J. RaptorRes. 31 (2):107-113 ¸ 1997 The Raptor ResearchFoundation, Inc.

HOW, AND WHY, IS THE GOSHAWK (ACCIPITER GENTILIS) AFFECTED BY MODERN FOREST MANAGEMENT IN FENNOSCANDIA?

PER WIDEN Universityof Karlstad,S-651 88 Karlstad,Sweden

ABSTRACT.-•TheNorthern Goshawk(Accipiter gentilis) is a common raptor in the boreal forest of Fen- noscandia(Norway, Sweden and Finland), with a presentbreeding density of about 3 pr/100 km2 of forestarea. Severalindependent studies show that goshawkpopulations in Fennoscandiahave declined by 50-60% from the 1950sto the 1980s.This declinecoincides in time with an intensificationof forest management, which has changed the forest landscape.Among other effects, forests are more frag- mented and the proportion of old forestis decreasing.Neither pesticideuse nor persecutioncan explain the goshawkdecline. However, changes in habitatand prey populationsare both importantfactors that are affectedby forestry.Goshawks need only a smallpatch of suitablehabitat for nesting,but for their foraginghome rangescover 2000-6000 ha, and in boreal forestareas they prefer large patchesof mature forest.I suggestthat changesin the borealforest landscape have resulted in a deteriorationof goshawk hunting ranges,making it more difficult for them to secureadequate food for breeding.This factor is more important than a shortageof suitablenest sites.Declining prey densities(e.g., grouse) may be associatedwith forestryand is alsoan important factor that may affect goshawknumbers. KEYWORDS: Accipiter gentilis;Northern Goshawk; forest management;, home range,, breeding; habitat selection; Fennoscandia;Sweden; Norway; Finland.

dComo,y Porque, esta el Acdpitergentills afectado por la administracitn forestal moderna en Fenno- scandia? RESUMEN.--EIAccipiter gentilis nortefio es un rapaz comfin en el bosqueboreal de Fennoscandia(No- ruega, Sueciay Finlandia) con una densidadde cria presentecomo 3 pr/100 km2 de /trea bosque, variosestudios independientes ensefian poblaciones de Acdpitergentilis en Fennoscandiaaun reducido por uno 50-60% de los 1950sa los 1980s.Estfi reduccitn coincidecon el tiempo de intensificacitnde administracitn de bosque,que ha cambiadoel paisajedel bosque.Entre otros efectos,bosques est/tn mas fragmentadosy la proporcitn de bosquesviejos se estareduciendo. Ni uso de pesticidani perse- cucitn puede explicarreduccitn del Accipitergentilis. Sin embargo,cambios en el h/tbitaty poblaciones de cazar son las dos importantesfactores que son afectadospor forestales.Accipitergentilis necesitan no mas una parcela chiquita de h•bitat convenientepara hacer nidos, pero susforrajes naturalescubren 2000-6000 ha, yen /treasde bosqueboreal ellos prefieren parcela grandes de bosque maduro. Yo, propongoque cambiosen el paisajede bosquesboreal han resultadoen un empeoramientoen campos de cazardel Accipitergentills, haciendo mas dificil para ellosa proveersuficiente comida para cria. Este factor es mas importante que una falta de nidos conveniente.La reduccitn de densidadde cazados, (por ejemplo, urogallo) puede ser asociadacon forestalesy es tambitn un factor importante que puede afectar la cantidad de Accipitergentilis. [Traducci6n de Rafil De La Garza, Jr.]

The forests of Fennoscandia (Norway, Sweden, area is productive forest which is very intensively and Finland) have been used by man for a very managed.About 40% of this area has been clear- long period of time. However,in the 1950s,a major cut since 1950 and is now covered by forest estab- change occurred in forest-managementpractices, lished according to modern methods (Anonymous including intensified methods based on clear-cut- 1989). ting, replanting and thinning. This practice grad- As a result of this intensivemanagement, the bo- ually replaced the traditional wayof harvestingfor- real forest landscape of Fennoscandia is now a estby selectivecutting. In Sweden,58% of the land highly fragmented patchwork of clear-cutsand for-

107 108 WID]•N VOL. 31, NO. 2

Table 1. Population studies showing goshawk density changesin boreal forestsof Fennoscandia.

DENSITY CHANGE IN CHANGE BREEDING (pr/100 STUDYAREA PE•OD PAIRS km 2) Central Norwaya 1964-93 8 •) 0 5.7 •) 0 SouthernNorway b 1950-84 13 -• 5 7.2 -• 2.7 Southern Norway• 1950-85 35 -• 20 9 -• 3 Southern Norway• 1985-88 20 -• 26 3 -• 4 North-central Sweden a 1950-76 12 -• 5 2.4 -• 1 Central Sweden" 1950-70 10 -• 5 2 -• 1 Central Sweden f 1960-80 35 -• 15 35 -• 15 Southern Finlandg 1974-81 25 -• 10 5 -• 2 Southern Finland h 1977-84 16 -• 10 5.3 -• 3.3

Tommeraas 1993. Figure 1. Map showing the location of goshawkpopu- Hansen 1985, FrydenlundSteen 1989. lation studies cited in the text. 1. Tommeraas (1993), 2. Selfisunpubl. data. Hansen (1985), Frydenlund Steen (1989), 3. Selfs (pers. Carelius (1978). Bylin (1975). comm.), 4. Carelius (1978), 5. Bylin (1975), 6. Lind (in Ltnd (in Nilsson, 1981). Nilsson 1981), 7. Wikman and Lind6n (1981) and 8. Wtkman and Lind6n (1981). Forsman and Ehrnsten (1985). Forsman and Ehrnsten (1985).

13 600. I judge the two latter estimates to be the est standsin different successionalstages. Less than most reliable and conclude that the Swedishgos- 5% of the Swedishforests are primeval, as com- hawk population is about 7000 breeding pairs, pared to 22% and 60% of the forestsin the U.S. which is equivalent to a breeding density of 1.9 and Canada, respectively(Olsson 1992). pr/100 km2 of land area and 2.9 pr/100 km2 of The Northern Goshawk(Accipiter gentilis) occurs forest area. •n forested areas throughout the Holarctic region The goshawkpopulation in Finland wasestimat- (Brown and Amadon 1968), and is one of the ed at about 6000 breeding pairs by Saurola more numerous birds of prey in Fennoscandia. (1985a), implying a breeding densityof 2.0 pr/100 The object of this paper is to review available in- km2 of land area and 3.0 pr/100 km2 of forestarea. formation about goshawkpopulation status and Thus, although the densityper land area differs trends in the Fennoscandian countries and to dis- between the Fennoscandiancountries, the density cusspossible effects of modern fbrest management per forest area is virtually the same,about 3 breed- on those trends. ing pr/100 km2 of forest.

POPULATION STATUS POPULATION TRENDS In Norway,the goshawkpopulation wasestimat- The best way to study long-term population ed to be 2700 breeding pairs (Bergo 1992). This is changesin raptors is to monitor a breeding pop- equivalentto 0.8 breedingpr/100 km2 of land area ulation of a given area for a long period of time. and 3.1 pr/100 km= of forest area. By examining trends in individual populations,we The Swedishgoshawk population wasestimated should be able to make conclusions regarding at 10 000 breedingpairs by Svensson(1979), based trends over larger areas. In Fennoscandia,a num- on a nationwide bird censusingprogram. However, ber of such local, long-term goshawkpopulation Ntisson (1981) suggestedthat there were only 6000 studieshave been reported, and they are summa- breeding pairs after analyzinga number of differ- rized in Table 1. The locations of the studies are ent local studies. Marcstr6m and Kenward (1981), shownin Fig. 1. A paired t-testbetween early and based on capture-recapture estimate of ringed late years show a statisticallysignificant decline (! (banded) birds, calculatedthat the number of gos- = 3.474, df = 8, P = 0.0084). hawk pairs older than two yr wasbetween 3500 and Thus, it is well documented from a number of JUNE1997 GOSHAWKSAND FORESTRY IN FENNOSCANDIA 109 different, independent studiesin all three Fenno- gestsorganochlorines have not been an important scandian countries that goshawkpopulations have factor in their population decline. decreased from around 1950 to around 1980. In Thus, although pesticide use ha•sbeen reported most studies, the decrease has been 50-60%. After as the causeof declinesin goshawkpopulations in that period, the pattern is less clear since most other parts of Europe (Bijlsma 1991), I conclude studies have not continued. However, the nation- that there is no evidence that this has been the wide raptor monitoring scheme in Finland indi- case in the boreal forest region. When the use of catesstable populations after 1989, when the pro- persistentpesticides stopped in the early 1970s, gram started (Haapala et al. 1994), and Selfis(pets. positivegoshawk population trends were reported comm.) reports a temporary,slight increase in one throughout Europe (Bijlsma 1991). In the boreal area of Norway. forest region, this has not occurred and goshawks did not recover when the pesticide situation im- WHY I-IAS THE GOSHAWK DECLINED? proved. In fact, several population studies show To determine the reasons for such a dramatic that goshawksdeclined even after mercury levels decline, we nmst look at all possibleenvironmental dropped. This can be compared to the Sparrow- factors, not only forest management. The factors hawk (Accipiternisus), which decreased drastically most often associatedwith declining raptor popu- in Swedenfrom the 1950s, but recovered markedly lations are pesticides,persecution, declining prey when organochlorines were prohibited in the populationsand habitat degradation or loss (New- 1970s (Wallin 1984). ton 1979). Persecution. Goshawkshave alwaysbeen perse- Pestiddes. Most adult goshawksin the boreal cuted in Europe, especiallyin farmland areas by forests of Fennoscandiaare not migratory and re- hunters wanting to protect small game species main in or close to the boreal forest throughout from predation. In Fennoscandia, this has mainly the year. Further, their most important prey species affected wintering juvenile goshawks.Locally, per- are also sedentary.Thus, they do not directly pick secution also affected adult breeding birds since up contaminants from other regions, probably some hunters specializedin finding and destroying making them lessvulnerable than other raptor spe- breeding goshawks.However, during the period of ciesto pesticidecontamination. However, juveniles goshawkdecline between1950-80, legal protection and some adult females move south and winter in has improved and there has been a gradual chang- farmland areas (Widtn 1985), where there is more ing opinion favoring raptors, leading to reduced prey, but also generally more pesticideuse than in pressure of persecution. Accordingly, Saurola forested habitats. (1985b) reports a 50% decreasein goshawkper- Mercury.In Sweden, alkyl-mercury was used for secution between 1960-80. Thus, persecution is seed dressingin agriculture from the 1940s until not likely to be the major reason for goshawkde- 1966, when it wasprohibited. This use causedwide- cline in Fennoscandia. spread contamination of the terrestrial fauna, and Prey Populations. The goshawkfeeds on a wide as a result many terrestrial bird specieswere seri- variety of prey species,but in the boreal forestsof ously affected (Berg et al. 1966, Borg et al. 1969, Fennoscandiadifferent grousespecies are the most Jensenet al. 1979, Westermarket al. 1975,Johnels important prey (Htglund 1964, Sulkava 1964, et al. 1979). Increased levels of mercury were Tornberg and Sulkava 1990), although in winter found in breeding female goshawks'feathers in the squirrels (Sciurusvulga•s) may also be a major prey period 1940-65, but decreasedto backgroundlev- item (Wid&n 1987). It is well documentedthat gos- els rapidly after alkyl-mercurywas banned in 1966 hawks respond numerically and functionally to (Johnelset al. 1979). short-term fluctuations in grouse populations (Lin- Organochlorines.A common way of assessingthe d&n and Wikman 1980, 1983) and they are likely impact of organochlorineson raptor populations to respond also to long-term population changes. is by measuring the eggshell thickness.Newton Sel•ts(pers. comm.) suggestedthat the goshawk (1979) concluded that whenever a population decline was caused by a decline in forest grouse, showedmore than 16-18% shell-thinningover sev- due to a long-term increasein the number of gen- eral years, it declined. Nygfird (1991) reported a eralist predators such as red foxes Vulpesvulpes 6.6% decreasein eggshellthickness in eggsfrom (Storaasand Wegge 1985, Storaas 1993). The in- goshawksin Norway after 1947, a result that sug- crease in goshawknumbers from 1985 in his area 110 WIDI•N VOL. 31, NO. 2

Birds/sq.km

15

10 - Capercaillie

...... ß ...... Black Grouse

.... ,• .... Hazel Grouse 5

0 I I I I 1970 1975 1980 1985 1990

Year

Figure 2. Population trends in forest grouse: Capercaillie (Tetraourogallus), Black Grouse (Tetraotetrix) and Hazel Grouse (Bonasabonasia) in southern Finland (Finnish Game and FisheriesRes. Inst. unpubl. data). was explained as a temporary reversalof this pro- clear how general this explanation is. Further, the cess,when the red fox drasticallydecreased due to fact that the goshawksin southern Finland failed to sarcopticmange, resulting in an increasein grouse respondto increasinggrouse populations in the late numbers. However, the red fox is now recovering 1970sand the early 1980s,indicates that the rela- and there will probablynot be any long-term effect tionshipbetween grouse and goshawksis not always on prey numbers.Thus, Selfisexplains the goshawk a simple numerical response. population changes as long-term numerical re- Habitat Degradation or Loss. Goshawk habitat sponsesto changing prey populations. can mean different things. Quite often it refers to Wikman and Lindfin (1981) found that the gos- nesting habitat (e.g., the site where the bird builds hawk decline coincided with a general decline in its nest and breeds). Less often it refers to the rest grouse numbers in the same area, but concluded of the bird's living space (e.g., the home range that that the rather moderate grouse fluctuations could is used to find the food necessaryfor survivaland not explain the 60% decline in the goshawkpop- raising of young). Here, I will cover both aspects, ulation. Grousepopulations were very low in 1976- since both of them are important for goshawksur- 77 when the goshawkdecline started. Although vival. grouse numbers increased for a number of years Nestinghabitat. Several reports (Carelius 1978, after 1977, goshawksfailed to respondnumerically Forsman and Ehrnsten 1985, Hansen 1985, Fry- and still remain at a low population level. More denlund Steen 1989, Tommeraas 1993) have indi- recent grouse data (Finnish Game and Fisheries cated that goshawkpopulation declineswere main- ResearchInstitute unpubl. data) showa continuing ly or partially due to the loss of nest sitesduring downwardtrend in numbersof Capercaillie (Tetrao modern forest management. urogallus),Black Grouse (Tetra0tetrix) and Willow The breeding habitat of Northern Goshawkshas Grouse (Bonasabanasia) in Finland (Fig. 2). been describedby severalauthors (Dietzen 1978, Thus, there is some indication that decline in Reynolds 1983, Reynolds and Meslow 1984, Link prey populations,mainly grouse,is a factor involved 1986), and generally it is found that goshawksdo in the long-term decline of Fennoscandiangoshawk not select nest sitesrandomly. Since nest sitesare populations. Unfortunately, for most of the studies relatively easyto find and describe,there is a ten- reporting goshawkdecline, there are no good cor- dency to emphasize the importance of that part of respondingdata on grousepopulations, so it is un- the bird's environment, as compared to the much JUNE1997 GOSHAWKS•o FoPmsTR¾IN FENNOSCANDIA 111 larger home range. Goshawksneed only a small pends not only on prey density,but also on differ- patch of suitablehabitat for nestingand successful ent habitat features that determine its ability to goshawkbreedings have been reported in forest hunt. This may be a major factor behind their pref- patchesas small as 0.4 ha (Lindell 1984). One gos- erence for hunting in mature forest. It is important hawk nest was recorded in an isolated willow tree for the hawk to reach perchesundetected by prey (Salix alaxensis)in Alaska, 145 km north of the tree and to remain undetected. At the same time, hab- line on the tundra (Swem 1992). itat must be open enough for the goshawkto ma- The reported habitat requirementsmay not be neuver and attack. The mature forest is the best specific,observed relationships may not be causal compromise;prey in more open or denser habitat and, if they are, they may not represent major re- is lessaccessible. For example, goshawksavoided straints(Kenward and Wid6n 1989). Although lack young forest, despite the fact that this habitat was of nest sites may become a problem on a local preferred by one important prey species,the Black scale,it seemsunlikely that it should become lim- Grouse (Kolstad et al. 1985). iting on a larger scalefor goshawkpopulations in Due to forestry, the proportion of old, mature boreal forests, even in stronglyimpacted systems. forest in Sweden has decreased (Svensson 1980) For example, the study area in central Sweden and the forest is being fragmented into smaller where Wid6n (1989) studiedgoshawk hunting hab- patches.Obviously, both trends may negativelyaf- itats was an area with very intensiveforest manage- fect goshawksin boreal Fennoscandia. ment, yet the proportion of mature forest suitable Kenward (1982) studied goshawkhabitat utiliza- for nestinggoshawks was about 24%. tion in three areas with mixed farmland/woodland I conclude that nesting habitat availabilityis not in centralSweden, containing 41-61% woodland.In likely to be a major factor behind the recorded all areas, he found preference for forest as com- decline in goshawknumbers. pared to farmland, although he did not separate Hunting habitat.Goshawks move over large areas successionalforest stages.He also found a prefer- when hunting, and in Sweden home range sizes ence for forestedge. The forestpatches he studied are between 2000-6000 ha (Kenward 1982, Wid6n were surroundedby farmlandwhere prey occurred, 1989). Important clues regarding hunting habitat predominantly Ring-necked Pheasants(Phasianus requirements might be found by taking a closer colchicus)and European hares (Lepuseuropaeus). look at how the goshawkuses this landscape,es- Goshawksused the forest edge as coverwhere they peciallywhere and how it hunts. perched and from where attackswere launched. Wid6n (1989) studied goshawkhunting habitat In the Wid6n (1989) studyarea, the forest patch- with radiotelemetry in continuous coniferous for- es were mainly surroundedby forestsin other suc- est in the boreal forest region of Sweden (Sj6rs cessionalstages (e.g., younger than the preferred 1965), at Grims6 Wildlife Research Station. Of the mature forest). These younger stagesoffered no area, 74% wasconifer-dominated forests. Bogs and good hunting habitats for the hawks and thus the fens comprised18% of the area and only 3% was edges were not preferred. farmland. Of the six different habitat classes,gos- DISCUSSION hawks strongly preferred mature forest. Some hawks were monitored more intensivelyin order Effects of Forest Management. Available data to record their predation, and resultsshowed that show that Fennoscandian goshawk populations most kills were made in mature forest, stronglyin- have declined by 50-60% from the 1950s to the dicating that this was the most important hunting 1980s,and I haveconcluded that neither pesticides habitat. It was also clear that goshawkspreferred nor persecutioncan explain this decline, but that large patchesof mature forest, although the pref- changesin prey populationsand habitatsare im- erence for large patcheswas evident in the mature portant factors.Further, it is striking that the de- forest only. It was also in the large patches that cline coincided in time with forest-managementin- most kills were made. tensification. Thus, we are left with the conclusion The goshawkhunts by making short flights be- that forest management, acting in different ways, tween perches, where it staysfor longer periods is a prime factor behind the goshawkdecline. I and from which nearly all attacksare made (Ken- suggestthat large-scalechanges in the boreal forest ward 1982, Widen 1984). With such a hunting landscape,caused by modern forest management, technique, it is obviousthat hunting successde- has resulted in a deterioration of goshawkhunting 112 WIDI•N VOL. 31, No. 2 range quality, and that this, although difficult to of nesting habitat is not a problem, but that habitat measure, is more important than nest-site avail- destructionmay act indirectly by depletinghabitat ability. When discussinghabitat suitability,it is im- for prey animals. portant to include prey accessibilityand densityin A general discussionabout grouse populations addition to nest-site availability. The goshawk re- in Fennoscandiais beyond the scopeof this paper, quires prey that it is able to catch. To discoverim- but consideringthe effectsthat forestryhas had on portant hunting habitat requirements, one needs the forest landscape, it would be surprising if to know where raptors hunt and their hunting suc- grouse have not been affected. cessin each place (Kenward and Widtn 1989). The goshawkproblem in boreal forestscannot be In Denmark, which is south of the boreal forest, solvedby creatingprotected areas; they need areas the population trend seemsto have been different. too large to be effectivelyprotected that way.We Here, the goshawk has increased from the 1960s must concentrateon determining what is important until the beginning of the 1980s (J0rgensen1989). for goshawksand use that knowledgeto direct for- This was explained as a result of decreased pres- estrypractices that establishadequate protection. sure from persecutionand pesticides. Recommendations. First, when mattire forest is My conclusion that hunting habitats are more fragmented by clear-cutting, the fragments should crucial than nesting habitats for goshawksin the be as large as possible. It is generally better to modern forest landscape does not indicate that make one large clear-cut than several small ones. availabilityof good nestinghabitat can be complete- Second, nest sitesmust be protected, even if they ly rejected as a possiblelimiting factor for goshawk are unoccupied. A surplus of well-spacedpatches populations. Since goshawksare territorial, with a of good nesting habitat is needed. Third, there regular spacingof nests(Widtn 1985), they cannot must be enough forest with old-forestqualities in breed close together, and therefore it is important the landscape. Research is needed to determine how the patchesof good nestinghabitat are spaced. how much is enough. Fourth, we need more re- Further, there must be more suitable habitat search on the goshawk'shunting technique and patches than are currently needed. New individ- hunting successin different habitats. uals recruited into the population must be able to ACKNOWLEDGMENTS find unoccupied sites.In order for the whole pop- ulation to survive, sites that are temporarily unoc- I am grateful to Vidar Selfiswho allowedme to use his unpublished manuscript on a goshawk population in cupied must be availablefor colonization by new south Norway, to Marcus Wikman who gaveme accessto breeders. A site that has become temporarily un- unpublished data from the Finnish Game and Fisheries occupied is a potential resourcefor new breeders, ResearchInstitute and to three referees for improving which are recruited into the population. If unoc- the manuscript. cupied sites are destroyed because there are no LITERATURE CITED longer any hawksthere, we lose that possibility.A raptor population may go extinct becauseof a lack ANONYMOUS.1989. Skogsstatistiskfirsbok 1989. Skogss- tyrelsen. of nest sites, even if we never destroy a single oc- BERG,W., A. JOHNELS,B. SJOSTRANDAND T. WESTERMARK. cupied nest site, but destroy those that are tem- 1966. Mercury content in feathers of Swedish birds porarily unoccupied. from the past 100 years.Oikos 17:71-83. Declining prey populationscan be an important BERGO,G. 1992. BestandsstOrrelse,reirbabitat og repro- factor, but the relationshipbetween prey decline duktionsbiologihjfi honsehauk. Fylkesmanneni Hor- and fbrestry needs to be explained. Sel•s (pers. daland, Miljovernavdelinga.R-NR 5/92. comm.) explainsgrouse number declinesas an ef- BIJLSMA,R.G. 1991. Trends in European Goshawks(Ac- fect of increasingnumbers of red fox, but does not dpitergentilis): an overview.Bird CensusNews 4:3-47. explain why foxes have become more common. BORG, K., H. WANNTORP, K. ERNE AND E. HANKO. 1969. Forsman and Ehrnsten (1985) argue that the gos- Alkyl mercury poisoning in terrestrial Swedishwild- life. Swedish Wildl. 6:302-377. hawk decline is due to modern forestry,affecting BROWN,L. ANDD. AMADON.1968. Eagles,hawks and fal- the goshawkin two different ways.Birds of optimal cons of the world. Country Life Books,London, U.K- prey size (e.g., grouse) are becoming rarer and are BYLIN,K. 1975. Dalarnasffiglar. Dalarnas Ornitologiska being replaced with smaller birds. Second, good F6rening. G•vle, Sweden. nesting habitat (e.g., mattire forests) is becoming CARELIUS,W. 1978. Duvh6kspopulationensutveckling rarer. Wikrnan and Lindtn (1981) argue that lack och t•nkbara st6dfitg•rder.Fdglar i X-18n9:21-27. JuNv.1997 GOSHAWKS^ND FOm•STR¾IN FENNOSCANDIA 113

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