Spring1982 Merchant--HuntingRelationship 27

On 6 occasionsthroughout January and February1980, I saw Prairie Falconsapparently hunting close to activelyhunting Harriers. On theseoccasions, I saw a Harrier hunting over open grasslandand cultivated grainfieldsin their typical low flying manner,while a Prairie Falconflew approximately30-50m aboveand 50-100mbehind. As the Harrier coursedacross the fields,the accompanyingfalcon stooped on risingbirds whichwere flushedby. the hawk. AlthoughI sawneither take prey, the associationappeared deliber- ate, Bourne (1960) and Watson (1977:92)observed similar relationshipsbetween the Hen Harrier (C. c. cyaneus)and Merlin (F. columbarius). Theseincidents may be an exampleof a behavioralsymbiosis. Prairie Falconsoften capture prey that flushesout in front of them (Enderson1964). However, potential prey in goodcover is oftenhesitant to flush due to the falcon'sflying ability. Conversely, the Harrier'slow flight patternand longlegs enable it to most effectivelycapture prey on, or very closeto, the ground(Watson 1977:87). For avian prey, the apparentre- sponseto a Harrieroverhead would thus be to flushahead of the hawk.It is apparentthen, that a PrairieFal- concould facilitate its ownhunting by utilizinga huntingHarrier asa flusher.By huntingin associationwith a Harrier, a Prairie Falcon may actually increaseits encounterrate with prey items. The benefit which the Harrierreceives from thisrelationship is lessapparent. Perhaps the hawkbenefits by takingbirds which are hesitantto flushin the presenceof the falcon.

Literature Cited Bourne,W. R. P. 1960.A huntingpartnership between two birdsof prey.Ibis: 102:136. Enderson,J. H. 1964.A studyof the prairiefalcon in the centralRocky Mountain region. Auk 81:332-352. Watson,D. 1977.The Hen Harrier.T. andA.D. Poyser,Berkhamsted. 307 pp.

FOOD OF THE SPOTTED IN by PhillipW. Wagner Utah Division of Wildlife Resources SaltLake City, Utah 84116

Cad D. Marti Departmentof Zoology WeberState College Ogden,Utah 84408 and

Thomas C. Boner Utah Division of Wildlife Resources SaltLake City, Utah 84116*

In thispaper we reporta sampleof preyof the MexicanSpotted Owl (Strixoccidentalis lucida) from south- ern Utah.Food habits of thisspecies are poorlyknown compared to manyother North Americanowls (Ear- hart and Johnson1970). Diet of the Mexicanrace is leastwell known.A few casualrecords are availablefrom Arizonaand (Huey 1932, Ligon 1926) but onlyseven prey individuals were previouslyreported for Utah (Kertell1977). Forsman (1976) and Barrows(1980) have reported the onlycomprehensive analysis of SpottedOwl foodsfrom (S. o. occidentalis)and California(S. o. caurina),respectively. Reports of other,mostly very small collections of prey, were reviewedby Barrows(1980) and Zarn (1974). The SpottedOwl is listedas a rare permanentresident in Utah (Behleand Perry1975) and is foundin habi- tatsvery different than the dense,old growthforests occupied by otherraces. Kertell (1977)felt that coolre- treatswere necessaryfor roostingand nestingin the hot summersof southernUtah; theseare found in nar- row, steep-walledcanyons.

*Presentaddress: 2215 S. Latah, Boise,Idaho. RaptorResearch 16(1):27-28 28 RAPTOR RESEARCH Vol. 16, No. i

In view of the differencein habitat,comparative studies of the 3 racesof SpottedOwl couldprove valuable in terlnsof trophicdivergence. Accordingly, we presenthere additionalfood data for the Mexicanrace. Even thoughthis sampleis limited in size and locality,some interesting comparisons are possiblewith diets of SpottedOwls from otherareas. SpottedOwl pelletswere collectedin 1977from below roostsin Capitol Reef NationalPark, Utah, where SpottedOwls were observed.The collectionsite was a deep,narrow sandstone canyon. Water in this,and the maincanyon it adjoins,was ephemeral. Vegetation in the canyonbottom was a mixtureof grasses,forbs, cacti and sparselyscattered boxelder (Acer negunda), cottonwood (Populus spp.) and bigtoothmaple (A. grandi- dentatum)trees. Vegetation on the plateauabove the canyonwas dominated by Utah juniper (Juniperusos- teosperma), pinyon (Pinusedulis) and mixture of shrubs(Shepherdia, Cercocarpus and Ephedra spp.).Prey identified are presentedin Table 1.

Table 1. Preyof the SpottedOwl from southernUtah.

Percent

Preyspecies Number frequency

Antrozouspallidus 1 0.9 Peromyscusspp. 16 15.2 Neotoma cinerea 14 13.3 Neotomalepida 53 50.5 Neotomaspp. 9 8.6 Orthoptera 1 0.9 Arachnida(scorpion) 1 0.9 unidentified invertebrates 10 9.5

Total 105 100.0

In California(Barrows 1980) and Oregon (Forsman 1976), nearly all preywas characteristic of foresthabi- tats.Interestingly, even though the habitat in southernUtah is very different, consisting of desertcanyons and plateaus,the majorprey was woodrats (Neotoma spp.) as it wasin California.Woodrats ranked second overall in diet biomassof OregonSpotted and were the mostimportant prey in drier habitatsthere. Fewer mammalianspecies occurred in the Utah diet and no birdswere found.These differences could be attribu- tableto the smallersample size from Utah. Obviously, much more study is neededto elucidatethe feeding ecologyof thisspecies in the distinctlydifferent areas of its distribution. We thankJerry Hocklenback for collectingsome of the pellets.

LITERATURE CITED Barrows,C. 1980.Feeding ecology of the Spottedowl in California.Raptor Res. 14:73-78. Behle,W. H. andM. L. Perry.1975. Utah . Utah Mus.Nat. Hist.Salt Lake City. Earhart,C. M. and N. K. Johnson.1970. Size dimorphism and foodhabits of North Americanowls. Condor 72:251-264. Forsman,E. 1976.A preliminaryinvestigation of the Spottedowl in Oregon.M.S. Thesis,Oregon State Univ., Corvallis. Huey,L. M. 1932.Note on the foodof an ArizonaSpotted owl. Condor34:100-101. Kertell,K. 1977.The Spottedowl at Zion NationalPark, Utah. WesternBirds' 8' 147-150. Ligon,J. s. 1926.Habits of the Spottedowl. Auk 43:421-429. Zarn,M. 1974.. Habitat Manage. Series Unique Endangered Species No. 10,Bur. Land Manage., Denver.