with abundantdrowned tamarisk, habitat that is especially commonin Bullfrog,Warm Creek, and Wahweapbays. Killdeer(Charadrius vociferus). Killdeer are commonmigrants in the Pagearea but are apparentlyvery rare on LakePowell. Our surveysgenerated only two records,of a singlebird at BullfrogBay on 29 November1994 andthree birds on AntelopeIsland on 18 April 1997. Thisspecies, like other smaller shorebirds, may be morecommon than the numbersindicate, probably easily overlooked from a boat on the water. American Avocet (Recurvirostraamericana). Rare; four sightings.Single birds wereat WahweapBay on 12 April 1996 andnear Antelope Island on 18 April 1997.

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A flockof sevenwas at WahweapBay on 18 April 1997, anda groupof fourwas at BullfrogBay on 17 April 1997. GreaterYellowlegs (Tringa melanoleuca).Rare winter lingererand early spring migrantwith two records,of two at BullfrogBay on 15 February1996 andthree in the samearea on 18 April 1997. LesserYellowlegs (Tringa flavipes). Rare springmigrant; one record.Three birds were at WahweapBay on 18 April 1997. Long-billedCurlew (Numenius americanus).Rare springmigrant, with a single recordof six birdsoff AntelopeIsland on 12 April 1996. Willet (Catoptrophorussemipalmatus). Rare springmigrant; three records.At Wahweap Bay two birdswere with MarbledGodwits on 20 April 1995 and four birds were sightedon 18 April 1997. The largestflock of 16 birdswas at Hall'sCreek Bay on 17 April 1997. Otherwisethis speciesis a sparsemigrant in springand fall at sewage-treatmentponds in the Page area (LaRueet al. 2001). MarbledGodwit (Limosa fedoa). Uncommonbut regularmigrant in April, most likelyto be seenat WahweapBay or aroundAntelope Island. The largestflight was of 168 birdson 20 April 1995 in the southernportion of the lake:100 at WahweapBay, 60 on AntelopeIsland, and 8 at Warm Creek Bay. Franklin'sGull (Larus pipixcan). Small numbersof Franklin'sGulls migrate throughthe Lake Powellarea in April and May. Most sightingswere from southern surveyareas or BullfrogBay. April 1997 wasa particularlygood month, with 59 birds countedin four surveyareas. The largestflocks were of 14 over BullfrogBay on 17 April 1997 and 43 overWahweap Bay on 18 April 1997. On 2 May 1997, 65 birds were countedat the Wahweap sewage-treatmentplant, about 1 mile from Lake Powell (LaRue et al. 2001). The numbersreported in the spring of 1997 are unprecedentedfor the U.S. Southwest,as mostFranklin's Gulls migrate east of the Rocky Mountains(Burger and Gochfeld1994). Regionally,most sightingsare of singleindividuals or very smallgroups (Rosenberg et al. 1991). Bonaparte'sGull (Larus philadelphia). Rare migrant. One recordof two birdsover WahweapBay on 27 October 1995. Mew Gull (Larus canus). Rare migrant. One record of a second-yearbird at WahweapMarina from 30 Novemberto 21 December1996. It wasthe firstMew Gull recordedfor Lake Powelland Glen CanyonNational Recreation Area. Ring-billedGull (Larus delawarensis).Common winter resident.Ring-billed Gulls startappearing at Lake Powellin late September;they departby late April or early May. The largestcount was of 359 on 13 and 14 March 1996, with the singlelargest surveycount of 205 on 14 March 1996 over WahweapBay. CaliforniaGull (Larus californicus).Common migrantin spring(March-April), especiallyin the southernportions of the lake, but rare on fall and winter surveys. There are recordsfor everymonth over the three yearsof surveysexcept January. The largestcount was of 205 birdsover WahweapBay on 12 April 1996. Herring Gull(Larus argentatus). Rare migrant.Four recordsof singlefirst-winter birds, at Hall's Creek Bay on 19 October 1994 and 13 March 1996, Warm Creek Bay on 5 December1996, and WahweapBay on 23 January1997. Forster'sTern (Sternaforsteri). Although this species is a commonfall and spring migrantthrough the regionin May andlate August or earlySeptember, sometimes in large flocks(e.g., 150 on a smallisland off northeastpoint of AntelopeIsland on 11 May 1995), it wasrecorded only once during the surveys.Four were over Bullfrog Bay on 18 April 1997.

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ACKNOWLEDGMENTS

We especiallythank A. J. Pinnock and John Do Grahame for their help in organizingand initiatingthe project. We gratefullyacknowledge the numerous biologistsand birderswho helpedon one or more surveys,including Nikolle Brown, Aaron Flesh,Chris FlorJan, Chris Goetze,Chuck LaRue, LaurieNess, Brenda Russell, Elliot Swarthout,and Mark Wotawa. Boat pilots were Tony Napolitan and Tom Haberle,who enduredlong hours of "getus closer to that bird"being shouted at them. John Ritenour,chief of the resource-managementdivision, provided support and encouragement.The projectwas conductedwith Glen Canyon National Recreation Area ONPS basefunding. We are gratefulto Ken Rosenbergand SteveSummers, who reviewedthe draft manuscript.

LITERATURE CITED

Behle, W. H., and Higgins,H. G. 1959. The birdsof Glen Canyon, in Ecological studiesof the floraand faunaof Glen Canyon(A.M. Woodbury,ed.), pp. 107- 133. Univ. Utah Anthropol.Paper 40. Behle, W. H. 1960. The birds of southeasternUtah. Univ. Utah Biol. Ser. 12:1-56. Benedict,R. J., Jr., and Hepp, G. R. 2000. Winteringwaterbird use of two aquatic plant habitatsin a southernreservoir. J. WildlifeMgmt. 64:269-278. Burger,J., and Gochfeld,M. 1994. Franklin'sGull (Larus pipixcan), in The Birdsof North America (A. Poole and E Gill, eds.),no. 116. Acad. Nat. Sci., Philadel- phia. Carothers, S. W., and Brown, B. T. 1991. The Colorado River through Grand Canyon. Univ. of Ariz. Press,Tucson. Grinnell,J. 1914. An accountof the mammalsand birdsof the lower ColoradoRiver Valleywith especialreference to the distributionalproblems presented. Univ. Calif. Publ. Zool. 12:51-294. LaRue, C. T., Spence,J. R., and Grahame,J. G. 2001. Annotatedchecklist of the birdsof Glen Canyon National RecreationArea, Arizona and Utah. Unpubl. report, National Park Service,Glen Canyon National RecreationArea. Pandey,S. 1993. Changesin waterbirddiversity due to the constructionof PongDam Reservoir,Himachal Pradesh,India. Biol. Conserv. 66:125-130. McCaw, J. H., III, Zwank,P. J., andSteiner, R. L. 1996. Abundance,distribution, and behaviorof Common Merganserswintering on a reservoirin southernNew Mexico. J. Field Ornithol. 67:669-679. McKnight,S. K., and Hepp, G. R. 1995. Potentialeffect of grasscarp herbivoryon waterfowl foods.J. Wildlife Mgmt. 59:720-727. Rahmani, A. R. 1989. Narora Reservoir:An excellenthabitat for waterfowl. Corsonat 3:7-9. Rizzo, M., and Nicolosi, P. 1999. Waterfowl surveyon Poma Reservoir(Sicily). Naturalista Siciliano 23:407-417. Rosenberg,G. H., and Benesh, C. D. 1999. Spring migration:Arizona region. N. Am. Birds 53:310. Rosenberg,K. V., Ohmart, R. D., Hunter,W. C., and Anderson,B. W. 1991. Birds of the Lower ColoradoRiver Valley. Univ. of Ariz. Press,Tucson. Stancill,W. J., and Leslie,D. M., Jr. 1990. Evaluationof waterfowlsurvey techniques on an Oklahoma reservoir. Wildlife Soc. Bull. 18:370-373.

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Stevens, L. E., Buck, K. A., Brown, B. T., and Kline, N. C. 1997. Dam and geomorphologicalinfluences on ColoradoRiver waterbirddistribution, Grand Canyon,Arizona, USA. RegulatedRivers; Res. and Mgmt. 13:151-169. Su, H., andLiu, H. 1995. The wtwrfowl[waterfowl] status of XiaruyueReservoir in the countyof Fanshiin Shanxi.Chin. J. Zool. 30:15-20. Tremblay,E. M. 1993. Use of the Upper Arrow Reservoirat Revelstoke,B.C., by waterfowl and other waterbirds. Br. Columbia Birds 3:3-12. Utschick,H. 1998. Waterfowlcommunities in the Perachriver reservoir20 years after inaguration.Ornithol. Anzeiger 37:221-226. Utschick,H. 2000. River reservoirsand nature conservation:Consequences from waterfowldynamics. Oekol. Voegel 22:283-300. Woodward,A. W. 1958. Preliminaryreport on biologicalresources of the Glen Canyonregion. Univ. Utah Anthropol.Paper 31.

Accepted24 September2003

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