STATUS OF THE OSPREY IN SOUTHEASTERN MONTANA BEFORE AND AFTER THE CONSTRUCTION OF RESERVOIRS JON E. SWENSON, Montana Departmentof Fish, Wildlife, and Parks, Box 36, Rosebud, Montana 59347 Ospreys (Pandion l•aliaetus)readily colonizesuitable habitat created by manmadeimpoundments. Henny et al. (1978a) found that about47 percent of the Ospreysin Oregon, and a greaterpercentage of thosein the interiorof the state, nest along reservoirs.In northern California, about 20 percent of the Ospreysnest along reservoirs,including 49 percent in the interior of the region (Henny et al. 1978b). Henny et al. (1978a,b) suspectedthat Osprey numbers had increased in both areas due to the construction of the reser- voirs. Also, Henny and Noltemeier (1975) and Henny et al. (1978b) have describedsituations where Ospreys or their progeny, nesting on natural lakes, have colonizednearby reservoirs as nestsites became less available at the natural lakes. Childress and Eng (1979) documented an increased Ospreypopulation with the constructionof shallowimpoundments in an ex- istingreservoir. However, the establishmentof a breedingOsprey population in an area wherebreeding Ospreys were not previouslyfound hasapparently not been documented.This paper documentssuch a situation. STUDY AREA AND METHODS The study area (Figure 1) comprisessoutheastern Montana, bounded on the northby the MissouriRiver (exceptthat the entireFort PeckReservoir on the MissouriRiver was included), on the southby Wyoming,on the westby the Bighorn River and the north-flowingportion of the MusselshellRiver, and on the east by North and South Dakota. This area containsno natural lakes, exceptfor oxbowson major rivers.Three mainstreamreservoirs have been constructed in this area: Fort Peck Reservoir (1,000 km 2) on the MissouriRiver in 1939, Tongue River Reservoir(14 km2) on the Tongue River in 1940 and Bighorn Lake or YellowtailReservoir (70 km2) on the BighornRiver in 1965. Other reservoirsare primarilysmall livestock reser- voirs. On three areasstudied by Smith (1953) in southeasternMontana, livestockreservoirs occurred at a densityof 0.1 per km• and 124 reservoirs variedin sizefrom 0.04 to 7.7 ha, averaging1.3 ha. SoutheasternMontana is dominatedby Big Sagebrush(Artemi$ia tri½len- tara)steppe, but some grass-dominatedsteppes and PonderosaPine (Pinus pon½lerosa)forests and savannasare present.Plains Cottonwood (?opulu$ ½leltoi½le$)predominates along larger rivers and isscattered along most major creeks. Determinationof the former and presentstatus of Ospreyswas based primarilyon a literaturesearch. Several ornithologists visited the areaprior to 1910. Althoughcoverage was not usuallyintensive, activities were concen- WesternBirds 12:47-51, 1981 47 OSPREY IN MONTANA tratedalong the watercourses,where Ospreys would be mostexpected. In- creasedenergy development since 1970 hasresulted in manywildlife studies in southeasternMontana. The resultsof these studies,discussions with other biologistsin the areaand my ownobservations were used to assessthe pres- ent statusof Ospreys. RESULTS HISTORICAL STATUS Lewisand Clarkdid not mentionthe Ospreyin theiraccounts of birdsseen along the Missouriand Yellowstonerivers in 1805 and 1806 in easternMon- tana and North Dakota, but they did recordthem from southwesternMon- tana (Reidand Gannon1927, Walcheck1976). Earlynaturalists did not mention seeing the Osprey during their explorations of the lower Yellowstone,Bighorn and Musselshell rivers (Allen 1874, McChesney 1879, Mearns1904). Cooper(1868) did not see Ospreys near the muddy waters of the MissouriRiver below Fort Benton, which is upstreamfrom my study area, whereas they were common on the rivers and their tributariesfrom therewestward. Thorne (1895) did notrecord Ospreys near Miles City, on the YellowstoneRiver, from 1888 to 1892. Cameron (1907) lived and traveledextensively in southeasternMontana during an 18-yearperiod aroundthe turn of the century,but did not observeOspreys. FortPeckRes. / 200 km , '•e•'•heørn •on gueR. • •'•'•'! Res. Figure1. Ospreystudy area in southeasternMontana. The lettersindicate the citiesof Billings(B) and Miles City (MC). The mapped area is shaded on the map of Montana. 48 OSPREY IN MONTANA Apparently, the only early referencesto Ospreysin this general area are the earlyfall recordsof Jonesand Dawson(1900), who observedthe species from a train alongthe YellowstoneRiver betweenBillings and MilesCity on 13 August 1900, and Visher (1911), who saw one on 2 September1910 along the Little MissouriRiver in northwesternSouth Dakota. These birds may have been migrantssince fall migrationgenerally occurs from mid- Septemberto mid-Octoberin southeasternMontana (Hinz 1977). PRESENT STATUS The Ospreyis a rare breedingbird in southeasternMontana. Only 11 pairs are known to nest there. Nine of thesepairs nest along Fort Peck Reservoir (CharlesM. RussellNational Wildlife Refuge files, 1980). One nestis present on the upper end of Tongue River Reservoir(Knapp 1977) and, although there are no known nestson BighornLake (Steve Swedbergpers. comm. 1981), one may occurnear YellowtailDam, basedon the repeatedobserva- tions of Ospreys there during two summers (R. Stevenson pers. comm. 1975). One activeOsprey nest was also located on a largelivestock reservoir 8 km westof Jordan (B. Hildebrandpers. comm. 1980). No Ospreynests were found by Hinz (1977) during his intensive2-year studyof the aquatic birdsof the lower YellowstoneRiver and, to my knowledge,there are no Osprey nestsalong any riversin southeasternMontana. In adjacentNorth Dakota, Stewart (1975) reported only three known nestinglocalities for Ospreys;all were alongreservoirs and all were recordedafter 1951. DISCUSSION The paucityof Ospreyobservations during the breedingseason by early naturalistsand the presentlack of Ospreysnesting along rivers strongly sug- gestthat the speciesdid not nestin southeasternMontana prior to the con- structionof reservoirs.In contrast,Ospreys occurred historically in western Montana (Betts1916, Saunders1921) and now nest there along natural lakes, riversand reservoirs(Childress and Eng 1979, MacCarterand Mac- Carter1979, Swenson1979). Earlyobservers noted that the Ospreywas not found on the lower MissouriRiver where the water was muddy (Cooper 1868, Grinnell 1876). The turbidwater, which is stillpresent in the riversof southeasternMontana, probablywould makefishing too difficultto allowthe Ospreysto raiseyoung. Hinz (1977) notedthat migrationof Ospreysalong the lower YellowstoneRiver occurredwhen turbidityand flow were low, which supportsthis contention. Ospreysnest in the boreallakes region of centralCanada (Houstonet al. 1977) and someof thesebirds probably migrate through southeastern Mon- tana. Ospreysfrom western Montana probablydo not migratethrough southeasternMontana, because the speciesdoes not appearto wanderwide- ly to the east or west duringmigration (Henny and Van Velzen 1972, Ken- nedy 1973, Melquist et al. 1978). Since not all 2-year-old Ospreys (subadults)return to their natal vicinity (Henny and Van Velzen 1972), subadultsfrom central Canadian populations were probably "short-stopped" 49 OSPREY IN MONTANA at favorable reservoirsin southeasternMontana and originallypopulated them. The reducedturbidity of the water and the creationof still, shallow areas in the large reservoirsprobably created suitable foraging habitat (Childressand Eng 1979). The very small population (probably 15-20 pairs) of Ospreys in southeastern Montana indicates that few of the reservoirs are suitable for Ospreysand that the area is marginalOsprey habitat. But it appearsthat the creation of these reservoirs has resulted in the establishment of a small breedingpopulation of Ospreyswhere one did not existpreviously. These resultsadd strengthto the conclusionof Henny et al. (1978a,b) that reservoir constructionhas increasedthe numbersand distributionof Ospreysin the western United States. ACKNOWLEDGMENTS I am gratefulto Mike Hedrick for providingme with the Osprey census data from the Charles M. RussellNational Wildlife Refuge, and to Bernie Hildebrandand Rich Stevensonfor allowingme to cite their Ospreyobserva- tions. I also thank Robert L. Eng, Kurt L. Alt and P. David Skaar for their constructivecomments on this manuscript. LITERATURE CITED Allen, J.A. 1874. Noteson the naturalhistory of portionsof Dakotaand Montanater- ritories. Proc. Boston Soc. Nat. Hist. 17:33-91. Betts, N.D. 1916. Birds seen in the valley of the South Fork of the Flathead River, Montana. Condor 18:161-163. Cameron, E.S• 1907. The birds of Custer and Dawson counties,Montana, Auk 24:241-270. Childress,D.A. and R.L. Eng. 1979. Dust abatementproject with wildlife enhance- ment on Canyon Ferry Reservoir,Montana. Pages 282-288 in G.A. Swanson, tech. coordin., The mitigationsymposium: a national workshopon mitigating lossesof fish and wildlife habitats.U.S. For. Serv. Gen. Tech. Rep. RM-65. Cooper, J.G. 1868. The fauna of Montana Territory. Am. Nat. 2:596-600. Grinnell, G.B. 1876. Birds. Pages72-92 in W. Ludlow, Report of a reconnaissance from Carrot, Montana Territory, on the Upper Missouri,to the YellowstoneNa- tional Park, and return, made in the summer of 1875. U.S. War Dep., Gov. Print. Off., Washington, D.C. Henny, C.J., J.A. Collinsand W.J. Deibert. 1978a. Osprey distribution,abundance, and status in western North America: II. The Oregon population. Murrelet 59:14-25. Henny, C.J., D.J. Dunaway,R.D. Malletteand J.R. Koplin. 1978b. Ospreydistribu- tion, abundance, and statusin western North America: I. The northern Califor- nia population.