j. RaptorRes. 31(2):175-186 ¸ 1997 The Raptor ResearchFoundation, Inc. THE LONG-EARED OWL (ASIO OTUS) AND FOREST MANAGEMENT: A REVIEW OF THE LITERATURE DENVER W. HOLT Owl ResearchInstitute, P.O. Box 8335, Missoula, MT 59807 U.S.A. ABSTRACT.--InNorth America, 13 of 20 breeding seasonstudies reporting on Long-earedOwl (Asio otus)reproduction were conductedin open country habitats,four in woodland or edge habitatsand three in predominantlywoodland habitat. Sixteenof 22 nonbreedingseason studies that reported com- munal roost siteswere located in forest/edge habitats,five reported locationsin open spaceand one wasfound within forest habitat.There is currentlylittle data to indicate either a negativeor positive effect of forest-managementpractices on this species.Although there appearsto be someevidence of population declinesin specificgeographic areas, these impactshave been attributed to lossof riparian vegetation,conversion of foraging areasto agriculturalfields and reforestationof open habitats.The Long-eared Owl's ecomorphologyis suggestiveof a speciesthat inhabits open country.Additionally, its primary food is small mammals (e.g., microtine and heteromyid rodents) which inhabit open country. Shouldthe Long-earedOwl be considereda forestowl? Research data would suggestno; however,studies from extensive deciduous and coniferous woodlands are needed. KEYWORDS: Long-earedOwl; forestry; habitat;, diet;, ecomorphology; Asio otus. El bfiho (Asiootus) y administracitn forestal:un revisode la literatura RESUMEN.-•Ennorte amtrica, 13 de 20 estudiosde tiempos de cria reportadasen el bfiho Asio otus fueron evaluadosen hfbitat del campo amplio, cuatro en bosqueso orillas de hfbitat, y tres en mayoria de hfbitat de bosque.Diecistis de 22 estudiosen tiempossin crla que reportaronsitios de percha comunalfueron 1ocalizadasen bosque/hfbitat de orilla, cinco lugaresreportados en espacioabierto, y uno fue encontradodentro de un hfbitat de bosque.Actualmente poca informacitn indica si los afectos de la administraci6nde bosquesson negativoo positivoen el especie.Aunque parece que un poco de pruebascon reduccitn de poblacionesen fireasespecificas geogrfficamente, estos impactos estrin atri- buido a la falta de vegetaci6ncerca de los rios, conversi6nde fireasde forraje a parcela agricolas,y repoblacitn forestalde hfbitat abiertos.La eco-morfologiadel buho evocauna especieque ocupa el campo abierto. Tambitn, su cornidaprincipipal es mamiferospequefios (i.e. microfine y roedor het- eronmyid) que ocupan camposabiertos. •Debe ser el bfiho consideradoun bfiho del bosque?Infor- maci6n investigadasugieren que no, sin embargo,estudios de bosqueconifero y de hoja caducaextensa es necesaria. [Traducci6n de Rafil De La Garza, Jr.] The Long-eared Owl (Asio otus)is a widely dis- Long-eared Owl has been considered an open tributed Holarctic species,with six recognizedsub- country species, inhabiting areas such as grass- species (Cramp 1985). In the Northern Hemi- lands, shrubsteppe,marshes and woodland patches sphere, it ranges from approximately30-65 ø lati- near open areas.Most studiesseem to support this. tude, with isolated populationsoccurring in North To my knowledge,there have been no attemptsto and East Africa, the Azores and Canary Islands evaluatethe affectsof forestrypractices on this spe- (Mikkola 1983, Marks et al. 1994). Someaspects of cies. Herein, I review the literature and use some Long-eared Owl natural history have been well inferencesfrom my ongoing 10 yrs of study to ad- studied in the U.S. and some European countries, dress some of the questions concerning the im- but most studies have been short in duration, av- pacts of forest management on Long-eared Owls. eraging about two seasons. POPULATION TRENDS In North America, two subspeciesare currently recognized (A. o. wilsonianusand A. o. tuftsi;see Few data exist for population trends of Long- Marks et al. 1994 for further discussion). The cared Owls in North America over the past 10, 25, 175 176 HOLT VOL. 31, No. 2 Table 1. Statusof the Long-eared Owl in North America. PROVINCE/REGION OR STATE STATUS POPULATION TREND a CANADA (Fyfe 1976) British Columbia Low Unknown Maritime Low/Medium Fluctuating NorthwestTerritory/Yukon Unknown Unknown Ontario/Quebec Low/Medium Fluctuating Prairie Low/Medium Fluctuating NORTHEASTERN UNITED STATES (Melvin et al. 1989) Connecticut Special Concern Delaware Unknown Massachusetts Special Concern Maryland Decreased Maine Unknown New Hampshire Special Concern New Jersey Unknown New York Unknown Pennsylvania Decreased Rhode Island Special Concern Vermont Special Concern MIDWEST (Petersen 1991) Illinois Endangered Unknown Indiana Uncommon Declining Iowa Threatened Unknown Kansas Uncommon Stable Michigan Special Concern Unknown Minnesota Regular Unknown Missouri Special Concern Unknown Nebraska Unknown Unknown North Dakota SpecialConcern Unknown Ohio Unknown Unknown South Dakota Rare Declining Wisconsin Special Concern Unknown WEST (Marti and Marks 1989) California SpecialConcern Declining Colorado Common Stable Idaho Common Unknown Montana Special Concern Unknown Nevada Common Stable Oregon Common Stable Utah Common Unknown Washington Unknown Unknown Wyoming Common Unknown Trend data not known tbr northeastern U.S. 50 or 100 yrs, but there are some regional data. ada; or 50 detections in the U.S. and Canada The Breeding Bird Survey (BBS) does not include (Droege pers. comm.). the Long-eared Owl in its data set from 1966-89. In Canada, Fyfe (1976) reported population For inclusion, a speciesmust have been detected trends and relative abundanceof raptorsfor prov- on >10 BBS routes in a physiographicregion; 25 incesor specificgeographic areas (Table 1). There or more detections in the three biomes (Eastern, were no data to support these designations.Also Central, Western); 35 or more detections in Can- in Canada, Christmas Bird Count (CBC) results Ju•E 1997 LO•O-EAR•DOW• CO•$ERV^q:•O• 177 50 45 40 35 30 25 20 15, 10. 5 62 64 66 68 70 72 74 76 78 80 82 84 86 88 YEARS Figure 1. Summary of winter counts of Long-eared Owls from Christmas Bird Counts in the northeastern U.S., 1963-87 (after Melvin et al. 1989). showed a significant decline in Long-eared Owl ern states, Melvin et al. (1989) concluded that no numbers,but thesedata shouldbe interpreted cau- clear population trend could be detectedfor Long- tiously (Kirk et al. 1994). eared Owls, although numbers seemedto fluctuate In the northeastern U.S., Melvin et al. (1989) about every three to six yr (Fig. 1). In New Jersey, reported that the Long-earedOwl was listed as a Bosakowskiet al. (1989, 1989a) analyzed 31 yr speciesof special concern in all the New England (1956-86) of Long-eared Owl Christmas Count states except Maine and decreasingin Maryland Data reporting one or more Long-eared Owls and and Pennsylvania(Table 1). Within the northeast- concludedthat the specieswas declining (Fig. 2). 30- 10- -- = Owls/I,000 party hrs 0 ø Total Owls 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 8'8 Year Figure 2. Long-earedOwls reported on New JerseyChristmas Bird Counts (dotted line) and per 1000 party hours (solid line). Regressionline (dashed), Y = -0.70x + 25.5, P < 0.0001, r -- 0.67 for party hours is significant. Regressionline, Y = -0.629x + 31.9, P = 0.005, for total owls had a lower correlation (r = 0.50) (after Bosakowski et al. 1989a). 178 HOLT VOL. 31, NO. 2 In the midwestern U.S., Petersen (1991) report- pairs intensively monitored for 9 consecutiveyr, ed that Long-eared Owls have declined in Indiana only 11 males and two females have returned to and South Dakota, are stable in Kansas and are of the same breeding site more than once. Addition- unknown status elsewhere (Table 1). This was ally, no mate fidelity has been recorded. These based on state and regional birding publications data buttressthe argument for highly migratory and raptor surveyforms. In Minnesota, however, and nomadic tendencies in Long-eared Owls. Evans (in Marks et al. 1994) noted a decline in mi- grant Long-earedOwls in his studyarea from 1976- PRIMARY FACTORS RESPONSIBLE FOR LONG-EARED OWL POPULATION TRENDS 93 (Fig. 3). In the western U.S., White (1994) reported the In most cases, there were insufficient data to Long-eared Owl as stable, but with some local convincingly conclude which /hctors influence lossesin the far west. He did not report how these population trends. Population declines have been speciesdesignations were assigned.Marfi and Marks attributed to habitat alteration, forest succession, (1989) reported a Long-earedOwl population de- urbanization, competition with Great Horned Owls cline in California and a stable or unknown popu- (Bubovirginianus), loss of habitat for prey species, lation status in the rest of the west (Table 1). In rodenticides (Bosakowskiet al. 1989a), shooting coastal southern California, Bloom (1994) has and habitat loss (Marks et al. 1994) and loss of shown the Long-eared Owl to have been extirpated riparian habitats and grasslands(Bloom 1994). in some areas,with small remnant populations still Some forestry practicesare also thought to have occurring inland. The number of historic nesting affected Long-eared Owls. In New Jersey, Bosa- areas have declined by 55% (Bloom 1994). In kowskiet al. (1989a) suggestedthat forest removal Montana, Long-eared Owls were listed as a species and thinning affected wintering Long-eared Owls of specialconcern (Marti and Marks 1989). I have and caused them to abandon the area. shown yearly fluctuationsin numbers during CBC On the contrary, many of the nonbreeding