sign in sign up
<<
Home , Aegolius, Boreal owl, Ural owl

j. RaptorRes. 31 (2):125-128 ¸ 1997 The Raptor ResearchFoundation, Inc.

BOREAL RESPONSES TO MANAGEMENT: A REVIEW

H•,ai HAKKARAINEN,Em4• KORPIM 'AKI,VESA KOIVUNEN AND SAMI KUPd•I Laboratoryof EcologicalZoology, Department of Biology,University of 7•trku,FIN-20014 7•trku,

ABSTRACT.--Modernforestry during the last decadeshas stronglyincreased fragmentation of forest habitats.This may resultin harmful effectson raptor specieswhich are strictlydependent on boreal ,such as the -eatingBoreal Owl (Aegoliusfunereus). The long-term data from Finland shows that in extensiveforest areas,fledgling production of Boreal is higher on intensivelyclear-cut territories than on lessclear-cut territories. Breeding frequency,clutch size and laying date, however, havenot been shownto be relatedto the proportionof clear-cutareas within a .Snap-trapping data suggeststhat large clear-cutareas sustainmore Microtusvoles than small clear-cut areas. The in- creasednumber of saplingsand clear-cutareas during the last two or three decadeshas created new suitablegrass habitats for Microtusvoles, and simultaneouslynew hunting habitatsfor BorealOwls. There is someexperimental evidence that the presenceof the (Strixuralensis) decreases the breeding densityof Boreal Owlswithin 2 km of Ural Owl nests.Therefore, forestfragmentation does not seem to harm BorealOwls at the presentday scale,but a lack of nest holeshas to be compensatedfor by settingnest boxesfar (>2 km) from medium-sizedand large raptorsthat can prey upon the . In the long-term,however, establishment of snagsand patchesof mature forestswith large trees, denseenough to satisfythe ecologyof the hole-nestingBlack (Dryocopus martius), will provide a natural way to establishnew nestingcavities for Boreal Owls. KEYWOP, DS: Aegoliusfunereus; uralensis;clear-cuttings; modern forestry; vole density.

Respuestadel Bfiho Boreal a la Administraci6nForestal: Un Reviso RESUMEN.--E1forestal moderno durante los filtimosd•cadas ha aumentadocon frecuenciala fragmen- taci0nde hfbitat de bosque.Esto puede resultar en efectosdafiosos en especiede rapacesque estfn estrictamentedependiente en bosquesboreal, como el Bfiho Boreal (Aegoliusfunereus) que comerato- nes.La informaci0nde Finlandiaensefia que larga duraci0nen fireasde bosquesenormes, la produc- ci6n de pajaritosde bfihoses mrs alto en territorioscortados-completo con intensidad queen territorios menoscortados-completo. La frecuenciade crla, tamafiode nidada,y la fechade poner,no han ensefi- ado estarrelacionado a la proporci0nde freas cortadas-completoentre el territorio.Informaci0n de trampassugiere que fireasgrandes que estfn cortadas-completosostienen mas ratones,y simultfnea- mentehfbitat nuevopara cazar para los bfihos. Hay un pocode pruebasexperimental que la presencia de Bfiho Ural (Strix uralensis)reduce la densidad de cria del Bfiho Boreal dentro de 2 km del nido del Bfiho Ural. Por lo tanto, la fragmentaci0ndel bosqueno pareceha cerle dafio al Bfiho Boreal en la escalapresente, pero la falta de nidosde agujeronecesita que estarcompensado con poniendonidos de agujerolejos (>2 km) de rapacesmedianos y grandesque puedencazar a los bfihosboreal. En la larga duraci0nel establecimientode toconesy parcelasde bosquemaduros con frboles grandes,de suficientedensidad para satisfacer la ecologfade losnidos de agujerode el CarpinteroNegro (Dryocopus martius),va proporcionaruna maneranatural para establecercavidades de nidosnuevos para el Bfiho Boreal. [Traducci6n de R•afilDe La Garza,Jr.]

During the last decades, modern forestry has from larger forestcomplexes (Hansson 1992). Rap- had a strong and perceivableimpact on boreal for- tors living in forest habitats are generally consid- est ,both in Palearctic and Nearctic ered to be one of the most sensitivegroups of ver- regions. At the landscapelevel, there is a lack of tebratesto and habitat change large pristine forests (Ohmann et al. 1988), while (Newton 1979, Forsmanet al. 1984, Carey et al. remaining mature forest patches have become in- 1992). This is at least in part becauseraptors in- ternally more homogeneous and more isolated habit large territories(Newton 1979) where astop

125 126 HAKKARAINEN ET AL. VOL. 31, NO. 2

Table 1. Annual breeding percentageof nest boxes,laying date (1 = 1 April), clutch sizeand fledglingproduction in sparselyand widely clear-cutterritories of Boreal Owls in the Kauhavaregion, westernFinland (ca 63øN,23øE). Statisticaltests were performed by Student'st, test and Mann-Whimey •test (two-tailed).N = number of territories.

PROPORTION OF CLEAR-CUT AREAS •ITHIN TERRITORY

LOW • HIGH b

i (_+ SD) N i (-+ SD) N TEST VALUE P Breedingpercentage 15 (9) 17 14 (15) 13 U = 139.0 0.22 Layingdate 1.41 (19.44) 14 1.10 (21.98) 10 T = 0.04 0.97 Clutch size 5.43 (0.88) 14 5.20 (1.26) 11 T = 0.54 0.59 No. of fledglings 2.45 (1.26) 14 3.55 (1.39) 11 T = 2.06 0.05 18% (SD = 7%, range = 10-30%) of total areawithin 1.5 km of nestwas clear-cut. 49% (SD = 11%, range = 35-70%) of total area within 1.5 km of nestwas clear-cut.

carnivorescapture prey which is scarceand diffi- THE EFFECTS OF CLEAR-CUT AREAS ON BOREAL OWLS cult to catch (Temeles 1985). Therefore, they ex- The long-term study (1981-95) conductedin the pend considerableenergy in each feeding event, Kauhavaregion of western Finland made it possi- especiallyif prey is sparselyand patchilydistributed ble to evaluate the effects of clear-cut areas on the within the territory. In addition, due to forest har- Boreal Owl. These areas comprise clear-cut areas vesting, there often is a lack of suitable nesting with 0.2-1.5 m high saplings(<10-yr old) covering places, such as natural cavitiesand large nesting about one-third of the forests in our study area. trees for many raptor . Boreal Owls breeding in areas that are primarily The Boreal Owl (Aegoliusfunereus)is a small noc- forestedwith a mean of 18% (SD = 7%, range 10- turnal hole-nestingraptor which commonlybreeds 30%) (herein referred to as sparselyclear-cut) of in coniferousforests in northern (Mikkola the total forest area clear-cut within 1.5 km of nests 1983). Microtusvoles (, agrestis; produced about one fledgling less than those in sibling vole, M. rossiaemeridionalis;and , areaswith a mean of 49% (SD = 11%, range 35- Clethrionomysglareolus) are the main prey of this 70%) of the area clear-cut (herein referred to as species(Korpim/iki 1988). Field and sibling widely clear-cut) (Table 1). Most of the territories inhabit fields as well as clear-cut areas, whereas the and areas sampledwithin sparselyclear-cut areas bank vole inhabits mainly forest habitats (Hansson were small cuts of <10 ha with most areas between 1978). In poor vole yearsalternative food sources 1-5 ha. In contrast,in the territories sampledwith- have to be used, such as (Sorexspp.) and in the widely clear-cut areas, most were relatively small passerinebirds (Korpim/iki 1988). Males are large cuts of up to 200 ha. In addition, territories resident after the first breeding attempt, while fe- within the widelyclear-cut areas exhibited relatively malesdisperse widely (up to 500 km) betweensuc- high fledgling production (i = 3.6) for Boreal cessivebreeding attempts (Korpim/iki et al. 1987). Owls (Korpim/iki and Hakkarainen 1991). Terri- In this review, we focus on how clear-cut areas in tories in both clear-cut areas were occupied with Boreal Owl territories affect reproductive output equal frequencyin different vole years (Table 2), and breeding frequencyof this species.We alsodis- indicating that Boreal Owls breed successfullyin cusshow clear-cutareas affect the main prey den- the neighborhood of large clear-cuts also in low sitiesof Boreal Owls. Finally,we identify how inter- vole years.Clutch size,breeding frequency and lay- specific interactionshave to be consideredwhen ing date, however,were not affected by the pro- setting new nest boxes for owl speciesthat suffer portion of clear-cutareas within a territory (Table from the lack of natural cavities. This review is 1). Therefore, forest management does not seem based on recent investigations(Hakkarainen and to harm Boreal Owls at present day scales,if no Korpim/iki 1996) and on snap-trappingdata which more than half of the total forest area is clear-cut are now examined especiallyfrom the perspective at long intervalsenough (>60 yr). In contrast,the of forest management. positive effects of clear-cutareas on fledgling pro- JvNv.1997 BOREALOWL AND FOREST M•d•AGEMENT 127

Table 2. The number of Boreal Owl nestsin proportion forests and clear-cutsmay increase the amount of of landscapewith clear-cutsof low and high percentages alternativeprey of Boreal Owls in poor vole years. (see Table 1), in different phasesof the vole cyclein the Prey abundance and fledgling production ap- Kauhavaregion, westernFinland (ca. 63øN, 23øE). pear to increase with forest fragmentation. How- ever, clear-cutting also decreases the number of PROPORTION OF CLEAR-CUT suitable natural cavities for Boreal Owls. Large AREAS WITHIN TERRITORY treesand aspengroves with suitablenesting cavities PHASE OF VOLE CYCLE LOW HIGH for the Black (Dryocopus martius) are

Low 1 2 decreasingdue to logging. There is a need to pro- Increase 7 4 tect thesesuitable nesting sites in forest landscapes. Peak 13 12 Alternatively,nest boxes can be provided for Bo- Total 21 18 real Owls to compensatefor the lack of natural cavities.

ESTABLISHING NEST-BOX LOCATIONS FOR BOREAL OWLS duction suggestthat this speciesmay achieveben- eficial fitness from clear-cut areas because, for Bo- Interspecific competition is expected to reduce real Owls, lifetime reproductive success(LRS) is the fitness of individuals (Roughgarden 1979). dependent on the successof males in rearing Therefore, coexistinglarge owl speciesmay reduce young to the fledgling state (Korpim/iki 1992). To- the breeding successof smallerowl species,includ- day,LRS is the best known estimateof fitness (Clut- ing preying upon these owls (Mikkola 1983, Hak- ton-Brock 1988, Newton 1989). karainen and Korpim/iki 1996). At our study site, What would be the reason for the higher fledg- the Ural Owl (Strixuralensis) is a large owl species ling production for Boreal Owls in areaswith high- that is probably most harmful to the Boreal Owl. er level of clear-cuts within territories? The in- Nest-box experiments,along with long-term obser- creasednumber of saplingsand clear-cutareas dur- vational data (Hakkarainen and Korpimgki 1996) ing the last two or three decades (Jgrvinen et al. revealed that Boreal Owls avoid breeding within 2 1977) has created new suitablegrass habitats for km of Ural Owl nests.When nesting •2 km from field voles (Henttonen 1989), which is the pre- Ural Owls, breeding wasdelayed substantially when ferred prey of Boreal Owls (Korpim/iki 1988, Koi- compared with breeding •4.5 km away. Further- vunen et al. 1996). Snap-trappingin the peak vole more, when in the neighborhood of Ural Owl year of 1994 in westernFinland alsosuggested that nests,male Boreal Owls were younger and paired large clear-cutareas sustaindense field vole pop- more often with short-wingedfemales. Most breed- ulations. Similar results have also been found in ing near Ural Owls failed during the courtshippe- (Hansson 1994). Because of intensive riod (Hakkarainen and Korpimgki 1996). This sug- growth of hay speciesin new clear-cutareas, hay- gests that inexperienced male Boreal Owls are eating field voles may colonize them successfully forced to establishtheir territories in the vicinity for about 10 yr (Hansson1978). In constrast,small of Ural Owls where they pair with lessexperienced clear-cuts(ca. 1-3 ha) may not achieve such high females. These findings suggestthat nest boxes for densitiesof field voles, especiallyif small clear-cuts Boreal Owls should be set •2 km from the medi- are isolated from source habitats, such as large um-sized and large raptors that may have adverse fields and large clear-cuts.This may explain why effects on Boreal Owls. fledgling production of Boreal Owls may increase In conclusion,moderate forestry may not harm with the increasingamount of clear-cutarea within Boreal Owls at the presentday scaleif suitablenest territories, especiallyif saplingsare tall enough (ca. holes are available. A lack of nest holes can be 2 m) for perch hunting by Boreal Owls (Bye et al. compensatedfor by erecting nest boxes, but boxes 1992). Densities of many species are also shouldbe set far from threatening allospecifics.In found to peak at forest edges(Helle 1984, Hansson the long-term, however,the establishmentof snags 1983), especiallyChaffinch (Fringilla coelebs)den- and patchesof old mature forestswith large trees, sities (Hansson1994). This speciesis the most im- dense enough for hole-nestingBlack Woodpeck- portant bird prey of Boreal Owls on our studysite ers, will provide a natural way to establishnew nest- (Korpimgki 1981, 1988). Therefore, the edges of ing cavitiesfor Boreal Owls. 128 •NEN EX AL. VOL. 31, NO. 2

LITERATURE CITED in Finland in 1945-1975). Silva Fenn. 11:284- 291. Bye, F.N., B.V. J^COBSEN•4D G.A. SONERUD.1992. Au- KOIVUNEN, V., E. KORPIMAKI, H. HAKKARAINENAND K. ditory prey locationin a pause-travelpredator: search NORRDAHL.1996. Prey choice of Tengmalm'sOwl height, searchtime, and attackrange of Tengmalm's (Aegoliusfunereus): preference of substandardindivid- Owls (Aegoliusfunereus). Behav. Ecol. 3:266-276. uals?Can. J. Zool.74:816-823. C•v, A.B., S.P. HORTONAND B.L. BISWELL.1992. North- KORPIMMCa,E. 1981. On the ecologyand biologyof Teng- ern : influence of prey base and land- malm's Owl (Aegoliusfunereus)in SouthernOstroboth- scapecharacter. Ecol. Monog•. 62:223-250. nia and Suomenselkfi western Finland. Acta Univ. Oul- CLUTTON-BROCK,T.H. 1988. Reproductivesuccess. Univ. uensis S• A. Sd. Rerum Nat. 118:1-84. Chicago Press,Chicago, IL U.S.A. 1988. Diet of breeding Tengmalm's Owls Aego- FORSMAN,E.D., E.C. MENLOW•4D H.M. WIGHT. 1984. liusfunereus: long-term changesand year to year vari- Distribution and biology of the Spotted Owl in Ore- ation under cyclicfood conditions.Ornisb•nn. 65: 21- 30. gon. Wildl. Monog•87:1-64. 1992. Fluctuating food abundance determines HAKKARAINEN,H. AND E. KORPIMJ•KI.1996. Competitive the lifetime reproductivesuccess of male Tengmalm's and predatory interactionsamong raptors:an obser- Owls.J. Anirn.Ecol. 61:103-111. vational and experimental study. Ecology77:1134- --AND H. HAKKARAINEN.1991. Fluctuating food 1142. supplyaffects the clutch size of Tengmalm'sOwls in- HANSSON,L. 1978. Small abundance in relation dependentof laying date. Oecologia85:543-552. to environmental variables in three Swedish forest --, M. LAGERSTROMAND P. S^UROLA.1987. Field ev- phases.Stud. For. Suec. 147:1-39. idence for nomadism in Tengmalm's Owl Aegoliusfu- 1983. Bird numbers acrossedges between ma- nereus. Ornis Scand. 18:1-4. ture forests and clear-cuts in central Sweden. MIKKOLA,H. 1983. Owls of Europe. T. & A.D. Poyser, Ornis Scand. 14:97-104. Calton, U.K. 1992. Landscape ecology of boreal forests. NEWTON,I. 1979. Population ecology of raptors. T. & Trends Ecol. Evol. 7:299-302. A.D. Poyser,Berkhamsted, U.K. 1994. Vertebrate distributions relative to clear- 1989. Lifetime reproduction in birds.Academic cut edgesin a boreal forestlandscape. Landscape Ecol. Press, London, U.K. 9:105-115. OHMANN,J.L., P.L. CARLESONAND A.L. OAKLEY.1988. Sta- HELLE,P. 1984. Effects of habitat area on breeding bird tus of forest-related wildlife and resources in Or- communities in northern Finland. Ann. Zool. Fenn. 21: egon. Pages 17-32 in Lettman [ED.], Assessmentof 421-425. Oregon'sforests. Oregon StateDept. Forestry,Salem, OR U.S.A. HENTTONEN, H. 1989. Metsien takenteen muutoksen ROUGHGARDEN,J. 1979. Theory of population genetics vaikutuksestamyyrakantoihin ja sitfi kautta pikkupe- and evolutionaryecology: an introduction. MacMil- toihin ja kanalintuihin--hypoteesi(English summa- lan, New York, NY U.S.A. ry). Suom.Riista 35:83-90. TEMELES,EJ. 1985. Sexual size dimorphism of bird-eat- JARVINEN,O., K. KUUSELAAND R.A. VAIS'ANEN. 1977. Met- ing hawks:the effect of prey vulnerability.Am. Nat. sien rakenteen muutoksen vaikutus pesimfilinnus- 125:485-499. toomme viimeisten 30 vuoden aikana (Summary: Ef- fectsof modern forestry on the numbersof breeding Received2 November 1995; accepted6 March 1997