Breeding Status of the Black Tern in California

WESTERN BIS

Volume 32, Number 4, 2001

BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

W. DAVID SHUFORD, JOAN M. HUMPHREY, andNADAV NUR, PointReyes Bird Observatory,4990 ShorelineHighway, Stinson Beach, California 94970

The Black Tern is the familiar spirit of all fresh-water swamps in California north of the Tehachipe--Dawson(1923) ABSTRACT: We surveyedbreeding Black Terns throughout California in 1997 and 1998, followingwinters of very high runoff. We estimatedthe state'snesting population at about 4150 pairs (+30%), of which 47% were in northeastern Californiaand 53% in the CentralValley. The 1940 pairsin northeasternCalifornia were at 60 sites;59% were at 10 sitesand 70% were in Modoc County. State and federalwildlife refugessupported <4% of the regionalpopulation; the rest were mostlyon U.S. ForestService and privatelands. Low emergents,primarily spikerush (Eleocharisspp.) and Juncus spp., dominatedmost nesting marshes in northeastern California.Percent cover of emergents(vs. open water) was >80% at 68% of breeding sites.About 90% of the CentralValley breeding population was in SacramentoValley rice fields.The restwere in the San JoaquinValley, primarily in floodedagricultural fieldswith residualcrops or weedsand secondarilyin rice fields.State, federal,or privaterefuges or reservesheld <1% of CentralValley terns. Currentlythe Black Tern is extirpatedlocally at Lake Tahoe and in the Sacra- mento-SanJoaquin River Delta. In the San JoaquinValley, formerly a center of abundance,terns typically now breed mainly in two smallareas of ricefields in the San JoaquinBasin. The BlackTern is quasi-extirpatedin the TulareBasin, where it nests irregularlyand locallyin ephemeralhabitats, mainly in extremelywet years. The 160,000 to 200,000 ha of ricecurrently planted annually in the SacramentoValley may far exceedthe averageamount of naturalshallow-water habitat available there beforeagriculture. We recommenda statewidesurvey of the Californiabreeding population about onceevery 10 years,during typical climatic and habitat conditions, and monitoring for populationtrends annually. Conservation should focus on restoring,enhancing, and providinglong-term protection for suitablewetlands and on maintainingisolation of coloniesfrom humansand groundpredators. Given the scarcityof water in the CentralValley in mostsummers, efforts to enhancetern habitatmay be mostfruitful in yearsof exceptionalrunoff. Researchis neededon nestingand foragingecology, habitatsuitability, demography, limiting factors, population response to changing water conditions,and the valueof rice fieldsversus wetlands as breedinghabitat.

WesternBirds 32:189-217, 2001 189 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Althoughthe New World subspeciesof the BlackTern (Chlidoniasniger surinamensis)breeds widely acrosssouthern Canada and the northern UnitedStates, concern has been expressed because the populationdeclined acrossthe contintent(Dunn and Agro 1995, Peterjohnand Sauer 1997, Shuford 1999) duringa period of rapid wetlandloss (Dahl et al. 1997). BreedingBird Surveydata imply that the Black Tern declinedacross the rangesurveyed, though not significantly,at an averagerate of -1.6ø'/o(95ø'/o confidenceinterval-4.4-1.1) annually(-41.3ø'/o overall) from 1966 to 1999 (Saueret al. 2000). Althoughextirpated from onlytwo states,the BlackTern has declinedin at least 14 of the 34 states,provinces, and territorieswhere it currentlybreeds (Shuford 1999). Consequently,the BlackTern is listedas threatenedor endangeredin sixstates and variously designated of conservation concernin 18 other statesor provinces.For the United Statesoverall, the Black Tern is listedas a "migratorynongame bird of management concern"(USFWS 1995), whereasin Canadait hasno officialstatus despite recommendationsfor listingas "threatened"by Gerson(1988) and "vulner- able" by Alvo and Dunn (1996). Knowledgeof the Black Tern's statusis poor in the western United States, includingCalifornia, where anecdotal informationled to its listingas a speciesof specialconcern (CDFG 1992). To fill gapsin knowledgeof breedingBlack Terns in California,Point ReyesBird Observatorysurveyed populations statewide in 1997 and 1998 as the focusof a project to assessthe statusof sevenspecies of "inland- breedingseabirds" (Shuford 1998, Shufordet al. 1999). Here we report current statewide population estimates,breeding distribution,breeding phenology,and habitatassociations of the BlackTern and comparethem with the historicalrecord. We alsomake recommendationsfor conservation, management,and long-termmonitoring of the BlackTern in California.

STUDY AREA AND METHODS

Prior to fieldwork, we searchedthe publishedand unpublishedliterature and contactedvarious field biologiststo identif• historic and potential breedinghabitats of the Black Tern in California. We cite data from Audubon Field Notes (AFN)and American Birds (AB)by volumeand page numberand unpublisheddata from notebooksof the editorsof the Middle PacificCoast region of North American Birds as MPCR files. In the field, we contactedadditional biologists for furtherinformation on potentialbreeding habitat. We later obtainedegg-set data on Black Terns from the California Academy of Sciences(CAS), Los Angeles County Museumof NaturalHistory (LACM), Moore Laboratoryof Zoology(MLZ), Museumof VertebrateZoology (MVZ), San BernardinoCounty Museum (SBCM), San Diego Natural History Museum(SDNHM), Santa Barbara Museumof NaturalHistory (SBMNH), and WesternFoundation of Verte- brate Zoology(WFVZ). We varied field surveymethods by region, to match local logistical constraints,and timedsurveys to followthe passageof mostmigrants and beginwith the initiationof nesting.

190 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Northeastern California The studyarea here includedvalleys of the CascadeRange, Klamath Mountains,and Sierra Nevada, the Modoc Plateau, and the Great Basin desert, that is, eastern Siskiyou,northeastern Trinity, eastern Shasta, Modoc, Lassen, Plumas, Sierra, and El Dorado counties.Potential Black Tern habitatin marshes,lakes, and reservoirsis scatteredwidely, primarily from 4000 to 6000 feet (1220-1830 m) elevationin intermountainvalleys or in depressionsin the Modoc Plateau. Precipitation,falling mostly from Octoberthrough April asrain and snow, in the climateyear (1 July-30 June) 1996-97 was 114.3 cm in the SacramentoDrainage Division and 79.8 cm in the Northeast Interior Basins Division (resultsfrom weather stations throughoutthe region averaged).Combined, these divisionsencompass most of the study area. As these figures represent 119% and 147%, respectively,of the long-term(n -- 104) averagesfor theseareas (Western RegionalClimate Center; http://www.wrcc.dri.edu/divisional.html),wetlandsin the studyarea were well suppliedwith water in summer1997. From 18 May to 19 July 1997, Shufordand colleaguessurveyed most potentialbreeding habitat in northeasternCalifornia for BlackTerns; all sites surveyedwere listedby Shuford(1998). In addition,K. Lavesand Shuford surveyedthe southshore of Lake Tahoe, E1Dorado County, on 14 June 1998, and M. McVey surveyedmost potentialbreeding wetlands in the ShastaValley, Siskiyou County, in springand summer1998 and 1999. Shufordand colleaguesalso opportunistically resurveyed various sites in the summersof 1998 to 2001, as indicatedin the text or Table 1. We conducted surveysmostly on foot and occasionallyby kayakor canoe.We wereunable to surveyonly a few areaswith high potentialfor nestingterns. We did not surveyPicnic Grove and Lakeshorereservoirs in the Devil'sGarden Ranger Districtof Modoc NationalForest because of logisticaldifficulties, and we were denied accessto a few private holdings,the largestbeing Steele Swamp,Modoc County, and Dixie Valley,Lassen County. Earlyin the seasonit waspossible at manysites to countboth adult Black Ternsusing the wetlandand all or mostof their nests.We soonrealized we would be unable to count all nests at all sites because of the time needed and our inabilityto countnests accurately once chicks began to leavetheir nests shortlyafter hatching.Thus, dependingon circumstances,we obtained three types of countsand usedthree correspondingmethods to estimate numbers of pairs of terns, presentedhere in order of their apparent reliabilityand annotatedwith respectto biases.When data are availableto make more than one estimate,we presentonly the method of apparent highestreliability. (1) Total nests:obtained by systematicallywalking all of a marsh and locating all or most nests by visuallyscanning areas where terns were agitated,flushing adults from nests,or followingterns back to nests.At sites where a thoroughsearch was impractical,we made partial nest counts, which servedonly to documentbreeding. We estimatedthe number of breedingpairs as the total numberof nestsat the time of the survey.This methodmay underestimatethe total becauseof the difficultyof findingall

191 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Table 1 Numbersof Adult Black Terns, Nests, and EstimatedPairs from Surveysof Wetlandsin NortheasternCalifornia in 1997

Number of adultsa Number of nestsb

Estimated Site Surveydate Disturbed UndisturbedTotal Partial pairsc

SiskiyouCounty ButteValley WA 14 July 22 -- -- 2 112 ButteValley National Grasslands 14 July 0 2 -- 1 2a GrassLake a 12 July -- 28 -- 2+ 22a OrrLake 30 May -- 8 -- -- 6a 24, 26 June -- 6 ------Dry Lake(T44N, R1W, sect.30, 31) 12 July -- 4 -- 2 3a Lower Klamath NWR e Unit 4E 18 June -73 65 -- 3 372 Unit 4D 18 June -- 18 12+ -- 12 • BarnumFlat Reservoir 1 July -- 68 -- 2+ 54a Subtotal 147 ModocCounty f Dry Lake(T44N, R6E, sect.4, 5) 20 June -- 12 -- -- 9 a FourmileValley 27 May 38 27 27 -- 27 • WildHorse Valley 28 May 6 8 3 -- 3 • BuchananFlat 26-27 May 36 29 21 -- 21 • WeedValley 3 June -- 203 -- 6 160 a BaseballReservoir 26 May 47 47 42 -- 42 • DryValley Reservoir 25 May 58 -- 30 -- 30 • HagerBasin (North) 24 May 22 13 14 -- 14 • HagerBasin (South) 24 May 51 21 18 -- 181 TelephoneFlat Reservoir 31 May 23 -- 7 -- 7 • South Mountain Reservoir 31 May-1 June 6 -- 2 -- 2 • PeaseFlat• 21 May -- 1 0 -- -- 17 July -- -60 -- -- 473 18 July -- 19 2+ -- -- MudLake (T46N, R12E,sect. 16) 22 May 26 8-10 16 -- 161 Crowder Mt. Reservoir 1 June -- 41+ 40 -- 401 WhitneyReservoir 20 June 10 ------52 Hackamore Reservoir 20 June 20 -- -- 4 102 SpauldingReservoir 21 June 40 -- -- 10 202 Beelet Reservoir 22 June 26 -- -- 10 132 Pinky'sPond 22 June 14 -- -- 3 72 WidowValley 22 June -- 82 -- 1 64 a BucherSwamp 22 June -- 122 -- 5 96 a Six Shooter Tank 23 June 18 12 -- 1 92

(continued)

192 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Table 1 (continued)

Numberof adultsa Numberof nestsb

Estimated Site Surveydate Disturbed UndisturbedTotal Partial pairsc

Deadhorse Flat Reservoir 23 June -- 45 -- 1 35 a SurveyorsValley 23 June -- 35 -- 1 28 a Boles Meadow 7 June -- 211 -- 15 166 a Fletcher Creek Reservoir 16-17 June -- 48 31 -- 311 Jack'sSwamp 5 June -- 64 26 -- 26 • DeadHorse Reservoir 29 May -- 7+ 11 -- 11 • JesseValley 26 June -- 13 -- 4 10 a Whitehorse Flat Reservoir 1 July -- 37 -- 4+ 29 a EggLake 30 June-1July -- 343 -- 1+ 270 a TaylorCr. wetlands 30 June -- 128 -- 2 101 a Subtotal 1367 LassenCounty MuckValley 2 July -- 53 -- 5 42 a HooverFlat Reservoir 3 July -- 7 -- -- 6 a Moll Reservoir 27 June 34 20 -- 3+ 172 16 July 13 Okendine'sSpring 27 June 9 5 -- -- 52 16 July -- AshValley (main) 27 June -- 66 -- -- 52 a AshValley (SE) 19 July -- 9 -- -- 7 a Red Rock Lakes complex 26-27 June 72 -- 2+ 57 a Boot Lake 25-26 June 15 -- 8 12 a PoisonLake h 5 July 43 -- 2 382 DryLake (GrassValley) 10 June 6 -- -- 5 a 5 July StraylorLake 26 May 11 -- -- 9 a 11 July LongLake (T34N, R8E, sect.22) 26 May 6 -- -- 53 11 July Ashurst Lake 26 May 7 -- -- • 13 June 2 -- -- 2 3 10 July Gordon Lake 9 June 12 -- -- 93 10 July 10 ------Pine Creek wetlands (T32N, R9E, sect.28) 10 June 9 7 3 10 July 5 McCoywaterpit 9 June 12 10 July 0 (continued)

193 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Table 1 (continued)

Numberof adultsø Numberof nests•

Estimated Site Surveydate Disturbed UndisturbedTotal Partial pairsc

EagleLake i 8-9 July -- 142 -- 3+ 112a Willow Creek WA 10 June -- 13 -- -- 10 a HorseLake 8 July 15 15 -- 1+ 8z Mountain Meadow Reservoir 7 July 22 20 -- -- 11z HoneyLake N (private) 15 June 5 5 -- 1 3• Subtotal 426 Total 1940 aNumbersof adultsfrom either disturbedor undisturbedcounts (see Methods). bNumbersof nestsfrom either total or partialcounts (see Methods). CNumbersof pairsestimated by threemethods, listed here in orderof apparentreliability, on the basisof •numbersof totalnests, Zcounts of totaldisturbed adults, and acounts of totalundisturbed adults(see Methods). When data enablemore than one type of estimate,the estimatepresented is from the methodof highestapparent reliability. dA countof 13 undisturbedadults at GrassLake on 24 June1999 yieldsan estimateof 10 breedingpairs that year;no ternswere seenthere on 28 May duringthe droughtyear of 2001. eCountsof undisturbedadults of 54 in Unit 6B, 220-!-_in Unit 6C, 10 in Unit 10A, and 146 in Unit 12C on 21 June2001 yieldestimates of 42, 173, 8, and 115 breedingpairs in thoseunits, respectively,that year. fA countof 57 undisturbedadults on 21 June1999 yieldsan estimateof 45 breedingpairs at LostValley, which was mostly dry anddevoid of waterbirdson 22 June 1997. •A count of 23 undisturbedadults at PeaseFlat on 20 June 1999 yieldsan estimateof 18 breedingpairs that year. bFiveadults at PoisonLake on 23 June 1999 showedno signsof siteattachment or other evidenceof breeding. 'A countof 160 undisturbedadults at EagleLake on 23 June 1999 yieldsan estimateof 126 breedingpairs that year.

nests, particularlyin large marshes,and, becauseof asynchronousegg layingamong colonies or subcolonies,some birds may not have initiatedor completedlaying at the time of surveys. (2) Totaldisturbed adults: taken from within the colonywhen the observer (or a predator) disturbedbirds, and all or most terns, includingadults attendingnests, joined a mobbingflock around the intruder.We estimated the numberof pairsas the bestcount of total disturbedadults rounded to the nearesteven number and dividedby two. This methoddoes not accountfor adultsforaging far from the colony,hence not attractedto mobbingflocks, adults not joining the mobbing flock, or failed breedershaving left the colony.We didnot usethis method at largewetlands, where we wereunable to obtainaccurate counts because of manyadults swirling rapidly around the observerand terns continuously joining or leavingthe mobbingflock as they

194 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA flushedfrom, or returnedto, nestsas the intruderapproached or left their "zone of concern." (3) Totalvisible undisturbed adults: taken from the edgeof the wetlandor from a vantagepoint within where the observerdid not attract mobbing adults.We estimatedthe numberof breedingpairs as the bestcount divided by 1.27 (standarderror 0.16), the mean ratio of undisturbedadults counted to nestsat the 10 siteswhere we collectedboth typesof data (317 total adults,247 totalnests) during the incubationperiod. The method'sprimary biases,adjusted by a correctionfactor, are that it underestimatestotal adults or pairs becauseof the difficultyof seeingmany incubatingand roosting terns obscuredby vegetationor other visual obstructionsand does not accountfor adultsforaging away from the colony.Also, the numberof visible adultsmay increase as nests hatch and adults spend more time foraging,or, conversely,may decreaseas nestsfail and adultsdisperse. To characterizehabitat at each breedingsite, observersrecorded the dominantspecies of emergentvegetation and visually estimated the percent cover of both emergentvegetation and open water. We estimatedthese variablesfor the entire wetland, except at managedrefuges where we estimatedthem for justthe dikedweftand units in whichterns were breeding ratherthan for the entirecomplex of units.

CentralValley The CentralValley, surrounded by mountainsexcept at its westernoutlet into the San FranciscoBay estuary,averages about 644 km longand 64 km wide. It is dividedinto the SacramentoValley, drainingsouth, the San JoaquinValley, drainingnorth, and the Sacramento-SanJoaquin River Deltawhere these rivers converge. The SacramentoValley is furtherdivided into the Colusa,Butte, Sutter,American, and Yolodrainage basins, the San JoaquinValley into the San JoaquinBasin and the (usuallyclosed) Tulare Basin. Over 90% of the CentralValley's presettlement wetlands have been lost (Frayeret al. 1989, Kempka et al. 1991), and the dominantland use is agriculture.Hence, breedinghabitat for waterbirdstypically is scarce. Precipitation,falling mainly from Octoberthrough April (asrain, or snowin adjacentmountains), is highlyvariable. Despite a massivereservoir storage and drainagesystem and high summertemperatures, in the wettestyears extensiveshallow water can persistthrough the breedingseason. Precipita- tion in the climateyear 1997-98, during El Nifio, was 153.7 cm in the SacramentoDrainage Division and 86.9 cm in the San JoaquinDrainage Division,representing 161% and 169%, respectively,of the long-term(n -- 104) averagesfor theseregions (Western Regional Climate Center; http:// www.wrcc.dri.edu/divisional.html).Hence the breedingseason of 1998 providedsome of the bestconditions for nestingwaterbirds in the Central Valleysince the 1950s. Shallow-waterbreeding habitat increased primarily in the Tulare Basin,where large areas of agriculturalland were flooded, intentionallyor unintentionally,and secondarilynear Los Banos,Merced County,on refugesand in flood-controlbypasses. Largeareas of cultivatedrice fields in the SacramentoValley, and smaller areasin the deltaand San JoaquinBasin, typically provide potential nesting

195 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA habitatfor the BlackTern. In 1998, the intenseand extendedrainy season delayedrice plantingin the SacramentoValley by about three weeks, and onlyabout 75% of the crophad been planted at the time of oursurveys (60% by 31 May, 90% by 7 June; 9 June 1998 "Weekly Weather and Crop Bulletin," Nafi. Agric. StatisticsServ., Agric. StatisticsBoard, U.S. Dept. Agric.).Other habitatsin the CentralValley sometimes suitable for breeding ternsinclude managed wetlands on refugesand duck clubs (limited summer water)and floodwater storage or rechargefacilities (e.g., South Wilbur Flood Area, Kern Fan ElementWater Bank).The averageMay to July tempera- tures of 62.5 ø F (16.9 ø C) and 66.5 ø F (19.2 ø C) for the Sacramentoand San Joaquindrainage divisions, respectively, were the secondlowest and lowest on record (WesternRegional Climate Center, http://www.wrcc.dri.edu/ divisional.html;n -- 105). Thesewere idealconditions for both surveyingin thistypically very hot climateand delayingdesiccation of the tern'sbreeding habitats. Becauseof the 187,000 ha of rice plantedin the SacramentoValley in 1998, and limitedaccess to privatelands, we were unableto surveyall potentialbreeding habitat. Instead, from 29 May to 10 June(also 18 June), seven observersconducted roadside transect surveysalong most lightly traveled roads in the SacramentoValley rice country (Glenn and Butte countiessouth to Yolo County)to estimatedensities of BlackTerns breeding there. Singleobservers covered routes by drivingroads at 24 to 32 km/hr and countingterns seen within the primarycensus zone of 0.1 mile (160 m) on each sideof the road. We surveyedwithout the aid of binoculars,except when neededto confirmidentifications or estimatenumbers accurately. We surveyedfrom 0600 to 1000 hours,later if temperatureswere under29 ø C; as temperaturesoften were belownormal, this meant sometimes all day. We haltedduring strong winds (>24 km/hr) or persistentrain. Observersrecorded weather conditions,start and stop times, route covered,miles driven, distance surveyed (each side of the roadtallied separately), number and age of terns, location(s)and habitat type where terns were observed,and any breedingevidence, including details of nest locations. Observersalso recorded any ternsseen beyond the primarycensus zone or off surveyroutes, but we did not use these data to calculatedensities of breedingterns in rice fields.Observers recorded all observationsof ternson mapsin the fieldfor lateruse in mappingpatterns of breedingdistribution. Observerswere asked to try to confirm nestingby returningto make observationsafter finishinga surveyor on a subsequentvisit. We considered confirmednesting all observationsof nests with eggs, adultssitting in incubationposture on an apparentnest, adultsfeeding non-flying young, adultsrepeatedly carrying food to the samespot (presumablyto an unseen chick),or nonflyingor veryweakly flying young. Because of delayedplanting, at the time of our surveyslittle growing rice had emergedabove water (I5% emergedon 31 May, 35% on 7 June; 9 June 1998 "WeeklyWeather and Crop Bulletin,"Nafi. Agric. StatisticsServ., Agric. StatisticsBoard, U.S. Dept. Agric.),and hencemost terns sitting on nestswere stillvisible. We calculateddensities of BlackTerns in ricefields by firstmultiplying the distancesurveyed on eachroute by 160 m, the widthof the primarycensus zone, then convertingthis to hectaresof habitatsurveyed. We next deter-

196 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA mined the mean density of terns per 100 hectares for each county (or groupingof counties)by calculatingthe meandensity for all of the county's routesweighted by distancesurveyed. We estimatedthe total numberof breedingterns in each countyby multiplyingtern densityper countytimes the numberof hectaresof plantedrice per county(M. Leighton,Calif. Agric. Statistics Serv. in litt.; National Agric. Statistics Serv., http:// www.nass.usda.gov:100/ipedb/), adjustedby a correctionfactor of 0.75, the estimatedproportion of rice plantedat the time of our surveys.Field observationsdid not suggestany evidenceof avoidanceof, or attractionto, roadsby nestingterns, which might have biased our estimates. By contrast, in the delta, San Joaquin Valley, and in habitatsin the SacramentoValley other than ricefields, we surveyedfrom the groundor by boatall knownpotential breeding habitat for BlackTerns. See Shuford et al. (1999) for a list of sitessurveyed. In 1998, we surveyedthe entire 807, 1817, 2220, and 1211 ha of planted rice in Stanislaus,San Joaquin, Merced,and Fresnocounties, respectively, rather than samplingthem as in the SacramentoValley. We countedmainly visible undisturbed adults and, rarely, total nestsvia thorough nest searches.We did not count total disturbedadults or total nests at most sites becauseof the potential to damagecrops by doingso. Partialnest counts at many sitesserved only to documentbreeding. Hence, dependingon availabledata, we estimated numbersof pairsof BlackTerns by either the "total nests"or "undisturbed adults" methods described above for northeastern California. In the latter case,the correctionfactor usedfor the Central Valley was that derivedin northeastern California in 1997.

RESULTS PopulationSize and Distribution We estimatedabout 4153 pairsof BlackTerns nested in the statein 1997 and 1998, 46.7% in northeastern California and 53.3% in the Central Valley. Northeastern California. An estimated1940 pairs nestedat 60 widely scatteredsites in this region(Table 1, Figure1). About 70.5%, 22.0%, and 7.6% of that population was located in Modoc, Lassen, and Siskiyou counties,respectively. The 10 siteswith >50 pairsof terns,which combined held 58.7% of the regional population, were Barnum Flat Reservoir, Siskiyou County; Weed Valley, Widow Valley, Bucher Swamp, Boles Meadow,Egg Lake, and TaylorCreek wetlands,Modoc County;and Ash Valley(main), Red Rock Lakescomplex, and EagleLake, LassenCounty. Central Valley. Of the estimated2213 pairsof BlackTerns that bred in the Central Valley in 1998, 89.8% were in the SacramentoValley and 10.2% in the San JoaquinValley (Tables 2 and 3, Figures2 and 3). From roadsidesurveys, we estimatedthat about2523 + 754 (1769-3277) adult terns, or about 1987 (1393-2581) pairs, bred in SacramentoValley rice fields(Table 2). Althoughthe birdswere spreadwidely, the largestnumbers were in the northernColusa Basin (Table 2, Figure2). In the San Joaquin Valley,about 75 pairsbred at five sitesin the San JoaquinBasin and 151 pairs bred at six sitesin the Tulare Basin(Table 3).

197 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

SlSKIYOU CO. I .

: I

! I

I : & I

GO. I •I•IF" Like I I I Honey

ColonySize (1997) ß 2-35 ß 1 36- 112 !•1 113-270

Other Records A 1899 - 1960 • 1961 -1998

50 0 50 Kilometers

Figure1. Distributionand size (number of pairs)of BlackTern coloniesin northeastern Californiain 1997 (seeTable 1), plottedwith historical(1899-1960) and otherrecent (1961-1998) recordsof confirmedbreeding (see Appendices 1 and 2).

198 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Talkie •- EstimatedNumbers of BlackTerns Breeding in the Sacramento Valleyfrom RoadsideSurveys of Rice Fields,29 May-10 June 1998

Hectares Survey Distance Ternsper Ternsestimated County plantedrice a routes(n) surveyed(km) b 100ha (+ SE)c (+ SE)d

Colusa 36,637 38 370.2 2.67 + 0.67 978 + 245 Sutter-Yolo- Sacramentoe 36,485/ 26 284.5 0.70 + 0.23 255+ 84 Butte 26,645 10 234.5 0.85 + 0.31 226 + 82 Glenn 25,131 44 352.8 3.68 + 1.56 925 + 392 Yuba 11,294 16 122.1 1.22 _+0.44 138 + 50 Placer 4239 4 47.0 0.00 + 0.00 0 Tehamag 363 0 0 -- 0 Totals 140,794 138 1411.11 1.80 + 0.54h 2523 + 754 aPlantedrice acreage adjusted to accountfor estimatethat only75% of the totalfor the year had beenplanted at the time of our surveys(see Methods). beachside of roadtallied separately. CDensityestimates for each countyare meansof surveyroutes, weighted by distancesurveyed. SE, standarderror. dTernnumbers estimated by multiplying densities on roadsidesurveys times acreage of available rice fields.Standard errors represent variation in densitiesof ternson surveyroutes but do not accountfor possibleerror in the estimateof the amountof plantedrice at the time of tern surveys. eDatafor thesecounties pooled because of smallsample sizes for Yolo andSacramento counties. Numberof surveyroutes and distancesurveyed, respectively, per county:Sutter, 15, 204.0; Yolo, 10, 69.4; Sacramento,1, 11.1. fNumbersof hectaresplanted rice per countyat time of survey:Sutter, 27,553; Yolo, 6177; Sacramento, 2755. gAithoughwe surveyedno routesin TehamaCo. in 1998, coveragesince the 1970s there has shownno evidenceof ternsthere in the breedingseason (S. Laymonin litt.).If ternsbreed there now the number would be small: 7 or 13 if densities were the same as for the entire Sacramento Valleyor for GlennCounty, respectively. hMeanof countydensity estimates, weighted by hectaresof rice.

NestingPhenology In northeasternCalifornia in 1997, we observedthe firstnests with eggs at Mud Lake, Modoc County, on 22 May and the first hatchedyoung at FletcherCreek Reservoiron 17 June. On the basisof the species'19-21 day incubationperiod (Dunn and Agro 1995), eggs at Mud Lake likely hatchedby at least 12 June. Collectiondates of egg setsfor the region extendfrom 23 May to 30 Juneand reacha peak in earlyJune (Figure 4). Observationsin the CentralValley in 1998 were inadequatefor assessing breedingphenology; dates of eggsets collected there extend from 3 May to 5 Julyand reacha peak from late May to earlyJune (Figure4).

Habitat Associations NortheasternCalifornia. Of 60 breedingsites in northeasternCalifor- nia, 52 (86.7%) were marshesdominated by low (<1 m) emergents,six

199 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Table 3 Numbersof Adult BlackTerns, Nests,and EstimatedPairs in the San JoaquinValley in 1998

Number of nestsb Estimated Site Surveydate Numberof Adultsa Total Partial Pairsc

MercedCounty Rice fields SW of Merced 22 June 30 -- -- 242 3 July 25 -- 2 -- RaccoonMarsh, West Bear CreekUnit, San LuisNWR 22 June 4 2 -- 2 • CinnamonSlough, Merced NWR 23 June 4 2 -- 2 • FresnoCounty Ricefields S of Dos Palos,Merced Co. 22-23 June 58 -- 5 46 z JamesBypass S of JamesRd. 1 July 2 1 -- 1• KingsCounty S of HaciendaRanch Flood Basin (T24S, R21E, sect.31, 32) 19 June 69 -- 7 54 z S of HaciendaRanch Flood Basin (T24S, R21E, sect.28, 33) 19 June 28+ -- 3 22 z 13 July -- -- 3-4 -- Tulare County Vicinityjct. Hwy. 43 andVirginia Ave. 25 June 35+ -- 2 28 z 2 mi W of Rd. 40 about3 mi S of Alpaugh 23 June 21 -- 1 16 z JustW of Rd. 40 about4 mi S of Alpaugh 22 June 32 -- 3 25 z Kern County Kern Fan ElementWater Bank (pond W-2), W of I-5 20 June 7 -- 1 6 z

Total 226 aNumbersof adultsfrom countsof undisturbedbirds (see Methods). bNumbersof nestsfrom either total or partialnest counts (see Methods). CNumbersof pairsestimated by two methods,listed here in order of apparentreliability, on the basisof •countsof totalnests or 2countsof totalundisturbed adults (see Methods). When data enablemore than one type of estimate,the estimatepresented is from the methodof highest apparentreliability.

2OO BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

[] OonfirmedBreeding [] Unemfflm•lBleeding Olher Reeord•

• lg•1 - lgg8 / v' MajorHydrok•io ee•in•

r.rlr

øo*

Woodland

2O 0 20 Kilometers

Figure2. Distributionof breedingBlack Terns in California'sSacramento Valley and Delta in 1998 (seeTable 2), plottedwith historical(1886-1960) and other recent (1961-1999) recordsof confirmedbreeding (see Appendices 1 and 2). Stippling denotesareas where rice currentlyis grown.

201 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

ColonySize (1998) •nto B 1-16 ß 17-54 Other Records & 1893- 1960 ß 1961 - 1997 STANISLAUSCO. / \ / MajorHydrologic Basins ,•,',,.--•,Rice Growing Areas MERCED CO.

,o ß

/ '•m• t/ •'• ,.':1oequin \ FRESNO '\ •' CO.

TULARE co.

I KERN CO.

%, '" Bakersõeld

-..•

50 0 50 Kilometers I

Figure3. Distributionand size (number of pairs)of BlackTern coloniesin California's San JoaquinValley in 1998 (seeTable 3) plottedwith historical(1893-1960) and otherrecent (1961-1997) recordsof confirmedbreeding (see Appendices 1 and 2). Stipplingdenotes areas where rice currenfiyis grown.

202 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

lOO CENTRALNORTHEASTERNVALLEY CALIFORNIA

5-DAY PERIODS

Figure 4. Temporaldistribution of egg-setrecords of the Black Tern in California. 1886-1960. Data from major Californiamuseums (see Methods, Appendix 1).

(10%) by a mixture of tall (>1 m) and low emergents.At Lower Klamath National Wildlife Refuge (NWR), Black Terns nestedin shallowlyflooded basinsdominated by residualbarley stubble and algalmats and lackingmuch live emergent vegetation.At Boot Lake, LassenCounty, in the Warner Mountainsat 6560 feet (2000 m), the highestcolony, breeding habitat was dominated by the floating yellow pond-lily (Nuphar luteurn ssp. polysepalum). Of 58 sites with emergent vegetation,50 (86.2%) were dominatedor co-dominatedby low emergentspikerush (Eleocharis spp.) or Juncus spp., sevenby a mixture of tall emergentssuch as tules(Scirpus spp.)or cattails(Typha spp.) and low emergents,and one by a low emergent composite(Arnica sp.). Percentcover of emergentswas >80% at 41 sites(68.3%), between60% and 80% at nine sites (15%), between 40% and 60% at three sites (5%), between 20% and 40% at no sites, and between 0% and 20% at seven sites (11.7%). All siteswith <20% emergentcover. except Lower KlamathNWR. were lakesor reservoirswith mostlyopen water fringedby marshvegetation. If we had limitedestimates of vegetativecover to actualbreeding sites, rather

203 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA thanthe entirewetland, the proportionof totalsites with >80% coverwould have been higher. Central Valley.Of the valleywidetotal, about2057 pairs(93.0%) bredin cultivatedrice fields,151 (6.8%) in agriculturalfields with residualcrops and weeds and shallowwater remainingfrom winter floods,and 5 (0.2%) in emergentwetlands of low stature.Of the four pairsthat bred in protected areas, two each were at Merced and San Luis NWRs in the San Joaquin Basin.All breedingevidence in the SacramentoValley was from rice fields, thoughone colonyin Glenn Countywas in sedgesin the cornerof a field ratherthan in the rice itself(Shuford pers. obs.). Of the 226 pairsin the San JoaquinValley, 66.8% were in floodedagricultural fields with residualcrops or weeds, 31.0% in rice fields,and 2.2% in emergentwetlands of low stature.

DISCUSSION Accuracyof 1997-1998 Surveys Althoughunable to estimatethe precisionof all methodsused to survey terns in 1997-1998, we suspectour overallpopulation estimate for the state was within 30% of the actual number. The 95% confidence interval was +60% for surveysin rice fieldsof the SacramentoValley (Table2) versus + 25% for the "undisturbed adults" method used in northeastern California and the San JoaquinValley (Tables 1 and 3). The precisionestimate for the lattermethod, though, is applicableonly for the incubationperiod, when it wasderived, even though this method was used for data collectedthrough- out the breedingseason. Although the "totalnests" and "disturbedadults" methods,also used widely in northeasternCalifornia and the San Joaquin Valley (Tables1 and 3), lack estimatesof precisionboth underestimated numbersof nestingpairs (see Methods). Another source of underestimation wasour inability to coversome potential tern nestinghabitat in northeastern California.Hence our overallestimate is more likely an under-than an overestimateof the statewidenesting population during the surveyperiod. To have conductedthe statewidesurvey in one rather than two years wouldhave been desirable also. We suspect,though, that numbersfrom the 1997-98 surveywere representativeof thosestatewide in 1998, when we surveyedthe entire Central Valley and water conditionsin northeastern California were similar to those in 1997.

Historical Patterns of Distribution and Abundance Pastdata on the distributionand abundanceof breedingBlack Terns in Californiaare mostlyanecdotal (Grinnell and Miller 1944, Cogswell1977, Shuford1999). Breedingpopulations were restrictedto two distinctareas: (1) the ModocPlateau and mountainvalleys of northeasternCalifornia and (2) the lowlandsof the CentralValley. Today the outlinesof the breeding range remain much the same (Figures1-3). In northeasternCalifornia, however,the speciesis extirpatedat Lake Tahoe.In the CentralValley it is extirpatedin the delta, and in much of the San JoaquinValley it is either extirpatedor breedsirregularly, only in exceptionallywet years.Grinnell and

204 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Miller (1944) consideredthe Black Tern a "locallycommon" breeder in California.Evaluating subsequent population trends is very difficult given the anecdotalnature of early accountsand the lack of recent BreedingBird Surveydata for Californiasufficient for trend analysis(Peterjohn and Sauer 1997, Sauer et al. 2000). Northeastern California. Historiclocations of confirmedbreeding for this regioninclude Tule Lake and AlturasMeadow, Modoc County; Grass- hopperMeadows/Lake and Eagle Lake, Lassen County; and Lake Tahoe, El Dorado County(Grinnell and Miller 1944; Appendix 1). Assessingpopula- tion trendsis problematicgiven the few knownhistoric breeding areas, the large numberof recentbreeding sites (Table 1), few of whichhave a long recordof occupancy,and the species'propensity to shift from site to site with fluctuatingenvironmental conditions. Extensive wetland loss, particularly in the KlamathBasin, may have been partiallyoffset on the Modoc Plateauby the creationof shallowreservoirs for livestockgrazing and recent enhancementfor waterfowl(T. Ratcliff,G. Studinskipers. comm.). BlackTerns have bred at EagleLake sinceat least 1918 (Appendix1). Using a combinationof nest countsin habitat visited,the behaviorand numberof ternsin suitablehabitat not wellsurveyed for nests,and the extent of suitablehabitat not visited,Gould (1974, in litt.) estimated300 breeding adultsat EagleLake in 1970 and 150 in 1971. From nestcounts, Lederer (1976) estimated46 breedingadults in 1974; Shaw (1998) estimated78 in 1996 and 64 in 1997. Our independentestimate in 1997, basedon counts of undisturbedadults, was 224 breedingadults (112 pairs;Table 1). A count of 160 undisturbedadults on 23 June 1999 yieldedan estimateof 252 breedingadults (126 pairs;Table 1, footnote).Together these numbers may reflectyear-to-year variation in nestingpopulation size, perhaps mirroring changingpatterns of emergentvegetation in responseto lake levels(G. Gouldpers. comm.)rather than a populationdecline followed by recovery, or, in part, the variationin surveytechniques among observers. BlackTerns formerlyreached their southeasternbreeding limit in the regionat LakeTahoe, where they nested mainly at RowlandsMarsh near the mouth of the Upper TruckeeRiver, El Dorado County (Orr and Moffitt 1971). That colonyonce held over 100 pairs,and, prior to 1920, colonies of fouror fivepairs bred near the mouthof EmeraldBay, at MeeksBay, and near Tahoe Vista; "a few pairs"also formerly nested annually west of Tallac (Orr and Moffitt 1971; Appendix 1). Habitat loss and degradationfrom developmentand lowering of waterlevels eliminated breeding Black Terns at Lake Tahoe(Orr and Moffitt 1971, Cogswell1977, K. Lavespers. comm., Shufordpers. obs.in 1998). Todaythe speciesreaches its southernlimit in the Sierra Nevada at Sierra Valley, Plumasand Sierra counties,and at Kyburz Flat, Sierra County, where breedingis irregular,particularly at Kyburz(Appendix 2). Black Terns have been reported breedingin the extensivemarshes of SierraValley since at leastthe early].970s (Appendix2), primarilyby birders looking off Marble Hot Springs Road (Dyson Lane), Plumas County. Numbersthere fluctuate annually (up to 50 on 27 May 1989, J. McCormick in litt.), and ternsare absentin somedrought years, such as 2001 (Shuford

205 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA pers.obs., 12-16 June)The speciesalso occurs in the SierraCounty portion of the marsh(e.g., up to nineadults N4 milesnorth of Sierraville15-20 June 1999; J. McCormick,Shuford pers. obs.),but thisarea getslittle coverage. Small's(1994) report of "the largestregular [breeding] concentration (1000+) in northern California" in the Klamath Basin is unsubstantiated. AlthoughZeiner et al. (1990) mapped the summerrange as includingthe ShastaValley, Siskiyou County, and Small(1994) citedCedar Lakes, Shasta Valley, as a recentbreeding area, we know of no documentedbreeding recordsfor that valley(Appendices 1 and 2, R. Ekstromin litt.). M. McVey (in litt.) did not find evidenceof BlackTerns breeding at any of numerous wetlandsin the ShastaValley he surveyedin 1998 and 1999. Central Valley.Grinnell and Miller (1944) reportedBlack Terns nesting in the CentralValley along the Sacramentoand San Joaquinrivers (latter near Merced)and at Los Banos, Merced County, Laton and Firebaugh,Fresno County,and BuenaVista Lake, Kern County.They alsonoted the species had colonizedrice fields.Egg-set data providea minimumof two nesting recordsfor the SacramentoValley, 39 for the delta (none reportedby Grinnelland Miller), and 399 for the San JoaquinValley (Appendix1). Althoughterns were widely scattered in the lattervalley, many egg sets were collectedfrom the Los Banos area of the San JoaquinBasin, perhaps reflectinglocal abundance, ease of observeraccess, or collectorbias. In the early 20th centurythe San JoaquinValley was of great importanceto breedingBlack Terns; Ray (1906), Chapman(1908), Tyler (1913), andvan Rossem(1933) describedthe speciesas very numerousthere. Among the few early quantitativeestimates were over I00 nestsnear Los Banosand SouthDos Palosfrom 19 to 22 May 1919 (J. G. Tyleret al., Appendix2), "many hundredsin sight in all directions"in overflowlands of the San JoaquinRiver near Los Banoson 29 May 1941 (W. B. Minturnfield notes), anda colonyof "about200 pairs"at BuenaVista Lake on 21 June1921 (A. J. van Rossemegg data slip, WFVZ 2470). SacramentoValley and delta recordsbeing so few may in part reflectlimited egg collectingthere. From the cessationof most egg collectingin the mid-I940s until our 1997-1998 surveys,the limitedinformation on the BlackTern's status in the Central Valley was primarilyanecdotal. Although Grinnell and Miller (1944) notedthe at leastpartial shift in breedingfrom reclaimedmarshes to cultivatedrice, it is unclearhow widespreador numerousterns were in rice fields,which in 1943 totaled 96,000 ha in California(National Agric. StatisticsServ.; http://www.nass.usda.gov:100/ipedb/).The estimateof 1000+ migrantBlack Terns at the WoodlandSugar Ponds, Yolo County, 8- 21 May 1955, thoughnotable at the time (AFN 9:355), far exceedsany such recent estimate for the SacramentoValley. Black Terns bred at SacramentoNWR in 1958 (Appendix2), whenrice was regularly grown on the refuge,but no ternsare knownto havebred on anyfederal refuge in the SacramentoValley since at leastthe early 1980s (J. Silveirapers. comm.). Greenberg(1972) reportedup to 48 BlackTerns in mid-Juneon two 6-mile (9.6-km) road transectsin Sutter and Sacramento countiesfrom 1969 to 1971, but data are too few for trend analysis.Cogswell (1977) concluded that BlackTern numbersdeclined in the CentralValley with lossof marshes,

206 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA increasedwith expansionof rice growing, and declinedagain "recently," perhaps from pesticideaccumulation. The anecdotalnature of his and others' claims of declines (AFN 24:638, AB 32:1205, AB 39:98) or upswings(AB 31:1185) in tern numbersin the SacramentoValley in the 1970s and 1980s make them hard to evaluate. Lee (1984) found six colonies(one in SacramentoCo., five in SutterCo.) while studyingBlack Tern nestingbiology in ricefields in 1976 and 1977 butmade no population estimates for the area. Numbersof BlackTerns recorded during surveys of pheasantbroods in ButteCounty in lateJune and earlyJuly, 1976-1992 (J. Snowdenin litt.), did not show any significanttemporal trend but appearedto track the county'srice acreage(Figure 5). Similarly,the only BreedingBird Survey route in California(no. 148) with moderatenumbers of BlackTerns (median 9, range 0-54), in Glenn and Colusacounties in the SacramentoValley, showedsubstantial variability in numbersand no clear trend from 1971 to 1999 (USGS PatuxentWildlife Research Center 2000; http://www.mp2- pwrc.usgs. gov/bbs/retrieval/). W. B. Minturn(field notes) was still observing up to 500+ at varioussites in the San JoaquinValley in May throughat least 1950ß In the Tulare Basin, BlackTerns probably bred regularly at Tulareand BuenaVista lakes until the 1940s and 1950s (Appendix1), whendams constructed on therivers feeding themcut off mostrunoff. Since then breeding in thatbasin has been irregular,

0.7 --•- TERNS PER MILE 1.2 ß .&. ACRES RICE

ß 0.6

0.5 / • 0.4- i\ l\:: ./\ 0.9 c/) 0.3 z i- 0.2 &.."" i / '... 0.7 o.1 0.6

o.o 0.5 1994

YEAR Figure5. Numbersof BlackTerns on CaliforniaDepartment of Fishand Game survey routesfor pheasantbroods in ButteCounty, 1976 to 1992 (seeMethods), relative to yearlytotals of rice acreagefor that county(National Agricultural Statistics Service 1999; http://www.nass.usda.gov: 100/ipedb/).

207 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA mainlyin extremelywet years.On 22 July1983, followingan El Nifiowinter, R. Hansen(MPCR files) found "many" nests and up to 70 BlackTerns, mosfiy fledgedyoung, at the HaciendaRanch Flood Basin and SouthWilbur Flood Area, KingsCounty. Also in the early 1980s, Black Terns nestedin thick ditch-grass(Ruppia rnaritirna)at J & W Farms agriculturalevaporation ponds,18 km southwestof Corcoran,Kings County (G. Gerstenbergpers. comm.).These ponds are no longeractive, though, and otherevaporation pondsin the basincurrently do not supportmuch emergent growth or any breedingBlack Terns (R. Hansen,J. Seay pers. comm.). Similarlocal extirpations have alsooccurred in the San JoaquinBasin. In the earlyto mid-1950s,Black Terns nested where a sloughflooded areas of spinysaltbush (A t rip lex spin i fera) interspersedwith vernal-pool-likehabitat at Volta WildlifeArea (WA) near Los Banos(R. Wilburpers. comm.). Black Ternsappear to havebeen stillwidespread around Los Banosat that time, as R. D. Ross (MPCR files) estimated 200-250 terns on a drive across Highway 152 on 15 June 1956. Subsequently,P. J. Metropulos(in litt.) foundthe species"common" in the Los Banosarea on 20 June 1970, V. Remsenand P. Myers(AB 27:914) counted43 southof Los Banoson 16 June1973, andR. J. Bacon(MPCR files) sighted two or threenesting pairs at MercedNWR in summer1983. BlackTerns apparently were nestingin the TractionRanch section of MendotaWA, FresnoCounty, when ponds werefirst developed there about 1990 (S. Bruggemannpers. comm.). Today ternsdo not nestregularly at any of the stateor federalrefuges in the San JoaquinValley (J. Allen, S. Bruggemann,R. Wilbur,D. Woolingtonpers. comm.).They likely breed regularly, though, in the limitedrice acreage near Mercedand SouthDos Palos,though this remainsto be documented.The currenttenuous status of breedingBlack Terns in the San JoaquinValley documentsa majorpopulation decline there over the last 100 yearsand an apparentshift of abundanceto the SacramentoValley. It ispossible, though, that the SacramentoValley has alwaysbeen an important,though poorly documented,breeding area. Extrali rnita 1 b reeding. Apparent nesting at MerrittLake, near Castroville, MontereyCounty (Silliman 1915), likelyrepresents an extralimitalattempt, as the specieshas not bred elsewherealong the coastof California.

Historical Habitat Shifts In the past, BlackTerns nestedin the CentralValley in ephemeralearly successionalwetlands created by natural overflow of rivers and lakes (Mailliard1904, Tyler 1913, van Rossem1933) or by flood irrigationof pasturelands(Chapman 1908). It is hard to estimate the extent of tern breedinghabitat, particularly ephemeral overflow lands, available prior to the massivealteration of the CentralValley's natural hydrology. Hall (1880) estimated324,000 ha of the SacramentoValley were subjectto inundation from annualoverflow and an additional117,000 ha by "occasionaltempo- rary overflow." In the San JoaquinValley, he estimated253,000 ha of swampland were subjectto periodicinundation. In the TulareBasin alone the fluctuatingmargins of TulareLake couldengulf many thousandsof additional hectares after a series of wet winters.

208 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Althoughit is unclearhow muchephemeral habitat remained through the terns'breeding season, the vastflood plains and natural flood basins delayed transmissionof floodflows, reduced peak flows and velocities, and increased summerriver flows,as the floodwatersslowly drained back into the rivers, sometimesthrough July, or evaporated(Bay Institute 1998). The buffering effectof the floodbasins shifted high upstream flows of Januaryto May to a period of high river outflowfrom March to June. Rainfall-inducedfloods (December-March)predominated in the SacramentoValley, whereaspro- longedsnowmelt floods (April-June) were the norm in the San Joaquin Valley,particularly in the TulareBasin (Bay Institute 1998). Hence, the latter regionlikely had the mostephemeral habitat for breedingterns. Today'swater-management infrastructure keeps rivers within their banks, exceptduring extreme floods, after whichwater usuallyrapidly drains or is pumpedback into river and bypasschannels, leaving few areasof shallow water where Black Terns couldbreed. The exceptionis the closedTulare Basin where in extreme winters flood waters are diverted into shallow storagebasins or run uncheckedinto fields.Flood frequency has decreased suchthat floods in the SacramentoValley that formerly occurred about every 2 yearsnow occuronce every 7 to 13 years,10-year floods every 100 years (BayInstitute 1998). Valleywide,the volumesof largefloods remain largely unchanged,but only in yearsof a veryheavy snowpack in the SierraNevada do floodflows in the SanJoaquin Valley approach historic levels. The greatloss of wetlandswas mitigated in the SacramentoValley by the expansionof rice to the currentannual level of 160,000 to 200,000 ha (Figure6), whichmay far exceedthe averageextent of shallow-waterhabitat availablethere previouslyin summer.By contrast,wetlands lost in the San JoaquinValley have been replaced to only a tiny degreeby rice, whichhas declinedthere sincethe mid-1950s (Figure6). Ternsformerly bred in rice fieldsas far southas Kern County(Appendix 1) but no longerdo so. MigratoryStopovers From 1949 to 1977, estimatedpeak countsof BlackTerns at Tule Lake NWR, Siskiyouand Modoccounties, from Julyto earlySeptember ranged from 2000 to 19,000 (n -- 17 years,median 5000, KlamathBasin NWR files),documenting it as an importantpostbreeding or migratorystopover for the species.Estimates of tern numbersat Tule Lake, 15 July-4 August 1997, rangedfrom 1000 to 6000 (J. Beckstrand,R. Ryno,R. Ekstromin Shuford1998). In five yearsfrom 1958 to 1972, peak countsat Lower KlamathNWR in Augustexceeded 1000 (maximum9000, KlamathBasin NWR files);large numbers have not beenreported there in recentyears. The onlyother key stopoversite known in the stateis the SaltonSea, Riverside andImperial counties, outside the breedingrange. Up to 15,000 havebeen estimatedthere in earlyAugust (Patten et al. in press),but the only census, 13-16 August1999, tallied4011 individuals(Shuford et al. in press).Small (1994) impliedthat numbers at the SaltonSea have declined since 1987, but M. A. Patten(in litt.) has no evidenceof this. Numbersof migrantson the southernCalifornia coast have declined greatly since the early20th century (Garrett and Dunn 1981).

209 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

--- CALIFORNIA ..... SACRAMENTO VALLEY -- DELTA AND SAN JOAQUIN VALLEY 6OO

500 o o o • 400

• 300

LU 2OO -- /

lOO / / ? o i i 1900 •920 1940

YEAR

Figure6. Historicchanges in acreageof plantedrice in California,1912 to 1998, and in the SacramentoValley and Delta and San Joaquin Valley, 1953 to 1998. Data from National Agricultural Statistics Service (1999; http://www.nass.usda.gov:100/ ipedb/); countyand districtbreakdowns available only since1953.

Current Threats Central Valley. Agriculturalpractices that rapidlydraw down water levels in rice fieldshave exposedtern neststo rat predationonly to destroy renestingattempts later when fields were reflooded above original levels (Lee 1984). In 1998, Shufordsaw terns sittingon nestsin muddyfields from whichthe waterhad beentemporarily drained, and latersome of thesenests were abandoned.The rapid increasein rice cultivationcoincided with the post-WorldWar II boom in chemicaluse in agriculture.Three egg yolks collectedfrom a BlackTern colonyin ricefields in the SacramentoValley in 1969 had 8.0, 9.1, and 11.8 ppm DDE (Greenberg1972), but there is no evidenceof deleteriouseffects of pesticidesor otheragricultural chemicals on ternsbreeding in rice fields.Dunn and Agro (1995) and Weselohet al. (1997) reviewedthe literatureon contaminantsin BlackTern eggsbut found no evidenceof reproductiveeffects. They concludedthat directchemical toxicity is generallynot a problem with these terns, but pesticidesmay reducefavored insect foods. Loss of insectdiversity or biomasscould lead to chick starvation.

210 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Conservation Priorities BlackTern conservationshould focus on protectingand enhancinghigh- qualitynesting habitat. Because of the variableand generallyarid climate in muchof the Californiabreeding range, the valueof managementefforts in years of short versusabundant water supplyshould be assessedcarefully. Waterlevels should be regulatedto protectimportant nesting and foraging habitatsfrom groundpredators and human disturbance,and management for terns shouldbe coordinatedwith activitiesto conserveother species groups via other multi-partnerconservation efforts (e.g., Central Valley HabitatJoint Venture, U.S. ShorebirdConservation Plan). Protection of key migratorystopovers, such as Tule Lake and the SaltonSea, is alsovital. Northeastern California. Becausefew Black Terns currentlynest on refuges,it would be valuableto see if spikerush-dominatedmarshes, the species' main breeding habitat in the region, could be establishedor expandedin these areas. Central Valley. Becausesummer water typicallyis scarcein the Central Valley,and becauseseabirds' productivity often runsin cyclesof boom and bust, efforts to enhance tern habitat may be most fruitful in years of exceptionalrunoff. Recent evidence of extensive,irregular nesting in flooded fieldswith residualvegetation or crop stubblein the TulareBasin indicates the specieswould benefit from more of this habitat. Perhapsfields with marginalcrop yields could be retiredfrom productionand put in a conservation bankto be floodedwhen excesswater is available.Such flooding should be weighedagainst possible waterbird mortality from botulismoutbreaks, which might be reducedby rotatingthe fieldsto be floodedand choosing areaswith no prior evidenceof disease.Scant breeding on newlyrestored wetlandson refuges near Los Banos perhaps could be increasedin the future, particularlyin years of high runoff. In such years, infrastructure improvementslikely could spread water overlarger areas within or adjacent to bypasses,such as the EastsideBypass near Los Banos and the James Bypass/FresnoSlough south of Mendota WA. Study also is needed of whethersuitable habitat on refugesadjoining bypasses could be increased duringyears of high flow by drawingupstream water, circulating it through refugeponds, and drainingit backinto the bypassdownstream. Maintaining a slow,steady flow likelywould reduce the chancesof botulism.

Monitoringand ResearchNeeds Shuford(1999) summarizedmonitoring and researchneeds for the Black Tern across North America. Efforts should be made to coordinate California surveysand researchwith thosein other statesand provincesto establisha broadperspective on populationtrends and ecology.Research is particularly neededon the foragingand nestingecology of BlackTerns in California. Studiesof habitatsuitability at boththe localand landscape level are needed to guide wetland protectionand acquisitionefforts (Naugleet al. 2000). Bandingstudies are neededto revealhow terns shiftwith changingwater conditions,as are demographicstudies to identifywhich breedinghabitats are sourcesor sinksfor the overallpopulation. Researchers should focus on variation in aspectsof reproductionmost likely to influencepopulation

211 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA trendsand on understandingfactors limiting nest success(Servello 2000), using methodsthat minimizedisturbance to nestingterns (Shealerand Haverland 2000). We recommenda statewidesurvey approximately every 10 years,during typicalclimatic and habitatconditions, to documentpotential range shifts andcalibrate long-term monitoring data. We recommendannual monitoring by trained observersusing samplingprotocols incorporating precision estimates;methods should be suitablefor localconditions and responsive to the shiftingof breedinglocations. NortheasternCalifornia. Monitoringshould be conductedin mid-June by countingundisturbed adults from pointswhere observersdo not attract mobbingterns. Surveys should be basedon a randomor stratifiedsampling of a subsetof potentialbreeding sites, accounting for the difficultyof reachingsome. Central Valley. Monitoringshould be conductedvia standardizedroad- side transectsin rice fieldsin the SacramentoValley. Concern about the potentialeffects of agriculturalpesticides and cultivationpractices on Black Terns(Lee 1984) begsfor expansionof researchon thesetopics. Studies are neededto assesswhether the valueof rice fieldsto BlackTerns equals that of ephemeraloverflow lands or naturalmarshes.

ACKNOWLEDGMENTS

Fundingwas suppliedby the CaliforniaDepartment of Fish and Game (CDFG), ChevronUSA, Inc.,the RichardGrand Foundation, Klamath Basin NWR Complex, the WeedenFoundation, U.S. Fishand WildlifeService's Nongame Migratory Bird Program,and individual donors to PointReyes Bird Observatory. We are verygrateful to the many individualswho providedvaluable information, advice, access to private or restrictedpublic lands, or helpin the field,without which this study would not have been possible.We especiallythank Lynne Stenzelfor insighton samplingdesign for roadsidesurveys in the SacramentoValley; AI DeMartini,Tim Manolis,Jim Snowden, BradStovall, and BruceWebb for help on roadsidesurveys; Grant Ballard and Diana Stralbergfor preparingdistribution maps; Jim Snowden for sharinglong-term data on Black Terns from CDFG surveysof pheasantbroods in Butte County; Martha Leightonof the CaliforniaAgricultural Statistics Service for dataon acreage by county of plantedrice in the CentralValley; Jay Dee Garr, CassMutters, and JackWilliams for insighton timingof rice plantingin 1998 and methodsof rice cultivation;Dawn Harris for unpublisheddata on Black Terns from surveysof duck ponds in the SacramentoValley; Rob Hansenand associatesfor arrangingaccess and helpingon surveysof the HaciendaRanch Flood Basin and the SouthWilbur Flood Area andfor supplyingunpublished field notesof Ward B. Minturn and John G. Tyler; Frances Bidstrup,Danny Cluck,Mike McVey, BobbyTatman, and DavidWimpfheimer for surveyingremote wetlandsin northeasternCalifornia; the Devil's Garden Ranger Districtof Modoc NationalForest, and particularlyGeorge Studinski,for logistical supportand sharinginformation about wetlands there; various other state and federal landmanagement agencies statewide for providingaccess to landsand personnelto help on surveys;Ken Blum of Tamal S•ka, TomalesBay Kayaking,for kayaking equipment;Helen Green for providingdata from the editorsof the MiddlePacific Coastregion of North American Birds on file with GoldenGate AudubonSociety; KarenCebra, Carla Cicero, Ren• Corado,Krista Fahy, Kimball Garrett, Ned Johnson, FredaKinoshita, Douglas Long, Bob McKernan, James Northern, and Philip Unitt for Black Tern egg-setdata, or confirmationof a lack thereof, from their respective

212 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA institutions;and Paul Fonteyn, Kevin Hunting, Dave Mauser,Gary Page,Tom Smith, and DeniseWight for supportand encouragementfor the project.John Cooper, GordonGould, Kevin Hunting, Tim Manolis,Bruce Peterjohn, and Tara Zimmerman madehelpful comments on draftsof the manuscript.This is contribution718 of Point ReyesBird Observatory.

LITERATURE CITED

Alvo, R., and Dunn, E. 1996. Updatedreport on the BlackTern Chlicloniasniger in Canada.Unpubl. report, Committeeon the Statusof EndangeredWildlife in Canada, c/o Canadian Wildlife Serv., EnvironmentCanada, Ottawa, Ontario, Canada K1A 0H3. Bailey,V. 1902. Unprotectedbreeding grounds. Condor 4:62-64. Bay Institute.1998. From the Sierra to the sea:The ecologicalhistory of the San FranciscoBay-Delta watershed. The Bay Instituteof San Francisco,55 Shaver St., Suite 330, San Rafael, CA 94901. CaliforniaDepartment of Fish and Game. 1992. Bird speciesof specialconcern. Calif. Dept. Fish& Game, 1416 Ninth St., Sacramento,CA 95814. Chapman,F. M. 1908. Campsand Cruises of an Ornithologist.Appleton, New York. Cogswell,H. L. 1977. Water Birdsof California.Univ. Calif. Press,Berkeley. Dahl, T. E., Young,R. D., and Caldwell,M. C. 1997. Statusand trendsof wetlands in the conterminousUnited States:Projected trends 1985 to 1995. U.S. Dept. Interior,Fish & WildlifeServ., Washington, D.C. Dawson,W. L. 1923. The Birdsof California.South Moulton, San Diego. Dunn, E. H., and Agro, D. J. 1995. BlackTern (Chlicloniasniger), in the Birdsof North America (A. Poole and F. Gill, eds.), no. 147. Acad. Nat. Sci., Philadel- phia. Frayer,W. E., Peters,D. D., and Pywell,H. R. 1989. Wetlandsof the California CentralValley: Status and trends. Unpubl. report, U.S. Fish& WildlifeServ., 911 NE 11th Ave., Portland, OR 97232-4181. Garrett, K., and Dunn, J. 1981. Birdsof SouthernCalifornia: Status and Distribution. Los AngelesAudubon Soc., Los Angeles. Gerson,H. 1988. Statusreport on the BlackTern Chlicloniasniger. Unpubl. report, Committeeon the Statusof EndangeredWildlife in Canada,c/o Canadian WildlifeServ., EnvironmentCanada, Ottawa, Ontario, CanadaK1A 0H3. Gould,G. I., Jr. 1974. Breedingsuccess of piscivorousbirds at EagleLake, California. Master'sthesis, Humboldt State Univ., Arcata, CA. Greenberg,D. 1972. Black Tern surveySutter County, California, 1969-71. Unpubl.report, Wildlife Mgmt. BranchSpecial Wildlife Invest. Calif. Dept. Fish & Game, 1416 Ninth St., Sacramento,CA 95814. Grinnell,J., Dixon, J., and Linsdale,J. M. 1930. Vertebratenatural history of a sectionof northernCalifornia through the LassenPeak region. Univ. Calif. Publ. Zool. 35:1-594. Grinnell,J., and Miller,A. H. 1944. The distributionof the birdsof California.Pac. Coast Avifauna 27. Hall, W. H. 1880. Drainageof the valleysand the improvementof the navigationof rivers.Report of the StateEngineer to the Legislatureof the Stateof California, Session1880, in three parts.

213 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

Kempka, R. G., Kollasch,R. P., and Olson,J. D. 1991. Aerial techniquesmeasure shrinkingwaterfowl habitat. Geo Info Systems(Nov/Dec), pp. 48-52. Lederer,R. J. 1976. The breedingpopulations of piscivorousbirds of EagleLake. Am. Birds 30:771-772. Lee, R. C., Jr. 1984. Nestingbiology of the BlackTern (Chlidoniasn iger) in ricefields of the CentralValley, California. Master's thesis, Calif. StateUniv., Sacramento. Mailliard,J. 1904. A few recordssupplementary to Grinnell'scheck-list of California birds. Condor 6:14-16. Naugle,D. E., Higgins,K. E, Estey,M. E., Johnson,R. R., and Nusser,S. M. 2000. Local and landscape-levelfactors influencing Black Tern habitat suitability.J. WildlifeMgmt. 64:253-260. Orr, R. T., and Moffitt, J. 1971. Birdsof the Lake Tahoe Region. Calif. Acad. Sci., San Francisco. Patten, M. A., McCaskie,G., and Unitt, P. In press.Birds of the SaltonSea: Status, Biogeography,and Ecology.Univ. Calif. Press,Berkeley. Peterjohn,B. G., andSauer, J. R. 1997. Populationtrends of the BlackTern fromthe North American Breeding Bird Survey, 1966-1996. Colonial Waterbirds 20:566-573. Ray, M. S. 1906. A-birdingin an auto. Auk 23:400-418. Ray, M. S. 1913. Some furthernotes from the Tahoeregion. Condor 15:111-115. Sauer,J. R., Hines, J. E., Thomas,I., Fallon,J., and Gough, G. 2000. The North AmericanBreeding Bird Survey, results and analysis1966-1999. Version98.1, USGS PatuxentWildlife Res. Ctr., LaurelMD (http://www.mbr-pwrc.usgs.gov/ bbs/bbs.html). Servello,F. A. 2000. Populationresearch priorities for BlackTerns developedfrom modelinganalyses. Waterbirds 23:440-448. Shaw, D. W. H. 1998. Changesin populationsize and colonylocation of breeding waterbirdsat EagleLake, California,between 1970 and 1997. M.S. thesis,Calif. State Univ., Chico. Shealer,D. A., and Haverland,J. A. 2000. Effectsof investigatordisturbance on the reproductivebehavior and successof BlackTerns. Waterbirds23:15-23. Shuford,W. D. 1998. Surveysof BlackTerns and other inland-breedingseabirds in northeasternCalifornia in 1997. Report98-03, Birdand Mammal Conservation Program, Calif. Dept. Fish & Game, 1416 Ninth St., Sacramento,CA 95814. Shuford,W. D. 1999. Statusassessment and conservationplan for the Black Tern (Chlidoniasniger surinamensis)in North America.U.S. Dept. Interior,Fish & Wildlife Serv., Denver Federal Center, Denver, CO 80225-0486. Shuford, W. D., Humphrey, J. M., and Nur, N. 1999. Surveys of terns and cormorantsin California'sCentral Valley in 1998. PointReyes Bird Observatory (Contr. 772), 4990 ShorelineHwy., StinsonBeach, CA 94970. Shuford,W. D., Warnock, N., Molina, K. C., and Sturm, K. K. In press.The Salton Sea as criticalhabitat to migratingand residentwaterbirds. Hydrobiologia (Dev. Hydrobiol.). Silliman,O. P. 1915. Another Mexican Ground Dove for California, and other notes. Condor 17:207. Small,A. 1994. CaliforniaBirds: Their Statusand Distribution.Ibis Publ., Vista, CA. Tyler,J. G. 1913. Somebirds of the Fresnodistrict, California. Pac. CoastAvifauna 9.

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U.S. Fish and Wildlife Service. 1995. Migratory nongame birds of management concernin the United States:The 1995 list. Office of MigratoryBird Manage- ment, U.S. Fish& WildlifeServ., Washington,D.C. Van Rossem,A. J. 1933. Ternsas destroyersof birds'eggs. Condor 35:49-51. Weseloh,D. V. C., Rodrigue,J., Blokpoel,H., and Ewins,P. J. 1997. Contaminant concentrationsin eggsof BlackTerns (Chlidonias niger) from southernOntario and southernQuebec, 1989-1996. ColonialWaterbirds 20:604-616. Zeiner,D.C., Laudenslayer,W. F., Jr., Mayer,K. E., andWhite, M. 1990. California's Wildlife, vol. II, Birds. Calif. StatewideWildlife Habitat RelationshipSystem, Calif. Dept. Fish& Game, 1416 Ninth St., Sacramento,CA 95814.

Accepted 14 September 2001

Appendix1. Numbersof egg setsof the BlackTern in California,1886- 1960, from major Californiamuseums.

Northeastern California ModocCounty: Alturas Meadow, 9 June 1918 (2); 3.7 mi W of Alturas,9 June 1918 (4). LassenCounty: Grasshopper Meadows/Lake, 2-22 June 1918 (20); Spaulding's, EagleLake, 3 June 1918 (7); EagleLake, 3-6 June 1918 (5), 22 June 1928 (1); hr. Truxell's,east shore of EagleLake, 23 May 1923 (1); Upper RagarMeadow, 1 June 1935 (1). E1Dorado County: hr. Bijou,Lake Tahoe, 19 June 1899 (1), 9 June 1911 (5), 10 June 1912 (2), 6 June 1918 (9); Lake Tahoe, 6 June 1910 (1); Rowland'sMarsh (i.e., Al-Tahoe),Lake Tahoe,22 June 1902 (1), 10 June 1909 (3), 23 May-15 June 1910 (7), 30 May-9 June1914 (18), 30 June1918 (1), 5 June1919 (1), 30 May 1920 (1), 14 June 1928 (1), 21 June 1930 (1), 15 June 1939 (2); hr. Tallac, Lake Tahoe, 22 June 1911 (1). CentralValley: Sacramento Valley ColusaCounty: Maxwell, 23 June 1939 (1). Yolo County:Woodland, 11 May 1886 (1). Central Valley:Sacramento-San Joaquin River Delta SacramentoCounty: 0.5 mi S of Freeport, 15 June 1899 (2); Bear Lake, 27 May 1923 (5);vic. Sacramento(?county, ?delta), 7 June1902 (1), 13 May 1906 (2); Stone Lake, 15-29 May 1921 (23), 4 June 1922 (1), 13-30 May 1923 (4). San Joaquin County: White Ranch, 9 mi N of Stockton, 3 June 1921 (1); KettlemanSwamp, 9.5 mi NW of Stockton,1 June 1947 (3). CentralValley: San JoaquinValley MaderaCounty: Chowchilla (egg record says "Merced Co."), 23 June1900 (5); 15 mi W of Madera,30 June1923 (1); "MaderaCo.," hr. Firebaugh,Fresno Co., 16-17 May 1927 (8); "MaderaCo.," 10 mi E of Firebaugh,Fresno Co., 26 May 1927 (4); 10 mi from Firebaugh(?county), 5 June 1927 (1); "MaderaCo.," 28 May 1928 (1), 9 June 1930 (3). MercedCounty: hr. Brito, 21 May 1919 (1); Dos Palos, 17-22 May 1912 (5), 8 June1927 (1); Gadwall,16 May 1914 (1), 1-2 July1917 (6), 12 May-4 June 1918 (14); Gustine,14May 1931 (1), 5 June1932 (1), 12 June 1934 (1), 7 June 1937 (5);

215 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA

LosBanos, 17 May 1898 (1), 8 June 1901 (1), 5 June 1905 (3), 2 June 1908 (2), 26 May 1910 (3), 2 July 1913 (1), 7 June 1914 (2), 29 May-25 June 1916 (12), 3-4 June1918 (4), 26 June1919 (1), 30 May 1920 (1), 28 May 1921 (1), 3-4 June1922 (3), 1-18 June 1923 (15), 21 May-21 June 1925 (9), 23 May-20 June 1926 (8), 3 June 1928 (1), 30 May-1 July 1930 (23), 14 June 1931 (1), 13 May-5 June 1932 (10), 12 May-12 June 1934 (4), 11-13 May 1935 (5), 25 May 1936 (4), 14 May-! June1937 (11), 4June 1938 (1), 10 May-7 June1939 (8), 19 May 1940 (4), 9 June 1941 (1), 9 June 1942 (2); 4-6 mi S of Los Banos,21-23 May 1919 (2), 30 May 1920 (1), 12-21 June 1931 (5); 8-10 mi E of Los Banos,7 May 1927 (1), 13 May- 1 June 1935 (5); 5-10 mi NE of Los Banos,9 May 1936 (1), 14 May 1937 (3), 31 May 1939 (1); "MercedCo.," 20 May 1899 (1), 25 May-1 July 1908 (16), 26 May 1909 (9), 15-28 May 1926 (2), 28 May 1928 (1), 9 June 1930 (2), 25 June 1931 (1), 12-19 May 1935 (4), 3 May-9 June 1936 (20), 10 May 1939 (1), 5 June 1946 (1), 22-23 June 1948 (4), 22-23 May 1949 (6); San JoaquinR. at Los Banos Crossing,15 May 1897 (2). FresnoCounty: Columbia Ranch, 24-25 June 1919 (4), 8-9 June 1920 (8), 22- 23 June 1921 (5); Firebaugh,28 May 1916 (2); "FresnoCo.," nr. SouthDos Palos, Merced Co., 20 May 1919 (3); nr. Laton, 21 June 1919 (2), 3 June 1922 (1); McNeil'sRanch SW of Fresno,7 June 1920 (1); Mendota,26 May 1915 (1), 7-21 June 1930 (5); Riverdale,25 May 1917 (1), 24 May 1919 (1). KingsCounty: 12 mi from Corcoran(egg record says "Kern Co."), 24 May 1940 (1); GernseySlough, 3 June 1946 (2); 3 mi E of Hanford, 24 May 1922 (1); nr. Stratford,23-24 May 1936 (10); borderof TulareLake, 4 mi W of Waukena,Tulare Co., 6 June 1893 (3); TulareLake, 8 June 1941 (11); TulareLake (KingsCo.), 24 May-8 June 1941 (18); 14 mi NW of Tulare, 6 June 1893 (1). Kern County:Buena Vista Lake, 10 June1907 (1), 19-20 June1914 (2), 18 June 1916 (1), 19-21 June 1921 (3), 11 June-5 July 1922 (8), 4 July 1937 (1), 5 June 1938 (4), 6 June 1948 (1), 20 June 1954 (2), 24 June 1956 (1); rice field between WheelerRidge and BuenaVista Lake, 12 June 1960 (2); Kern River,5 June 1938 (2).

Appendix2. Sightrecords of confirmedbreeding of BlackTerns in Califor- nia, 1899 to 1999, other than thoselisted or summarizedin the text.

Northeastern California SiskiyouCounty: Lower Klamath NWR, Unit 13A, mid-July1995 (22 nests, Klamath BasinNWRs files). Siskiyou/ModocCounty: Tule Lake, earlyJuly 1899 ("nests,"Bailey 1902). ModocCounty: Beeler Reservoir, 19 June 1976 (nest,B. E. Deuel). LassenCounty: Eagle Lake, 22 June 1921 (15-20 nests,Grinnell et al. 1930), summer1974 (23 nests,Lederer 1976); Delta Bay, EagleLake, late May-mid July 1971 (1 nest, Gould 1974); North Basin,Eagle Lake, late May-late June 1996 (29 nests,Shaw 1998), early June-midJuly 1997 (21 nests,Shaw 1998); southwest shore,Eagle Lake, late May-mid July 1971 (6 nests,Gould 1974); nr. Spaulding's, Eagle Lake, 9 June 1925 ("many nests,"Grinnell et al. 1930), late May-mid July 1970 (30 nests,Gould 1974), late May-mid July 1971 (33 nests,Gould 1974), early June-midJuly 1997 (11 nests,Shaw 1998); eastsidebays (Troxel and Duck Island bays),Eagle Lake, late May-mid July 1971 (11 nests,Gould 1974), late May-lateJune 1996 (10 nests,Shaw 1998). PlumasCounty: Sierra Valley, 23 July 1973 (nest,G. Zamzow),14 June 1989 (nest,D. Shufordet al.), 13 June 1998 (nest,D. Shuford,J. McCormick). SierraCounty: Kyburz Flat, 28 June 1973 (nest,G. Zamzow),19 July 1973 (nest, G. Zamzow). E1Dorado County: Emerald Bay, Lake Tahoe, 10 August1918 ("parentsfeeding

216 BREEDING STATUS OF THE BLACK TERN IN CALIFORNIA young,"J. W. Mailliardin Orr and Moffitt 1971); Rowland'sMarsh (i.e., A1-Tahoe), Lake Tahoe, 1 June 1909 ("scoresof nests,"Ray 1913). CentralValley: Sacramento Valley ButteCounty: W of Biggs,6 July 1987 (2 nests,J. Snowdenin litt.); 3 mi S of Durham, 1 June 1985 (2 nests,J. Hornstein);2 mi NE of Richvale,3 July 1984 (7 nests,J. Snowden in litt.). Glenn County:Sacramento NWR, 9 June 1958 (2 chicksbanded; refuge files). ColusaCounty: S sideof WhiteRd. 0.7 mi W of BrowningRd., 26 June 1999 (2+ nests,B. Williamsin litt.). Sutter County:S of KirkvilleRd. adjacentto Sutter Bypass,June-July 1976 (3 nests,Lee 1984); jct. Hwy. 113 and Varney Rd., June-July 1976 (10 nests,Lee 1984); E of ArmourRd. betweenKirkville and Varney roads, May-July 1977 (2 nests, Lee 1984); jct. Hwy. 113 and KirkvilleRd., June-July1977 (8 nests,Lee 1984); N of KirkvilleRd. adjacentto SutterBypass, June-July 1977 (11 nests,Lee 1984); N of Robbins,June 1969 ("colonyof 12 terns[with] nests," Greenberg 1972). SacramentoCounty: jct. Hwy. 99 and ElkhornBlvd., 24 May-22 June 1976 (13 nests,Lee 1984). CentralValley: San JoaquinValley MercedCounty: nr. LosBanos, 16 June 1903 (youngof yearjust beginning to fly, Chapman1908), prior to 1923 (photoof chicks,Dawson 1923); San JoaquinRiver nr. Merced,prior to 1904 ("numberof nestsrecorded," Mailliard 1904). Merced/FresnoCounty: vic. Los Banosand South Dos Palos, 19-22 May 1919 (>100 nestsexamined, J. G. Tyler et al.). FresnoCounty: nr. Laton,31 May 1910 ("setof 3 eggs,"C. Lambin Tyler1913), 27 May 1917 (colonyof about30 pairs,8 eggsets, N. K. Carpenter,A.M. Ingersoll fide J. G. Tyler);Firebaugh, 30 May 1912 (severalbirds "sitting on nests,"Tyler 1913); Riverdale,25 May 1917 (colonyof 20-25 pairs,13 eggsets, J. G. Tyler,N. Carpenter);pond S of Fowler,30 May 1918 (nest,J. G. Tyler);Mendota, 30 May 1928 (3 nests,W. B. Minturn, J. G. Tyler);White's BridgeRd., Mendota, 17 May 1930 (nest,W. B. Minturn),7 June 1930 (about20 nests,W. B. Minturn,J. G. Tyler), 1 May 1937 (7 nestsbeing built, W. B. Minturn), 22 May 1937 (8 nests,W. B. Minturn, C. Chandler),14 May 1941 (partlycompleted nest, W. B. Minturn), 7 June 1941 (nest,W. B. Minturn). Fresno/MaderaCounty: Mendota Dam (i.e., MendotaPool), 3 June 1933 (8 nests, W. B. Minturn,J. G. Tyler), 23-24 June 1933 (7 nests,W. B. Minturn,J. G. Tyler). Madera County:12 mi W of Madera, 9 June 1934 (2 nests,J. G. Tyler). KingsCounty: Hacienda Ranch Flood Basin and South Wilbur Flood Area, 22 July 1983 ("manynests", one photographed,R. Hansen);East HaciendaRanch Flood Basin, 29 June 1997 (5 nests,R. Hansen in litt.)

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