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RAPTOR RESEARCH

A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC.

VOL. 20 SPRING 1986 NO. 1

POPULATION ECOLOGY OF THE HARRIS' IN

WAYNE H. WHALEY

ABSTRACT- The Harris' Hawk (Parabuteounicinctus) was studied in Arizona during 1976-1977.Where 2 separate populationsonce resided in Arizona,1 nowremains and occupies 3,880 km 2 of the ArizonaUpland subdivision, .The former populationalong the ColoradoRiver is extirpated. Nestswere built or old nestsrepaired from Januaryto Augustand eggswere laid from mid-Januaryto mid-August. Subsequentclutches were documented in 50 nestingranges. Occasionally second clutches were laid beforeyoung of first broodswere fledged. Fledging dates ranged from April to October.At 9 locationsactive nests were 0.8 km apartand at 2 locationsnests were 0.5 km apart.Within 2 studyareas nesting density was 2.5 km2/activenest. In 1977 Harris' reoccupied91% of the nestingranges used in 1976. More than 2 adultswere observedat 46% of 227 nestingranges. Productivityfor 396 nestingattempts averaged 3.16 eggs/clutchand ! .62young fledged/nesting attempt. Seventy-four percentof the nestingattempts were successful. Foodconsisted mainly of rabbitsand groundsquirrels. Mortality occurred mainly during the egg laying and incubation period.Early nest failures resulted in secondbroods, but successfulpairs also had secondbroods. Habitat loss is the major causeof declineof the populationfollowed by excessivehuman disturbance.

Researchon raptors hasbecome increasingly im- apparentextinction in southernCalifornia (R. Guy portant as a result of the marked declinein several McCaskie pers. comm.), and with the recent (late speciesover the past 3 decades(Arnold 1954; Cot- 1960) increaseduse for , knowledge of the tam et al. 1961; Berger, Sindelarand Gamble 1969; Harris' Hawk's status in Arizona is critical. Peterson 1969; Sprunt 1969; Henny and Wight The primary purposeof this studywas to estab- 1972). lish base-line data on nesting distribution and In the southwest,particularly in Arizona, the abundance of the Harris' Hawk in Arizona and to rangesof somespecies ofraptors extendmarginally compare thesedata with the historicrecord to de- into the United States,and here populationstudies termine nestingsuccess of the present population. are usuallymost informative. Most of theseborder specieshave received little investigation.For exam- STUDY AREA AND METHODS ple, the Aplomado Falcon (Falcofemoralis)showed Arizona falls into a southwesternbi-seasonal climatic pattern of signsof declineas early as 1890 (Phillips,Marshall winter precipitation,spring dry period, summer precipitation, and Monson 1964). Its range and statusin Arizona and fall dry period.The springdry period(May -June) hashigher waspoorly documented(Phillips et al. 1964) until temp and the greatestinfluence on the plant and com- munity (Lowe 1976). the study of Hector (1975). Where it was once Sellers(1960) dividedthe stateinto homogeneoussections with thought to be locally fairly common, it is extinct respectto climate,topography, and vegetation.From the south- (Hector 1975).Because of habitatdestruction, Gray westsection (the area of importancein this study)to the plateau Hawk (Buteonitidus) populations have declined sectionthere are extreme changesin climaticconditions. The plateausection has an averageannual temp 20 to 25ø F lower and during the last century (Richard Glinski pers. annualprecipitation 38 to 51 cmhigher than the flat desertsof the comm.). southwest section. The southwest section contains the lowest, hot- The Harris' Hawk (Parabuteounicinctus superior) is test and driest areas of the state (Sellers 1960). another relatively unstudied southwesternraptor. Of the 6 life-zonesin Arizona, only the Lower Sonoran, con- Studies by Hensley (1959) and Mader (1975a, tainingportions of the Sonoran,Mojave and ChihuahuanDesert (Fig. 1), wasimportant to this study.The SonoranDesert has 2 1975b, 1977) are the only major works on this subdivisionsin Arizona-- the Lower Coloradoand Arizona Up- speciesin Arizona. Becauseof sudden decline and land subdivisions(Fig. 1). The Lower Coloradosubdivision (ele-

1 RAPTORRESEARCH 20 (1): 1-15 2 WAYNEH. W•AI•EY VOI•. 20, NO. 1

LOWER SONORAN LIFE-ZONE

Sonoran Desert 50-1200 m. (a)Ar•zona Upland • (b)Lower Colorado •"• MohaveDesert / Ch•huahuanDesert .'.• H•stor•cald•str•but•on • Presentnesting dJstributmn •

•Ciarkdale (Havesu Wlldl Refuge)

Blythe0

Caclus Natl

50 0 50 I00 kilometers

Figure1. Mapof thehistorical and present distribution of theHarris' Hawk in Arizonain relationto vegetational zones. vation 30-90 m) is primarily a creosotebush-bursage (Larrea- The enters Arizona in a small southeastern Franseria)community and includesthe hottestand mostarid re- sectionof the state,where it liesmostly above an elevationof 1070 gionsin Arizona.This subdivisionis characterized by sandyand m. This relativelycomplex desert is essentially shrubby with many gravellyplains and mesas, sand dunes, lava flows, silty valleys, salt grasses,several small of cacti,and few deserttrees. basins,rocky hills, and desertpavement. The ArizonaUpland Field work was conductedin 1976 and 1977 from January subdivision(elevation 150-1220 m) is typified by a paloverde- throughOctober of eachyear. The Harris' Hawk in Arizonahas saguarocactus (Cericidium-Cereus) association. It attainsgreatest never been observednesting outside the Lower SonoranLife- developmenton therocky soils of desertmountain slopes and on zone, so I eliminated the northern half of the state from the thecoarse soils of upperbajadas that flank mountain ranges. The survey.After a broadgeneral search of the LowerColorado sub- ArizonaUpland subdivisionhas far greaternumbers of plant division,I determined that the Arizona Upland subdivisionwas speciesthan the Lower Coloradosubdivision. themost important area to nestingHarris' Hawks. Hills, windmill The MojaveDesert (elevation 240-1580 m) scarcelyreaches into towers,and otherelevated points were used to locatenests. In flat northwesternArizona. The higheraridity, lack of summerrains countryI usedan 8.5 m extensionladder mounted on thebed and andlonger periods of belowfreezing winter temp cause this desert cabof a pickuptruck which allowed visual clearance above the to be poorer in plant and animallife than the SonoranDesert vegetation. (Lowe and Brown 1973). All nest siteswere plotted on USGS 1:250,000topographic SPRING 1986 HARRIS' HAWK IN ARIZONA 3 quadranglesand seriesmaps. Throughout the populationcon- young/nestwere reported with only 2 parent t•nuumthere were local concentration points and from 2 of these caringfor them. Nestswere often built on top of old populousareas I attemptedto find all activenests to determine totalnesting density. The meandistance between nests was deter- Great Blue Heron (Ardea herodias) nests and were mined by measuringthe distancefrom eachnest and its nearest commonlyonly 3 to 5 m abovewater (Gale Monson neighborusing the distancebetween any 2 nestsonly once. By pets. comm.). A population decline started in the halving the mean distance,a value r (radius)was obtainedand late 1950's and by 1969 the Harris' Hawk disap- usedto determineaverage nesting range sizeby the formula A = r 2 under the assumptionthat nestingranges were circular. I used peared from the refuge. A wild populationhas not only thosenesting ranges that were activein a givenyear. sincebeen observedalong the Colorado River. A Each nest was visited a minimum of twice in order to determine concurrent decline and extinction was noted at Im- numberof eggslaid and numberof youngfledged (in 1976 nests perial National Wildlife Refuge to the south. An werevisited 3 to 5 times).When a clutchappeared small or incom- extensivelist of sourcesconcerning Harris' Hawks plete,a later visitwas scheduled in order to obtaindata for full clutch size. Young were aged by comparisonwith color photo- along the Colorado River is included in Whaley graphsof knownage birdstaken at 5 d intervals. (1979, AppendicesA and B). The Present Population (1976-1977). The RESULTS present Harris' Hawk population in Arizona oc- Distribution and Habitat Characteristics cupies3,880 km2 in Arizona Upland habitat with elevationsranging from 396 to 1,036 meters (X = Past Populations.-- Historically, there were 2 701 m). Lowe and Brown (1973) delineateprime localizedpopulations of Harris' Hawk in Arizona. Arizona upland habitatas the region "... eastthen One populationwas resident in westernArizona in north of a line drawn from Ajo to Tucson to Flor- Lower Coloradohabitat along the ColoradoRiver enceJunction, then northwestto Wickenburg"and from Yuma northward to Topock (Fig. 1). The the Harris' Hawk followedthis distributionclosely Lower Colorado population was extirpated by (see Fig. 1). Nearly all nests were placed in 1969. A secondpopulation approximately 280 km paloverde-saguarocactus habitat or in the more eastward in Arizona Upland habitat (Fig. 1) re- local narrow strips of blue paloverde-ironwood mainstoday. The 2 localitiesare separatedby a dry, (Circidiumfloridum-Olneya)habitat of the large ar- barren expanseof the Lower ColoradoDesert. royos.Three exceptionswere nestsplaced in large The earliest record for Harris' Hawk in Arizona cottonwoodtrees in riparian communitiesthat were wasreported near Topock by Kennerly(1859). The juxtapose to the aforementioned habitat. No nests Lower Colorado populationlikely originatedfrom were found, nor birds seen, in riparian com- Baja , extendingits range into the United munities along rivers that were not associatedwith Statesalong suitable segmentsof the Colorado the Arizona Upland subdivision(Fig. 1). River (Fig. 1). Along the river, nestingsites were near small lakes, lagoonsand swampsin flooded Nest Site Characteristics mesquiteand in willowand cottonwoodtrees (Wiley 1916, 1917; Bancroft 1920; Rowley 1936). Prey Saguarocactus was the preferred plant species items included the Purple Gallinule (Porphyrula used for nest sites(Table 1). Five active nestsand 42 martinica), Sora (Porzana carolina), Common Teal old nestswere placedon electricaltransmission tow- (Anascyanoptera), and Northern Flicker (Colapies ers along a 13.7 km sectionof 110 kV powerline auratus)(Miller 1925, 1930). Gale Monson (pers. crossingpaloverde-saguaro cactus habitat. Another comm.; past manager of Havasu Natl. Wildl. nestwas placed on a toweralong a 345 kV electrical Refuge) included the American Coot (Fulica transmissionline crossingexcellent Harris' Hawk americanus),Muskrats (Andatra zibethicus),Cotton habitat. Rats(Sigrmodon hispidus), and Abert'sTowhee (Pipilo Nest height ranged from 2.3 m [foothill aberti) as food found in nests. Harris' Hawks were paloverde(C. microphyllum)tree] to 21.3 m (electri- frequentlycommon at placesalong the river near cal transmissiontower). The average height for HavasuNational Wildlife Refuge with a resident nestsin saguarocacti, blue paloverde trees, and averageof 30 individual/yfrom 1947-59.As many foothill paloverdetrees was 5.8 m, 6.3 m and 4.4 m, as 50 individualswere often reported, and nests respectively.Seventy-two percent of all nestswere were sometimesless than 0.8 km apart (U.S.D.I. placedin mature saguaro• 4.9 m tall with substan- Fish and Wildlife Service 1952). Generally, 2 tial arms. 4 WAYNE H. WHALEY VOL. 20, NO. 1

Table 1. Harris' Hawk nest sites in 1976 and 1977 in activenesting ranges. On 11 February 1977, I ob- Arizona. served7 copulationsin 2 h, involvinga female and both males at a territory near FlorenceJunction. Polyandrousmating behavior has been previously NUMBER OF PERCENTAGE reported for this species(Mader 1975a). NEST SUPPORT NESTS OF TOTAL Nest Construction. -- Harris' Hawks build or repair nestsfrom January to August. Often one of severalalternate nests is repaired or pairsmay use SaguaroCactus 230 75.2 the same nest several times in succession. Several Foothill Paloverde 37 12.1 Blue Paloverde 23 7.5 nestsmay be repaired and 1 chosenfor use. In 1 Electrical Tower 6 2.0 territory 8 nestswere located, one of which had Cottonwood 3 1.0 been repaired and was ready for eggson 10 Feb- Ironwood 3 1.0 ruary 1977 (copulationobserved on 28 January Mesquite 2 .6 1977). Materials are continuallyadded to nests Pine 1 .3 while eggsand nestlingsare present. Palm 1 .3 Timing of Incubation, Hatching, Fledging. -- Using a 35-d incubationperiod and a 45-d nestling

Totals 306 100.0 period (Mader 1975b),I determinedthe time spans for beginning of incubation,for hatching and for fledging of young (Fig. 2). Eggs were laid from mid-Januaryto mid-August. Fifty percent of all first clutches(N = 284) were laid between 20 Feb- Breeding SeasonPhenology ruary and 22 March (Fig. 2). A portion of clutches Courtship. -- Courtship behavior of Harris' laid during and after April weresecond clutches for Hawksis typicalof mostraptors (Brown and Ama- the givenyear (Fig. 2). don 1968),but on 18 February1977 I noteda very Double or triple clutchesoccurred 61 times in- unusual "group courtship" display involving 8 volving50 (21.6%) of the nestsstudied; 39 (63.9%) adults.The adultsflying at an altitude of 150-180 followed a successfulfirst attempt, and 22 (36.1%) m, continuallyengaged in soaring,tail chasing,and followed an unsuccessfulfirst nestingattempt (X 2 stooping,accompanied by much vocalizing.The = P • .05). Of thosefollowing a successfulbrood, long vertical stoops,which often involved all 8 the time interval between first and second clutches hawks,were followedby tail chasingand eventual averaged106 d. Within 8 nestingranges the short return to their former altitude where the event was interval between clutches(• = 75 d) indicated that repeated.Similar behaviorhas been reported for eggswere laid before the first young had fledged. Eleonora's Falcon (Falco eleonorae)when near the This wasconfirmed within 2 nestingranges. Within breeding cliffs (Brown and Amadon 1968) but is one, 2 eggswere laid in the samenest with a 23 to 25 apparentlyrare in falconiforms.The observedbe- d old chick. In the time interval from fiedg- havior lasted approximately45 min, when the ing of the first attempt to completionof the next adultsdeparted in 3 directions.Later, an activenest clutchwas 28 d (range7-59 d) for 6 secondattempts wastbund in eachof the 3 areaswhere the respec- (Brannon 1980). tive groups appeared to have flown. At 2 of these January egg laying was documentedonly once nests,3 adults were present. during the study period (eggslaid mid-January Copulationsoccurred over a 6-month period 1976).On 12 February 1977 anothernest contain- from 28 January to 26 July. Each copulationbout ing 3 eggswas fbund whichmay havebeen started lasted from 15 to 40 sec. (X = 24 sec, N = 23). in January,but egg-layingor incubationdate could Courtshipbehavior did not alwaysprecede mating; not be determined since the eggsnever hatched. on several occasionsI witnessedcopulations in Whenever pairs commencedlaying of the first whicha maleflew directly to a femaleand copulated clutchearly in the year,3 clutches/breedingseason withoutobvious display by eithersex. More than 1 werelaid duringboth 1976and 1977. adult maleswere observedat manyof the nestsites; Hatching dates for 284 clutchesspanned 8 2 males were recorded at 41% and 3 at 5% of 227 months(mode = April) and fledgingdates spanned SPRING 1986 HARRIS' HAWK IN ARIZONA

7 mo (mode -- May) (Fig. 2). The latestfledging 7) andRed-tailed Hawk (Buteojamaicensis) in 1977 date wasnear 28 October.An extremelylate fledg- and appeared to have little influence on Harris' ing dateof 8 Novemberhas been reported for Har- Hawks reoccupancyof old territory. The Red- ris' Hawks in Texas (Brannon 1980). tailed Hawk usurpationresulted in the Harris' Hawkslocating a new nest160 m from their 1976 NestingDensity and Territorial Fidelity site.

Nestingdensity of Harris' Hawksin Arizona was Productivity 1 nest/2.5km 2 in 1977 for both StudyAreasA andB (Fig. 3). The 'meandistance between nests in both I recorded a total of 396 nesting attempts (in- studyareas was 1.8 km. At 9 locationsactive nests cluding secondand third clutches)involving 306 were only 0.8 km apart, and at 2 locationsactive nestswithin 231 activenesting ranges. In order to nestswere just 0.5 km apart. As a result of the compareproductivity with that from other studies observedclose nesting patterns, I expect that ter- (Mader 1975b; Griffin 1975; Griffin 1976; Bran- ritories overlap. non 1980), a successfulnest was one in which a Territorial attachment seems strongly de- nestlingreached the age of at least28 d. Of 319 veloped. Eighty-four percent of 123 active ter- nesting attempts, 72% were successful.Seventy- ritoriesoccupied in 1976 were reoccupiedand ac- sevennests had incompletedata. Seventy-fivenests tivein 1977.Another 9 territoriesoccupied in 1976 failed during the egglaying and incubationperiod. had adultspresent in 1977but activenests were not Fifteen nestsfailed during the nestlingperiod (2 found. On this basis, Harris' Hawks reoccupied were man-caused, 2 were caused by inclement 91% of 123nesting territories used in 1976.Mader weather, and cause of failure could not be deter- (1982) found that the SavannaHawk ( mined for 11). meridionalis)also has strong territorial attachment Mean clutch size in 1976 was 3.04 (N = 67) and from year to year. 3.22 (N = 95) in 1977 with a combinedmean of 3.16 Eight nestsused by Harris' Hawksin 1976were (N = 162) (clutch size/number of clutches: 1/4, usedby GreatHorned Owl (Bubovirginianus) (N = 2/29, 3/73, 4/51, 5/5) for the studyperiod. Number

letof •wo Clutchel ] •ndoe tlo clutchel onlyone clutch known

47

3?

ii

dAN FEe uln. •pn. UAY dUN JUL AUa FEB u• APe MAY JUN dUL AUG SEPT APR. MAY JUN dUL. AUG. OCT MONTH MONTH MONTH

Figure2. Numberof nestsin relationto (A) monthwhen incubation begins, (B) month of hatchingand (C) month of fledgingfor 284Harris' Hawk nesting attempts in Arizonain 1976and 1977. 6 WAYNEH. WHALEY VOL. 20, NO. 1

Study Area A

Study Area B

¸ o

I 2 5 4 HARRIS'HAWK NESTS:

Kilometers Z•0 19761977

Figure3. Proximityof Harris'Hawk nests in StudyArea A (230km 2 ), containing39 nestingranges with 51 activenests, andin StudyArea B ( 135km2), containing 26 nestingranges with 38 activenests. Large circles containing • 1 symbolindicate 1 nestingrange and are not intendedto delineatethe sizeof a range. of fledglings/nestranged from 1 to 4 (number a 51% lossin productivitybetween egg laying and fledglings/numberbroods: 1/59, 2/75, 3/71, 4/24) fledging,most resulting from eggsfailing to hatch and averaged1.62 young/allattempts (Table 2). (41%, Table 3). Egg losswas recorded for 89 nests, I calculatedproductivity using the more com- 42% due to nest failure (lossof completeclutches) pletedata of 71 nestingattempts of 1976 and com- and 58% due to partial hatching of clutches.A paredthese values with productivityobtained when Texas population had a 41% productivity loss usingthe lesscomplete, but larger samplesize, of (Brannon 1980).At least612 youngfledged during the foregoing.Using only the 1976data, "hatching" the study period. Two hundred twelve nestlings and fledging successwere calculated(Table 3). were banded in 1977. Sex ratio of nestlingswas 1.2 Values obtained for "mean clutch size"and "young •: 1.0 • •. fledged/all attempts"were similar to the corres- Harris' Hawksin sub-adultplumage were found pondingvalues from the largersample. There was to breed occasionally.Ten sub-adultswithin 6 ter- SPRING HARRIS' HAWK IN ARIZONA 7

Table 2. Harris' Hawk nestingsuccess in Arizona, 1976 and 1977.

TOTAL NUMBER NUMBER OF YOUNG FLEDGED OF NESTING SUCCESSFUL NUMBER OF YOUNG FLEDGED PER SUCCESSFUL ATTEMPTS NESTS 1 YOUNG PER ALL ATTEMPTS ATTEMPTS

1976 143 102 (71%) 229 1.60 2.25 1977 176 127 (72%) 289 1.64 2.28 Total nests and young 319 229 (72%) 518 1.62 2.26

1A nestwas considered successful if a chickwas raised to an ageof at least28 days.Only nestswhere adequatefiedging 'data wasobtained appear in the table. ritoriessucceeded in raising7 young.In eachcase can Kestrel (Falcospa,verius) (Craig and Powers the female was a sub-adult. In 3 territories all hawks 1976) and ( regalis) were sub-adults. (Clayton White pers. comm.). Cholla cactus(Opuntia sp.) may also cause mor- Mortality Factors tality in Harris' Hawks.On 26 May 1976 I found a Hatchingsuccess (59%, Table 3) indicatesa high recently fledged Harris' Hawk partially im- mobilized(could not fly and could hardly walk) on eggloss. Laying of infertileeggs, nest abandonment the ground near its nest.Cholla cactusjoints were and destructionby predatorscontributed to re- stuckon its neck and betweenits legs.On another ducedhatching success. Infertility appearedto be occasion I chased down and caught an older the mostcommon cause (e.g., one pair laid 4 eggsin both 1976 and 1977; incubation times were 65 and fledgling that was having difficulty flying and 73 d, respectively,with no hatchingand no embryo development in both years). Forty-sevenyoung died or disappearedfrom nests during the 2-y Table 3. Summaryof productivitydata for 71 Harris' period(7 youngwere taken by man, 5 werekilled by Hawk nestingattempts in Arizona in 1976. man, 5 died of disease, 2 died when a cactus con- taininga nestfell, and 1 died whenit fell from its nest). Cause of death of 27 young could not be RESULTS RANGE determined.Other mortalityfactors for adultsand fledglingswere electrocutions(8 casesreported), Mean clutch size 3.07 1 - 5 and accidentaltrapping of Harris' Hawksby coyote trappers. Young fledgedper 1.63 0 - 4 In 1976 a resident of Owl Head Ranch near Tuc- all attempts son stated that he found a dead Harris' Hawk and Youngfledged per 2.18 1 - 4 other birds floating in the metal livestockwater successfulattempt tanks on his ranch. In July 1978 a deadjuvenile Percenthatching 59 41% productivityloss female Harris' Hawk wasfound floating in a large success (eggsfailed to hatch) livestockwater tank (Larry Livingstonpers. comm.) Percentfledging 90 10% productivityloss not far from where it wasbanded as a nestlingin success (youngfailed to fledge) May 1977. Drowningdeaths may be a significant Percent successful 75 causeof mortality,especially during the dry period nestingattempts (May-June)when livestock tanks are the onlyavail- ablesource for drinkingand bathing. Drownings in Percent unsuccessful 25 water tanks have been documented for the Prairie nestingattempts Falcon (Falcomexicanus) (Enderson 1964), Ameri- 8 WAYNE H. W•ALE¾ VOL. 20, No. 1 keepingits balancewhen landing. The was grip. Survivalof a raptorin suchcondition is ques- obviouslyweakened. I found 2 chollacactus joints tionablesince food would be difficult or impossible claspedin its feet suchthat it couldnot releaseits to obtain.

Table 4. Preyitems observed at nestsof Harris'Hawks in Arizonain 1976and 1977.

NUMBER OF PERCENTAGE SPECIES ITEMS OF TOTAL

Mammals:

Cottontail Rabbit Sylvilagusaudubonii 144 22.4 Harris' Ground Squirrel C itellus harrisii 79 12.3

White-throated Woodrat Neotomaalbigula 76 11.8 Black-tailedJackrabbit Lepuscalif ornicus 9 1.4 Round-tailed Ground Squirrel Citellus tereticaudus 5 0.8

PocketGopher Thomomysbottae 2 0.3 Merriam's Kangaroo Rat Dipodomysmerriami 1 0.2 Banner-tailed KangarooRat D. spectabilis 1 0.2 Arizona Pocket Mouse Perognathus amplus 1 0.2 UnidentifiedLagomorphs 65 10.1 UnidentifiedKangaroo Rats 4 0.6 Unidentified Ground Squirrels 3 0.5 Unidentified Mice 2 0.3

Total 392 61.1

Birds:

Gambel'sQuail Callipeplagambelii 56 8.7 Cactus Wren Campylorhynchusbrunneicapillus 42 6.5 Screech Owl Otus kennicottii 14 2.2

Northern Flicker Colaptesauratus 13 2.0

(Table 4 continued) SPRING 1986 HARRIS' HAWK IN ARIZONA 9

(Table 4 continued)

NUMBER OF PERCENTAGE SPECIES ITEMS OF TOTAL

Elf Owl Micrathenewhitneyi 8 1.2 Mourning Dove Zenaida macroura 6 0.9

Curve-billed Thrasher Toxostoma curvirostre 4 0.6

Gila Woodpecker Melanerpesuropygialis 3 O.5 Road Runner Geococcyxcalif ornianus 2 0.3 American Kestrel Falcosparverius 1 0.2 Cooper'sHawk Accipitercooperii 1 0.2 Unidentified Thrashers 12 1.9

Unidentified Doves 5 0.8

Unidentified Birds 12 1.9

Total Birds 179 27.9

Reptiles:

Desert Spiny Sceloporusmagister 63 9.8 Regal Horned Lizard Phrynosomasolare 2 0.3 Zebra-tailed Lizard Callisaurus draconoides 1 0.2 Western Whiptail Lizard Cnemidophoroustigris 1 0.2 Leopard Lizard Crotaphytuswislizeni 1 0.2 Unidentified 2 0.3

Total Reptiles 70 11.0 Total Number of Prey Items 641 100.0 10 WAYNE H. WHALEY VOL. 20, NO. 1

Food Habits The terminology "continuous breeder" follows Immelmann's (1971) definition that within a A quantitativeanalysis of food habitsin Harris' populationeggs are laid during everymonth of the Hawkswas not possibleduring this study because of year.This isnot the case(as currently known) in the time restraintsimposed by the large number of Arizona population since no egg laying has been nestsbeing observed. Often the only signof occur- recorded for the period October-December. renceof an avianprey specieswas the presenceof Lack (1968) and Immelmann (1971) suggested feathers which denoted little or nothing of the that, since the reproductive period is the most number of individuals taken. Thus I could only rigorousand criticalperiod of a bird'sannual cycle, indicatethat a particularspecies was found. Since it is imperativethat it be scheduledat a time when certainbody parts of largermammals (i.e., hind feet young can most profitably be raised with a of CottontailRabbits [Sylvilagus audubonii] and tails minimum of energyexpenditure on the part of the of Harris' GroundSquirrels [Citellus harrisii]) were adults. A good example, Eleonora'sFalcon of the not eatenand remained in the nestfor long periods Mediterranean region, delaysbreeding until Au- of time, a more accuratefigure for the number of gust when it can feed its young on the numerous these speciestaken could be obtained.The food passerinesin fall migration (Walter 1979). Eleon- datapresented represents a qualitativestudy of the ora's Falconsfeed mainly on insectsduring the re- entirepopulation, which may provide some idea of mainder of the year. the total gamut of prey speciestaken throughout Harris' Hawks seemto follow a similarpattern, as the Harris' Hawk populationin Arizona. they breed during periods of great prey abun- Harris' Hawks are quite catholic in feeding dance.Breeding starts quite early in Arizona. Incu- habits. Twenty-five vertebrate specieswere re- bationbegins in Februaryand March and hatching corded (Table 4), of which 61.1% were mammals. occursprimarily in April (Fig. 2). Prey speciesalso Brannon (1980) found 65.6% of Harris' Hawk prev exhibit long breeding seasonsin Arizona. Harris' in Texas to be mammals. Cottontail Rabbit appear Ground Squirrelbreeds from late Februaryto May to be importantin the diet, carcassesat timescov- with its conceptionperiod running from :31March eringthe entiretops of nests.At onenest, pairs of to late May (Neal 1965). On this basis,Harris' hind feet indicatedthat at least22 lagomorphshad Ground Squirrelsare beingborn whenthe majority been taken. Harris' Ground Squirrels, White- of Harris' Hawk eggsare hatching.Cottontail Rab- throated Woodrats (Neotomaalbigula), Gambel's bits breed year-round in Arizona with peaks for Quail (Callipeplagambelii), and CactusWrens (Cam- conceptionstarting in April (peak hatch time for pylorhynchusbrunneicapillus) also appear to be im- Harris' Hawks) and running through July portant in Harris' Hawk diets in Arizona. Four (Hungerford, Lowe and Madsen 197:3). The raptors, ScreechOwl (Otiskennicottii), Elf Owl White-throated Woodrat has successive litters from (Micrathenewhitneyi), Coopers' Hawk (Accipiter January to August (Vorhies and Taylor 1940), cooperii),and American Kestrel (Falcosparverius) which spansthe time during which most Harris' were taken. Hawks are breeding. Thus, local abundanceand long breeding seasonsof prey speciesmay be an DISCUSSION important facilitatory factor for an extended breeding seasonof Harris' Hawks in southern Phenologyof the BreedingSeason Arizona. Harris' Hawksin Arizonamay lay eggsas early as Severalother prey speciesthat havelong breed- January(Ellis and Whaley 1979) and sometimesing seasonsare Gambel'sQuail (March to Sep- fledge young as late as December(Radke and tember, Bent 19:32),Cactus Wrens (raise :3broods Klimosewski1977) which gives them the distinction from Februaryto August,Anderson and Anderson of havingthe longestknown "breeding season" (as 1960), Curve-billed Thrasher (Toxostomacu,virostre) definedby Moreau1950) of anytemperate North (Februaryto July, Smith 1971), and Mourning American falconiform. In , Mexico (27 Nø), Dove (Zenaidamacroura) (March to September, eggsare evenlaid in November(Ellis and Whaley Brown 1967). The Harris' Hawk's catholicprey 1979),suggesting that there are continuousbreed- habitson specieswith long reproductiveperiods ers in somesouthern parts of the SonoraDesert. may have contributedto the developmentof an SPRING 1986 HARRIS' HAWK IN ARIZONA 11 extended breeding seasonand increasedproduc- females each laid 16 eggsduring the 2-yr period. tivity through double brooding. One of theselaid 4 clutchesof 4 eggs,all but one of When the environmentpermits a speciesto raise which was in the same nest. • 1 brood/yr, breedingbegins as early as possible FledgingRate. -- Productivityof Harris' Hawks eventhough the timing of the first attempt may be in Texas is lower than for Arizona and less favorable (Lack 1968). A speciesusing this populations.Mader (1975) found that 1.60 young strategy would tend to produce the maximum fledged/allattempts (N -- 50) and 2.35 fledged/suc- number of offspring under the prevailing cir- cessfulattempts (N = 34), whichcompares well with cumstances(Lack 1954). Harris' Hawksmay follow my results for Arizona (Table 2). Griffin (1975) thisstrategy, as second and third breedingattempts reported similar resultsfor New Mexico, with 1.59 appear to be influencedby an early first attempt (N = 17) and 2.45 (N = 11) young/attemptand (Fig. 2). The outcome(i.e., successor failure) of the young/successfulattempt, respectively. Griffin first breedingattempt appearsto be lessimportant (1976) reportedvalues of 0.83 (N = 18) and 1.87(N than timing. Of femalesthat laid doubleand triple = 8) young/attemptand young/successfulattempt, clutches,97% of the first breeding attemptswere respectively,for western Texas. Brannon (1980) startedbefore April, the majoritybeginning in Feb- reported similar resultsof 1.37 (N = 24) and 2.06 ruary. The only January laying represented the (N = 16) for young/attemptand young/successful first of 3 clutchesproduced in 1976 by a trio of attempt for west Texas populations. Lower pro- adultswhich fledged 5 youngfrom two of the three ductivityin Texas populationsis likely due to grea- attempts. Without subsequentnesting, their pro- ter fluctuationsin prey abundance(Griffin 1976) ductivityfor 1976 wouldhave been just 2 young. and lessdiversity in prey species.Texas populations Within 6 other territories high productivity was are more nomadic,as year to year shiftsin breeding attained through extra breeding attempts.Adults distributionsoccur in accordancewith rainfall pat- in 4 territoriesproduced 6 and thosein 2 territories terns and prey abundance. produced 7 young/yr. Most of the clutcheslaid from June to August were secondand third at- Dispersalof Young and Nest Helping tempts (Fig. 2). An early laying pair of Harris' Harris' Hawks in Arizona are nonmigratory. Hawks in Texas produced 7 young during 3 suc- Early reportsof large migratoryflocks (250 to 500) cessfulnesting attempts in one season(Brannon (Chambers 1921 and 1924; Allan Phillips pers. 1980). Triple clutchesin 1 seasonhave been re- comm.)are unreliable,and likely the result of mis- ported 3 times previously for Harris' Hawks identification since Harris' Hawks in Arizona have a (Mader 1977; Whaley 1979),but in all casesonly 2 long breeding seasonwhich affords no time for of the 3 attempts were successful.Harris' Hawks migration. begin egg laying earlier in Arizona than in Texas (seeBrannon 1980), where clutchesare started in Harris' Hawks occasionally wander during winter, but generallyremain near or within their March and April. nesting ranges year round. Families often re- mained together. On 2 occasionsI saw winter Productivity groupsof 7 and 8 hawkscomprised of adultsand Clutch Size. -- Mean clutch size for Harris' Hawk color-markedjuveniles. Wilder (1916) also noted populationsin thisstudy was 3.16 (N = 162) with 4 large winter groupsof 10 to 20 hawksalong the and 5 eggs/clutchregularly laid. Four eggs/clutch Colorado River in December. are not uncommon for Harris' Hawks in Texas Juvenilesdo not exhibit a strong tendency to (Griffin 1976) and Arizona (this study) whereas disperse from the natal area. On 10 November alongthe ColoradoRiver 2 eggs/clutchare the rule 1977 two color-marked Harris' Hawks were (Bendire 1892). Mader (1975b) obtained an aver- trapped lessthan 0.4 km from where they fledged age of 2.96 eggs/clutch(N = 50) for Arizona, and ca. 173days earlier (Rich Glinski pers. comm.). On Griffin (1976) calculatedan averageof 2.85 eggs/ 9 occasionswithin those1977 nestingranges where clutch (N = 20) for western Texas. South Texas nestingoccurred twice in 1 year, color-marked populationsappear to have a smallerclutch sizeof juvenilesof earlier nestingattempts were allowed 2.33 eggs/clutch(N = 24) (Brannon 1980). Some within the immediatevicinity of, and often on the femalesin my studywere exceptionalegg layers;3 nest containingeggs or young of subsequentnest- 12 WAYNEH. WHALEY VOL. 20, No. 1 ing attempts.Those juveniles often seemedas con- 1940's.With flooding controlled, agricultural ac- cerned about my presenceas the adults. On 22 tivitiesalong the river increased.By the 1930'sand occasionsin 1976 unmarkedjuveniles which were 1940's,salt cedar (Tamarixpentandra) spread over likelystill in natalranges were sighted near active large areasof the river and began to competewith nests. the cottonwoodcommunity which was rejuvenating On 24 September1977, while preparing to band from pastfloods. Dredging operations began along 3 youngfrom a secondnesting (the firstbrood of 3 the river during the 1940'sand may have been a young fledged ca 120 d earlier), a color-marked sourceof disturbance.Previously inaccessible areas female from the first brood brought prey to the of the swampwere now accessibleby motor pow- nest. Also, on 3 occasionsin 1979 Brannon (1980) ered craft so subsequentlythere wasincreased use observedprey deliveriesby juveniles to the nestsof of the river for recreationalactivities during the their parents' secondbreeding attempts. On 12 1950's(Gale Monsonpers. comm.). At HavasuNa- May 1977 two juveniles that had fledged 2 or 3 tional Wildlife Refuge, where Harris' Hawks often weeksearlier were observedincubating 3 eggsof nestedlow over the waterin drownedout mesquite their parents' second clutch. Nest-helping by trees, increasedrecreational activities may have juvenilesfledged earlier the sameseason has not been a major factor during the nestingperiods. been previouslyreported in raptors. The helper Fishermenwere seendestroying nests, probably systemof the Harris' Hawk mayprove to be similar under the mistakenimpression of destroyingCor- to that of the Florida Scrub Jay (Aphelacomamorant (Phalacrocorax sp.) nests (Gale Monson pers. coerulescens)(Woolfenden 1975). Young of comm.). Harris' Hawks were occasionallyharassed GalapagosHawk (Buteogalapagoensis) also remain by duckhunters who often referred to them as,"the near the natal area for severalmonths after fiedg- big black hawk that catchesducks" (Miller 1925). ing and occasionallyretain closeties with their pa- Monsonreported that Harris' Hawk numberswere rents (de Vries 1973). On 1 occasionde Vries wit- sometimesslightly depleted by waterfowlhunters nesseda 5-month-oldjuvenile still begging food in the open areasabove Topock (U.S.D.I. Fishand from the male parent while the female was in- Wildlife Service 1949). cubatingeggs of a secondnesting attempt. A combinationof the abovefactors likely had an Harris' Hawks do not appear to dispersegreat impacton Harris' Hawk populationsalong the Col- distancesfrom their natalarea over long periodsof orado River. Drastic habitat alteration and in- time. Basedon 13 band returns,sightings and cap- creasedrecreational activities perhaps yielded the ture-releases,juveniles (• 5 months fledged) greatestimpact. traveledan averagedistance of 15 miles(range ( 5 milesfor a male during 3 yearsand 30 milesfor a The Present Population female during 6 months). On 20 May 1977 I Qualitatively,the most obviouscharacteristic of banded a male nestling near Florence Junction. Harris' Hawk habitatin Arizona is the presenceof The samemale wastrapped in its nestingterritory healthystands of paloverde-saguarodesert scrub of nearly8 yrs later on 12January 1985 (Jim Dawson the Arizona Upland subdivision.The presentdis- pers. comm.) 35 miles south of where it had tribution of Harris' Hawks in Arizona strictlyfol- fledged. lowsthe Arizona Upland subdivisionof the Sono- ran Desert with no nests occurring outside this PastPopulations of the ColoradoRiver habitat. Thus, this hawk habituates the most struc- The Harris' Hawk wasa common resident along turally complexhabitats within the SonoranDesert, the Colorado River for at least 134 years. The where prey densityand diversityis the greatest. populationdid not range far from the riparian The nestingdistribution of the Harris' Hawk in community(U.S.D.I. Fish and Wildlife Service Arizona has shrunk sincethe early 1900'sdue in 1950); thus, events that may have affected this part to the extirpation of populationsalong the habitatmay also have impacted the Harris'Hawk Colorado, Gila, Santa Cruz, and San Pedro Rivers. populationsin that region. Extensiveflooding Along the Gila and Santa Cruz habitat has been alongthe Colorado River in theearly 1900's evoked severelyaltered (Dawson 1921;Rea 1977). In order construction of several dams in the 1930's and to determine susceptabilityof the presentpopula- SPRING 1986 HARRIS' HAWI• IN ARIZONA 13

Table 5. Land ownershipstatus for 306 nestsites and 396 nestingattempts for Harris' Hawk in Arizonain 1976 and 1977.

LAND NUMBER OF PERCENTAGE NUMBER OF PERCENTAGE OWNERSHIP ACTIVE NESTS OF TOTAL NESTING ATTEMPTS OF TOTAL

State Trust Land 140 45.8 184 46.5 Patented Land 73 23.9 84 21.2 BLM Land 40 13.0 57 14.4 Forest Service 18 5.9 24 6.0 Indian Reservation 18 5.9 23 5.8 Patented or State 7 2.3 10 2.5 BLM or State 5 1.6 8 2.0 RegionalPark 3 .9 3 .8 U.S. Park 2 .7 3 .8

Totals 306 100.0 396 100.0

tion to possible habitat encroachment, I deter- thank other members of my committee, David H. Ellis and mined land ownership statusfor 306 active nest StephenM. Russell,for their guidance.I expressappreciation to my field assistants,JerryRoberts, Greg Depner and Kevin Coates, sites(Table 5). A large proportion of nestsare on for their determination when things got rough. I thank the patentedland, and thereforeare more vulnerable Havasu National Wildlife Refuge and Imperial National Wildlife to the effectsof man'spresent and future activities. Refuge for accessto their files. SeveralArizona falconersand Sincethe Harris' Hawk appearsto be habitat re- private individualsprovided field assistance,for which I express appreciation.Eleanor Radke provided some color-marking mate- strictedin itsnesting, the retentionof bothstate and rial and bandingassistance. federal lands with healthy stands of paloverde- I am especiallyindebted to my wife, Connie, for her patience saguarowill be crucial for its future welfare in during my extendedabsences while gathering field data. Arizona. Urban sprawlnear severalHarris' Hawk populationsmay resultin continuedloss of nesting rangein Arizona. Harris' Hawk numbersnear Tuc- son and Cave Creek have declined recently as a LITERATURE CITED result of urban development. The Cave Creek ANDERSON, A.H. AND A. ANDERSON. 1960. Life histories population is currently threatened due to urban of the CactusWren. pt. 3: the nestingcycle. Condor sprawl and may soon be decimated (Jim Dawson 62:351-369. pets.comm.). Other habitatsthat are threatenedby ARNOI.D, L.W. 1954. The GoldenEagle and its economic urban development are in areas near Rio Verde, status.U.S. Fishand Wildl. Serv.,Circ. No. 27.35 pp. ApacheJunction, and Florence. BANCROFT,G. 1920. The Harris' Hawk as a breeder in California. Condor 22:156.

ACKNOWLEDGMENTS BENDIRE, C. 1892. Life histories of North American birds.2 vols.U.S. Natl. Mus. Spec.Bull. No. 1. 446 pp. Researchwas conductedas part of the M.S. degree require- BEST, A.C. 1932. Life histories of North American Gal- mentsat the Arizona CooperativeWildlife ResearchUnit (AC- linaceousbirds. U.S. Gov. Print. Office. 490 pp. WRU) of the Universityof Arizona.The ACWRU is sponsored BERGER, D.D., C.R. SINDELAR AND K.E. GAM- jointly by the Universityof Arizona,the U.S. Fishand Wildlife Service,the ArizonaGame and FishDepartment, and the Wildlife BEE. 1969. The statusof breeding Peregrinesin the ManagementInstitute. easternUnited States.Pages 165-173 in J. J. Hickey, I thankLyle K. SowIs,leader of theArizona Coopertive Wildlife ed. PeregrineFalcon populations: their biologyand ResearchUnit, for his guidancethroughout this project.I also decline.Univ. of Wis. Press,Madison. 596 pp. 14 WAYNEH. WHALEY VOL. 20, No. 1

BRANNON,J.D. 1980. The reproductive ecology of a IMMELMANN,K. 1971. Ecologicalaspects of periodicre- Texas Harris' Hawk ( unicinctus harrisi) production.Pages 341-389 in D.S. Farner and J.R. population. M.S. Thesis, Univ. of Texas, Austin. 56 King,eds. Avian Biology. Vol. 1. AcademicPress. New PP. York, N.Y. 586 pp. BROWN,L. AND D. AMADON.1968. ,hawks and KENNERLY,C.B.R. 1859. Report of birdscollected on the falcons of the world. McGraw-Hill Book Co. New route.Pages 19-35. Zoological Report No. 3 in Reports York, N.Y. 945 pp. of explorationand surveysfor a railroad route from BROWN,R.L. 1967. The extentof breedingby immature the MississippiRiver to the Pacific Ocean, Part 6. Mourning Doves (Zenaiduramacroura marinella) in Route near the thirty-fifth parallel,explored by Lt. southern Arizona. M.S. Thesis. Univ. of Ariz., Tucson. A.W. Whipple, War Dept. Wash.D.C., vol. 10. 56 pp. LACK,D. 1954. The natural regulationof animal num- CHAMBERS,W.L. 1921. A flightof Harris' Hawks.Condor bers. Oxford Univ. Press (Clarendon) London and 23:65. New York. 343 pp. 1924. Another flight of Harris' 1968. Ecological adaptations for Hawks. Condor 26:75. breedingin birds. Methuen and Co. LTD, London. COTTAM,C., D.A. MUNRO,R.H. POUCH,H.A. HOCHBAUM, 409 pp. R.A. MCCABE,I.N. GABRIELSON.1961. Report to the LowE, C.H. 1976. The vertebrates of Arizona. Univ. of AmericanOrnithologist's Union by the committeeon Ariz. Press,Tucson. 270 pp. bird protection.Auk 79:463-478. LOWE,C.H. ANDD.E. BROWN.1973. The naturalvege- CRAIG,Y.H. ANDL.R. POWERS.1976. Raptor mortality tation of Arizona. A.R.I.S. Coop. Pub. No. 2.53 pp. due to drowning in a livestockwatering tank. Condor MADER,W.J. 1975a. Extra adultsat Harris' Hawk nests. 78:412. Condor 77:482-485. DAWSON,W.L. 1921. The seasonof 1917.J. Mus. Comp. 1975b. Biologyof the Harris' Hawk in Ool. Santa Ba•bara, California. 2 (1/2):27-36. southernArizona. Living Bird 14:59-85. DE VR•ES,T. 1973. The GalapagosHawk: an ecogeo- 1977. Harris' Hawks lay three graphical study with special reference to its sys- clutchesof eggsin one year.Auk. 94:370-371. tematic position. M.S. Thesis. Free Univ. of Amster- 1982. Ecologyand breedinghabits of dam. 108 pp. the in the Llanos of Venezuela. Condor ELLIS, D.H. AND W.H. WHALEY. 1979. Two winter 84:261-271. breedingrecords for the Harris' Hawk. Auk 96:413. MILLER, L. 1925. Food of the Harris' Hawk. Condor ENDERSON,J.H. 1964. A study of the Prairie Falcon in 27:71-72. the CentralRocky Mountain Region. Auk 81:332-352. 1930. Further notes on the Harris' GRIFFIN,C.R. 1976. A preliminarycomparison of Texas Hawk. Condor 32:210-211. and Arizona Harris' Hawks (Parabuteo unicinctus) MOREAU,R.E. 1950. The breeding seasonsof African populations.Raptor Res. 10:50-54. birds. 1. Land birds. Ibis 92:223-267. GRIFFIN,R. 1975. Reproductiondata on sixteenHarris' NEAL, B.J. 1965. Reproductive habits of round-tailed Hawk nestsin southeasternNew Mexico. (Compiled and Harris' antelope ground squirrels.J. . during summer of 1975). MS available from: En- 46:200-206. dangeredSpecies Program, N.M. Dept. of Game and PETERSON,R.T. 1969. Populationtrends in Ospreysin Fish, Santa Fe. the northwesternUnited States.Pages 333-337 in J.J. HECTOR,D.P. 1975. The habitat,diet and foragingbe- Hickey, ed. PeregrineFalcon populations: their biol- havior of the Apolmado Falcon (Falcofemoralis).M.S. ogyand decline.Univ. of Wis.Press, Madison. 296 pp. Thesis, Oklahoma StateUniv., Stillwater. 189 pp. PHILLIPS,A., J. MARSHALLAND G. MONSON.1964. The HENNY,C.J. AND H.M. W•6HT. 1972.Population ecology birdsof Arizona.Univ. of Ariz. Press,Tucson. 212 pp. and environmental pollution: Red-tailed and RADKE,E.L. ANDJ. KLIMOSEWSKI.1977. Late fledging Cooper'shawks. Pages 229-250 in Populationecology date for Harris' Hawk. Wilson Bull. 89:469-470. of migratory birds: a symposium. U.S. Dept. of REA,A.M. 1977. Historicalchanges in the avifaunaof Interior Wildl. Res.Report No. 2. 278 pp. the Gila River Indian Reservation, central Arizona. HENSLEY,M. M. 1959. Notes on the nestingof selected Ph.D. Thesis.Univ. of Ariz., Tucson.346 pp. speciesof birds of the SonoranDesert. Wilson Bull. ROWLEY,J.S.1936. Noteson somenests found in eastern 71:86-92. RiversideCounty, California. Condor38:219. HUNGERFORD, C.R., C.H. LOWE AND R.L. MAD- SELLERS,W.D. 1960. The climate of Arizona in Arizona SEN. 1973. Populationstudies of the desertcottontail Climate.Univ. of Ariz. Press,Tucson. 616 pp. (Sylvilagusandubonii) and black-tailedjackrabbit (Lepus S•t•TH, E.L. 1971. The effects of heat and aridity on californicus)in the SonoranDesert. DesertBiome, U.S. reproductive successof the Curve-billed Thrasher. Intern. Biol. Program, Res.Mem. 73-20. 15 pp. Ph.D. Thesis.Univ. of Ariz., Tucson. 55 pp. SPRING 1986 HARRIS' HAWK IN ARIZONA 15

SPRUNT,A. 1969. Populationtrends of the Bald Eaglein WALTER,H. 1979. Eleonora's falcon. Univ. Chicago North America. Pages347-351 in J.J. Hickey, ed. Press. Peregrine Falcon populations: their biology and de- WI-IALE¾,W.H. 1979. The ecologyand statusof the Har- cline. Univ. of Wis. Press,Madison. 596 pp. ris' Hawk (Parabuteounicinctus) in Arizona. M.S. Thesis U.S.D.I. Fis I-i AND WILDLIFE SERVICE. 1949. Univ. of Ariz., Tucson. 119 pp. September-DecemberQuarterly Narrative Report, WILDER, H.E. 1916. Some distributional notes on HavasuNational Wildlife Refuge.Located at: Refuge California birds. Condor 18:127-128. Hdqtrs., Topock, Arizona. WILEY,L. 1916. Bird notesfrom Palo Verde, Imperial U.S.D.I. FISH AND WILDLIFESERVICE. 1950. January- County, California. Condor18:230-231. April Quarterly Narrative Report, Imperial National 1917. Nestingof the Harris' Hawk in Wildlife Refuge. Locatedat: Refuge Hdqtrs., Mar- southeastern California. Condor 19:142. tinez Lake, Arizona. WOOLFENDEN,G.E. 1975. Florida ScrubJay helpers at U.S.D.I. FISH AND WILDLIFESERVICE. 1952. January- the nest. Auk 92:1-15. April Quarterly Narrative Report, Havasu National Wildlife Refuge. Locatedat: Refuge Hdqtrs., To- Arizona CooperativeWildlife ResearchUnit, 214 Biological pock, Arizona. SciencesBldg., University of Arizona, Tucson, AZ 85721. VORHIES,C.T. ANDW.P. TAYLOR. 1940. Life historyand Present address:Dept. of Zoology, 574 WIDB, Brigham ecologyof the white-throatedwood rat (Neotomaal- Young University, Provo, UT 84602. bigula albigula) Hartley, in relation to grazing in Received25 April 1985:Accepted 15 August 1985 Arizona. Univ. of Ariz. Agr. Exp. Sta. Tech. Bull. No. 86:455-529.