Vol.59'] MARSHALLAND LEATHAM, Birds o[ GreatSalt Lake Islands 35 194 '• a BIRDS OF THE GREAT SALT LAKE ISLANDS BY WILLIAM H. MARSHALL AND LYNDON j. LF_•r•AM T•. nestingcolonies of birdson theislands of GreatSalt Lake, Utah, arejustly famous and havereceived considerable ornithological atten- tion. Suchpublications as those of Behle(1935), Woodbury and Behle (1933),Palmer (1916),and Cottamand Williams (1939),deal almost exclusivelywith theserookeries. Little hasbeen published on non- colonialbirds of the islandssince Ridgway (1877)visited certain of them in 1869. During the summerof 1938, field work for the U.S. Bureau of BiologicalSurvey provided an opportunityto obtain noteson birds of all the islands. Although the lists differ little from those for the mainland,they are of interestfrom severalpoints of view, as for comparisonwith Ridgway'slists of 1869,for the completecounts of individuals on certain small islands, and for the correlation of bird occurrenceswith certainhabitats. Most of the notesrepresent sight records,though, as indicatedin the lists,all birds of doubtful field identification were collected. Acknowledgmentsare due to Dr. D. I. Rasmussen,of the Biological Survey,and to Lee Kay, Utah Fish and GameCommission, for initiat- ing the seniorauthor's interest in the islandson the annual bird- colonycensus of 1937,when Bird and Gunnison Islandswere visited; to ProfessorT. C. Adams,of the University of Utah, who provided the data on acreagesof the islands;and to A.D. Smith, of Utah StateAgricultural College, who identifiedmany of the plantsfound. Specimensprepared, as indicatedin the lists, were identifiedby Drs. H. C. Oberholserand ClarenceCottam in Washington,D. C. Text-figure1 indicatesthe placesand datesat which observations were made. Work in the field out of camp usmdlyamounted to at least eight hours,and, of course,all daylight hours spent in camp providedsome opportunities for taking notes. Marshall visitedall the islands except Gunnison in 1938, and was on that island in 1937. Leatham was on Stansbury,Carrington, and Bird Islands. E. O. Chatelain and R. J. Jansen,undergraduate students at Utah State College,were on Dolphin and Fremont Islands,respectively. A brief discussionof the islandsas bird habitats may be of value in presentingthe situation. It mustbe clearlystated that Gunnison is the only area that hasbeen an island,in a strictsense of the word, continuouslysince 1850 (Adams, 1938). This fact is probably of small significance,however, to birds other than colonial nesters. 36 MARSHALLAND LEnTSriM, Birds o[ GreatSalt Lake Islands ]'Auk I. Jan. The habitatsagree somewhat with thosediscussed by Linsdale (1938). The geologicbasis of these,obvious in the field, suggeststhe follow- ing designationsthat are usedin the text. (1) Sand bars:-fringes of sand depositedaround each island to 0o! TEXT-FIe.1.--Map of Great Salt Lake, Utah. the height of about fifteenfeet abovethe salt flats. Theseare water depositsof recentyears. The abundantplants are Sarcobatusvermic- ulatus and Atriplex con[erti[olia, with ½hrysothamnusnauseosus, Oryzopsishymenoides, Artemisia spinescens,DistichIls stricta, and Donaliaspp. also found in scatteredspots. One area of high and apparentlywind-deposited sands on Stansburysupported a grove of Juniperusutahensis. Vol.59'] MARSHALLAND LEATHAM, Birds of GreatSalt Lake Islands 37 194• a (2) Benchlands(Gilbert, 1890):--graveldeposits at variouslevels oœ ancient lakes that support chiefly Artemisia tridentata and (or) Bromustectorum, although a wide variety oœother plants alsooccurs; œromindications on CarringtonIsland such bunch grasses as Or•zopsis hymenoides,stipa comata,and Agropyron•_picatum may have been more abundantbeœore recent fires and heavywinter useby domestic sheep. (3) Original islands:-areason Stansburyand AntelopeIslands that wereabove the highestlevel oœLake Bonneville. Theseareas support extensivegroves oœ the mountain mahoganies(Cercocarpus montanus and C. ledi[olius)as well as someJuniperus utahensis and a few Pseu- dotsugataxi[olia (one small ravine on Stansbury). Rhus trilobata, Agropyronspicatum, and Astragalusspp. were also commonon the highestareas. (4) Springs:--œresh-watersprings are foundonly on AntelopeIsland, whereAcer negundo,Populus nigra vat. italica,Salix spp.,and a five- acre field oœalfalfa are maintainedby irrigation. This is the only permanenthuman habitation on the islands,and was usedas a base by Ridgwayin 1869,as well as by the seniorauthor in 1938. Acer glabrum, Salix spp., Rumex crispus,Urtica spp., and other plants grow in the non-utilizedspring areas. Brackishsprings on the shores oœAntelope, Stansbury, and Fremont Islandssupport dense growths oœDistichlis stricta and Scirpuspaludosus. AntelopeIsland is the only one havingall oœthese habitats; Stans- bury and Fremont lack fresh-watersprings; Carrington until recent yearshad a brackishspring, but now, like Dolphin, Gunnison,and Bird Islands,it hasonly sandbars and benchlands. BadgerIsland (aslocally known) is merelya large sandbar about midway betweenCarrington and StansburyIslands. Both the original islandsand benchlandareas have cliffs and talus slopesthat are oœsignificance to bird life. For convenience,bird lists by islands,with commentswhere sig- nificant,will be presented.For the smallislands, the total numbers oœbirds are estimatedbut no quantitative data were obtainedfor the larger islands. DOLPHIN ISLAND This northernmostand probablydriest island is about fiœtyacres in extent. It was visited June 4 to 6, 1938. PACIFICNIGHTHAWK, Chordeiles minor hesperis.--Twobirds were seen over the island in the evening. They might easily have come from the mainland, though there was suitable nesting habitat on the island. 38 MARSHALLAND LEATHAM, Birds of GreatSalt Lake Islands I'Auk L Jan. AMERICANRAVEN, COr'ilUS corax sinuatus.--Onedried-up body of an immature bird was found on the sand bar. UTAH HORNEDLARK, Otocoris a. utahensis.--A nest of four eggs was found in DistichIis stricta, and from six to eight adults were often seen feeding about the sand bars of the island. SAGETHRASHER, Oreoscoptes montanus.--One pair with a nest (four eggs)in an •ltriplex confettirolla bush was observed. DESERTSPARROW, •lrnphispiza b. deserticoIa.--Twopairs noted in •ltripIex con- fertifoIia. BREWER'SSPARROW, Spizella b. breweri.--Twoor three breedingpairs wereon the island,nearly alwaysseen in ,'1triplexconfertifolia. On this small island, which was completelycovered during two days,we found the following nestingdensities. TABLE 1 Speciesand Acreageof Acreageof numberof Totalacres nesting Acresper feeding Acresper nests per nest• cover• nest• caver• nesf: Distiehlis Horned Lark DistichIls and flats 2 25 ){ • 100 s0 Sage Thrasher Atriplex Brushy 1 50 5 2.5 40 40 Desert Sparrow Atriplex Brushy 2 50 5 2.5 40 40 Brewer's Sparrow Atriplex Brushy 3 16 5 1.6 40 13 Authors' estimates based on observationsof nesting and feeding activities of this species on all islands. 1Zesult of dividing number of nests into estimated acreages. GUNNISON ISLAND While Dr. D. I. Rasmussen,Lee Kay, and the seniorauthor were on this islandon June 23, 1937,one family of Rock Wrens,$alpinctes o. obsoletus,was observed,and one pair of Prairie Falcons,Falco mexicanus, was noted. On June 18 to 19, 1935,Dr. Rasmussenfound two Prairie Falcons' (Falcomexicanus) nests and severalpairs of RockWrens (Salpinctes o. obsoletus)which may be considerednesting birds. In addition sevenAmerican Ravens (Corvusc. sinuatus)and a small flock of Black-neckedStilts (Himantopusmexicanus) visited the island. Vol.59'[ MARSHALLAND LEATHAM, Birds of GreatSalt Lake Islands 39 •94• a Dr. Alfred M. Bailey,Director of the ColoradoMuseum of Natural History, Denver, Colorado, has very kindly made available to the authorsthe following additional noteson the bird life of this island. On May 28, 1937: AMERICANRAVEN, Cor•us corax sinuatus.--Anest with five young found. YE•OW-HEADm)BLACKmRD, Xanthocephalus xanthocephalus.--Six females observed. Cowram),Molothrus ater subsp.--Onepair observed. On June 8, 1937: (?) WRmHT'SFLYCATCHER, Ernpidonax wrighti.--One pair collected. BLaCK-HEADEDGROSBEAK, Hedyrneles rnelanocephalus papago.--A female bird col- lected. EASTERNYELLOW WARBLER,Dendroica aestiva aestiva.--One female collected. WmT•N CroPraNGSt'Am•OW, Spizella passerina arizonae.--One female collected. Dr. Bailey's expedition was on this island during a very stormy periodwhich may well explain the occurrenceof thesespecies on this, the most desert-like of the islands. BIRD ISLAND Area twenty-twoacres; visited in the evening of June 30, 1938. One Prairie Falcon (Falcomexicanus) in the air and five Utah Horned Larks (Otocorisa. utahensis)on the sandbar to the southwere seen. It is probable that the falcon was the sameone seenon Carrington Island, and that the larks were visitors also. There is little, if any, suitablenesting area for thesebirds on this tiny islandas the pelican, gull and heron colonyutilizes most of the acreage. CARRINGTON ISLAND Carrington Island, with an area of 1,740 acres,was visited from June 29 to July 2, 1938,with the exceptionof the eveningof June 30. The entire islandwas well coveredduring this period. WF•TERN I?•_,D-TAILEDHAWK, Buteo borealis calurus. MARSH HAWK, Circus hudsonius. PRAIRIE FALCON, Falco mexicanus. One individual of each of these birds was noted, but no hawk nest was found. WESTERNMOVamNg DOVE, Zenaidura macrouramarginella.--Four mourning doves were seen. SHORT-RAgr•OWL, .4SiO [. fiammeus.--Twobirds were often seenforaging during the evenings. They