NESTING BIOLOGY OF THE CALIFORNIA BLACK IN SOUTHWESTERN ARIZONA

RONALD E. FLORES and WILLIAM R. EDDLEMAN• Department of Natural ResourcesScience, 210B WoodwardHall, Universityof Rhode Island,Kingston, RhodeIsland, 02881 (addressreprint requests to firstauthor)

The nestingrequirements and reproductivebiology of the California (Laterallus jamaicensis½oturniculus) are poorly known. The main reasons for this are that Black Rails inhabit dense marshes and their smallsize and secretivenature have madethem difficultbirds to study(Todd 1977). Additionally,inland breeding populations are sparselydistributed, relativelyinaccessible, and declining(Snider 1969, Rosenberget al. 1991, Evenset al. 1991). As a result California and Arizona list the California BlackRail as threatenedand endangered,respectively (California Depart- ment of Fishand Game 1988, Arizona Game and FishDepartment 1988). Informationon reproductionis essentialto managementand protectionof this threatenedsubspecies. Most of the informationon nestingby CaliforniaBlack Rails is from clutchesof eggs collectedin the late 1800s and early 1900s in coastal habitat (Bent 1926). Egg datesfor 29 nestsrange from 12 March to 23 May. The averageclutch size for 31 egg setsin museumcollections is 6.1 _ 1.4 (standarddeviation), ranging from 3 to 8 (Wilbur 1974). Nests are "deeplycupped and placed on damp groundor elevatedin vegetation" (Wilbur 1974). Heaton (1937b) statedthat BlackRail chickshatch one at a time, and both Heaton (1937a) and Huey (1916) concludedthat adults readily abandontheir nests. Further informationon Black Rail nesting habitat, nest success,incubation period, brood survival,renesting and double-clutchingpotential, and reproductivebehavior is lacking.Our study summarizes information obtained from five California Black Rail nests that we monitoredalong the lower ColoradoRiver 27 km northeastof Yuma, Arizona, and relatesthis informationto the ecologyand managementof this subspecies.

STUDY AREA AND METHODS

We monitoredCalifornia Black Rail nests as a part of a generallife history studyof the speciesconducted at Mittry Lake WildlifeManagement Area, YumaCounty, Arizona, from March 1987 to December1988. We studied Black Rails in 15.5 hectaresin the northeastcorner of the management area (southYuma ProvingGround Slough), an old oxbowof the Colorado River.The slough'swater levelvaries by no more than 7 ½mannually. The marsh is rechargedby a feeder canal from Imperial Dam that releases 10-15 cubicfeet per secondand seepagefrom the Gila GravityCanal of about3-4 cubicfeet per second(Earl Burnett, U.S. Bureauof Reclamation, Yuma ProjectsOffice, pers. comm.). Historically,several wildfires have burned the studyarea, most recentlyin November 1979. Most of the emergentvegetation was burned during the last fire but has sincegrown back (Todd1980). The area receivedlocal scouring and slightflooding in

Western 24:81-88, 1993 81 BLACK RAIL NESTING BIOLOGY

1983. Most emergentplants recovered in 1984-85, but an open channel stillremained along the westernedge of the studyarea. Southerncattail (Typha dorningensis) is the dominantemergent, encom- passing 65% of the study area, with three-squarebulrush (Scirpus americanus), California bulrush(S. californicus), and inland saltgrass (DistichIls stricta)distributed along the shoreline.The marshis bordered by a desertupland with scatteredstands of honey and screwbeanmesquites (Prosopisjuliflora and R pubescens)and sectionsof arrowweed(Tessaria sericea), seepwillow (Baccharis glutinosa), and saltcedar (Tamarix chinensis)extending into the wetland. We trappedBlack Rails by usinga modifiedversion of a drop-doortrap usedby Zembaland Massey(1983) to catch Light-lootedClapper Rails (Rallus Iongirostrislevipes). Traps were placedalong drift fencescon- structedby staplingsurveyor's stakes to 1-m-talllengths of 1.8-cm-mesh blackplastic netting. Drift fenceswere placed perpendicular to zonesof shallowwater where Black Railsvocalized or were known to occur,and the baseof the fencewas covered with mudor vegetationso that railscould not find their way aroundthe fence. Birdsencountering the drift fenceswere channeledinto trapsplaced along the fencing. We sexedBlack Rails by plumagecolor (Russell1966, Eddiemanand Floresunpubl. data). Maleshad uniformlycolored dark gray throatsand ventralplumage, whereas females had light gray to dullwhite throatsand mediumto pale grayventral plumage. We glued2- g radiotransmitters (Model SOPB-1038-LD, WildlifeMateri- als, Inc., Carbondale, IL) to the backs of captured Black Rails with cyanoacrylicglue in combinationwith eyelashcement (Stenzel 1982). We locatedthe taggedBlack Rails from three fixed telemetry stations (two travel trailersand one plywoodshed), each equipped with a dual 12-elementnull- peak Yagi antennasystem placed on a mastprojecting through the roof. Azimuths were determined from a needle fastenedto the mast, which pointedto a compassrose on a tablearound the mast.Azimuths were taken from each stationon three beacontransmitters at the beginningof each trackingsession. The averagedeviation between measured and surveyed azimuthsat each stationwas usedto calibratethe compassrose prior to each trackingsession. Bird locationswere determinedby plottingnear- simultaneousazimuths obtained from telemeteredbirds by two assistantsat differentstations communicating via two-way radios.Tracking was con- ductedso that eachdaylight and crepuscular hour of the daywas monitored for an equal amount of time during each week. Pointswhere otherwise activebirds generated radio signals of steadystrength for longperiods were where we searched for nests. We searchedfor nestsby locatingincubating telemetered birds with a hand-heldantenna, then lookingin clumpsof vegetationfor the nest. In threecases, scolding adults indicated when nestswere nearby.Information recordedon nestsincluded location, description, habitat type, clutchsize, fate, and hatchingdate. Incubationshifts were monitoredby meansof an automaticactivity recorder with a TelonicsTDP-2 data processor(Telonics, Inc., Mesa, AZ) connectedto our telemetrysystem. The antennaswere lockedin positionpointing in the generaldirection of the selectedbird when BLACK RAIL NESTING BIOLOGY the activityrecorder was used. The radioreceiver was connected to the data processor,allowing peak signalamplitude and pulseinterval to be recorded on a Rustrakstrip-chart recorder. Movement of birdsresulted in a variable signal amplitudeand a wavy line on the chart paper, whereasstationary birds yielded a relativelystraight line. All other data on nestingwere recordedopportunistically. Data are expressedas means plus or minus standarddeviations. Clutch sizes and water depth at nestsites and random siteswere comparedby meansof Mann-WhitneyU tests(Zar 1984).

RESULTS

We found five nestsduring nine nest searches,the first BlackRail nests describedfrom Arizona. One pair was foundincubating in one nest (both adults had been fitted with transmitters),two nests were located because telemetered males were incubating, one nest was located because a telemeteredfemale was incubating,and one nest was found incidentally. Nestswere found on 19 April, 17 June,9 July, 13 July,and 23 July1988, with the first suggestionof incubationby a te]emeteredbird on 30 March 1988. The latter nest was not located, however.Incubation began and hatchingoccurred at the fivenests that were locatedon 18 April and 5 May, 14 June and 2 July, 25 June and 15 July, an unknowndate and 21 July, and unknowndate and 23 July, respectively.Clutch size averaged4.8 _+ 1.5, rangingfrom 3 to 7. While we were handlingher, one femalelaid an egg, which weighed9 g, or 29% of her bodyweight. Nestsvaried in distancefrom uplandhabitat but were consistentlyplaced over shallow water (Table 1). All nests were elevated above the mud substratein clumps of vegetation (three in California bulrush, one in southerncattail, and one in three-squarebulrush) and consistedof a well- definedbow] with a canopyand ramp. Fournests were constructed prima- rily of southerncattail, one of spikerush(Eleocharis sp.) Water depth at nest sitesaveraged 1.2 __1.2 cm and approachedbeing significantly]ess

Table 1 Characteristics of Five California Black Rail Nests at Mittry Lake WildlifeManagement Area and of two EasternBlack Rail Nests

This study

Measurement (cm) Mean __S.D. ø Range EasternBlack Rails

Inside diameter 7.4 __0.6 7-8 8.3 b Outside diameter 12.6 __ 1.5 11-15 11.4 b Bowl depth 4.4 + 1.7 3-7 6.4 • Height abovesubstrate 6.4 __3•4 2-11 2.5 c Water depth at nest site 1.2 __1•2 0-3 --

aS,D.. standard deviation. bone nest:E. W. Nelsonin Bent (1926). COnenest: Harlow (1913). BLACK RAIL NESTING BIOLOGY than the averagewater depth at 272 randomlyselected sites (• -- 5.7 __7.7 cm; Mann-WhitneyU test, U -- 374.0, P -- 0.07). The incubationperiod recordedfor three nests was 17 to 20 days, beginningwith the first day of incubationas indicatedby the activity recordedby the birds' transmittersand endingwith the hatchingdate as confirmedby nestvisits. Both sexes incubated the eggs.Two femalesspent 43.0 to 47.0% of their time duringthe day incubating,whereas one male spent 47.2% of his time incubating(Table 2). One female exhibitedan unusualincubation pattern in that she sat only one or two very long incubationshifts during the daylighthours, whereas the othertwo sat 7-10 shiftsof much shorterduration. No other bird was detectednear her nest, so we assumed she had lost her mate or her mate did not assist in incubation.Black Rails aggressively defended three nestsby givingscolding vocalizations(Reynard 1974:753), raisingtheir wings, and attemptingto chargeus. All clutcheshatched successfully, and we found no evidenceof partial clutch predation,egg abandonment,or egg infertility.Newly hatched broods were observedin two of the nests; both times the broods and parentsleft the nestwithin 24 hoursafter the clutcheshatched completely. One femalewas recapturedwith an egg in her oviduct18 daysafter her clutch hatched, suggestingthat Black Rails lay secondor replacement clutches.One telemeteredmale seemedto be incubatingin April, but we couldnot find his nest.He wasfound incubating another nest in July.

DISCUSSION

The timing of Black Rail nestingwe observedwas similarto that of previousstudies (Huey 1916, Wilbur 1974), but extendedfurther into the summer.The shorter nestingseason in tidal marshesin Californiamay reflectselection against nesting during the high summertides of June and July,a selectivepressure absent on the lowerColorado River. Alternatively, thisapparent difference may be an artifactof the paucityof informationon Black Rail nesting. Nest-siteselection by BlackRails at Mittry Lake was stronglyinfluenced by water depth, and BlackRails are knownto nestin water shallowerthan do other speciesof rails(Fredrickson and Reid 1986). We foundno nests over water deeperthan 2.5 cm. Nestsof CaliforniaBlack Rails in south- western Arizona resembled Black Rail nests from other locations. The measurements of the nests were similar to those recorded for Eastern Black Rails(L. j. jamaicensis)(Table 1), andtheir construction was typical of rallid nestsin havinga ramp, canopy,and well-definednest bowl (Ripley 1977). At Mittry Lake BlackRails typically used dead southerncattail for nesting material, even though other emergentssuch as Californiabulrush and three-squarebulrush were the dominantspecies at mostnest sites. The averageclutch size of 4.8 __1.5 observedat Mittry Lake does not differ significantlyfrom the 6.1 __1.4 for 31 CaliforniaBlack Rail clutches in museumcollections (Wilbur 1974; Mann-WhitneyU test, U -- 56.0, P -- 0.09) but is lessthan the 8 __1.4 recordedfor 21 nestsof Eastern Black Rails(Clark 1884, Bent 1926, Stone 1937) (• -- 8.0 __1.4; Mann-Whitney BLACK RAIL NESTING BIOLOGY

U test, U -- 23.0, P -- 0.003). The smallerclutch size noted in thisstudy mayhave been an artifactof thelate dates on which most nests were found. Three of the five nestswere foundin Julyand may havebeen renesting or secondnesting attempts. In otherrallids clutch size in laternests tends to be smaller(Fredrickson 1970). We observedthat a BlackRail can lay an egg that is almost30% of her body weight. Therefore,Black Rails may lay clutchesweighing almost 200% of theirbody weight. Although little infor- mationexists on the time requiredto lay a clutchof eggs,one eastern individuallaid 6 eggs in 6 to 8 days (Wayne 1905), implying that a tremendousenergy demand on female Black Rails during the nesting season.The participationof both sexesin incubationfollows the general patternof rallids(Ripley 1977), althoughwe observedone exception to this patternwith one female(Table 2). From past accountsby oologists(Huey 1916, Heaton 1937a), we expectedthat BlackRails would readily abandon their nests,but no nests were abandonedduring our study.Perhaps the collectionof all or part of the clutchor disturbanceof nestingbirds early in incubationexplains the abandonmentof nestsfound in the past. Some previousreports suggest that BlackRails defend the nestsite weakly (Huey 1916, Heaton 1937b). We found that some Black Railswere stronglyaggressive in nest defense. Their behavioraround the nestclosely resembled that of the GalapagosRail (Laterallus spilonotus),which also raisesits wings and chargesintruders near the nest(Franklin et al. 1979). We did not activelyseek nests until our monitoringindicated incubation was well underway(at least10-14 days),so nestdefense may becomestronger as incubationadvances. The high nest successwas similarto that observedin many temperate rallids(Zimmerman 1977, Bateman1977). The absenceof predationon the nestsreflected the lack of predationon Black Rails at Mittry Lake in general.No telemeteredbirds were lostto predationduring the studyand we think that this was due to the high densityof the vegetationthey inhabited.

Table 2 Incubation Patterns of Three California Black Rails at MirtryLake WildlifeManagement Area, April-July 1988 ø

Sex

Male Female Female b

No. of daysobserved 3 4 4 No. of recessesper day 7.7 _+0.5 9.0 _+0.7 2.8 _+0.4 No. of incubation shifts per day 7.2 _+1.9 8.0 _+0.7 1.8 __0.4 Lengthof shift(minutes) 48.6 _+44.8 47.5 _+43.4 256.3 _+172.6 Percentageof time on nest 47.2 _+ 6.8 43.0 _+ 2.2 47.0 _+4.4

aDatapresented are means+ standarddeviations except for numberof daysobserved. blncubated alone.

85 BLACK RAIL NESTING BIOLOGY

The Black Rail broods we observedbehaved like those observedby Heaton(1937b), with the parentsand brood leaving the nestsoon after all the eggshatched. Chicks remained in the nestuntil all eggshatched, but we couldnot determineexactly how long they stayed between hatching and the time they left with their parents.Adults and the broodremained in the generalarea of the nestand frequently returned to the nestsite to roostfor the evening.

MANAGEMENT IMPLICATIONS

The relativelylarge clutchsize, long breedingseason, and apparentlow predationof CaliforniaBlack Rails in southwesternArizona suggestthis specieshas a high reproductivepotential. The requirementfor shallow water at suitablenest sites, however, limits this potential by restrictingBlack Railsto the shallowerparts of marshes.Being placedover shallowwater alsomakes Black Rail nestsvulnerable to water-levelfluctuations. Ingersoll (1909) reportedfinding at least30 BlackRail eggsthat had floatedout of nestsafter hightides in a saltmarsh near San Diego, California.The weekly and daily fluctuationsin water flow on the ColoradoRiver thus preclude BlackRails from nestingin mostwetlands connecting to the river.The only sites where Black Rails occur on the lower Colorado River are where water levelsare controlledby limitinginflow and/or outflow(such as Mittry Lake) or at seeps(Evens et al. 1991). Enhancementof existingand potential nesting habitat at inland sites would be possiblewith structuresto maintain or manipulatewater levels (Fredricksonand Reid 1986). Potentialsites for manipulationof habitatare availableon severalstate and federalwildlife refuges in southernCalifornia and alongthe ColoradoRiver (Eddieman et al• 1988). Acquisitionof water rightswhere needed and inclusionof BlackRails as a managementpriority are neededbefore managementprograms can proceed.Then, improve- ment of existingwater-control structures by maintenanceof dikes and additionof reliablepumping capability could provide the toolsfor manage- ment of Black Rail habitat. Water could be added or removed as needed to maintainmoist soil or shallowwater for Black Rail nesting,with particular attention paid to minimizing water level changesduring the March-July nestingperiod. Additionalwetland management areas might be createdin existingcroplands adjacent to the river or near other water sources. Additionally,the preservationof hydrologicregimes at existingnesting habitatsuch as seepsadjacent to canalsor in isolatedsettings such as the Bill Williams River (Rosenberget al. 1991) is needed to maintain small inlandpopulations of Black Rails,which may be most subjectto random extinction(Evens et al. 1991). Practicessuch as concretelining of canals presumablydisrupt or eliminatethe seepagethat providesshallow water neededfor nestinghabitat of BlackRails.

ACKNOWLEDGMENTS

We thank the U.S. Bureauof Reclamationand the ArizonaDepartment of Game and Fish for fundingthis study. The staff of Imperial National Wildlife Refuge providedhousing and the useof a housetrailer. We alsoextend a specialthanks to

86 BLACK RAIL NESTING BIOLOGY the U.S. Army YumaProving Grounds for providingtrailer space and base privileges, and to CherylFought, Lance Vanderzyl, and Valerie Morrell from the environmental departmentof the YumaProving Ground for providingoffice space and lab facilities. The staffof the Universityof Wyomingand S. H. Anderson,leader of the Wyoming CooperativeResearch Unit, providedlogistical support for thisstudy. We alsothank the U.S. Fish & WildlifeService, National EcologyResearch Center, Fort Collins, Colorado,for lendingus the activityrecording system. We especiallythank Gary L. Heller,Courtney J. Conway,Barbara A. Groshek,Sarah T. Hooper,and JenniferL. Plympton for their dedicatedfield assistance.P. V. August, T. Corman, S. A. Laymon,T. Manolis,G. W. Page, J. Rorabaugh,and L. Z. Ward providedhelpful commentsthat improvedthe manuscript.This is contribution2695 of the Rhode IslandAgricultural Experiment Station.

LITERATURE CITED

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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. Russell,S. M. 1966. Statusof the Black Rail and Gray-breastedCrake in British Honduras. Condor 68:105-107. Snider, P. R. 1969. The nestingseason. Southwest region. AudubonField Notes 23:681. Stenzel,J. R. 1982. Ecologyof breedingYellow Rails at Seney NationalWildlife Refuge.M.S. thesis•Ohio StateUniv., Columbus. Stone, W. 1937. Bird Studiesat Old Cape May: An Ornithologyof CoastalNew Jersey,vol. 1. DelawareValley Ornithol. Club and Acad. Nat. Sci. Philadelphia, Philadelphia. Todd, R. L. 1977. Black Rail, Little Black Rail, BlackCrake, FarallonRail (Laterallus jamaicensis),in Managementof MigratoryShore and Upland Game Birdsin North America(G. C. Sanderson,ed.), pp. 71-83. Int. Assoc.Fish and Wildlife Agencies,Washington, D.C. Todd, R. L. 1980. Publicationof wildlifemanagement information. Spec. Rept., ArizonaGame & FishDept. Proj. W-53-R-30. Prog. Narr. Obj. XIII (WP5, J1). 2222 W. GreenwayRd., Phoenix,AZ 85023. Wayne.A. T. 1905. Breedingof the LittleBlack Rail ( jamaicensis) in South Carolina. Warbler 1:33-35. Wilbur,S. R. 1974. The literatureof the CaliforniaBlack Rail. U.S. Fishand Wildlife Serv. Spec. Sci. Rept.--Wildlife 179. Zar,J. H. 1984. BiostatisticalAnalysis, 2nd ed. Prentice-Hall, Englewood •Cliffs, NJ. Zembal,R., and Massey.B. W. 1983. To catcha Clapper Rail--twice. N. Am. Bird Bander 8:144-148. Zimmerman,J. L. 1977. Virginia Rail (Railus limicola), in Managementof Migra- tory Shore and Upland Game Birdsin North America (G. C. Sanderson,ed.), pp. 46-56. Int. Assoc.Fish and WildlifeAgencies, Washington, D.C.

Accepted 19 September 1992